the mammoth peak sheeted complex tuolumne batholith sierra nevada california a record of initial growth or late thermal contraction in a magma chamber the mammoth peak sheeted intrusive complex formed in the interior of a 7 10 km deep magma chamber specifically in the half dome granodiorite of the tuolumne batholith central sierra nevada ca usa the sheets consist of fractionated melts with accumulated hornblende biotite magnetite titanite apatite and zircon the accumulation especially of titanite had a profound effect on minor and trace elements nb ta ti ree u th p zr hf etc increasing their contents up to five to six times our thermal mechanical modeling using the finite element method shows that cooling generated tensile stresses resulted in the inward propagation of two perpendicular sets of dilational cracks in the host granodiorite we interpret the sheeted complex to have formed by a crack seal mechanism in a high strength crystal rich mush whereby outward younging pulses of fractionated magma were injected into these syn magmatic cracks at the margin of an active magma chamber thermal mechanical instabilities developed after the assembly of the sheeted complex which was then overprinted by late nw se magmatic foliation this case example provides a cautionary note regarding the interpretation that sheeted zones in large granitoid plutons imply a diking mechanism of growth because the sheeted dike complexes in plutons 1 may display inverse growth directions from the growth of the overall intrusive sequence 2 need not record initial chamber construction and instead may reflect late pulsing of magma within an already constructed magma chamber 3 have an overprinting magmatic fabric indicating the continued presence of melt after construction of sheeted complexes and thus a prolonged thermal history as compared to dikes and 4 because the scale of the observed sheeted complexes may be small 1 in comparison to large homogenous parts of plutons in which there is no evidence for sheeting or diking thus where extensive dike complexes in plutons are absent such as in much of the tuolumne batholith the application of an incremental diking model to explain chamber construction is at best speculative

high thermal maturity in the lower saxony basin intrusion or deep burial abstract the lower saxony basin lsb is situated at the southern rim of the northern permian basin the most important hydrocarbon bearing province in europe in its southern part areas of high thermal maturation up to 6 rr occur which were previously explained as being caused by magmatic intrusions of turonian to santonian age that affected carboniferous to lower cretaceous rocks in this area 2d numerical basin modelling was carried out in order to reconstruct the temperature histories along two parallel n s trending seismic sections along these sections new data about maturity distribution and temperature history were obtained by vitrinite reflectance measurements and apatite fission track analysis for the areas with highest maturity values low coalification gradients were established which agree well with earlier published data on wells further towards the west this new information does not support previous hypotheses on high heat flows from magmatic intrusions even if lateral heat transport is taken into account instead comparisons with a recently published map of the subsurface structure of the lsb indicate that maturity distribution may be closely related to major tectonic structures deep burial of individual structures of the lsb which are bordered by deep e w to ese wnw trending faults is further suggested by a rapidly increasing thicknesses of preserved cretaceous strata towards the south and b structural restoration of one of the seismic sections to achieve a fit between measured and calculated palaeo temperature and vitrinite reflectance data deep burial of carboniferous source rocks during cretaceous time has to be assumed due to an inversion phase in the early and middle upper cretaceous major amounts of sediment were removed and further uplift occurred in tertiary times in contrast the northern part of the lsb experienced maximum burial and temperatures during tertiary times

crystallization of orbicular rocks exemplified by the slattemossa occurrence southeastern sweden the orbicular rock at slattemossa southeastern sweden has a quartz monzodioritic composition the cores of the orbicules crystallized directly from the orbicule forming magma cores made up of xenoliths have not been observed outside the core follow first an inner mafic a felsic and then an outer mafic shell the orbicules occur in a matrix which is similar to the core they grew simultaneously and show an almost perfect parallelism in evolution after initial normal crystallization of the magma superheating probably triggered by a sudden addition of volatiles destroyed earlier formed nuclei and also affected the already crystallized part of the rock cooling caused heterogeneous nucleation and rapid crystallization which formed the inner mafic shell this is enriched in mafic minerals especially biotite compared to the core at the same time the grain size becomes significantly smaller depletion in malic components possibly intensified by a sudden change in physical conditions destabilized biotite and amphibole crystallization causing oversaturation in plagioclase components forming a felsic shell having a sharp boundary with the mafic shell plagioclase is extremely altered mafic minerals were then stabilized probably due to depletion of plagioclase components and an outer mafic shell formed with the return to homogeneous nucleation matrix formation concluded the crystallization orbicules might have moved in the magma causing some squeezing of magma surrounding the orbicules but major movements involved the settling of the whole package of orbicules and matrix in the surrounding non orbicular magma less

is there a relationship between magmatic fabrics and brittle fractures in plutons a view based on structural analysis anisotropy of magnetic susceptibility and thermo mechanical modelling of the tanvald pluton bohemian massif abstract the present study focuses on the thermal and mechanical aspects of cooling of plutonic systems with respect to their internal structure analysis of the tanvald pluton and the nearby liberec granite the krkonose jizera plutonic complex bohemian massif using the anisotropy of magnetic susceptibility ams method indicates the decoupled magnetic fabrics formed by different processes in these two plutons two regional sets of vertical fractures cut across the plutons and their host rocks they are interpreted as having been formed as opening mode fractures joints after emplacement and cooling our thermo mechanical finite element modelling indicates that the thermal stresses within the tanvald pluton were compressive and that fracture criteria were not met during pluton cooling these results imply that the emplacement depth and confining pressure significantly affect the state of stress within a pluton during cooling and may play a crucial role in the formation of early fractures in plutons consequently the formation of early fractures during pluton cooling is driven by external conditions overriding the role of internal magmatic fabrics we argue that no genetic geometric or temporal correlation can exist between magmatic fabrics and fractures in granitoid plutons and thus that the original concept of hans cloos based on fabric joints relationships should be reconsidered instead an alternative classification of fractures in plutons should include cooling fractures syntectonic fractures uplift fractures and post uplift fractures

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

igneous banding schlieren and mafic enclaves in calc alkaline granites the budduso pluton sardinia abstract this study deals with the origin of igneous layering in plutons and especially the extent layering is related to mafic silicic magma interactions the budduso pluton sardinia shows three main scales of organization i large scale lithological variations correspond to three main magmatic units with differentiation increasing from the outer hornblende bearing biotite granodiorite monzogranite to the middle biotite monzogranite and the inner leucomonzogranite units the striking homogeneity of 87 sr 86 sr initial ratios 0 7090 4 and e nd t values 5 6 0 1 strongly suggests that magma isotopic equilibration was achieved prior to emplacement whereas mixing mingling structures observed within the pluton reflect second stage processes involving broadly cogenetic components ii metre to decametre scale igneous layering may be isomodal or modally graded locally with cross layering biotite and plagioclase compositions are similar in both biotite rich and quartzofeldspathic layers as are the trace element patterns which differ only by relative abundances this precludes an origin by fractional crystallization a penetrative submagmatic fabric superimposed on the layering and corresponding mainly to flattening can be ascribed to interference between pluton growth and regional deformation iii composite layering and schlieren are commonly associated to mafic microgranular enclaves locally within synmagmatic shear zones or disrupted synplutonic dykes in that case there is a progressive shift in biotite x fe values from the core of enclave 0 65 to the host monzogranite 0 72 schlieren in the monzogranite show biotite x fe values similar to that of the host rock whereas schlieren close to mafic enclaves show lower x fe values 0 69 towards those of enclave rims these features can be ascribed to three main processes i assembly of differentiated mixed mingled magmatic pulses ii local hydrodynamic sorting related to density currents in a mush and segregation of residual melt iii mechanical disruption and chemical hybridization of mafic magmas during ascent or within the pluton related to magma dynamics none of these processes affect the whole pluton but they are limited to specific magmatic units therefore pluton growth by incremental assembly of magma batches is not incompatible with magma chamber processes

emplacement setting of the granite sheeted pluton of esperanca brasiliano orogen northeastern brazil abstract anisotropy of magnetic susceptibility ams and isotopic u pb sm nd data were combined to study the emplacement setting of the granite sheets that constitute the esperanca pluton in the borborema province northeastern brazil the sheets dip moderately to the se along the contact zone between the paleoproterozoic basement rocks and early neoproterozoic orthogneisses and metasediments granite fabrics were determined mainly using ams in 136 sites distributed within the central and western part of the pluton the sheets normally have susceptibility lower than 0 35 msi but locally where a ti poor magnetite appears with titanite the susceptibility increases up to 5 msi comparison between the silicate fabric and ams showed inconsistencies between the shape of mineral and magnetic ellipsoids despite of their orientations that fit fairly well to each other ams indicated the deformation was partitioned between the lower tonalite syenogranite and upper leucogranite and coarse porphyritic granite sheets in the lower sheets the curvilinear lineation trajectory is attributed to a dominant heterogeneous pure shear event that flattened laterally the still molten tonalite and syenogranite into the regional foliation the associated microstructures are typically magmatic zircon u pb data of the syenogranite yielded a crystallization age of 592 5 ma in the upper sheets the fabric recorded a component of simple shear deformation that displaced the coarse porphyritic granite and the top gneissic host rocks to the southwest microstructures are mostly of post full crystallization type tdm model ages and nd t 0 values indicate that the magma contaminated by partial melting of the regional host rocks sheet propagation at the emplacement level would have exploited the contact zone between crustal blocks of different rheologies when the melt pressures would be able to tensionally fail the anisotropy of the host rocks

depositional features and stratigraphic sections in granitic plutons implications for the emplacement and crystallization of granitic magma abstract many granitic plutons contain sheet like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature more mafic magma during crystallization of the granitic plutons small scale structures associated with these bodies e g load cast and compaction features silicic pipes extending from granitic layers into adjacent gabbroic sheets indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber on granitic crystal mush and beneath crystal poor magma while the mafic magma was incompletely crystallized these structures indicate way up typically toward the interior of the intrusions and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition hence these plutons preserve a stratigraphic history of events involved in the construction filling replenishment and crystallization of the magma chamber the distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions which usually preserve mutual intrusive contacts and dike sill relations of different magma types the considerable thickness of material that can be interpreted as depositional and the evidence for replenishment suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton thus magma chambers may be constructed much more slowly than presently envisaged the present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber along with the underlying solidified granite and country rock sank during continuing episodes of magma chamber replenishment these internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber

crustal memory and basin evolution in the central european basin system new insights from a 3d structural model abstract the central european basin system cebs is composed of a series of subbasins the largest of which are 1 the norwegian danish basin 2 the north german basin extending westward into the southern north sea and 3 the polish basin a 3d structural model of the cebs is presented which integrates the thickness of the crust below the permian and five layers representing the permian cenozoic sediments structural interpretations derived from the 3d model and from backstripping are discussed with respect to published seismic data the analysis of structural relationships across the cebs suggests that basin evolution was controlled to a large degree by the presence of major zones of crustal weakness the nw se striking tornquist zone the ringkobing fyn high rfh and the elbe fault system efs provided the borders for the large permo mesozoic basins which developed along axes parallel to these fault systems the tornquist zone as the most prominent of these zones limited the area affected by permian cenozoic subsidence to the north movements along the tornquist zone the margins of the ringkobing fyn high and the elbe fault system could have influenced basin initiation thermal destabilization of the crust between the major nw se striking fault systems however was a second factor controlling the initiation and subsidence in the permo mesozoic basins in the triassic a change of the regional stress field caused the formation of large grabens central graben horn graben gluckstadt graben perpendicular to the tornquist zone the ringkobing fyn high and the elbe fault system the resulting subsidence pattern can be explained by a superposition of declining thermal subsidence and regional extension this led to a dissection of the ringkobing fyn high resulting in offsets of the older nw se elements by the younger n s elements in the late cretaceous the nw se elements were reactivated during compression the direction of which was such that it did not favour inversion of n s elements a distinct change in subsidence controlling factors led to a shift of the main depocentre to the central north sea in the cenozoic in this last phase n s striking structures in the north sea and nw se striking structures in the netherlands are reactivated as subsidence areas which are in line with the direction of present maximum compression the moho topography below the cebs varies over a wide range below the n s trending cenozoic depocentre in the north sea the crust is only 20 km thick compared to about 30 km below the largest part of the cebs the crust is up to 40 km thick below the ringkobing fyn high and up to 45 km along the teisseyre tornquist zone crustal thickness gradients are present across the tornquist zone and across the borders of the ringkobing fyn high but not across the elbe fault system the n s striking structural elements are generally underlain by a thinner crust than the other parts of the cebs the main fault systems in the permian to cenozoic sediment fill of the cebs are located above zones in the deeper crust across which a change in geophysical properties as p wave velocities or gravimetric response is observed this indicates that these structures served as templates in the crustal memory and that the prerift configuration of the continental crust is a major controlling factor for the subsequent basin evolution

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

tectonic subsidence modelling of the polish basin in the light of new data on crustal structure and magnitude of inversion abstract the polish basin pb is one of a set of basins developed on the paleozoic platform of western europe in the late paleozoic between the variscan orogen and the east european craton eec its main depocentral axis the mid polish trough mpt was active during most of the basin development as a maximum subsidence zone with almost uninterrupted sedimentation the present base of the permian in the mpt ranges in depth from ca 3000 to 3500 m near the baltic coast to up to 8000 m to the southeast the mpt lies parallel and adjacent to the edge of the eec and appears to be related to a distinct structural zone within the crust the tornquist teisseyre zone ttz subsidence of the mpt can be explained in terms of crustal extension transtension and related lithosphere cooling coupled with the structural predetermination of the underlying ttz tectonic subsidence analysis of the preserved and reconstructed stratigraphic record suggests the occurrence of a late permian early triassic rifting phase however there is a deficit of geologically observable extensional features faulting of this age implying an important relationship between this phase of apparent basin subsidence and earlier post variscan late carboniferous early permian tectonism the match between crustal structure implied by basin modelling studies and available deep seismic sounding dds data is not always clear this is probably related to the heterogeneous basement which comprises the outer zone of the variscan belt in the southwest eec crust in the northeast and a complex of caledonian reworked precambrian crustal blocks in the central part of the basin changes to crustal architecture as a result of alpine tectonics may also play a role increased tectonic subsidence rates during oxfordian kimmeridgian times late jurassic correlate with intensified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin in contrast accelerating tectonic subsidence beginning in the cenomanian is a precursor of compressional deformations in the basin that culminated in alpine related basin inversion during the latest late cretaceous and earliest tertiary taking inversion into account the maximum depth of the base zechstein structural surface at the end of the cretaceous is estimated to have been as much as 5000 m near the baltic sea to more than 10 000 m in the southeasternmost part of the basin because of the erosion of these sediments however constraints on cretaceous subsidence and in turn the magnitude and exact timing of late cretaceous paleogene inversion are poor

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

effect of lateral viscosity variations in the top 300 km on the geoid and dynamic topography summary we have investigated the impact of lateral viscosity variations lvv in the top 300 km of the mantle on the long wavelength gravitational response of the earth in contrast to the previous studies we demonstrate that the lvv may play a crucial role if a model with imposed plate velocities and partial layering is considered assuming lvv in the top mantle associated with the continental roots and the oceanic asthenosphere we are able to explain a significant portion of the geoid 85 per cent and of the free air gravity data 55 per cent without invoking a complex radial viscosity profile or assuming a lithosphere with an unrealistically low uniform viscosity the best fit to the data is found for models in which mass anomalies located at the boundary between upper and lower mantles reduce the mass flux across the 660 km discontinuity by a factor of 3 these models are characterized by a low average value of viscosity in the asthenosphere below the oceans 10 19 pa s and a large viscosity contrast 100 between the young suboceanic mantle and the deep continental roots the viscosity in the deep upper mantle is found to be around 3 10 20 pa s while a value higher by at least two orders of magnitude is typical for the lower mantle the predicted dynamic surface topography is influenced by the surface plate velocities and its amplitude amounts to a few hundred metres besides investigating the viscosity structures that reflect the different thicknesses of the lithosphere in continental and oceanic regions we have searched for a large scale pattern of lateral viscosity variation in the top 300 km that yields the best fit to the geoid the pattern obtained by this inversion shows a good correlation with the ocean continent distribution and 90 per cent of the geoid and 67 per cent of the free air gravity can be explained

magmatic flare up at the carboniferous permian boundary in the ne german basin revealed by shrimp zircon ages shrimp ages of 12 volcanic samples indicate intense magmatic activity to have occurred at the carboniferous permian boundary throughout much of the ne german basin rhyolitic crystal rich samples have been taken from quarries in the halle volcanic complex hvc and in the flechtingen ignimbrite and from drill cores of the kotzen mirow friedland and penkun areas ten samples yielded 206pb 238u ages between 302 and 297 ma 3 ma respectively which indicate that the magmatic activity took place concentrated in a relatively short time span throughout much of the ne german basin two hvc samples have ages of 307 and 294 ma this remarkably synchronous magmatic activity occurred during the initial phase of the basin development considering published volume estimates 48 000 km3 extrusion rates during this time period probably were in the order of 0 01 km3 a 1 implying magma production rates of 0 1 km3 a 1 the calc alkaline sio2 rich volcanic rocks originated from magmas that presumably formed during anatexis and subordinate magma mixing in an intra continental transtensional setting the basaltic magma which must have provided the thermal input into the lower crust probably formed during decompressional melting of lithospheric mantle fertilised by previous magmatic processes the dated volcanic rocks occur in three geotectonic provinces namely the a mid german crystalline rise which forms the northern part of the internal variscides the b external variscides and the variscan foreland which is considered as c eastern avalonia many of the old zircons found in the hvc samples reflect the magmatic activity of the mid german crystalline rise 325 400 ma however cadomian 500 650 ma and older gondwanian elements 1674 2373 ma are also present although the flechtingen and kotzen areas are located within the external variscides it seems more likely that the middle to lower crust that experienced anatexis formed part of the eastern avalonia plate overridden by the variscan front thus the old zircons found in flechtingen 350 and 538 ma and kotzen 345 ma but certainly those present in the penkun drill cores 1483 ma represent eastern avalonia tectonic history the anatectic magmas in the friedland area probably formed partly from baltic crust thrusted below eastern avalonia during the caledonian orogeny among the old zircons from the friedland samples in addition to proterozoic ages 1456 ma we found testimony of caledonian 443 ma and of clearly post caledonian 387 ma magmatism

calamity peak layered granite pegmatite complex black hills south dakota part i structure and emplacement the calamity peak pluton is a satellitic granite pegmatite intrusion located 2 km southwest of the main harney peak granite dome in the black hills south dakota many aspects of the structural development of the calamity peak pluton 1 km 2 mimic those of the larger harney peak dome 100 km 2 thus the model described here for the calamity peak pluton provides a general basis for evaluating the evolution of proterozoic granite pegmatite intrusives of the harney peak granite system the overall structure of the intrusive rocks at calamity peak is that of a dome as shown by the general geometry of the pluton contacts and by a domical pattern of internal textural layering textural layering is defined by alternating bands of pegmatite and fine grained granite 0 1 2 0 m thick fine grained layers are in turn banded on a scale of 2 20 mm owing to modal variations of tourmaline quartz and feldspars textural differentiation of at least some of these layers resulted from segregation of initially homogeneous magmas into pegmatitic upper and aplitic lower components during crystallization relationships between the pluton and regionally dipping schistose country rocks however do not support a simple domal structure schistosity conforms to the contact only along the southern margin of the pluton the side facing with the regional dip country rock schistosity is at a high angle to the contact at the apparent floor of the pluton which is exposed in the core of the dome and along the northern margin the side that opposes the regional dip in order to explain the structural observations it is inferred that the initial intrusive body at calamity peak consisted of a flat lying discordant sheet intruded into steeply dipping quartz mica schist country rock however an arcuate sheet concave downward cannot be ruled out new magma pulses possibly several thousands were successively emplaced along the hanging wall contact of earlier pulses as indicated by the upward truncation of early layers creating a composite layered pluton intrusions of individual magma pulses were localized in three major composite sheets which form structurally and chemically discrete portions of the pluton growth of the pluton proceeded by forcible distension and plastic deformation of overlying country rocks schistosity was molded into a conformable attitude in portions of the hanging wall and pre intrusive country rock lineations were deflected around the pluton the layered granite pegmatite series is crosscut by four successive stages of fracture filling bodies the orientations and compositions of these bodies record the late stages in the structural and fluid evolution of the plutonic system

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

crustal structure below the polish basin is it composed of proximal terranes derived from baltica abstract the large scale seismic refraction and wide angle reflection experiment polonaise 97 together with lt 7 and ttz profiles carried out with the most modern techniques gave a high resolution of crustal structure of the trans european suture zone tesz in nw and central poland the results of seismic investigations show the presence of relatively low velocity rocks vp

numerical modelling of burial and temperature history as an approach for an alternative interpretation of the bramsche anomaly lower saxony basin the lower saxony basin germany is one of the several sedimentary basins within the central european basin system in its southwestern part anomalously high maturity of organic matter has been observed to reach 4 5 vrr in upper jurassic and lower cretaceous sedimentary rocks in an area which coincides with a magnetic and a positive gravimetric anomaly this anomaly was often interpreted as the consequence of a deep seated igneous intrusion the so called bramsche massif however results obtained from calibrated numerical modelling are not in accordance with this scenario instead a burial by approximately 4 km of now eroded cretaceous rocks was revealed to be the probable cause for the anomaly data and modelling results from six boreholes and two pseudo wells support this view

new information on the thermal history of the southwestern lower saxony basin northern germany based on fission track analysis the southwestern part of the lower saxony basin lsb is characterized by gravity and magnetic anomalies and by an extremely high thermal maturity of organic matter this was for many years attributed to a late cretaceous intrusion but actually deep burial is being debated the complex thermal history of the area has been studied by fission track analysis zircon data provide evidence for widespread hydro thermal activity during the permian and upper jurassic lower cretaceous apatite ages indicate a major cooling event in the mid cretaceous 89 72 ma reflecting the time of inversion of the lsb during the cretaceous the cooling of the basin centre was rapid compared to the basin margins apatite fission track ages from borehole samples which are recently within the upper part of the apaz indicate a young heating of the sedimentary sequences until present

polyphase thermal evolution in the infra cambrian ara group south oman salt basin as deduced by maturity of solid reservoir bitumen petrographic and organic geochemical analyses on solid reservoir bitumen from the late precambrian to early cambrian ara group indicate polyphase thermal evolution in the south oman salt basin sosb the ara group constitutes a complex petroleum system in the deep subsurface 3 5 km of interior oman salt diapirs encase isolated partly highly overpressured carbonate bodies intra salt stringers which represent a predominantly self charging hydrocarbon system a large number of stringer cores show that reservoir quality is decreased by the presence of solid reservoir bitumen by using different microscopy techniques this solid reservoir bitumen has been identified within pores pore throats and microfractures of the carbonates solid bitumen reflectance measurements brr were converted to vitrinite reflectance vrr using a new improved calibration vitrinite reflectance geothermometry shows that maximum paleo temperatures have a highly heterogeneous distribution paleo temperatures of 380 c were obtained from coke like solid reservoir bitumen which most likely formed from thermal cracking of oil in our model this process is related to hydrothermal fluids deriving from deeper pre salt strata of the sosb which entered the intra salt carbonate stringers during times of basement tectonic activity via hydrofractures this caused the formation of high maturities pyrobitumens in close vicinity to the fractures and precipitation of migrabitumens with increasing distance to the ht source which is supported by the geochemical composition of the solid reservoir bitumens the influx of these fluids into the carbonate stringers is considered to represent a major contribution to their strong overpressures 2007 elsevier ltd all rights reserved

transcurrent shearing granite sheeting and the incremental construction of the tabular 3 1 ga mpuluzi batholith barberton granite greenstone terrane south africa structural petrographic and geochronological studies show that the tabular 3 1 ga mpuluzi batholith in the barberton granite gneiss terrane in south africa was emplaced via a combination of external and internal processes external structural controls are indicated by systematic variations in intrusive relationships and strain along the margins of the mpuluzi batholith and are consistent with an emplacement of the granite in a dilational jog within a ne ene trending system of dextral transcurrent synmagmatic shear zones internally the mpuluzi batholith is essentially made up of granite sheets the structurally higher parts of the granite are made up of shallowly dipping sheets that are underlain by an anastomosing network of steeply dipping variably deformed dykes and sheets these granite sheets at lower structural levels intruded either into the actively deforming shear zones or into extensional sectors between and along the bounding shear zones multiple intrusive relationships and geochronological evidence suggests that granite sheeting and the assembly of the pluton occurred over a period of 3 13 ma the spatial and temporal relationship between deformation and magma emplacement reflects episodes of incremental dilation related to deformation along the bounding shear zones and granite sheeting the transition to the mainly subhorizontal granite sheets at higher structural levels of the tabular mpuluzi batholith indicates the intrusion of the granites during subhorizontal regional shortening where the reorientation of the minimum normal stress to vertical attitudes at the shallow levels of emplacement allowed for vertical dilation and subhorizontal emplacement of the granite sheets

new basin modelling results from the polish part of the central european basin system implications for the late cretaceous early paleogene structural inversion combined subsidence and thermal 1d modelling was performed on six well sections located in the north western mid polish trough swell in the eastern part of the central european basin system the modelling allowed constraining quantitatively both the mesozoic subsidence and the magnitude of the late cretaceous paleocene inversion and erosion the latter most probably reached 2 400 m in the mid polish swell area the modelled upper cretaceous thickness did not exceed 500 m and probably corresponded to 200 300 m in the swell area as compared with more than 2 000 m in the adjacent non inverted part of the basin such upper cretaceous thickness pattern implies early onset of inversion processes probably in the late turonian or coniacian our modelling coupled with previous results of stratigraphic and seismic studies demonstrates that the relatively low sedimentation rates in the inverted part of the basin during the late cretaceous were the net result of several discrete pulses of non deposition and or erosion that were progressively more pronounced towards the trough axis the last phase of inversion started in the late maastrichtian and was responsible for the total amount of erosion which removed also the reduced upper cretaceous deposits according to our modelling results a late cretaceous heat flow regime which is similar to the present day conditions about 50 mw m2 was responsible for the observed organic maturity of the permian mesozoic rocks this conclusion does not affect the possibility of late carboniferous permian and late permian early triassic thermal events

heterogeneous tectonic inversion of the mid polish trough related to crustal architecture sedimentary patterns and structural inheritance abstract using a 3 d structural model we performed a basin scale analysis of the tectonically inverted mid polish swell which developed above the nw se oriented teisseyre tornquist zone the later separates the paleozoic west european platform from the precambrian east european craton the model permits a comparison between the present depths and sedimentary thicknesses of five layers within the permian mesozoic and cenozoic successions the inversion of the nw se trending mid polish trough during the late cretaceous paleogene resulted in uplift of a central horst the mid polish swell bounded by two lateral troughs these structural features are induced by squeezing of a weak crust along the teisseyre tornquist zone the swell is characterized by an inherited segmentation which is due to ne sw transversal faults having crustal roots from nw to se we distinguish the pomeranian kujavian and malopolska segments that are separated by two transversal faults during the inversion the zechstein salt occurring in the pomeranian and kujavian segments in the nw acted as decoupling level between the basement and the post salt cover leading to disharmonic deformation conversely because no salt occurs in the se both basement and cover were jointly deformed the vertical tectonic uplift at the surface is estimated to amount to 3 km in the malopolska segment the structural inheritance of the basement is expressed by the heterogeneous geometry of the swell and tectonic instability during mesozoic sedimentation the reasons for the inheritance are seen in the mosaic type paleozoic basement sw of the teisseyre tornquist zone contrasting the precambrian east european craton which acted as a stable buttress in the ne the horst and trough geometry of cenozoic sediments blanketing the mid polish swell reveals the ongoing intracontinental compressional stress in poland

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

sheeted intrusion of the synkinematic mcdoogle pluton sierra nevada california field microstructural and geochronologic evidence indicates that the late cretaceous mcdoogle pluton located near the eastern margin of the sierra nevada batholith was emplaced as a subvertically sheeted complex into a steep reverse sense shear zone evidence of internal subvertical sheeting includes abundant concordant wall rock inclusions and screens that separate the pluton from adjacent jurassic plutons preservation of a ghost tectonostratigraphy in the distribution of the inclusions and rare interphase contacts the solid state tectonic fabric in the wall rocks and the magmatic submagmatic and weak solid state fabrics in the mcdoogle pluton all are concordant and record northeast southwest horizontal shortening subvertical extension and a significant component of northeast side up simple shear intrusive contacts generally are concordant with the fabrics but where discordances occur the wall rock fabric invariably is truncated by the contact however late synkinematic emplacement of the mcdoogle pluton is indicated by synintrusive boudinage of apophyses of the pluton and by the overall concordance of pluton fabrics including magmatic lineation zircon u pb isotope dates were obtained from the quartz monzodiorite central phase of the mcdoogle pluton 94 4 ma the mafic granodiorite border phase 94 8 0 6 ma and an older hornblende granodiorite included in the central phase 97 6 0 4 ma granodiorite orthogneiss in the wall rock yielded a u pb zircon date of 164 2 1 6 8 ma which we interpret to be the crystallization age and which is indistinguishable from a new age of 164 5 2 3 ma for the twin lakes pluton a u pb titanite date of 94 4 0 9 ma from the 164 ma orthogneiss sample may reflect thermal effects of the intruding mcdoogle pluton synkinematic growth of titanite in the shear zone or perhaps both the age of the sawmill lake shear zone that hosts the mcdoogle pluton is bracketed between 148 ma the age of the independence dike swarm and 92 ma the age of the lamarck pluton that crosscuts both the mcdoogle pluton and the shear zone fabrics regional evidence suggests a shear zone age younger than 110 ma but older deformation is possible the predominance of horizontal shortening over transcurrent motion and an age older than 90 ma exclude a direct relationship to the dextral sierra crest shear system which has been proposed to pass near the study area the location age constraints and kinematics of the shear zone are consistent with both the later stages of movement in the east sierran thrust system and isostatic sinking of the arc magmatic complex into its substrate

assembly of a dike fed magma chamber the jackass lakes pluton central sierra nevada california the mechanisms of ascent assembly and emplacement of granitic magma in the crust are critical to understanding the dynamics of continental margin growth yet these mechanisms remain controversial and poorly understood detailed study of structural and petrologic fabrics in the middle cretaceous jackass lakes pluton wall rock system central sierra nevada california coupled with u pb geochronology indicates that the pluton formed via sheet like assembly of a dike fed magma chamber final emplacement of the pluton was facilitated by multiple brittle and ductile mechanisms that were active at different times and places within the system this supports hybrid viscoelastic emplacement models as realistic alternatives to end member models i e dike versus diapir fracture propagation which initiated 40 of the space required for emplacement may have been facilitated by a small component of arc parallel dextral shear that produced north northwest striking tension gashes a combination of ductile wall rock shortening during lateral expansion of sheets and return flow of elongate strongly deformed wall rock septa produced an additional 25 of the space required other mechanisms including coeval formation of the overlying minarets caldera and stoping in the subvolcanic part of the magma chamber must account for the remaining 35 space implying that vertical transfer of material is an important emplacement mechanism at shallow crustal levels

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

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

hydrocarbon downward accumulation from an upper oil source to the oil reservoir below in an extensional basin a case study of chezhen depression in the bohai bay basin abstract there is a disputable theory that hydrocarbon can be injected into the reservoir and migrate downward in an oil reservoir with an upper oil source which is still questioned now however although some examples are previously found questions still remain about the theory regarding oil sources oil migration pathways and migration forces that related to downward hydrocarbon migration for this reason the chezhen graben in the bohai bay basin is selected to study all the problems above geo chemical evidence show that lower es3 source rock t6 in seismic profiles has a close genetic relationship with the underlying es4 t7 in seismic profiles and ordovician oil therefore the upper source lower reservoir type can be formed inside the lower gentle slopes and sag zones and inside the cambrian and permian reservoirs the fluid inclusion experiment shows that the lower es3 source rock underwent 3 over pressure evolution stages meanwhile there is a huge pressure difference between the lower es3 source rock and underlying es4 reservoirs which is the migration force of downward migration in the lower areas of gentle slopes and sags the early generated and early ended faults are terminated at the source rock of es3 member and can be re opened under the over pressure influence of the source rock and regional tensile stress then they become the pathways of the so called downward migration the distance of downward migration can be calculated through the accumulation dynamic which is obtained by hydrocarbon pressure subtracting the reservoir hydrostatic pressure pressure attenuation and displacement pressure the research result on downward migration process is of great significance to broaden the hydrocarbon exploration fields

late cretaceous cenozoic thermochronology in the southern songliao basin ne china new insights from apatite and zircon fission track analysis abstract the late cretaceous cenozoic thermochronology in the southern songliao basin was determined using apatite and zircon fission track analysis data it is crucial to deciphering the evolution of the songliao basin and changes in the movement direction of the pacific plate we present eight new apatite and eight corresponding zircon fission track data from borehole samples across the baixingtu uplift the apatite fission track aft thermochronological modeling reveals that the basin underwent two distinct compression and extension related uplift stages of rapid cooling during the late cretaceous cenozoic stage i during the late cretaceous early paleogene 70 52 ma stage ii in the late paleogene early neogene 38 10 ma the aft data vary from 76 0 5 0 to 25 3 1 9 ma and the zircon binomial peak fitting ages ranged from 79 to 61 ma all younger than the stratigraphic ages 92 88 ma of their host rocks one sample had similar fission track ages apatite 76 0 5 0 ma and zircon 79 0 3 0 ma within reasonable error representing a magmatic event the data were divided into four groups i 79 76 ma magmatic cooling event ii 69 61 ma uplift of the whole region and exhumation and erosion iii 37 34 ma and iv 25 ma various uplift events related to tectonic inversion causing partial uplift exhumation and erosion in the basin this created favorable conditions for formation and storage of mineral resources especially sandstone uranium ore deposits our results combined with previous research suggest that the variation in uplift and exhumation began in the basin s se part and propagated to the nw 5 8 ma later the tectonic inversion in the southern songliao basin at least began 37 34 ma this corresponds with the time of the paleo pacific plate shifting to nww motion and the india asia collision these regional scale uplift exhumation and inversion events were probably responses to the subduction and turning of the paleo pacific plate from the southeast and the collision of the indian subcontinent from the southwest it is important to study the tectonic inversion in the whole east of china since the late cretaceous and the change of the direction of the pacific plate movement

maturity modelling integrated with apatite fission track dating implications for the thermal history of the mid polish trough poland abstract the mid polish trough mpt is situated in the easternmost part of the central european basin system cebs and stretches nw se across the polish basin it was characterised by pronounced subsidence and thick sediment accumulation between the permian and the late cretaceous late cretaceous early paleogene basin inversion led to the formation of the mid polish swell mps the study area is located within the pomeranian segment of the mpt mps nw poland and experienced up to 7 km permian mesozoic subsidence petromod 1 d modelling was performed on several well sections in order to study permian to recent burial uplift evolution the modelling was calibrated with new vitrinite reflectance vrr data and allowed to constrain the magnitude of uplift and related erosion as well as provided a first overview of the temperature history the base of the studied permian mesozoic successions attained maximum burial depths of 4800 5400 m before the onset of the inversion less than in the axial trough area the thickness of pre and most probably also syn inversion upper cretaceous deposits is estimated as 300 m erosion associated with inversion processes removed between 900 and 1400 m of the mesozoic sediments i e 1000 1500 m less than in the most inverted central part of the trough vrr data suggest constant permian mesozoic heat flows corresponding to present day values 40 45 mw m2 apatite fission track aft ages modelled with the petromod module petrotracks show a good fit with aft ages directly measured on well samples and further support the assumption of steady heat flow in the range 40 45 mw m2 palaeotemperatures appear to have decreased towards the east european craton margin which is compatible with the present day distribution of heat flow thermal history modelling shows a relatively simple permian mesozoic heat flow pattern in the pomeranian segment of the mpt such a scenario implies that the present day heat flow distribution has not changed essentially since mesozoic times

a tectonic model for the emplacement of the main donegal granite nw ireland the main donegal granite is shown to lie in a major late stage ne sw trending transcurrent sinistral shear zone in the caledonides of nw ireland the zone which is bent both laterally and upwards around the pluton has displacements which diminish sw along its length from a maximum of approximately 20 km at the ne end of the pluton the granite has also been deformed by this sinistral shear but it has a strain component of its own the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone strain variations between granite and wall rock and an early plagioclase fabric associated with the petrographic banding of the granite suggest that intrusion and deformation were more or less synchronous at around 400 ma it is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend split lengthwise and progressively create an internal low pressure zone into which the main granite was emplaced the wide variety of emplacement styles of the other radiometrically synchronous plutons of the batholith can be attributed to the progressive development of the shear zone thorr and fanad in tension between the zone and a complimentary structure to the n ardara and toories in local compression at the shear zone termination rosses in tension on the outer arc of the bending zone and trawenagh bay as displaced main granite magma in a similar tensional setting during the final stages of deformation

four magmatic fabrics in the tuolumne batholith central sierra nevada california usa implications for interpreting fabric patterns in plutons and evolution of magma chambers in the upper crust for the first time four distinct magmatic fabrics are documented in a composite plutonic body the tuolumne batholith central sierra nevada california usa one type of fabric was formed by strain caused by highly localized magma flow type 1 whereas the other three chamber wide fabrics recorded strain increments during boundary processes along batholith margins type 2 superimposed by increments of heterogeneous regional tectonic strain types 3 and 4 our present work indicates that in contrast to studies that consider magmatic fabrics to be simple structures formed by a single process magmatic lineations and foliations in plutons may reflect accumulated finite strain and form as composite structures recording multiple strain increments in relatively static actively deforming and rheologically complex crystal mushes at lower melt percentages we demonstrate that multiple magmatic fabrics in a single batholith may record remarkably different processes and thus preserve a temporal record of strain in the batholith from strain during internal chamber processes to postem placement regional tectonic strain however it may be commonly very problematic to infer the exact nature of flow or even fabric forming process from the preserved rock record our study also exemplifies how examination of magmatic fabric patterns in plutons complemented with geochronology may provide crucial constraints on the interplay among successive magma emplacement fabric preservation temporal evolution of strain fields in a crystallizing magma chamber and the development of crystal mush zones

comparative organic petrology of interlayered sandstones siltstones mudstones and coals in the upper carboniferous ruhr basin northwest germany and their thermal history and methane generation in the coal mining ruhr area upper carboniferous rocks ca 4000 m consist of interlayered sandstones siltstones mudstones and coals they were deposited in a tropical paralic environment where alternating fluvial sedimentation occasional marine ingressions and swamp growth resulted in an irregular cyclic succession the total sedimentary package contains on an average 6 vol of organic matter about 70 vol of the organic matter occurs in coal seams the rest as dispersed organic matter in clastic rocks the organic matter is autochthonous in the coals and allochthonous in associated sandstones and siltstones it consists of about 70 vitrinite 20 inertinite and 10 liptinite the overall maceral group composition is the same for coals and dispersed organic matter this surprising similarity is caused by a nearly exclusive input of land plant derived organic matter to swamps and fluvial systems and a similar degree of preservation highest average liptinite contents of total macerals were found in unrooted mudstones highest average inertinite contents in coarse grained siltstones and highest average vitrinite percentages in sandstones

how to deal with missing overburden investigating exhumation of the fragment of the mid polish anticlinorium by a multi proxy approach abstract tectonic inversion and erosion conceal basin geological history as simple stratigraphic reconstructions can be inaccurate thermal modelling techniques are often applied in this paper we show the advantages of a multi proxy approach for exhumation studies which explores full range of all possible solutions the part of the mesozoic central european basin that was inverted into the mid polish anticlinorium in the late cretaceous is chosen as a case study the analysis consists of three steps first a wide range of possible geological scenarios is constructed accounting for two alternatives of the overburden sequence southern and northern that result from the impact of the holy cross fault on mesozoic deposition the second stage comprises apatite fission track and vitrinite reflectance analyses carried out on a 1500 m long vertical profile inverse modelling of these data to obtain thermal histories and 1d thermal modelling of burial erosion using the petromod software in the third step results of modelling exercises are combined with probabilities of the overburden variants to define an ensemble of the most likely geological scenarios by applying this workflow we conclude that exhumation of the mid polish anticlinorium began in the latest turonian early campanian and that 1 7 2 3 km of uppermost triassic cretaceous rocks were removed the heat flow was similar or slightly higher than the present day value and during the jurassic the study area was located on the northern side of the holy cross fault where deposition was faster we also investigate the impact of elevated late palaeozoic heat flow on our samples and find that it was overprinted by high late cretaceous temperatures all this is achieved by presenting the results as an ensemble of the most likely solutions within the wide modelling space

construction solidification and internal differentiation of a large felsic arc pluton cathedral peak granodiorite sierra nevada batholith the tuolumne batholith tb sierra nevada batholith usa is an archetypal large zoned arc intrusion c 1200 km 2 previous work proposed that compositional zonation observed in the tb was produced in situ by inward differentiation of a large magma chamber and or large scale intrachamber magma mixing recent geochronology shows that the tb was intruded over 8 9 ma making single pulse fractionation or mixing in a magma chamber of tb dimensions unlikely we examine processes responsible for compositional variation in the cathedral peak granodiorite which is the largest mapped unit of the tb new field geochemical and geochronological work along a roughly contact perpendicular 5 km transect indicates 1 magmatic foliation is steeply dipping 60 2 field evidence for repeated separation of crystals from melt and local magma mixing is observed 3 u pb zircon ages at opposing ends of the transect are indistinguishable within error c 87 5 ma 4 bulk composition varies only modestly but trace elements show variable degrees of scatter 5 end t and 87 sr 86 sr i have small variation compared with that in the whole tb geochemical and isotopic data are compatible with fractionation of major silicates and accessory minerals however the geochemical spatial variation minor isotopic variation and field evidence suggest that fractionation was highly disorganized and also involved mixing with new input magma and remobilization of crystal mush as the pluton solidified our observations are consistent with the construction of a large and dynamic magma system within the last c 1 ma of tb growth

geothermal regime and source rock thermal evolution in the chagan sag inner mongolia northern china abstract the chagan sag has the greatest oil and gas exploration potential among other sags in the yingen ejinaqi basin inner mongolia the average geothermal gradient in the chagan sag is 33 6 c km whereas the heat flow ranges from 65 9 mw m 2 to approximately 85 5 mw m 2 with an average value of 74 5 mw m 2 thermal history reveals that the chagan sag experienced the following 4 stages of thermal evolutions 1 a rapidly increasing geothermal gradient stage from the early cretaceous bayingebi formation depositional period to the early cretaceous suhongtu formation depositional period 2 a geothermal gradient peak stage during the early cretaceous yingen formation depositional period 3 a high geothermal gradient continuation stage during the late cretaceous wulansuhai formation depositional period and 4 a thermal subsidence stage during the cenozoic tectonic subsidence analysis reveals that the area experienced an initial synrift subsidence during the early cretaceous followed by a subsequent long term thermal subsidence since late cretaceous thermal and tectonic subsidence histories of this area are of great significance to petroleum exploration and hydrocarbon resource assessment because they bear directly on issues of source rock maturation the maturation histories of the 3 sets of source rocks in the sag were modeled on the basis of the present geothermal field thermal history and tectonic subsidence history the results reveal that the hydrocarbon generation of the chagan sag was controlled by the early cretaceous geothermal fields and the source rock maturity reached the maximum at the end of the yingen formation depositional period moreover the maturation evolution degree shows a difference for the 3 sets of source rocks the source rocks of the bayingebi 1 and 2 formations reached the middle mature and dry gas stage in contrast the source rocks of the suhongtu 1 formation only reached the early mature and middle mature stage this work may provide new insights for the understanding of the oil and gas exploration potential of the chagan sag

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

mesoscale pervasive felsic magma migration alternatives to dyking abstract this paper reviews the literature on dyking as a mechanism of felsic magma extraction from a source and transport to shallower crustal levels and review the recent literature suggesting a range of alternative mechanisms of magma migration in hot crustal zones which produce mesoscale pervasive granite sheet intrusions recent papers have strongly favoured dyking as the main mechanism controlling magma migration however the initiation of dykes from a felsic magma source is fraught with difficulties even when magma is immediately available for transportation as in magma chambers within a partially molten source magma may reside in a range of structures with a wide range of shapes sizes and degrees of connectivity whereas the growth of individual dykes within a partially molten zone and the self propagation of large dykes into subsolidus crust have both been studied in some detail little attention has been given to the crucial intermediate step of the growth of a dyke network capable of producing wide crustal scale dykes the rarity of granite dyke swarms suggests that if dyking is the preferred mechanism of magma transport felsic magma sources produce only few major transporting dykes during their lifetime alternatively dyking is not an important mechanism the parameters controlling the volume of the catchment drained by one such dyke as well as other basic geometrical parameters controlling the structure of the dyke network within the source are unknown the ability of dyking to drain a partially molten source depends crucially on these variables and particularly on the horizontal permeability of the source the slow velocity of viscous felsic magmas traveling in rock pores implies that magma drained during dyking is mostly that previously extracted from the pores and resident in irregular magma bodies or dyke networks the observation that large volumes of buoyant magma are commonly present in migmatite zones and that dyking in these zones plays a secondary role suggest that dyking is inefficient and is able to extract only a fraction of the total melt available in the source in support of this conclusion recent detailed studies of exhumed hot crustal zones have revealed a range of alternative migration mechanisms characterized by mesoscale pervasive magma flow outcrop scale as opposed to porous flow pervasive migration gives rise to magma sheets preferentially emplaced parallel to high permeability zones such as foliation or bedding planes apart from local dyking three alternative mechanisms have been proposed to account for pervasive migration of magmas namely tectonic pumping magma wedging into low viscosity rocks and volatile driven intrusion because of their unfocused pervasive character these mechanisms are restricted to hot crust where magmas are not exposed to rapid freezing a model is proposed whereby heat advected with the magma pushes crustal geotherms upwards allowing pervasive magma migration to shallower depths

modelling diverse processes in the petrogenesis of a composite batholith the central bohemian pluton central european hercynides the multiple intrusions making up the central bohemian pluton in the central european hercynides have petrographic and geochemical features consistent with the presence of four main granitoid suites major element trace element and sr nd isotopic compositions are used to model their petrogenesis partial melting of metabasic locks or of a chur like mantle source are interpreted to have produced melts parental to the most primitive calc alkaline sazava suite interaction of basic with more acidic magmas followed by extensive amphibole plagioclase dominated fractionation accounts for the production of trondhjemites alternatively the trondhjemites correspond to small degree melts of a metabasic source afc assimilation fractional crystallization modelling with a paragneiss as a contaminant and increasing d nd values simulates the characteristics of the blatna suite closed system fractionation of strongly enriched mantle derived magmas or their interaction with leucogranitic melts is deduced for the petrogenesis of the shoshonitic certovo bremeno suite partial melting of a metasedimentary source followed by k feldspar dominated fractionation accounts for the granites of rite ricany suite the progression from relatively primitive calc alkaline granitoids towards evolved k rich calc alkaline and shoshonitic rocks is interpreted to reflect the increasing enriched mantle input in the petrogenesis of the later suites the evidence for hercynian subduction is equivocal and the mantle enrichment could have been significantly older

how extensive are subsolidus grain shape changes in cooling granites abstract the hypothesis that granites sensu lato commonly undergo extensive grain shape changes recrystallization during cooling is not supported by microstructural evidence especially the abundance of non truncated zoning patterns in mineral grains regional metamorphic felsic gneisses that have undergone extensive neocrystallization recrystallization at amphibolite facies conditions which some have suggested are equivalent to those in slowly cooling granites typically lose igneous microstructures including oscillatory zoning and are characterized by polygonal to irregularly xenoblastic grains of quartz and feldspar as well as by rounded inclusions of quartz in feldspar and vice versa in contrast granites typically show oscillatory zoning especially in plagioclase elongate euhedral to subhedral feldspar grains and euhedral plagioclase inclusions in quartz and k feldspar the contrast between these two situations is probably the result of felsic gneisses undergoing chemical reactions and regional deformation especially in the presence of water released pervasively from dehydration reactions which are strong driving forces for the production of new grains whereas the minerals in cooling granites are chemically compatible without strong deformation and so do not react with each other or recrystallize therefore massive granites without solid state foliations generally do not undergo grain shape changes owing to inadequate driving forces as well as to decreasing temperature an important implication of this conclusion is that internal structures formed during chamber construction and magmatic flow in granite plutons are not likely to be removed by subsolidus intergranular microstructural changes

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

the great tonalite sill emplacement into a contractional shear zone and implications for late cretaceous to early eocene tectonics in southeastern alaska and british columbia the late cretaceous to early tertiary great tonalite sill of southeast alaska and british columbia is a very long 1 000 km and thin 25 km orogen parallel composite batholith which lies between the insular superter rane including the alexander and wrangellia terranes and the intermontane superterrane including the stikine and cache creek terranes the batholith is delineated by many steep sheet like plutons which are dominated by northwest southeast striking concordant fabrics with steep lineations that formed during deformation in a country rock shear zone prior to the complete crystallization of the magmas deformation in this shear zone is dominated by northeast southwest directed contraction orthogonal to the orogenic strike associated with a component of northeast over southwest high angle shear the steep multiple dike like nature of the body and its emplacement during orogenic contraction imply that ascent and emplacement have been achieved by dike wedging mechanisms along the deep reaching shear zone the remarkable narrowness of the great tonalite sill is probably the result of melting at the base of a very localized zone of thickened crust produced by the associated narrow contractional shear zone extending along the orogen length such a shear zone of late cretaceous to early tertiary age lying along 800 km of the possible boundary between the insular and intermontane superterranes implies that it may represent the actual boundary between them if this hypothesis is correct it implies that the large scale tectonic regime during emplacement of the great tonalite sill was predominantly orthogonal and not obliquely dextral as has been indicated from paleomagnetic data

mafic injections in situ hybridization and crystal accumulation in the pyramid peak granite california located in the northern sierra nevada the middle jurassic pyramid peak granite and associated dioritic rocks display superbly exposed interlayered sheets of mafic felsic and hybrid rocks the mafic hybrid layers show a consistent asymmetry sharply chilled on one side and gradational through hybrids to granite on the other and dip to the southwest load casts and silicic pipes along the chilled mafic northeastern margins of the sheets indicate that depositional way up is to the southwest and that the adjacent mount tallac roof pendant was the original floor of the intrusion orientations of the pipes indicate that the layers were tilted after deposition and solidification we interpret the sheets to be intramagmatic flows that formed by injections of mafic magma into a silicic magma chamber followed by flow across the crystal rich base of that chamber the granitic and hybrid rocks interlayered with the mafic sheets represent material that accumulated on the chamber floor between episodes of mafic replenishment most contamination of the mafic sheets probably occurred because of flow front instabilities generated as the mafic magma entered and spread across the chamber floor the upward gradation from diorite to granite with decreasing abundance and size of mafic enclaves can best be explained by convective stirring at the upper boundaries of the dioritic replenishments the pyramid peak granite was probably initiated as a thin concordant sheet intruding into gently dipping jurassic supracrustal rocks the pluton was constructed incrementally with many replenishments of felsic and mafic magma and dominantly solidified by accumulation of crystals on the floor of the chamber the present steep dips of the layers suggest that downward warping of the chamber floor may have been a factor in accommodating the incrementally constructed pluton

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

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

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

sheeting and dyking emplacement of the gunnison annular complex sw colorado abstract emplacement of the proterozoic gunnison annular complex colorado involved brittle failure and both subhorizontal sheeting and steeply dipping dyking the annular complex consists of a central diorite body 1730 ma surrounded by a ring of metamorphosed supracrustal rocks in turn ringed by tonalite and granodiorite 1721 ma the older central diorite was emplaced as sills parallel to bedding prior to regional deformation of the gunnison volcanic arc 1730 1710 m y ago this central body was deformed during regional shortening into an upright bowl with inward dipping walls the surrounding country rocks were folded and locally transposed against the central body forming an arcuate foliation conforming roughly to the shape of the body this foliation and bedding acted as mechanical planes of weakness which localized the syn deformational emplacement of the outer ring intrusions as multiple magma sheets parallel to steeply dipping bedding and foliation portions of the outer rings were also injected along concentric inward dipping shear fractures generated under high magma pressure a process similar to cone sheet emplacement in volcanic ring dyke complexes multiple mechanisms were therefore involved in the emplacement of this sheeted annular plutonic complex which otherwise superficially resembles a subvolcanic ring dyke complex

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved