a petrogenetic grid for pelites in the ballachulish and other scottish thermal aureoles the ballachulish granite is a composite devonian intrusive complex surrounded by a distinctive thermal aureole developed in regionally deformed and metamorphosed dalradian sediments on the w coast of scotland the most abundant rocks in the aureole are pelites which show a progression of assemblages from quartz muscovite chlorite up to a variety of high grade assemblages involving combinations of cordierite corundum spinel and rarely hypersthene and garnet metamorphic zones have been mapped around the granite which are defined by the following reactions going upgrade mu chl q cd bi v mu bi q cd kf v or mu cd q bi as v mu q as kf v q bi as cd kf v or mu cd bi as kf v mu cor kf v bi as cor kf cd v the restricted occurrences of assemblages involving spinel hypersthene and garnet do not allow higher grade zones to be mapped variations in the reaction sequence as a consequence of bulk compositional factors in particular the development of quartz bearing versus quartz absent assemblages are described details of the mineral assemblages from ballachulish are combined with high grade assemblage data from the belhelvie lochnagar and comrie aureoles to construct a comprehensive schematic petrogenetic grid the grid involves the minerals quartz chlorite muscovite biotite cordierite alumino silicate k feldspar corundum spinel hypersthene and garnet whose assemblage relationships are modelled in the system k 2 o feo mgo al 2 o 3 sio 2 h 2 o kfmash

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

evidence for a rapid release of carbon at the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm and associated carbon isotope excursion cie are often touted as the best geologic analog for the current anthropogenic rise in pco2 however a causal mechanism for the petm cie remains unidentified because of large uncertainties in the duration of the cie s onset here we report on a sequence of rhythmic sedimentary couplets comprising the paleocene eocene marlboro clay salisbury embayment these couplets have corresponding 18o cycles that imply a climatic origin seasonal insolation is the only regular climate cycle that can plausibly account for 18o amplitudes and layer counts high resolution stable isotope records show 3 5 13c decrease over 13 couplets defining the cie onset which requires a large instantaneous release of 13c depleted carbon during the cie a clear 13c gradient developed on the shelf with the largest excursions in shallowest waters indicating atmospheric 13c decreased by 20 our observations and revised release rate are consistent with an atmospheric perturbation of 3 000 gigatons of carbon gtc

an abyssal carbonate compensation depth overshoot in the aftermath of the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum was associated with a massive release of carbon marine sediments suggest a temporary deepening of the calcite compensation depth indicating extensive silicate weatheringin the aftermath of the event the palaeocene eocene thermal maximum was associated with a massive release of carbon marine sediments suggest a temporary deepening of the calcite compensation depth indicating extensive silicate weatheringin the aftermath of the event during the palaeocene eocene thermal maximum petm about 56 million years ago thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years followed by gradual sequestration over approximately 200 000 years if silicate weathering is one of the key negative feedbacks that removed this carbon a period of seawater calcium carbonate saturation greater than pre event levels would be expected during the event s recovery phase in marine sediments this should be recorded as a temporary deepening of the depth below which no calcite is preserved the calcite compensation depth ccd previous and new sedimentary records from sites that were above the pre petm ccd show enhanced carbonate accumulation following the petm a new record from an abyssal site in the north atlantic that lay below the pre petm ccd shows a period of carbonate preservation beginning about 70 000 years after the onset of the petm providing the first direct evidence for an over deepening of the ccd this record confirms an overshoot in ocean carbonate saturation during the petm recovery simulations with two earth system models support scenarios for the petm that involve a large initial carbon release followed by prolonged low level emissions consistent with the timing of ccd deepening in our record our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the ccd and at least in the north atlantic an over deepening of the ccd

paleogene sedimentation changes in lenghu area qaidam basin in response to the india eurasia collision the cenozoic india eurasia collision is evidently recorded in the qaidam basin which is located in the north margin of the tibetan plateau the present study describes a dextrorotary phenomenon at the end of the eocene in lenghu area in the northern qaidam basin discovered in sedimentary and tectonic records this phenomenon is interpreted to have been a result of the levorotatory movement along the altyn tagh fault atf based on the following evidence first provenance as analyzed by heavy mineral assemblages was slightly deflected from southwestward to the westward by about 45 second paleocurrent inferred from dip logging and seismic reflection changed clockwise by approximately 25 third there is evidence of increases in fault activity in the area especially in northwest southeast trending branches relative to older west east trending branches increases in faulting coincide with abrupt increases in sediment supply in the oligocene after earlier decreases based on total sand content during the eocene our results demonstrate that the northern margin of the tibetan plateau synchronously responded to the initiation and termination of the india eurasia collision the levorotatory strike slip of the atf was immediately triggered by the complete collision at the end of eocene and the strike slip movement caused the dextrorotary phenomenon in the lenghu area

pro and retrograde p t evolution of granulites of the beit bridge complex limpopo belt south africa constraints from quantitative phase diagrams and geotectonic implications interpretations based on quantitative phase diagrams in the system cao na2o k2o tio2 mno feo mgo al2o3 sio2 h2o indicate that mineral assemblages zonations and microstructures observed in migmatitic rocks from the beit bridge complex messina area limpopo belt formed along a clockwise p t path that path displays a prograde p t increase from 600 c 7 0 kbar to 780 c 9 10 kbar pressure peak and 820 c 8 kbar thermal peak followed by a p t decrease to 600 c 4 kbar the data used to construct the p t path were derived from three samples of migmatitic gneiss from a restricted area each of which has a distinct bulk composition 1 a k al rich garnet biotite cordierite sillimanite k feldspar plagioclase quartz graphite gneiss 2 a k poor al rich garnet biotite stauro lite cordierite kyanite sillimanite plagioclase quartz rutile gneiss and 3 a k al poor fe rich garnet orthopyroxene biotite chlorite plagioclase quartz rutile ilmenite gneiss preservation of con tinuous prograde garnet growth zonation demonstrates that the pro and retrograde p t evolution of the gneisses must have been rapid occurring during a single orogenic cycle these petrological findings in combination with existing geochronological and structural data show that granulite facies metamorphism of the beit bridge metasedimentary rocks resulted from an orogenic event during the palaeoproterozoic c 2 0 ga caused by oblique collision between the kaapvaal and zimbabwe cratons abbreviations follow kretz 1983

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

two massive rapid releases of carbon during the onset of the palaeocene eocene thermal maximum the release of massive amounts of carbon led to abrupt warming 55 5 million years ago an analysis of soil carbonates shows two distinct carbon injections at the event onset each releasing over 0 9 petagrams of carbon per year over hundreds to thousands of years

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

how long lived is ultrahigh temperature uht metamorphism constraints from zircon and monazite geochronology in the eastern ghats orogenic belt india abstract along the coast of peninsular india the eastern ghats expose a deep crustal section through a composite proterozoic orogenic belt to quantify the late mesoproterozoic early neoproterozoic pressure p temperature t time t evolution of the eastern ghats province new shrimp u pb zircon and monazite age data from multiple localities are reported and integrated with the results of phase equilibria modelling samples of residual granulite migmatite and enderbite yield a spread of weighted mean 207pb 206pb zircon and monazite ages between ca 970 and ca 930 ma based on ranges of spot ages from several samples the late prograde to peak ultrahigh temperature uht metamorphism counter clockwise evolution ccw to t 950 c at p 8 kbar and initial cooling is interpreted to have occurred between ca 1130 and ca 970 ma regionally extensive enderbite and charnockite magmas were emplaced into the hot suprasolidus crust around the time of peak metamorphism for the residual granulites and migmatites the retrograde p t t path is characterized by close to isobaric cooling to the variable but elevated solidi for different samples weighted mean ages between ca 970 and ca 930 ma in several samples are interpreted to record the timing of crystallization of melt trapped by the percolation threshold in each of these samples two additional weighted mean ages of ca 980 ma from korhonen f j saw a k clark c brown m bhattacharya s 2011 new constraints on uht metamorphism in the eastern ghats province through the application of phase equilibria modelling and in situ geochronology gondwana research 20 764 781 extend this range back in time by 10 my the variability in the calculated weighted mean ages across the region is interpreted to be due mainly to differences in the temperature of the elevated solidus from sample to sample suggesting a slow cooling rate of 1 c my during the retrograde stage of this long lived uht metamorphism these results demonstrate that the eastern ghats province sustained uht conditions t 900 c for 50 my and perhaps for as long as 200 ma from ca 1130 to 930 ma during a single ccw tectono metamorphic event

illite smectite formation and potassium mass transfer during burial diagenesis of mudrocks a study from the texas gulf coast paleocene eocene abstract mudrock samples from a well penetrating eocene and paleocene strata 1235 4455 m of the texas gulf coast have been studied to assess geochemical redistribution in mudrocks during burial diagenesis and the mechanism by which detrital smectitic illite smectite i s is transformed into diagenetic illitic i s idealized smectite and illite end member compositions for interstratified i s are estimated to be k0 00x 10 56mg0 39fe0 57al1 13si3 90o10 oh 2 and k0 53x 10 18mg0 17fe0 16al2 28 si3 40o10 oh 2 respectively there is no obvious difference in the amount of k addition to i s in random and ordered interstratified i s aluminum substitution into both tetrahedral and octahedral sites suggests that the smectite to illite reaction is a complete dissolution precipitation reaction rather than a solid state k 1 al 3 for si 4 substitution reaction depth relat d mineral trends and mass balance calculations suggest that illitic i s may form from kaolinite and possibly illite or mica as well as from smectitic i s although most whole rock element abundances are invariant over the sampled depth interval k2o content increases from ca 2 0 weight percent at 1500 m of burial to ca 3 8 weight percent at 4000 m some of this increase is probably caused by import of k into the shale via fluids derived from interbedded sandstones implying that gulf coast mudrocks behave as open chemical systems during burial diagenesis if this is the case a minimum of 103 pore volumes of fluid must have passed through the most k enriched shales to have introduced the added potassium provided that the k content of present day formation water is representative of that of ancient formation water

transient drying during the paleocene eocene thermal maximum petm analysis of paleosols in the bighorn basin wyoming abstract the paleocene eocene thermal maximum petm was a transient episode of global warming that occurred at the paleocene eocene boundary the event is marked by a sharp decline in carbon isotope values that is globally recognized from marine and continental sections the negative isotope excursion has been attributed to the release of methane hydrates from oceanic sediments although studies concur that temperatures rose during the petm changes in precipitation are not well understood alluvial paleosols in the bighorn basin that span the petm interval contain a continuous and highly resolved record of climate including information on precipitation they show a significant but transient decrease in precipitation at the onset of the petm but a gradual return to pre petm levels by the end of the interval the paleosols also show additional although less dramatic wet dry cycles within the petm interval that may correspond to precessional cycles that have been identified in the marine record of the petm this study counters interpretations of increased precipitation for wyoming at this time and shows the importance of detailed case studies of continental strata to test climatic generalizations and models that have been developed for petm precipitation patterns

orthopyroxene sillimanite sapphirine granulites from the bamble granulite terrane southern norway silica deficient sapphirine bearing rocks occur as an enclave within granulite facies proterozoic gneisses and migmatites near grimstad in the bamble sector of south east norway hasleholmen locality the rocks contain peraluminous sapphirine orthopyroxene gedrite anthophyllite sillimanite sapphirine corundum cordierite spinel quartz and biotite in a variety of assemblages feldspar is absent fe2 fe2 mg in the analysed minerals varies in the order spinel gedrite anthophyllite biotite sapphirine orthopyroxene cordierite characteristic pseudomorph textures indicate coexistence of orthopyroxene and sillimanite during early stages of the reaction history assemblages containing orthopyroxene sillimanite sapphirine cordierite corundum developed during a high pressure phase of metamorphism and are consistent with equilibration pressures of about 9 kbar at temperatures of 750 800 c decompression towards medium pressure granulite facies generated various sapphirine bearing assemblages the diagnostic assemblage of this stage is sapphirine cordierite sapphirine occurs in characteristic symplectite textures the major mineralogical changes can be described by the discontinuous fmas reaction orthopyroxene sillimanite sapphirine cordierite corundum the disequilibrium textures found in the hasleholmen rocks are characteristic for reactions which have been in progress but then ceased before they run to completion textures such as reaction rims symplectites partial replacement corrosion and dissolution of earlier minerals are characteristic of granulite facies rocks they indicate that despite relatively high temperatures 700 800 c equilibrium domains were small and chemical communication and transport was hampered as a result of dry or h2o poor conditions

diagenetic controls on evolution of porosity and permeability in lower tertiary wilcox sandstones from shallow to ultradeep 200 6700 m burial gulf of mexico basin u s a abstract reservoir quality is a critical risk factor in deep to ultradeep reservoirs at depths 4 5 km analysis of paleogene wilcox sandstones on the upper texas gulf coast provides insight into the evolution of reservoir quality during shallow to ultradeep burial diagenesis reduction of porosity and permeability with burial in wilcox sandstones was evaluated using subsurface samples from 200 to 6700 m at temperatures of 25 230 c diagenesis and petrophysical properties were interpreted from petrographic data and core analyses wilcox sandstones are mostly lithic arkoses and feldspathic litharenites having an average composition of q59f22r19 provenance did not change significantly during wilcox deposition in this area nor does average sandstone composition vary among lower middle and upper wilcox sandstones however composition does vary with sequence stratigraphic position lowstand slope fan deposits contain more rock fragments than do deposits from highstand or transgressive systems tracts given observations from this onshore dataset wilcox sandstones deposited in deepwater environments in the gulf of mexico are likely to contain more rock fragments than their linked highstand equivalents pore types in wilcox sandstones change from a mix of primary and secondary pores and micropores at shallower depths to predominantly secondary pores and micropores in deeper sandstones wilcox sandstones show steady porosity reduction from an average of 33 at 38 c to 12 at 132 c with little additional loss at higher temperatures by 132 c most primary pores have been lost by mechanical compaction or occluded by quartz cementation volume of secondary pores remains nearly constant despite dissolution of 3 5 average potassium feldspar during deep burial volume of this late dissolution of potassium feldspar is offset by precipitation of ankerite albite illite and minor quartz in secondary pores the proportion of microporosity which occurs in authigenic clays altered grains and matrix increases in the deepest sandstones change in proportion of pore types and reduction in total porosity with increasing temperature changes porosity permeability transforms because most deep to ultradeep wilcox sandstones are dominated by secondary pores and micropores porosity permeability transforms have lower slopes than those for shallower sandstones

diffusion in coronas around clinopyroxene modelling with local equilibrium and steady state and a non steady state modification to account for zoned actinolite hornblende retrograde coronas of caledonian age between clinopyroxene and plagioclase in the jotun nappe complex norway illustrate the effects of diffusion kinetics on mineral distributions among layers and on the compositions of hornblende actinolite one corona type comprises a symplectite of epidote quartz adjacent to plagioclase and a less well organized intergrowth of amphibole quartz replacing clinopyroxene the observed mineral proportions imply an open system reaction but the similarity of al si ratios in reactant plagioclase and product symplectite indicates approximate conservation of al2o3 and sio2 the largest inferred open system flux is a loss of cao mostly derived from consumption of clinopyroxene the approximate layer structure pl ep qtz hbl qtz act hbl qtz cpx is modelled using the theory of steady state diffusion controlled growth with local equilibrium to obtain a solution it is necessary to use a reactant plagioclase composition which takes into account aluminous epidote inclusions the results indicate that in terms of onsager diffusion coefficients lii ca is more mobile than al lcaca lalal 3 where means greater than or approximately equal to this behaviour of ca is comparable with that of mg in previously studied coronas around olivine si is non diffusing in the present modelling because of silica saturation oxidation of some fe2 to fe3 occurs within the corona mg diffuses towards its source clinopyroxene to maintain local equilibrium other coronas consist of two layers hornblende adjacent to plagioclase and zoned amphibole quartz adjacent to clinopyroxene in the zoned layer actinolitic hornblende forms relict patches separated from quartz blebs by more aluminous hornblende a preliminary steady state local equilibrium model of grain boundary diffusion explains the formation of low al and high al layers as due to al immobility zoning and replacement are qualitatively explained in terms of evolution of actinolite to more stable aluminous compositions this is modelled by a non steady state modification of the theory retaining local equilibrium in grain boundaries while relatively steep zoning profiles develop in grain interiors through slow intracrystalline diffusion replacement of actinolite by hornblende does not require a change in p t conditions if actinolite is a kinetically determined non equilibrium product the common preservation of a sharp contact between hornblende and actionolite layers may be explained by ineffectiveness of intracrystalline diffusion according to the theory given sufficient grain boundary al flux a metastable actinolite quartz layer in contact with hornblende may be diffusionally stable and may continue to grow in a steady state

rapid high t decompression recorded by archean granulites in the northern wyoming province insights from petrological modelling this study places new constraints on the pressure temperature p t path and duration of high temperature ht metamorphism recorded by archean granulite facies metasedimentary rocks from the northern wyoming province in the eastern beartooth mountains mt and wy usa these rocks exist as m to km scale xenoliths within a c 2 8 ga calc alkaline granitoid batholith different interpretations of the timing of ht metamorphism relative to batholith intrusion in previous works has led to ambiguity over the mechanism by which these rocks were heated i e batholith intrusion vs a later cryptic event the p t path recorded by these rocks and the duration of this path may be indicative of the heating mechanism but are not currently well constrained here we combine phase equilibria thermobarometry and diffusion modelling of major element zonation in garnet in order to constrain the p t path of ht metamorphism and the durations of different parts of this path it is shown that these rocks record a tight clockwise p t path characterized by near isobaric heating at 6 5 7 kbar to 770 800 c ht decompression to 6 kbar 780 800 c followed by limited decompression while cooling diffusion modelling of major element zonation in garnet suggests that ht decompression was brief likely 1 ma and that cooling rates following this decompression were on the order of 10 100 c ma substantial changes in apparent thermal gradient along this p t path indicate that the rocks record a significant but short lived thermal anomaly that occurred in the wyoming mid crust in the late archean this article is protected by copyright all rights reserved

mechanism of induced seismicity at the geysers geothermal reservoir california the geysers reservoir is situated in a 60 80 km wide right lateral shear zone associated with the north american pacific plate boundary a small fraction of the shear may be occurring as permanent aseismic creep which is being converted to stick slip movement in the geysers reservoir due to steam production two mechanisms could be responsible for the induced seismicity a large 100 bars increase in effective rock pressure and an increase in the coefficient of friction the first mechanism requires that the initial state of the reservoir be predominantly liquid dominated the second mechanism is a consequence of dehydration of the reservoir causing both the hardening of clay and fault gouge and the precipitation of silica

contrasting assemblages and petrogenetic evolution of corona and noncorona gabbros in the grenville province of western labrador contrasting coronas around olivines pyroxenes and ilmenites occur in metagabbros in two adjacent terranes in the grenville province of western labrador in the parautochthonous gagnon terrane coronas around olivines display evidence of evolution from double coronas of orthopyroxene and fluorine rich pargasitic amphibole through triple coronas of orthopyroxene garnet clinopyroxene pargasitic amphibole to double coronas of orthopyroxene garnet clinopyroxene parentheses enclose phase occurring as inclusions in previous phase in the allochthonous lac joseph terrane coronas around olivines consist of orthopyroxene clinopyroxene spinel or orthopyroxene pargasitic amphibole spinel brackets enclose phases occurring in symplectic intergrowths possible reactions that explain the development of these assemblages are investigated and it is concluded that the system was closed at the level of the corona the silica required for the olivine plagioclase reaction in gagnon terrane was gene

time scales of tectonic landscapes and their sediment routing systems abstract in regions undergoing active tectonics the coupling between the tectonic displacement field the overlying landscape and the redistribution of mass at the earth9s surface in the form of sediment routing systems is particularly marked and variable coupling between deformation and surface processes takes place at a range of scales from the whole orogen to individual extensional fault blocks or contractional anticlines at the large scale the attainment of a steady state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system with a time scale dependent on the vigour of the erosional system generally in the range 10 6 10 7 years the catchment fan systems associated with extensional fault blocks and basins of the western usa are valuable natural examples to study the coupling between tectonic deformation landscape and sediment routing systems even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation these response times originate from the development of uniform steady state relief during the accumulation of displacement on a normal fault c 10 6 years the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate c 10 6 years or the relaxation times of the integrated catchment fan system in response to changes in climatic and tectonic boundary conditions 10 5 10 6 years the presence of extensive bedrock or alluvial piedmonts increases response times significantly the sediment efflux of a mountain catchment is a boundary condition for far field fluvial transport but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre fluvial systems appear to act as buffers to incoming sediment supply signals with a diffusive time scale c 10 5 10 6 years dependent on the length of the system and the extent of its floodplains stream channels and proximal gravel fans the vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems landscapes are best differentiated as buffered or reactive depending on the ratio of the response time to the repeat time of the perturbation furthermore landscapes may be regarded as steady or transient depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions the response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture

bedrock composition regulates mountain ecosystems and landscape evolution earth s land surface teems with life although the distribution of ecosystems is largely explained by temperature and precipitation vegetation can vary markedly with little variation in climate here we explore the role of bedrock in governing the distribution of forest cover across the sierra nevada batholith california our sites span a narrow range of elevations and thus a narrow range in climate however land cover varies from giant sequoia sequoiadendron giganteum the largest trees on earth to vegetation free swaths that are visible from space meanwhile underlying bedrock spans nearly the entire compositional range of granitic bedrock in the western north american cordillera we explored connections between lithology and vegetation using measurements of bedrock geochemistry and forest productivity tree canopy cover a proxy for forest productivity varies by more than an order of magnitude across our sites changing abruptly at mapped contacts between plutons and correlating with bedrock concentrations of major and minor elements including the plant essential nutrient phosphorus nutrient poor areas that lack vegetation and soil are eroding more than two times slower on average than surrounding more nutrient rich soil mantled bedrock this suggests that bedrock geochemistry can influence landscape evolution through an intrinsic limitation on primary productivity our results are consistent with widespread bottom up lithologic control on the distribution and diversity of vegetation in mountainous terrain

persistent environmental change after the paleocene eocene thermal maximum in the eastern north atlantic the paleocene eocene thermal maximum petm 56 ma is associated with abrupt climate change carbon cycle perturbation ocean acidification as well as biogeographic shifts in marine and terrestrial biota that were largely reversed as the climatic transient waned we report a clear exception to the behavior of the petm as a reversing climatic transient in the eastern north atlantic deep sea drilling project site 401 bay of biscay where the petm initiates a greatly prolonged environmental change compared to other places on earth where records exist the observed environmental perturbation extended well past the 13 c recovery phase and up to 650 kyr after the petm onset according to our extraterrestrial 3he based age model we observe a strong decoupling of planktic foraminiferal 18 o and mg ca values during the petm 13 c recovery phase which in combination with results from helium isotopes and clay mineralogy suggests that the petm triggered a hydrologic change in western europe that increased freshwater flux and the delivery of weathering products to the eastern north atlantic this state change persisted long after the carbon cycle perturbation had stopped we hypothesize that either long lived continental drainage patterns were altered by enhanced hydrological cycling induced by the petm or alternatively that the climate system in the hinterland area of site 401 was forced into a new climate state that was not easily reversed in the aftermath of the petm

ultrahigh temperature granulite metamorphism 1050 c 12 kbar and decompression in garnet mg70 orthopyroxene sillimanite gneisses from the rauer group east antarctica highly magnesian and aluminous migmatitic gneisses from mather peninsula in the rauer group eastern antarctica preserve ultrahigh temperature uht metamorphic assemblages that include orthopyroxene sillimanite quartz garnet sillimanite quartz and garnet orthopyroxene sillimanite garnet that ranges up to xmg of 71 5 coexists with aluminous orthopyroxene that shows zoning from cores with 7 5 8 5 wt al2o3 to rims with up to 10 6 wt al2o3 adjacent to garnet peak p t conditions of 1050 c and 12 kbar are retrieved from fe mg al thermobarometry involving garnet and orthopyroxene in very good agreement with independent constraints from petrogenetic grids in feo mgo al2o3 sio2 and related chemical systems sapphirine orthopyroxene and cordierite form extensive symplectites and coronas on the early phases the specific reaction textures and assemblages involving these secondary phases correlate with initial garnet xmg with apparent higher pressure reaction products occurring on the more magnesian garnet and are interpreted to result from an initial phase of ultrahigh temperature near isothermal decompression uht itd from 12 to 8 kbar at temperatures in excess of 950 c later textures that involved biotite formation and then partial breakdown along with garnet relics to symplectites of orthopyroxene cordierite or cordierite spinel may reflect hydration through back reaction with crystallizing melts on cooling below 900 850 c followed by itd from 7 to 8 kbar to c 5 kbar at temperatures of 750 850 c the tectonic significance of this p t history is ambiguous as the rauer group records the effects of archean tectonothermal events as well as high grade events at 1000 and 530 ma late stage biotite formation and subsequent itd can be correlated with the p t history preserved in the proterozoic components of the rauer group and hence with either 1000 or 530 ma collisional orogenesis however whether the preceding uht itd history reflects a temporally unrelated event e g archean or is simply an early stage of either the late proterozoic or pan african tectonism as recently deduced for similar uht rocks from other areas of the east antarctica remains uncertain

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

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

southern gulf of mexico wilcox source to sink investigating and predicting paleogene wilcox reservoirs in eastern mexico deep water areas source to sink analyses show that northern gulf of mexico gom wilcox group siliciclastic deep water systems are linked to transport of sediments from the laramide tectonic belt into the deep basin less is known however about southern gom sedimentation new drilling and discoveries in the mexican deep water have generated considerable interest since the opening of mexico to international exploration to investigate paleogene deposition in mexico s offshore areas a three phased approach was employed 1 seismic mapping of deep water depocenters 2 regional stratigraphic analysis of potential basin entry points and 3 prediction of submarine fan dimensions using empirical scaling relationships isochore and structural mapping of the wilcox depocenters used available well and seismic data potential basin entry points were identified by evaluation of wilcox fluvial deltaic systems and tectonic elements empirical scaling relationships previously established between fluvial and deep water segments provide first order predictions of submarine fan dimensions paleogene wilcox source to sink systems of the greater gom basin change north to south as a function of varied tectonics and sedimentary accommodation the united states sector was a passive margin continental scale drainage systems fed a broad gently dipping shelf by contrast the southern gom basin was a tectonically active margin smaller scale fluvial systems sourced from the hidalgoan uplands flowed directly into foreland basins located on the slope results presented here indicate that several systems rimming the southern gom were able to effectively transfer sediment from the mountain belt into the basin regional observations and semiquantitative predictions of fan dimensions provide a context for future detailed work based on new well and seismic information

effective bulk composition changes due to cooling a model predicting complexities in retrograde reaction textures diffusive processes are a strong function of temperature thus during cooling of rocks mineral grains may develop zoning profiles as successively larger parts of the grain close to the diffusive exchange with the rock one of the consequences of this process is that during cooling successively larger parts of zoned minerals depending on grain size are effectively removed from the reacting part of the rock volume thus the effective bulk composition of metamorphic rocks changes during cooling and the rate of its change will be a function of grain size because the sequence of metamorphic reactions seen by a given rock is a strong function of its bulk composition this process may have the consequence that two rocks of identical overall bulk composition but of different grain size may experience a different sequence of reactions qualitatively identical peak paragenesis may therefore react to form qualitatively different retrograde reaction textures the model is applied to examples in the pelitic system there garnet is usually the slowest diffusing phase developing zoning profiles during cooling and the effective removal of garnet from the reacting rock volume will cause changes of the effective bulk composition it is shown that during cooling of pelitic rocks from amphibolite facies conditions typical aluminous peak parageneses of garnet muscovite kyanite biotite may react to form either staurolite chlorite or muscovite or different combinations thereof depending on grain size during cooling from the granulite facies aluminous peak parageneses of garnet cordierite sillimanite may form biotite either on the expense of cordierite or garnet also depending on grain size the two examples are illustrated with a series of reaction textures reported for amphibolite and granulite terrains in the literature

isobaric cooling and anti clockwise p t paths in the variscan odenwald crystalline complex germany mineral assemblages in al2o3 rich sio2 and k2o poor metapelitic rocks from the western odenwald crystalline complex variscan mid german crystalline rise southern germany include corundum spinel cordierite sillimanite garnet and staurolite quartz is absent from almost all samples therefore the applicability of conventional geothermobarometry is very limited or even impossible detailed petrographic investigation on selected samples permits inference of the sequence of appearance and disappearance of several mineral assemblages the recognition of such partial re equilibration stages and their associated mineral assemblages together with mineral stabilities predicted from kfmash pseudosections enables the determination of the pressure temperature p t trajectories experienced by these rocks during the variscan metamorphism the rocks were metamorphosed under low p high t conditions and underwent an anti clockwise p t evolution a pressure increase from about 2 kbar to 4 0 5 kbar was accompanied by heating peak metamorphic conditions were reached at pressures of 4 0 5 kbar and temperatures of at least 640 c probably even higher the retrograde evolution is characterised by near isobaric cooling from 640 c to approximately 550 c the rocks underwent the anti clockwise evolution in a subduction related magmatic arc setting the close spatial association of the low p high t rocks with recently discovered metabasic eclogites in the eastern part of the odenwald crystalline complex may indicate a fossil paired metamorphic belt in the central european variscides

comparative geobarometry of pelitic hornfelses associated with the newer gabbros a preliminary study physical conditions of contact metamorphism have been estimated for pelitic hornfelses collected from the inner aureoles of the morven cabrach knock huntly and belhelvie newer gabbro intrusions using a few well calibrated mineral equilibria inner aureole temperature estimates range from 700 c to 850 c calculated pressures all fall between 4 kbar and 5 kbar implying the existence of between 15 km and 18 5 km of overburden at each locality at the time of intrusion of the newer gabbros the results indicate that the four newer gabbros mentioned above were all emplaced at a similar crustal level and that there has been no net regional tilting of the ne dalradian since then the results are not incompatible with some large scale late stage d 3 gentle folding as implied by the regional isograd pattern

alluvial response to the paleocene eocene thermal maximum climatic event polecat bench wyoming u s a abstract the stratigraphic interval spanning the paleocene eocene thermal maximum in the northern bighorn basin wyoming shows changes in the alluvial record that can be tied to a high resolution climate record the complexity and stratigraphic spacing of paleosols change through the study section comparison to the climate record reconstructed from paleosols indicates the changes correspond to paleocene eocene thermal maximum climatic fluctuations in particular the middle of the section contains thick welded paleosols and thin avulsion deposits that link to times of well drained floodplains and lower mean annual precipitation stratigraphic intervals below and above the main part of the paleocene eocene thermal maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation these strata contain thinner paleosols and thick avulsion deposits differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the paleocene eocene thermal maximum welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the paleocene eocene thermal maximum intervals with widely spaced paleosols indicate more rapid accretion we hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield because precipitation was reduced much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin welded paleosols formed because of diminished sediment supply to the basin with a return to wetter conditions during the recovery phase of the paleocene eocene thermal maximum upstream water flux increased stored sediment moved to the basin and vertically spaced thinner paleosols developed the results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change

chemical weathering of fluvial sediments during alluvial storage the macuapanim island point bar solimoes river brazil abstract modification of sediment composition by chemical weathering depends both on the overall intensity of weathering and on its duration at macuapanim island solimboes river amazon main channel brazil a number of alluvial deposits have been exposed to intense tropical weathering for differing lengths of time in the very fine sand fraction the detrital component shows a steady and marked increase in compositional maturity with increasing sediment age immature sands of arkosic to litharenitic composition show a progressive loss of lithic fragments feldspars and accessory minerals with a concomitant enrichment in quartz this process produces first cycle sands whose detrital component is of quartz arenite composition among the salts quartz is enriched over time relative to more nstable phases particularly plagioclase this enrichment is probably largely caused by the destruction of plagioclase through chemical weathering but silt size quartz may also be produced through the breakdown of sedimentary and metasedimentary lithic fragments in the sand fraction in the clay fraction an increase in the relative abundance of smectite accompanies the breakdown of volcanic lithic fragments in the sand fraction and probably reflects the degradation of volcanic glass the clay fractions of the oldest samples examined contain less smectite somewhat more kaolinite and markedly more vermiculite as compared to younger samples but an extensively leached cation poor clay fraction analogous to the quartz dominated silts and sands is never attained the compositional mat rity of the clay fraction is everywhere lower than that of associated silts and sands perhaps because of a continual influx into the clay fraction of immature cation rich clays derived from the physical breakdown of lithic fragments in coarser size fractions this effect is enhanced by the translocation of fines whereby younger less weathered fine material is juxtaposed with older more mature coarse material in the lower levels of the alluvial stratigraphy reworking of floodplains during channel migration results in the reincorporation of older material stored on the floodplains into the sediment load if sediments have been intensely weathered during storage on the floodplain then the result will be a net dilution and replacement of younger relatively immature sands transported by the river by older more mature material from the floodplain the relative proportion of the older sands in the bedload will increase downstream resulting in a progressive downstream increase in the compositional maturity of the bedload of the river

extensive deposits on the pacific plate from late pleistocene north american glacial lake outbursts abstract one of the major unresolved issues of the late pleistocene catastrophic flood events in the northwestern united states e g from glacial lake missoula has been what happened when the flood discharge reached the ocean this study compiles available 3 5 khz high resolution and airgun seismic reflection data long range sidescan sonar images and sediment core data to define the distribution of flood sediment in deepwater areas of the pacific ocean upon reaching the ocean at the mouth of the columbia river near the present day upper continental slope sediment from the catastrophic floods continued flowing downslope as hyperpycnally generated turbidity currents the turbidity currents resulting from the lake missoula and other latest pleistocene floods followed the cascadia channel into and through the blanco fracture zone and then flowed west to the tufts abyssal plain a small part of the flood sediment which was stripped off the main flow at a bend in the cascadia channel at its exit point f

metamorphism of carbonaceous material in the tono contact aureole kitakami mountains japan abstract optical and x ray studies of carbonaceous material in the tono contact metamorphic aureole kitakami mountains northeast japan have revealed that metamorphic graphitization proceeded through two discontinuous changes first optically anisotropic domains develop within the coaly phytoclast forming transitional material and then ordered graphite crystallizes by the decomposition of pre existing carbonaceous materials coaly material disappears in the uppermost chlorite zone transitional material appears in the middle of the lower chlorite zone graphite appears in the upper chlorite zone and its modal abundance increases across the andalusite iso grad to the cordierite isograd where all the carbonaceous materials have converted to graphite the apparently continuous variation in the crystallographic parameters of the bulk carbonaceous material during graphitization is largely due to variation in the modal proportions of three types of carbonaceous materials the temperature of graphitization in the present area is at least 100 c higher than the temperature in the sanbagawa and new caledonia high pressure metamorphic terrains probably due to the slow reaction rate of metamorphic graphitization and to the short duration of contact metamorphism

metamorphic reactions in dry and aluminous granulites a perple_x p t pseudosection analysis of the influence of effective reaction volume in high mg al metapelites monophase sapphirine corona occur around spinel corundum aggregates in monomineralic cordierite layers and bi phase orthopyroxene sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates p t phase topologies computed perple x software using compositions of cordierite rich layers that host the reaction textures did not match the assemblages for the discontinuous reactions spinel corundum cordierite sapphirine and sapphirine cordierite orthopyroxene sillimanite instead the reaction assemblages were reproduced using p t pseudosection analysis for micro domain reaction volumes estimated from compositions of product phases in the volume proportion they occur the results are consistent with known phase relations deduced using schreinmakers p t grids apparently the compositions of cordierite rich layers that hosted the reaction textures were inadequate chemical proxies for determining p t x relations of phase boundary controlled reactions influenced by compositions of the nearest neighbor minerals in the proportion they react effective composition and not in the proportion they existed in the layer bulk rock in other words p t x phase topologies and reconstructed p t paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures

significance of post peak metamorphic reaction microstructures in the ultrahigh temperature eastern ghats province india ultrahigh temperature uht granulites in the eastern ghats province egp have a complex p t t history we review the p t histories of uht metamorphism in the egp and use that as a framework for investigating the p t t history of mg al rich granulites from anakapalle with the express purpose of trying to reconcile the down pressure dominated p t path with other uht localities in the egp mafic granulite that is host to mg al rich metasedimentary granulites at anakapalle has a protolith age of c 1580 ma mg al rich metasedimentary granulites within the mafic granulite at anakapalle were metamorphosed at uht conditions during tectonism at 960 875 ma meaning that the uht metamorphism was not the result of contact metamorphism from emplacement of the host mafic rock reworking occurred during the pan african c 600 500 ma event and is interpreted to have produced hydrous assemblages that overprint the post peak high temperature retrograde assemblages in contrast to rocks elsewhere in the egp that developed post peak cordierite the metasedimentary granulites at anakapalle developed post peak generation 2 reaction products that are cordierite absent and nominally anhydrous therefore rocks at anakapalle offer the unique opportunity to quantify the pressure drop that occurred during so called m2 that affected the egp we argue that m2 is either a continuation of m1 and that the overall p t path shape is a complex counter clockwise loop or that m1 is an up temperature counter clockwise deviation superimposed on the m2 path therefore rather than the rocks at anakapalle having a metamorphic history that is apparently anomalous from the rest of the egp we interpret that other previously studied localities in the egp record a different part of the same p t path history as anakapalle but do not preserve a significant record of pressure decrease this is due either to the inability of refractory rocks to extensively react to produce a rich mineralogical record of pressure decrease or because the earlier high p part of the rocks history was erased by the m1 loop irrespective of the specific scenario models for the tectonic evolution of the egp must take the substantial pressure decrease during m2 into account as it is probable the p t record at anakapalle is a reflection of tectonics affecting the entire province this article is protected by copyright all rights reserved

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

chemical heterogeneity in an enderbite hosted pseudotachylite eastern india evidence for syn deformation multi reaction melting in pseudotachylite the origin of chemical and mineralogical heterogeneity in tens of microns wide layers and domains in enderbite hosted couple of centimeters wide pseudotachylite vein is examined based on the results of bse and x ray element imaging and electron probe microanalyses of major elements of host rock minerals clasts microphenocrysts and pseudotachylite matrix the pseudotachylite layers and domains containing variable proportions of orthopyroxene and magnetite microphenocrysts continue as mantles around quartz k feldspar plagioclase and garnet clasts the clasts are chemically modified along margins and intra clast pseudotachylite injections the chemical modifications are extensive in smaller clasts 5 m diameter at least three chemically distinct layers and domains in the pseudotachylite and their fine grained matrices plot in sharply defined well segregated and non overlapping fields in feo mgo al2o3 sio2 feo cao mgo and cao na2o k2o and feo vs feo feo mgo diagrams the compositions of the layers and domains smeared between a feldspar quartz component and a ferromagnesian component of garnet fe ti oxides orthopyroxene possibly correspond to fractionated quenched melts or admixtures of microphenocrysts that cannot be resolved by the microbeam techniques employed the compositional variations are incompatible with deformation driven crystal fractionation in melt instead the layers and domains possibly are crystal melt mushes produced by syn deformation ultra high temperature 1 250 1 375 c melting reactions involving variable proportions of host rock minerals determined by time transient local phase aggregates experiencing strain the similar element variation trends in pseudotachylite examined here and those reported from anorthosite metapelite and charnockite elsewhere suggests local phase aggregate controlled multi reaction melting is a phenomenon commoner than hitherto realized in pseudotachylites

persistence of carbon release events through the peak of early eocene global warmth a series of unusual greenhouse gas induced warming events occurred in the eocene an isotope reconstruction of these hyperthermals indicates multiple events of a constant size and frequency consistent with orbital forcing of the carbon cycle

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

linking gas fluxes at earth s surface with fracture zones in an active geothermal field the percolation of fluids is of utmost relevance for the utilization of underground resources however the location and occurrence of fractures are not always known and important characteristics of faults such as stress state and permeability are commonly uncertain using a case study at the brady s geothermal field in nevada usa we demonstrate how permeable fractures can be identified and assessed by combining fault stress models with measurements of diffuse degassing and emanations at earth s surface areas of maximum gas emissions and emanations correspond to fault segments with increased slip and dilation tendency and represent a fingerprint of the geothermal system at depth thus linking gas fluxes with fault stress models serves as a measure of the connectivity between surface and subsurface

ultra high temperature metamorphism of metapelitic granulites from kondapalle eastern ghats belt implications for the indo antarctic correlation a suite of quartz and corundum bearing metapelitic granulites intruded by layered gabbronorite pyroxenite anorthosite at kondapalle eastern ghats belt preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions in the quartz bearing associations the reactions are a biotite sillimanite quartz garnet liquid b garnet sillimanite spinel magnetite quartz c fe2tio4 o2 ferrian ilmenite magnetite d reversal of reaction b e fe2o3 rich ilmenite plagioclase quartz fe2o3 poor ilmenite garnet o2 reactions in the corundum bearing associations are f spinel biotite sillimanite garnet liquid g biotite sillimanite garnet ti rich spinel corundum liquid h biotite sillimanite garnet corundum liquid i fe2tio4 feal2o4 o2 ferrian ilmenite fe3o4 al2o3 in ilmenite j garnet corundum spinel sillimanite to examine the paragenetic evolution of the metapelitic granulites a petrogenetic grid for the kfmash system at high temperatures and pressures involving quartz and corundum was constructed the sequence of inferred reactions documents an anticlockwise heating cooling path reintegrated compositions of spinel with 10 mol fe2tio4 and feldspars indicate ultra high temperature uht of metamorphism 1000 c comparable with the liquidus temperature of the enclosing magmatic rocks crystallization pressures inferred for the magmatic rocks and the pressure constraints imposed by the petrogenetic grid on the metapelite assemblages indicate that the emplacement of the igneous suite and the accompanying uht metamorphism occurred in the lower crust 8 kbar reported u pb cooling ages of monazite and allanite from a late pegmatite suggest the uht metamorphism to be older than 1600 ma the deduced p t history and the absence of grenvillian high grade metamorphism in the study area provide important constraints on the configuration of east gondwana in particular on the continuation of the napier rayner terrane boundary into the eastern ghats belt

diffusion metasomatism in silica undersaturated sapphirine bearing granulite from rumdoodle peak framnes mountains east antarctica at rumdoodle peak near mawson base east antarctica an enclave of metasedimentary granulite is enclosed in the mawson charnockite an extensive c 960 ma intrusion the enclave contains a disrupted layer of black spinel orthopyroxene phlogopite gneiss which was truncated by a quartz rich vein a reaction band that developed between these units is composed of a sequence of mineral zones that contain spinel orthopyroxene sapphirine cordierite and plagioclase the sequence of mineral zones approximately matches that predicted by a model of closed system diffusion metasomatism involving the exchange of si for fe and mg the reaction bands differ from the model in the presence of micro scale disequilibrium textures that include double coronas composed of cordierite surrounding sapphirine and sapphirine surrounding spinel the growth of the reaction band was controlled by diffusion along intergranular pathways with local equilibrium maintained adjacent to grain boundaries the presence of corona textures is a result of slow reaction rates due to limited diffusive exchange of si and al across mineral grains

sapphirine kornenipine bearing rocks and crustal uplift history of the limpopo belt southern africa sapphirine kornerupine bearing rocks occur within the anorthosites of the messina layered intrusion in the limpopo mobile belt of zimbabwe the xmg range of the major minerals is as follows cordierite 0 98 0 93 enstatite 0 97 0 86 chlorite 0 98 0 92 phlogopite 0 98 0 90 sapphirine 0 98 0 86 kornerupine 0 94 0 88 gedrite 0 96 0 85 spinel 0 92 0 78 there are four rock types the constituent minerals of which have different x m g values which decrease in the above mineral order other minerals are corundum sillimanite and relict kyanite we recognise twenty reactions without phlogopite and nine reactions involving phlogopite the textural relations and the plots of the microprobe data of coexisting minerals in the mgo al2o3 sio2 h2o system are consistent with the following sequence of main reactions 1 enstatite corundum cordierite sapphirine 4 sapphirine sillimanite cordierite corundum 8 kornerupine corundum cordierite sapphirine 13 kornerupine cordierite sapphirine enstatite 15 enstatite spinel chlorite sapphirine 18 cordierite sapphirine chlorite corundum 20 sapphirine chlorite corundum spinel the early reactions are shown by coarse grained reaction intergrowths kornerupine and gedrite breakdown is shown by finer grained symplectites and the latest reactions by very fine grained products in micro fractures these selected reactions illustrate a remarkably steep trajectory from thept peak close to 10 kbar and 800 c to the minimum observable at 3 5 4 5 kbar and 700 c as indicated by the pure mash system very rapid uplift took place under nearly isothermal conditions the protolith of this material was possibly sedimentary derived from altered volcanic rocks the bulk composition is close to the composition of kornerupine or to a mixture of alunite chlorite and pyrophyllite these texturally and mineralogically complex rocks contain a wealth of relevant data for documenting crustal uplift history

p t x relationships in the precambrian al mg rich granulites from in ouzzal hoggar algeria the al mg rich granulites from the in ouzzal craton algeria show a great diversity of mineral reactions which correspond to continuous equilibria as predicted by phase relationships in the feo mgo al2o3 sio2 system the sequence of mineral reactions can be subdivided into three distinct stages 1 a high p stage characterized by the growth of coarse mineral assemblages involving sapphirine and the disappearance of early corundum and spinel bearing assemblages 2 a high t stage characterized by the development of sa qz bearing assemblages and 3 a later stage in which garnet bearing assemblages are replaced by more or less fine symplectites involving cordierite during the course of early mineral reactions the distribution coefficient kd between the various ferromagnesian phases decreased significantly whereas al2o3 in pyroxene increased concomitantly these observations when combined with topological constraints clearly indicate that the high p stage 1 was accompanied by a significant rise in temperature estimated at 150 50 c under near isobaric conditions in agreement with the reaction textures by stage 2 pressure and temperature were extreme as evidenced by the low kd value between orthopyroxene and garnet kd 2 06 1 99 the high alumina content in pyroxene up to 11 8 and the high magnesium content in garnet 100 mg mg fe 60 6 mineral thermometry based on fe mg exchange between garnet and pyroxene and on al solubility in pyroxene gives temperatures close to 970 70 c at 10 1 5 kbar these results are in agreement with the development of sa qz assemblages on a local scale late mineral reactions have been produced during a decompression stage from about 9 to 6 kbar except for local re equilibration of mg and fe at grain boundaries there is no evidence for further reactions below 700 c we interpreted the whole set of mineral reactions as due to changes in pressure and temperature during a tectonic episode located at c 2 ga because of the lack of evidence for further uplift after the thermal relaxation which occurred at c 6 kbar it is possible however that the exhumation of this granulitic terrane occurred in a later tectonic event unrelated to its formation

predominant floodplain over mountain weathering of himalayan sediments ganga basin we present an extensive river sediment dataset covering the ganga basin from the himalayan front downstream to the ganga mainstream in bangladesh these sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column mineral sorting is the first order control on the chemical composition of river sediments taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain by comparing sediments sampled at the himalayan front with sediments from the ganga mainstream in bangladesh it is possible to budget weathering in the floodplain assuming a steady state weathering regime in the floodplain the weathering of himalayan sediments in the gangetic floodplain releases ca 189 92 10 9 and 69 22 10 9 mol yr of carbonate bound ca and mg to the dissolved load respectively silicate weathering releases 53 18 10 9 and 42 13 10 9 mol yr of na and k while the release of silicate mg and ca is substantially lower between ca 0 and 20 10 9 mol yr additionally we show that sediment hydration h2o is a sensitive tracer of silicate weathering that can be used in continental detrital environments such as the ganga basin both h2o content and the d h isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions by comparing the chemical composition of river sediments across the floodplain with the composition of the eroded himalayan source rocks we suggest that the floodplain is the dominant location of silicate weathering for na k and h2o overall this work emphasizes the role of the gangetic floodplain in weathering himalayan sediments it also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account 2012 elsevier ltd all rights reserved

the ancestral mississippi drainage archived in the late wisconsin mississippi deep sea fan the response of continental scale drainage systems to short term i e millennial scale climate change is unknown but has wide implications for understanding climate feedbacks and terrestrial marine fluxes the late wisconsin mississippi river to deep sea fan of north america was one of earth s largest sediment routing networks during the most recent glacio eustatic cycle to understand late pleistocene sediment production and dispersal related to the partly glaciated ancestral mississippi system we sampled late wisconsin deep sea fan channel fill and lobe deposits for detrital zircon u pb and u th he double dating analyses from deep sea drilling project leg 96 cores and u s geological survey piston cores our results suggest a late pleistocene glacial mississippi system that forced a larger transfer of sediment from cordilleran magmatic provinces and the canadian shield when compared to the modern drainage this indicates a potentially more expansive and or erosive ancestral mississippi catchment and the efficient dispersal of terrigenous sediment nutrients and solutes into the deep sea via high discharge meltwater and glacial lake outbursts during ice retreat

initial generation of sand across climate zones of the mojave sierra nevada and klamath batholiths in california u s a the generation of modern plutoniclastic sediment across california varies with climate resulting in significant mineralogical and geochemical differences between parent rock weathering profile material and low order stream sand with average precipitation of 15 cm yr in the arid zones and 120 cm yr in the temperate zones feldspar is relatively decreased in stream sand compared to parent rock by 2 and 20 respectively potassium feldspar is more resistant to weathering than plagioclase but is less stable than quartz in temperate climates hornblende and biotite are more easily weathered in temperate than arid climates although their occurrence in medium grained stream sands is affected by hydraulic sorting and comminution during transport temperate climate sands have lower concentrations of cao and na2o compared to k2o and al2o3 reflective of the expected faster loss of plagioclase than potassium feldspar during weathering with the exception of biotite the mineralogy of medium grained stream sand reflects that of medium grained weathering profile material in both climates confirming the findings from constant climate case studies that the composition of proximal sand is largely achieved within weathering profiles and during initial erosion we encourage continued attention to climate as a control on sand composition in provenance and paleoclimate studies where a moderate precipitation shift is capable of producing a significant loss of feldspar the differential response of common minerals to chemical weathering should be considered for studies and modeling related to bedrock erodibility sediment supply and landscape evolution

sapphirine bearing granulites from the sipiwesk lake area of the late archean pikwitonei granulite terrain manitoba canada sapphirine occurs in the orthopyroxene cordierite and feldspar sillimanite granulites in the sipiwesk lake area of the pikwitonei granulite terrain manitoba 97 40 w 55 05 n the orthopyroxene cordierite granulites have extremely high al2o3 24 5 wt and mgo 24 6 wt contents and contain sapphirine up to 69 2 wt al2o3 aluminous orthopyroxene up to 8 93 wt al2o3 cordierite spinel phlogopite and corundum sapphirine forms coronas mantling spinel and corundum corona sapphirine is zoned and its composition varies through the substitution mg fe mn si 2 al as a function of the phases with which it is in contact textural and chemical relationships of sapphirine with coexisting phases indicate that spinel cordierite reacted to form orthopyroxene sapphirine under conditions of increasing pressure moreover decreasing core to rim variation of al2o3 in orthopyroxene porphyroblasts suggests decreasing temperature during sapphirine formation on the basis of experimentally determined p t stability of the assemblage enstatite sapphirine cordierite and the al content of hypothetical fe2 free orthopyroxene associated with sapphirine and cordierite metamorphic temperatures and pressures are estimated to be 860 890 c and 3 0 11 2 kbar

competition between erosion and reaction kinetics in controlling silicate weathering rates article i nfo weathering rates of minerals may be limited by the reaction kinetics of the constitutive minerals or the supply of fresh minerals delivered to the near surface by denudation we use a model of denudation and reaction kinetics to analyze the relative importance of each in moderating silicate weathering fluxes in different erosional environments for different commonly occurring silicate minerals we find that minerals that reside in the near surface weathering zone for far longer than the reaction takes to complete as is the case with slow denudation produce weathering fluxes that respond most strongly to changes in denudation rate conversely when transit through the weathering zone is rapid relative to a given mineral s weathering timescale the weathering responds most vigorously to changes in the reaction kinetics based on field and laboratory measured values of silicate weathering kinetic constants observed weathering zone thicknesses in relation to denudation rates and denudation rates inferred from topography it appears that fresh mineral supply may play a sub equal or dominant role in moderating silicate weathering fluxes for four mineral phases considered if correct this suggests that the concentration of atmospheric co2 which is regulated by silicate weathering over geologic timescales may depend on those factors that control long term erosion rates across earth s surface

mayotte coral reveals hydrological changes in the western indian ocean between 1881 and 1994 we reconstruct the hydrologic history of the tropical western indian ocean by calculating the 18oseawater from coupled coral sr ca and 18o measurements in a massive porites coral from mayotte comoros between 1881 and 1994 we found that the precipitation evaporation balance varies naturally on time scales of 5 6 years and 18 25 years high low ssts are associated with positive negative 18oseawater implying that atmospheric variability is linked with remote climate modes in the indian ocean and the tropical extratropical pacific ocean warm el nino southern oscillation events are associated with a negative freshwater balance at mayotte this case study demonstrates that a much denser network of 18oseawater reconstructions is crucial for understanding the spatial patterns of hydrological conditions

p t grids for silica undersaturated granulites in the systems mas n 4 and fmas n 3 tools for the derivation of p t paths of metamorphism abstract considering the minerals cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and corundum co in the system feo mgo al2o3 sio2 fmas the stable invariant points are co ga cd and sa constraints imposed by experimental data for the system mas indicate that under low ph2o conditions the invariant points occur at high temperature 900 c and intermediate pressure 7 10 kbar this temperature is higher than that commonly advocated for granulite facies metamorphism in granulites fe mg exchange geothermometers may yield temperatures of 100 150 c below peak metamorphic conditions and evidence for peak temperatures is best preserved by relict high temperature assemblages and by al rich cores in orthopyroxene application of the fmas grid to some well documented granulite occurrences introduces important constraints on their p t histories rocks of different bulk compositions occurring in close proximity in the field may record distinct segments of their p t paths this applies particularly to rocks with evidence for reaction in the form of coronas symplectites and zoned minerals consideration of curved reaction boundaries and xms isopleths may explain apparently contradictory results for the stability of cordierite obtained from low temperature experiments and thermochemical calculations on the one hand and hightemperature experimental data on the other

quantifying sediment supply to continental margins application to the paleogene wilcox group gulf of mexico sediment supply to the ocean influences basin margin growth and reflects upstream landscape evolution including patterns of sediment routing denudation and tectono climatic perturbations in source areas constraining sediment supply is useful for inputs to stratigraphic forward models and for predictions of reservoir presence and quality because of the importance of sediment supply geoscientists have developed various methods to estimate it here we apply monte carlo simulation mcs to the bqart model that is used to describe an empirical relationship between river catchment paleogeography climate and sediment load we calculate a range of sediment supply from north american source areas to the gulf of mexico that suggests an overall decrease in median sediment supply from the late paleocene to the early eocene from 404 514 to 144 204 million tons per year depending on the published paleogeographic model that we used to guide our selection of input variables comparison of these estimates with downstream sediment records shows that the subsurface depositional rates are within the 10th 90th percentile range of this bqart mcs uncertainty model the 50th percentile values of bqart mcs results are overall larger than the published wilcox sediment volume which indicates that the size of wilcox deep water fans might be underestimated we use source of change analysis to show the influence of each river catchment input of the bqart model on change in sediment supply from the late paleocene to the early eocene integration of empirical based methods such as bqart with physics based experimental and modeling approaches might provide better constrains on sediment supply and deposition in frontier areas of oil and gas exploration

early cenozoic drainage reorganization of the united states western interior gulf of mexico sediment routing system continental scale drainages host the world s largest rivers and offshore sediment accumulations many of which contain significant petroleum reserves rate of sediment supply in these settings may be a signal of external controls e g tectonics on landscape evolution yet deciphering these controls remains a major challenge in interpreting the ancient stratigraphic record integration of new and published detrital zircon u pb ages from the united states rocky mountain region and gulf of mexico gom sedimentary basin demonstrates profound changes in the u s continental drainage divide that controlled the rate of sediment delivery to the northern gom during paleocene eocene time sedimentation rate increased dramatically during deposition of the lower wilcox group reaching approximately three times the cenozoic average accompanied by pronounced shoreline regression and delivery of a large volume of sand to the basin floor we hypothesize that this increase in sediment delivery to the gom resulted from drainage capture of a significant portion of the sevier laramide structural province 900 000 km2 that included the headwaters of the california and idaho rivers capture of the california river drainage may have occurred in the vicinity of the hanna basin of eastern wyoming that previously emptied northward into a shallow seaway but was subsequently diverted southward to the rockdale delta which accumulated within the houston embayment during the time of deposition of the lower wilcox group detrital zircon u pb ages from wilcox samples within the rockdale delta show a remarkable similarity with contemporaneous laramide synorogenic units including enrichment in detritus derived from the cordilleran arc and basement terranes of western north america relative to older and younger units in the houston embayment a subsequent order of magnitude decline in sedimentation rate to the gom can be partly attributed to well documented drainage closure 800 000 km2 that accompanied lake formation in interior laramide basins ca 53 51 8 ma our results demonstrate that tectonically induced drainage migration in the high relief segments of continental scale drainages can have a pronounced effect on the rate of sediment transfer to continental margins

models for orthopyroxene plagioclase and other corona reactions in metanorites dahomeyide orogen west africa coronal reaction textures occur in metanorite and related intrusions in the pan african dahomeyide orogen of west africa they apparently formed by retrograde subsolidus reactions during cooling of the intrusions from 900 to 700 c at c 9 1 kbar the coronas that formed around orthopyroxene opx consist of sequential layers of diopside dio hornblende hbl garnet grt and plagioclase pl with inclusions of kyanite ky or sillimanite sil three well organized mineral assemblage sequences have been identified and modelled using steady state diffusion theory for closed and open systems the mineral sequence opx hbl qtz hbl pl ky formed by diffusion controlled reactions in a closed system as layer thicknesses are very sensitive to relative component mobilities defined by onsager diffusion coefficient lii models of this corona type i that satisfy modes require lcaca lmgmg lfefe lalal lsisi however small open system fluxes involving loss of al and gain of ca are required to obtain the best fit between model and observed mineral proportions under steady state diffusion the monomineralic hornblende layer grew by replacing plagioclase whereas the hbl qtz grew by opx replacement the type ii corona which consists of the sequence opx dio grt dio pl sil is also stable under steady state diffusion in a closed system modelling results show that the diopside grew by replacing opx whereas most of grt dio grew by replacing plagioclase stable solutions to the closed system diffusion model that approximate the mode are restricted to the l ratio regions where fe mg and ca are more mobile than si and al but are unstable when lalal 100 lsisi however type ii corona mineral proportions were only closely matched when open system loss of al and gain of small amounts of fewere considered in the diffusion models and relative mobilities were lfefe lcaca lmgmg lalal lsisi the modelling results indicate that ca and mg were the most mobile elements in the formation of type i corona whereas fe and ca were the most mobile components in the growth of type ii coronas a third corona type consisting of the mineral sequence act hbl grt pl sil is only stable in open systems and requires large external fluxes involving gain of fe al mg and na and loss of ca to obtain a solution of the diffusion model that approximates the estimated mineral proportions extensive recrystallization of plagioclase to produce sillimanite or kyanite inclusions accompanying corona formation may explain the open system behaviour indicated by the diffusion models

a high resolution benthic stable isotope record for the south atlantic implications for orbital scale changes in late paleocene early eocene climate and carbon cycling abstract the late paleocene and early eocene were characterized by warm greenhouse climates punctuated by a series of rapid warming and ocean acidification events known as hyperthermals thought to have been paced or triggered by orbital cycles while these hyperthermals such as the paleocene eocene thermal maximum petm have been studied in great detail the background low amplitude cycles seen in carbon and oxygen isotope records throughout the paleocene eocene have hitherto not been resolved here we present a 7 7 million year myr long high resolution orbitally tuned benthic foraminiferal stable isotope record spanning the late paleocene and early eocene interval 52 5 60 5 ma from ocean drilling program odp site 1262 south atlantic this high resolution 2 4 kyr record allows the changing character and phasing of orbitally modulated cycles to be studied in unprecedented detail as it reflects the long term trend in carbon cycle and climate over this interval the main pacemaker in the benthic oxygen isotope 18 o and carbon isotope 13 c records from odp site 1262 are the long 405 kyr and short 100 kyr eccentricity cycles and precession 21 kyr obliquity 41 kyr is almost absent throughout the section except for a few brief intervals where it has a relatively weak influence during the course of the early paleogene record and particularly in the latest paleocene eccentricity paced negative carbon isotope excursions 13 c cies and coeval negative oxygen isotope 18 o excursions correspond to low carbonate caco 3 and coarse fraction cf values due to increased carbonate dissolution suggesting shoaling of the lysocline and accompanied changes in the global exogenic carbon cycle these negative cies and 18 o events coincide with maxima in eccentricity with changes in 18 o leading changes in 13 c by 6 5 kyr in the 405 kyr band and by 3 1 kyr in the higher frequency 100 kyr band on average however these phase lags are not constant with the lag in the 405 kyr band extending from 4 5 kyr to 21 2 kyr from the late paleocene to the early eocene suggesting a progressively weaker coupling of climate and the carbon cycle with time the higher amplitude 405 kyr cycles in the latest paleocene are associated with changes in bottom water temperature of 2 4 c while the most prominent 100 kyr paced cycles can be accompanied by changes of up to 1 5 c comparison of the 1262 record with a lower resolution but orbitally tuned benthic record for site 1209 in the pacific allows for verification of key features of the benthic isotope records which are global in scale including a key warming step at 57 7 ma

direct evidence of the feedback between climate and weathering long term climate moderation is commonly attributed to chemical weathering the higher the temperature and precipitation the faster the weathering rate weathering releases divalent cations to the

the origin of olivine plagioclase coronas in metagabbros from the adirondack mountains new york olivine plagioclase coronas in metagabbros from the adirondack mountains new york usa are spatially well organized reaction textures consisting most commonly of sequential layers of orthopyroxene clinopyroxene plagioclase and garnet the textures are characteristic of diffusion controlled reaction kinetics although similar coronas have been interpreted by previous workers in terms of an isochemical steady state diffusion model petrographical relations and material balance calculations establish that coronas in the adirondack metagabbros cannot be treated as isochemical and do not form in a single stage steady state process instead they evolve through time in a complex open system reaction in this study the isochemical diffusion model is modified to account for elemental fluxes across the outer boundaries of the coronal reaction band thereby approximating the open system behaviour of the coronas the sequence and relative proportions of product minerals calculated by the open system steady state model correspond closely to those observed in coronas of the adirondacks over a wide range of values for the relative diffusivities of chemical components involved in the reaction regardless of the particular method used to determine material balance in the reaction texture despite this correspondence petrographical evidence for successive replacement of coronal product layers reveals that the adirondack coronas evolved through one or more transient states rather than forming in a single stage steady state process there is no evidence that the successive replacement of coronal product layers resulted from changes in pressure or temperature but there is petrographical evidence that these changes resulted from modification of the composition of reactant plagioclase as the corona forming reaction proceeded this is confirmed by the fact that the evolution of the coronas over time can be replicated with the open system diffusion model by simulating the effect of the gradual exhaustion of plagioclase as a source of the ca and si components required for reaction these simulations suggest that successive stages in the evolution of the coronas are characterized by these product sequences i orthopyroxene clinopyroxene plagioclase garnet ii orthopyroxene clinopyroxene garnet and iii orthopyroxene garnet all of these stages and the transitions between them are observed petrographically coronas in adirondack metagabbros appear therefore to have originated in a complex open system diffusion controlled reaction in which the product assemblages changed as the reaction progressed

silicon diffusion in forsterite aggregates implications for diffusion accommodated creep silicon diffusion rates were determined in fine grained 4 5 m hot pressed forsterite aggregates at 900 to 1200 c and 0 1 mpa using a 30si tracer and standard sims analysis there is no measurable difference in diffusion rates between samples buffered by excess mgo or sio2 nor samples run in dry n2 or h2 co2 the results yield the arrhenius parameters d0 bulk 5 4 10 9 m sec and q 203 36 kj mol at 1200 c the grain boundary diffusion rate of 30si is similar to 26mg si 10 times greater 10 less than fe and 105 less than o in addition the 30si grain boundary diffusion rate is 109 greater than the si volume diffusion rate and indicates that diffusional transport of si in forsterite aggregates is dominated by grain boundaries

paleocene wilcox cross shelf channel belt history and shelf margin growth key to gulf of mexico sediment delivery abstract shelf margins prograde and aggrade by the incremental addition of deltaic sediments supplied from river channel belts and by stored shoreline sediment this paper documents the shelf edge trajectory and coeval channel belts for a segment of paleocene lower wilcox group in the northern gulf of mexico based on 400 wireline logs and 300 m of whole cores by quantitatively analyzing these data and comparing them with global databases we demonstrate how varying sediment supply impacted the wilcox shelf margin growth and deep water sediment dispersal under greenhouse eustatic conditions the coastal plain to marine topset and uppermost continental slope succession of the lower wilcox shelf margin sediment prism is divided into eighteen high frequency 300 ky duration stratigraphic sequences and further grouped into 5 sequence sets labeled as a e from bottom to top sequence set a is dominantly muddy slope deposits the shelf edge of sequence sets b and c prograded rapidly 10 km ma and aggraded modestly 80 m ma characterizes sequence sets d and e which is associated with smaller 9 10 m thick on average and isolated channel belts this stratigraphic trend is likely due to an upward decreasing sediment supply indicated by the shelf edge progradation rate and channel size as well as an upward increasing shelf accommodation indicated by the shelf edge aggradation rate the rapid shelf edge progradation and large rivers in sequence sets b and c confirm earlier suggestions that it was the early phase of lower wilcox dispersal that brought the largest deep water sediment volumes into the gulf of mexico key factors in this lower wilcox stratigraphic trend are likely to have been a very high initial sediment flux to the gulf because of the high initial release of sediment from laramide catchments to the north and northwest possibly aided by modest eustatic sea level fall on the texas shelf which is suggested by the early flat shelf edge trajectory high amalgamation of channel belts and the low overall aggradation rate of the sequence sets b and c

sapphirine bearing granulites and related high temperature metamorphic rocks from the higo metamorphic terrane west central kyushu japan the higo metamorphic unit in west central kyushu island southwest japan is an imbricated crustal section in which a sequence of units with increasing metamorphic grade from high northern part to low southern part structural levels is exposed the basal part of the metamorphic sequence representing an original depth of 23 24 km consists mainly of garnet cordierite biotite gneiss garnet orthopyroxene gneiss orthopyroxene bearing amphibolite and orthopyroxene bearing s type tonalite these metamorphic rocks underwent high amphibolite facies up to granulite facies metamorphism with peak p t conditions of 720 mpa 870 c in addition sapphirine bearing granulites and related high temperature metamorphic rocks also occur as tectonic blocks in a metamorphosed peridotite intrusion the sapphirine bearing granulites and their related high temperature metamorphic rocks can be subdivided into five types of mineral assemblages reflecting their bulk chemical compositions as follows 1 sapphirine corundum spinel cordierite 2 corundum spinel cordierite 3 garnet corundum spinel cordierite 4 garnet spinel gedrite corundum and 5 orthopyroxene spinel gedrite these metamorphic rocks are characterized by unusually high al2o3 and low sio2 contents which could represent a restitic nature remaining after partial melting of pelitic granulite under the ultra high temperature contact metamorphism at the peak metamorphic event of the higo metamorphic unit the metamorphic conditions are estimated to be about 800 mpa and above 950 c which took place at about 250 ma as a result of the thermal effect of the regional gabbroic rock intrusions

scales of disequilibrium and rates of equilibration during metamorphism mounting evidence suggests that partial disequilibrium meaning disequilibrium for some elements but not for others may be a common but rarely detected phenomenon during metamorphic mineral growth even in ordinary prograde reactions that progress to completion detailed examination of compositional variations in garnet crystals over a range of metamorphic grade suggests distinctly different scales of equilibration for common elements with strong temperature dependence under lower greenschist facies conditions fe and mg may equilibrate at hand sample scale whereas mn and ca may not equilibrate even at millimeter scale although mn may achieve hand sample scale equilibration under upper greenschist facies conditions ca and many trivalent cations e g rees may not do so until temperatures exceed those of the middle amphibolite facies even in the lower granulite facies some elements e g y yb show indications of disequilibrium at sub centimeter scales during garnet growth analysis and numerical modeling of undisputed disequilibrium textures demonstrate that the most common impediment to equilibration during metamorphism is the sluggishness of intergranular diffusion the same mechanism known to govern porphyroblast crystallization in many metamorphic environments despite this importance to petrology few quantitative determinations exist of inter granular diffusion rates under metamorphic conditions using numerical simulations of coupled intergranular and intracrystalline diffusion processes in coronal textures around partially resorbed garnet crystals from the llano uplift u s a a very precise and relatively accurate estimate is obtained for the rate of intergranular diffusion of al in fluid undersaturated systems this result and an earlier estimate for fluid saturated systems provide bracketing values for al diffusivity during metamorphism

progressive inversion for hypocenters and p wave and s wave velocity structure application to the geysers california geothermal field seismicity at the geysers is induced by some aspect of steam production accurate earthquake locations particularly hypocentral depth are needed to determine the relationship between geothermal energy production and seismicity progressive p and s wave velocity hypocenter inversions were done using data from 39 microearthquakes at the geysers to estimate microearthquake locations and determine if the geothermal field has a distinctive seismic signature comparable final vp vs and vp vs velocity models were obtained from four different starting velocity models the elevation interval of maximum steam production coincides with minimum observed vp vs and vp vs increases below the primary production zone suggesting that reservoir rock becomes more fluid saturated with increasing depth a vp vs peak at the condensation zone production zone elevation delineates the top of the stream reservoir earthquake locations are confined to two depth intervals a zone of shallow seismicity occurs immediately below the condensation zone and above maximum depths of steam production a more arealy restricted zone of seismicity is located below maximum production depths and is abruptly terminated at an elevation of 3 7 km

two stage decompression in orthopyroxene sillimanite granulites from forefinger point enderby land antarctica implications for the evolution of the archaean napier complex magnesian metapelites of probable archaean age from forefinger point sw enderby land east antarctica contain very high temperature granulite facies mineral assemblages which include orthopyroxene 8 9 5 wt al2o3 sillimanite garnet quartz k feldspar that formed at 10 1 5 kbar and 950 50 c these assemblages are overprinted by symplectite and corona reaction textures involving sapphirine orthopyroxene 6 7 wt al2o3 cordierite and sometimes spinel at the expense of porphyroblastic garnet or earlier orthopyroxene sillimanite these textures mainly pre date the development of coarse biotite at the expense of initial mesoperthite and the subsequent formation of orthopyroxene 4 6 wt al2o3 cordierite plagioclase rinds on late biotite the early reaction textures indicate a period of near isothermal decompression at temperatures above 900 c decompression from 10 1 5 kbar to 7 8 kbar was succeeded by biotite formation at significantly lower temperatures 800 850 c and further decompression to 4 5 1 kbar at 700 800 c the later parts of this p t evolution can be ascribed to the overprinting and reworking of the forefinger point granulites by the late proterozoic c 1000 ma rayner complex metamorphism but the age and timing of the early high temperature decompression is not known it is speculated that this initial decompression is of archaean age and therefore records thinning of the crust of the napier complex following crustal thickening by tectonic or magmatic mechanisms and preceding the generally wellpreserved post deformational near isobaric cooling history of this terrain