crustal contamination in palaeogene east greenland flood basalts plumbing system evolution during continental rifting abstract palaeogene central east greenland flood basalts have sr nd and pb isotope characteristics consistent with crustal contamination of icelandic type basalts in the lower basalts of central east greenland amphibolite facies gneiss is the dominant contaminant at low stratigraphic levels whereas contamination with granulite facies gneiss prevails in the upper part of the lava succession the contamination probably occurred by partial melting of the crust and can be modelled by assimilation fractionation crystallisation processes similar contaminants have been detected in lavas from odp leg 152 off the se greenland coast although in a reverse sequence contamination in lower basalts and odp leg 152 lavas which erupted through an archaean proterozoic substrate differs from lavas in ne greenland which overly the caledonian fold belt and large mesozoic sediment deposits in the ne greenland lavas the dominant contaminant appears to be a dacitic component formed by partial melting of mesozoic sediments changes in magma supply rates from the mantle may be the determining factor for the sequence of contaminants and may also control the depth of ponding in crustal chambers the compositional variation of the least contaminated east greenland basalts suggests that melts were produced from mantle sources similar to present day iceland and north atlantic morb at the time of continental breakup but distinction between mantle sources is very complicated ree systematics indicate a maximum in initial depth of mantle melting at kangerlussuaq during formation of the east greenland flood basalts consistent with a plume being centered in that region

berthierine chamosite corrensite and discrete chlorite from evolved verdine and evaporite associated facies in the jurassic sundance formation wyoming late jurassic sandstones of the shallow marine sundance formation contain authigenic chlorite minerals that occur as rosette like pore fillings of interstratified berthierine chamosite b c and honeycomb like pore linings of corrensite and discrete chlorite b c is nearly ubiquitous in sundance sandstones but is absent near the top of the formation whereas corrensite and discrete chlorite were detected only in uppermost sundance sandstones within 4 m of the contact with the overlying non marine morrison formation glauconite grains are common and occur as laminae along bedding planes and cross beds indicating reworking and deposition as clasts in tidally influenced regimes the mineralogical chemical and morphological properties of the b c and corrensite indicate that they are authigenic and formed during burial diagenesis from precursor minerals odinite in the case of b c and saponite in the case of corrensite and discrete chlorite odinite has been recognized in numerous shallow marine sands of the holocene verdine facies and the shallow marine conditions associated with sundance deposition would have been ideal for odinite formation saponite commonly forms in aeolian and evaporitic environments implying that the saponite precursor to corrensite and discrete chlorite formed in uppermost sundance sands that were exposed to an influx of oxidizing groundwater following regression of the sundance sea x ray diffraction xrd indicates that the proportion of 7 a b layers in b c ranges from 5 to 28 and chemical analysis by scanning electron microscope energy dispersive x ray spectrometry sem eds indicates positive correlation between b and fe fe mg the polytype of the b c is ibb and the corrensite and discrete chlorite are disordered iib these are the expected polytypes and b for sandstones exposed to burial diagenetic conditions of 3000 4000 m and temperatures 90 120 c

clay mineral evolution changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4 567 ga of planetary evolution in our solar system reflect evolving tectonic geochemical and biological processes clay minerals were absent prior to planetesimal formation 4 6 billion years ago but today are abundant in all near surface earth environments new clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in earth s evolution notably the formation of a mafic crust and oceans the emergence of granite rooted continents the initiation of plate tectonics and subduction the great oxidation event and the rise of the terrestrial biosphere the changing character of clay minerals through time is thus an important part of earth s mineralogical history and exemplifies the principles of mineral evolution

phyllosilicate minerals in the hydrothermal mafic ultramafic hosted massive sulfide deposit of ivanovka southern urals comparison with modern ocean seafloor analogues we have studied textural relationships and compositions of phyllosilicate minerals in the mafic ultramafic hosted massive sulfide deposit of ivanovka main uralian fault zone southern urals the main hydrothermal phyllosilicate minerals are mg rich chlo rite variably ferroan talc mg si rich and ca na k poor saponite stevensite and serpentine these minerals occur both as alteration products after mafic volcanics and ultramafic protoliths and except serpen tine as hydrothermal vein and seafloor mound like precipitates associated with variable amounts of ca mg fe carbonates quartz and fe and cu co ni sulfides brecciated mafic lithologies underwent perva sive chloritization while interlayered gabbro sills underwent partial alteration to chlorite illite actinolite saponite talc bearing assemblages and later localized deeper alteration to chlorite saponite ultramafic and mixed ultramafic mafic breccias were altered to talc rich rocks with variable amounts of chlorite carbonate and quartz chloritization locally accompanied by formation of disseminated sulfides required a high contribution of mg rich seawater to the hydrothermal fluid which could be achieved in a highly permeable breccia dominated seafloor more evolved hydrothermal fluids produced addition of silica car bonates and further sulfides and led to local develop ment of saponite after chlorite and widespread replacement of serpentine by talc the ivanovka deposit shows many similarities with active and fossil hydro thermal sites on some modern oceanic spreading centers characterized by highly permeable upflow zones how ever given the arc signature of the ore host rocks the most probable setting for the observed alteration min eralization patterns is in an early arc or forearc seafloor subseafloor environment characterized by the presence of abundant mafic ultramafic breccias of tectonic and or sedimentary origin

chlorite and biotite weathering fe2 rich corrensite formation and fe behavior under low po2 conditions and their implication for precambrian weathering fresh and weathered granite from drill cores in tono gifu japan was examined to understand weathering products and the mechanisms of chlorite and biotite weathering under low p o 2 conditions a fresh sample from 365 m depth a slightly weathered light green sample from 367 m depth and a nearly fresh sample from 369 m depth but with brown stains on fractures were investigated the xrd sem empa and tem analysis of green grains present within chlorite biotite and plagioclase grains and in veins was found to be fe 2 rich corrensite about 40 wt feo with fe fe mg 0 94 the corrensite is interpreted to have formed from chlorite and biotite via a dissolution precipitation mechanism the 2 fe value of 0 69 which when combined with the presence of amorphous fe 3 hydr oxides confirmed by tem indicates that the fe 2 fe value of corrensite is 0 69 these results indicate that on dissolution of chlorite and biotite fe 2 was transported as fe 2 and precipitated as fe 2 rich corrensite and a part of the dissolved fe 2 was oxidized to amorphous fe 3 hydr oxides under low p o 2 conditions the formation of fe 2 rich corrensite and that of fe 2 rich smectite or vermiculite in the laboratory at 1 atm of p co 2 and 3 10 5 atm of p o 2 murakami et al 2004 suggest that a possible fe 2 bearing product during precambrian weathering is fe 2 rich sheet silicates but not siderite

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

anoxic dissolution processes of biotite implications for fe behavior during archean weathering abstract iron rich biotite fe mg 5 dissolution experiments were carried out in a batch system under o 2 deficient conditions p o 2 5 atm referred to as anoxic conditions at 1 atm of p co 2 ph 4 6 and 100 c for 7 120 days for a better understanding of anoxic weathering processes and fe behavior during weathering before 2 2 ga for comparison oxic fe rich biotite dissolution experiments were conducted under present atmospheric conditions at ph 4 7 and 100 c for 7 80 days referred to as oxic conditions by using the same starting biotite as that for the anoxic experiments the concentrations of fe in solution after the dissolution experiments were larger by one to more than two orders of magnitude under anoxic conditions than under oxic conditions high resolution scanning and transmission electron microscopy revealed that fe ii rich vermiculite or smectite was precipitated as a secondary mineral at the edge of biotite under anoxic conditions in contrast to the formation of fe iii and al hydr oxides under oxic conditions the results suggest that part of fe ii is released to water as anoxic weathering proceeds explaining the decrease of fe content in pre 2 2 ga paleosols relative to their parent rocks the fe mg molar ratio of the secondary vermiculite or smectite was more than 7 while the starting fe rich biotite had a value of about 5 the fe mg molar ratio was less than 2 5 in solution the results of the anoxic experiments suggest that fe ii rich vermiculite or smectite could be the precursor of the chlorite preserved in pre 2 2 ga paleosols this is further corroborated by the increase in fe mg molar ratios in chlorite with decreasing depth in some precambrian paleosols

comparing e field changes aloft to lightning mapping data 1 a newly developed balloon borne instrument contains electric and magnetic sensors for determining how lightning alters electric field vectors relative to a coordinate system fixed with the earth by combining data from this instrument with results from the compact lightning mapping array lma at langmuir laboratory in central new mexico and the national lightning detection network nldn charge transported to ground by several strokes in a cloud to ground cg lightning flash can be quantified as the flash progresses the locations of the charge centers drained by successive strokes are seen to move further from the ground strike point using this new instrument and two different models to map lma source points onto charge centers the charge transported in an intracloud ic flash is also estimated details of the instrument design and data analysis are also presented

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

the pumpellyite actinolite and contiguous facies in part of the phyllite quartzite series central northern peloponnesus greece variations in assemblage and composition of the constituent minerals in basic and intermediate metavolcanics encountered in the zarouchla group of the phyllite quartzite series are consistent with a progressive sequence corresponding to temperature conditions estimated at 290 380 c minimum values under a total pressure greater than 3 5kbar and possibly as high as 5 kbar in the absence of more critical evidence the parageneses recorded in the metavolcanic rocks are interpreted as belonging to a prograde facies series from the lawsonite albitechlorite facies through the pumpellyite actinolite facies to the greenschist facies the present distribution of mineral assemblages does not show a simple increase of metamorphic grade in a given direction but is apparently related to the tectonic evolution of the metamorphic sequence

temperature composition relationships of authigenic micaceous minerals in the los azufres geothermal system smectite illite celadonite and chlorite are the major products of alteration of rhyolites and andesites in the upper part of the los azufres geothermal system changes in mineral assemblages and composition of phases are observed as a function of depth and host rock lithology two different sequences characterize the rhyolites and the andesites from the surface to a depth of about 1500 m kaolinite smectite interlayered illite smectite illite muscovite rhyolites and kaolinite smectite interlayered illite smectite illite celadonite illite chlorite chlorite andesites

kinetics of biotite dissolution and fe behavior under low o2 conditions and their implications for precambrian weathering abstract biotite dissolution experiments were carried out to better understand the dissolution kinetics and fe behavior under low o 2 conditions and to give an insight into the precambrian weathering mineral dissolution with a continuous flow through reactor was employed at 25 c for up to 65 days varying partial pressure of atmospheric oxygen p o 2 ph 6 86 and 3 01 and fe content in mineral 1 06 and 0 11 mol of fe per o 10 oh f 2 for biotite and phlogopite respectively independently for the examination of their effects on biotite dissolution low p o 2 conditions were achieved in a newly developed glove box p o 2 6 10 4 atm referred to as anoxic conditions which was compared to the present ambient air conditions 0 2 atm of p o 2 oxic conditions the biotite dissolution rate was slightly faster under anoxic conditions at ph 6 86 while it was not affected by p o 2 at ph 3 01 there was no direct effect of fe content on dissolution rate at ph 6 86 while there was a small difference in dissolution rate between biotite and phlogopite at ph 3 01 the 1 5 order of magnitude faster release rate of fe under anoxic conditions for biotite dissolution at ph 6 86 resulted from the difference in ratio of fe 3 precipitates remaining in the reactor to fe dissolved about 60 and 100 under anoxic and oxic conditions respectively which is caused mainly by the difference in p o 2 the results infer that the fe 2 and fe 3 contents in the paleoproterozoic paleosols fossil weathering profiles are reflected by atmospheric oxygen levels at the time of weathering

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

integrated tem xrd and electron microprobe investigation of mixed layer chlorite smectite from the point sal ophiolite california five basalt samples from the point sal ophiolite california were examined using hrtem and aem in order to compare observations with interpretations of xrd patterns and microprobe analyses xrd data from ethylene glycol saturated samples indicate the following percentages of chlorite in mixed layer chlorite smectite identified for each specimen i l2036 almost equal to 50 ii l2035 almost equal to 70 and 20 iii 1a 13 almost equal to 70 iv 1b 42 almost equal to 70 and v 1b 55 100 detailed electron microprobe analyses show that chlorite analyses with high si k na and ca contents are the result of interlayering with smectite like layers the fe fe mg ratios of mixed layer phyllosilicates from point sal samples are influenced by the bulk rock composition not by the percentage of chlorite nor the structure of the phyllosilicate measurements of lattice fringe images indicate that both smectite and chlorite layers are present in the point sal samples in abundances similar to those predicted with xrd techniques and that regular alternation of chlorite and smectite occurs at the unit cell scale both 10 and 14 angstrom layers were recorded with hrtem and interpreted to be smectite and chlorite respectively regular alternation of chlorite and smectite 24 angstrom periodicity occurs in upper lava samples l2036 and 1a 13 and lower lava sample 1b 42 for as many as seven alternations per crystallite with local layer mistakes sample l2035 shows disordered alternation of chlorite and smectite with juxtaposition of smectite like layers suggesting that randomly interlayered chlorite 0 5 smectite exists images of lower lava sample 1b 55 show predominantly 14 angstrom layers units of 24 angstrom tend to cluster in what may otherwise appear to be disordered mixtures suggesting the existence of a corrensite end member having thermodynamic significance

deep seismic and geochemical constraints on the nature of rift induced magmatism during breakup of the north atlantic abstract the deep crustal structure of the norwegian and east greenland conjugate passive margins has been investigated with two ship multichannel reflection and refraction techniques in the region from the iceland faeroe ridge to the greenland fracture zone the data demonstrate the presence of thick 15 20 km igneous crust that was emplaced along the conjugate margins during the initiation of seafloor spreading seaward dipping units comprise the uppermost 3 6 km of the thick crust the thickness of igneous crust diminishes seaward with oceanic layer 2 approaching normal thickness nearer to the margin than does oceanic layer 3 wide angle reflection techniques used in conjunction with expanded spread profiling reveal deep moho reflections beneath 20 km thick oceanic crust that continue seaward into the ocean basin margins that have experienced unusually prolific magmatic activity during breakup have been termed volcanic to distinguish them from non volcanic margins that have evolved into accreting plate boundaries without excessive volcanism the origin of volcanic margins cannot be determined from seismically derived crustal thicknesses alone however thermal and chemical properties of the mantle source may be revealed in the compositions of magmatic products emplaced within volcanic passive margins a combined investigation of crustal structure and associated basalt composition could better resolve processes that result in volcanic passive margins on the voring plateau of the norwegian margin seismic lines coincide with dsdp leg 38 drill sites whole rock major element abundances in the freshest basalts are compatible with moderate extents of partial melting of mantle much like that believed to underlie modern mid ocean ridge systems and would be expected to result in the emplacement of oceanic crust about 9 2 km thick this is about the thickness of oceanic crust located seaward of the dipping basaltic units off the hatton more and voring plateau margins and 10 km south of iceland on the reykjanes ridge these results together with regional heat flow depth gravity and geoid anomalies suggest that the mantle beneath this region has experienced a moderate long lived temperature increase compared to mantle beneath normal ocean basins the much greater thicknesses of igneous crust adjacent to the margins do not appear to reflect an unusually hot flux associated with their construction since this would lead to much greater extents of partial melting than are inferred from the basalt geochemistry evidently the difference between volcanic and non volcanic margins is not simply proximity to a hot spot instead we suggest that the magmatism is closely related to the continental rifting phase tectonism resulting in an abrupt transition from continental to oceanic lithosphere may induce small scale convection that results in the circulation of a greater amount of mantle material into the pressure temperature field where partial melting begins than would occur through passive upwelling alone initial crustal thicknesses are enhanced as a result of the convective partial melting crustal thickness is expected to diminish as this secondary convection slows but the degree of partial melting of the source should not change dramatically

electron microscopy of a muscovite biotite interface an intergrowth of muscovite and biotite from mitchell creek mine upson county georgia was studied with a high resolution transmission electron microscope atomic arrangements of the interface between muscovite and biotite have been derived revealing far more complexity for the interface structure than that proposed previously based on optical and x ray analysis gresens and stensrud 1971 it was found that the muscovite has an almost perfectly ordered 2m 1 structure while the biotite is highly disordered despite such disorder in biotite both octahedral layers and k ion interlayers of the two minerals are connected perfectly at the interface while about 60 of the tetrahedral sheets are discontinued across the interface occasional occurrences of coherent intergrowths of chlorite like structure in biotite were recognized in the vicinity of the interface journal abstract

magmatic tectonic evolution of a volcanic rifted margin abstract many north atlantic continental margins are underlain by huge volcanic edifices near the continent ocean boundary a deep crustal hole drilled on the voring plateau odp leg 104 has provided important constraints on the initial breakup history and the subsequent margin evolution by penetrating more than 900 m of igneous rocks and interbedded sediments below a post early eocene cover the rocks constitute two distinct different volcanic series the upper series comprising a seaward dipping reflector wedge consists of transitional mid oceanic tholeiitic lava flows and thin volcaniclastic sediments dacitic flows some dikes and thicker interbedded sediments constitute the lower series the margin evolved by paleocene crustal extension accompanied by uplift and pervasive intrusion of the rift zone just prior to breakup magma from shallow crustal melts produced the lower series the upper series was constructed during an intense rapidly waning subaerial volcanic surge following breakup near the paleocene eocene transition it covers both the new oceanic crust and large areas of the continental crust the dipping wedge was formed by subsidence due to loading and thermal contraction possibly amplified by tectonism when the surge abated the injection center rapidly subsided and normal oceanic crust was formed there is a direct temporal and compositional relationship between the onshore north atlantic volcanic province and the margin volcanism compared to the transverse part of the province including the iceland hotspot which has been active over 60 m y the volcanic margins reflect a 2500 km long transient segment related to continental breakup lasting only about 3 m y the volcanic surge and uplift at breakup are related to a modest regional increased temperature at the base of the lithosphere this mode of margin formation has had important paleoenvironmental implications

mapping the lateral development of lightning flashes from orbit optical lightning measurements from the lightning imaging sensor lis are used to map the lateral development of lightning flashes and produce statistics that describe their motion through the electrified cloud this is accomplished by monitoring the frame by frame group level evolution of the optical signals produced during each flash while the optical flash properties recorded by lis gravitate towards the most exceptional optical signals produced during the flash group level data describe the evolution and lateral development of the flash resulting from physical lightning process that emits enough light out of the top of the cloud to be detected from orbit the groups that comprise lis flashes constitute examples of complex lateral flash structure that can extend 80 km in length with dozens to hundreds of visible branches the lateral development of individual flashes is described in terms of its speed and direction of motion whether the development extends the overall length of the flash or reilluminates an existing segment and whether it is directed inbound or outbound with respect to the origin sixty five percent of propagating groups are directed outbound from the origin 22 extend the length of the flash and 3 5 reilluminate an existing branch lis flashes are commonly oriented from east to west and develop at speeds ranging from 104 to 106 m s consistent with large scale leader development these results provide evidence that lightning imagers may be used in conjunction with lightning mapping array systems to document physical lightning phenomena across global domains

early cenozoic crust at the norwegian continental margin and the conjugate jan mayen ridge multichannel seismic profiles at the voring plateau margin off norway and the northern jan mayen ridge have provided a framework for the early tertiary evolutionary history of these areas which were adjacent prior to the opening of the norwegian sea we propose that their paleogene evolution is quite similar and that the two acoustic basement reflectors ee and jo were formed in the early eocene by extrusion of flow basalts from the time of opening to about anomaly 23 time oceanic seafloor was generated by icelandic type spreading during that time the central jan mayen fracture was the main transform the seaward dipping reflector sequences are flow basalts generated by the icelandic spreading the existence of less well developed dipping sequences seaward of the primary ones probably reflects that these regions submerged later because of higher initial elevation during the early eocene subaerial spreading episode which is related to the north atlantic volcanic province basalt flows also covered the adjacent thinned and heavily intruded continental crust it is proposed that the continent ocean boundary is located just landward of anomaly 24b a short distance seaward of the voring plateau escarpment reflector k is only recognized landward of this boundary in a region of transitional crust the escarpment experienced syndepositional faulting and the most elevated parts of the voring marginal high did not subside below shallow water depths before oligocene miocene time we suggest that the voring margin and the jan mayen ridge represent volcanic passive margins the evolution of this margin type may relate to initial uplift due to rifting in previously thinned crust

tertiary mineralization and magmatism east greenland lead isotope evidence for remobilization of continental crust abstract well defined lead isotope signatures of sulphides from mineral occurrences associated with tertiary igneous rocks in east greenland fall in two distinct groups 1 sulphide samples from the region south of scoresby sund kangerlussuaq igneous complex have lead characterized by retarded uranogenic evolution and slightly elevated thorogenic isotopic ratios 2 sulphide samples from the region north of scoresby sund werner bjerge kap simpson and kap broer ruys igneous complexes have lead compositions typical of modern average terrestrial lead these distinct signatures in both conventional and 208 pb 204 pb 207 pb 204 pb diagrams lie within linear trends defined by previously published lead isotope data for unmineralized tertiary basalts and intrusive rocks the linear trends are mixing lines between the lead in the tertiary mantle derived magmas and lead remobilized from continental crust tertiary magmas in the region south of scoresby sund remobilized and incorporated lead from low high 208 pb 204 pb crustal sources similar in isotope composition to archaean high grade metamorphic gneisses exposed in the area non to sub parallel distinct lead mixing lines in the 208 pb 204 pb 206 pb 204 pb diagram for the tertiary igneous complexes in this region suggest strong heterogeneity of the remobilized crust more than one half of the lead from sulphide mineral occurrences within the kangerlussuaq alkaline intrusive complex may be derived from local continental crust in the region north of scoresby sund the tertiary magmas remobilized moderately radiogenic lead from local basement and sedimentary basins palaeoproterozoic mesoproterozoic gneisses neoproterozoic ordovician sediments caledonian granites and palaeozoic mesozoic sediments these crustal rocks lack the very low 206 pb 204 pb and 207 pb 204 pb ratios typical of the gneisses from the kangerlussuaq region and mixing trends between mantle derived and crustal lead are therefore much less extensive however because the mantle derived magmas had very low total lead contents even small additions of crustal lead are traceable sulphide mineralized alkaline intrusive complexes are shown to be highly contaminated with crustal lead and it is further shown that the pre tertiary rocks of north east greenland are likely local crustal sources of lead for contaminated tertiary plateau basalts many stratabound sediment hosted hydrothermal base metal occurrences in the palaeozoic mesozoic jameson land basin are thought to be tertiary in age but do not appear to contain tertiary igneous derived lead on the contrary the hydrothermal alteration zones associated with several of the mineralized tertiary igneous complexes attest to extensive fluid rock mass transfer lead and other base metals were leached from the country rocks homogenized and incorporated into sulphide minerals

early tertiary magmatism in ne greenland abstract between 73 and 74 n in ne greenland a lower series of quartz tholeiite lavas is overlain by an upper series which varies from quartz tholeiitic to basanitic the lower series basalts are attributed to large melt fractions produced east of the present outcrop where lithospheric thinning permitted the iceland plume to ascend to shallow levels relocation of eruption sites up to 150 km further west preceeded upper series activity in this small degree melts generated principally from garnet lherzolite facies sources were followed by products of more extensive shallower melting which gave rise successively to the upper series lavas a post upper series basaltic dyke swarm and its associated caldera complex palaeomagnetic observations and 40 ar 39 ar dating suggest that the lower series and part of the upper series erupted in c24r at 58 57 ma rejuvenescent activity at c 32 ma marking the termination of volcanism may relate to decompressive mantle melting associated with late regional uplift

radio interferometric observations of cloud to ground lightning phenomena in florida radio frequency observations of cloud to ground lightning in florida have been analyzed to document a number of features of the lightning the observations have been made using an interferometer system which determined the direction to the lightning radiation as a function of time during close lightning discharges observations are presented for about 50 radiating events during five multiple stroke normal polarity flashes to ground the results confirm and extend results of a similar study of new mexico lightning by rhodes et al 1994 dart leaders in cloud k events and attempted leaders are found to be the same phenomena namely a negative polarity streamer that propagates horizontally and or vertically to ground at estimated speeds of about 10 7 ms 1 down to 10 6 ms 1 the step or impulsive fast electric field change produced by some k events is found to be caused by positive breakdown back at the starting point of the negative streamer after the streamer has progressed over some or all of its distance this breakdown appears to initiate a forward stroke along the streamer channel which can renew the breakdown at the front end of the channel k breakdown which happens to occur during a continuing current discharge to ground produces an m event channel brightening when it connects with the conducting channel to ground the step fast field change of the m events is found to be produced at the time of connection inside the cloud no fast field change is detected when this breakdown reaches ground that would be associated with a return stroke m events can also be initiated by fast 10 7 ms 1 positive streamers which often propagate away from the leader source region within a few milliseconds of the arrival of a return stroke back in the source region these streamers often generate an even faster negative recoil event back along their extent which propagates down the channel to ground as the m event in all cases the current increase or channel brightening produced by k and m events is predicted to occur in a forward direction that is toward or down the channel to ground in the same direction as the initiating negative streamer positive breakdown is detected only immediately following return strokes or during some k streamers in both cases the electric stresses are expected to be very large suggesting that positive breakdown which produces a conducting channel is difficult to initiate results for one flash suggest that negative charge was left at low altitude by the initial stroke to ground this forced the subsequent leaders to develop a new path to ground first as series of attempted leaders and then as a dart stepped leader

comparative mineral chemistry and textures of safod fault gouge and damage zone rocks abstract creep in the san andreas fault observatory at depth safod drillhole is localized to two foliated gouges the central deforming zone cdz and southwest deforming zone sdz the gouges consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of mg smectite clays that formed as a result of shearing enhanced reactions between the serpentinite and quartzofeldspathic rocks the cdz takes up most of the creep and exhibits differences in mineralogy and texture from the sdz that are attributable to its higher shearing rate in addition a 0 2 m wide sector of the cdz at its northeastern margin ne cdz is identical to the sdz and may represent a gradient in creep rate across the cdz the sdz and ne cdz have lower clay contents and larger porphyroclasts than most of the cdz and they contain veinlets and strain fringes of calcite in the gouge matrix not seen elsewhere in the cdz matrix clays in the sdz and ne cdz are saponite and corrensite whereas the rest of the cdz lacks corrensite saponite is younger than corrensite reflecting clay crystallization under declining temperatures and clays in the more actively deforming portions of the cdz have better equilibrated to the lower temperature conditions

chlorite illite muscovite interlayered and interstratified crystals a tem stem study phyllosilicates in rocks which are transitional from mudstone to slate from lehigh gap pa have been studied by a variety of techniques including high resolution transmission electron microscopy and analytical electron microscopy the principal minerals are white mica which is transitional from illite in mudstone to ordered twolayer mica in slate and chlorite 7a berthierine occurs more rarely dioctahedral and trioctahedral layers are shown to be interleaved in individual crystals at all scales between the following two end members 1 both random and regular 1 1 interlayering at the scale of individual layers as shown in part by lattice fringe images 2 packets of trioctahedral and dioctahedral layers up to a few thousand angstroms or microns in thickness detectable with ordinary optical techniques the complete range of intermediate structures is represented in samples which are in transition to slate bulk analytical empa x ray diffraction or other measurements are shown to result in averages over both kinds of layers when tem techniques are not used

volcaniclastic rocks of the reydarfjordur drill hole eastern iceland 2 alteration volcaniclastic rocks of basaltic to rhyolitic composition interlayered with basaltic to icelanditic lava flows in a 1918 m drill hole in eastern iceland are altered to zeolite and pumpellyite prehnite facies assemblages major alteration minerals are chlorites illite chlorite mixed minerals illites k feldspar laumontite quartz and sphene others include julgoldite and secondary allanite smectites as well as mordenite and heulandite are restricted to the upper 900 m epidote and minor pumpellyite prehnite wairakite and anhydrite are restricted to the core below 900 m the boundary between zeolite and prehnite pumpellyite facies is marked by the appearance of chlorite epidote quartz assemblages at around 900 m the typical paragenesis prehnite pumpellyite epidote chlorite occurs near the base of the drill hole at 1855 m textures indicate generally prograde metamorphic conditions the broad compositional spectrum ranging from basalt to rhyolite abundance of vitric fragments and high initial porosity and permeability of the volcaniclastic rocks were major factors governing alteration the site of growth crystal shard vesicle pore and vein of a secondary phase strongly influences composition habit amount paragenesis and time of crystallization for example sphene and to a lesser degree epidote are less rich in fe and better crystallized in plagioclase than in the adjacent matrix the different mineral assemblages developed within plagioclase crystals through the section most clearly reflect the metamorphic changes the abundance of vitric rhyolitic clasts shards and pumice favored k al si enriched fluids from which phases like illite and adularia crystallized these phases were not found in interlayered basalt flows mehegan et al this issue low ca activity is also indicated by the occurrence of wairakite and pumpellyite rather than prehnite which is common in the basalts secular changes during metamorphism in pore fluid composition are shown by zonations in mineral compositions for example the depletion of epidote and juldoldite pumpellyite in fe with time appears to reflect decreasing o2 bulk rock chemical changes are more intense in the volcaniclastic rocks compared to the basalt lavas h2o fe3 fe2 and in part co2 values are higher in the upper part of the hole reflecting the higher porosity and glass content of the clastic rocks they decrease markedly downhole approaching values of the lava flows due to more pervasive metamorphic alteration and thus similar mineral assemblages and physical properties

contact metamorphism hydrothermal alteration of tertiary basalts from the isle of skye northwest scotland alkali olivine basalts from skye were simultaneously contact metamorphosed by tertiary gabbro and granite intrusions and altered by the hydrothermal convection system that the plutons induced four metamorphic zones were mapped around the plutons furthest from the intrusions in the primary olivine zone metabasalts are composed of combinations of igneous olivine augite plagioclase titaniferous magnetite ilmenite zeolites gyrolite sulfides and chlorite smectite intergrowths closer to the plutons in the smectite zone saponite and carbonate appear primary olivine and gyrolite disappear and zeolites decrease dramatically in abundance still closer to the plutons in the amphibole zone actinolite edenite chlorite sphene epidote andradite and quartz appear and saponite and chlorite smectite intergrowths disappear along parts of the contact between gabbro and basalt in the orthopyroxeneolivine zone orthopyroxene metamorphic olivine and biotite appear and amphibole chlorite sphene epidote andradite carbonate and quartz disappear whole rock chemical data indicate only minor change in the major element chemical composition of the metabasalts during progressive metamorphism hydrothermal alteration two pyroxene eothermometry and various mineral fluid equilibria suggest the range of peak temperatures attained in the metamorphic zones orthopyroxene olivine zone 900 1 030 c amphibole zone 400 900 c smectite and primary olivine zones 5 smow mineralogically more altered basalts from the smectite zone have whole rock 18o 2 to 5 still more mineralogically altered basalts from the amphibole zone with one exception have 18o 2 completely recrystallized hornfelses from the orthopyroxene olivine zone have 18o 0 the principal mechanism of isotope exchange between basalt and metamorphic hydrothermal fluid probably was heterogeneous mineralfluid reaction

low grade metamorphism and geotectonic setting of the macuchi formation western cordillera of ecuador the cretaceous eocene basic to intermediate marine volcanic rocks of the mucuchi formation constitute the western cordillera in northern ecuador their chemical features mostly correspond to those of tholeiitic basalts with some calc alkaline affinities and suggest an oceanic island arc setting the macuchi rocks are affected by low grade non deformative metamorphism characterized by zeolite prehnite pumpellyite and lower greenschist facies assemblages depth zonation is suggested by the downward mineral sequence i laumontite pistacitic epidote pumpellyite prehnite ii pumpellyite prehnite pistacitic epidote iii actinolite biotite pistacitic epidote chlorite this broad zonation and the chemistry of individual minerals point to an interaction between the volcanic rocks and sea water under a moderate to high thermal gradient 75 c km alteration appears to have been dependent primarily on fluid control volume pressure composition temperature and reaction kinetics which together partly overshadow the role of load pressure compositional variations of a mineral species at the scale of a contiguous flow or even at the scale of a thin section show that intensity of alteration was spatially uneven depending on rock permeability and consequently metastable equilibrium commonly exists however a progressive approximation to equilibrium as a result of p t control is shown by the mineralogy a high fo2 of the fluid phase is evident from the mineral chemistry the metamorphism of the macuchi volcanics is similar to the hydrothermal burial type produced during the development of a volcanic arc where lavas and volcanoclastics accumulated in a shallow marine environment however some of its characteristics point to a transition toward systems defined by a higher t p ratio such as those found in ocean floor metamorphism a model is proposed in which the macuchi volcanics are assigned to an oceanic island arc generated contemporaneously with a marginal basin which has opened as the outcome of progressive north south attenuation of the continental crust due to mantle diapirism

contrasts in composition and evolution of tertiary cfbs between west and east greenland and their relations to the establishment of the icelandic mantle plume

episodic volcanism during break up of the north atlantic evidence from the east greenland plateau basalts abstract the lower tertiary upper paleocene lower eocene plateau basalts in the scoresby sund region of east greenland formed during three distinct magmatic episodes the activity of the first episode was centred in the present inland areas to the northwest and produced a voluminous regional basalt sequence lower sequence the activity of the second episode was centred to the southeast offshore the present atlantic coast and this also produced a voluminous regional basalt sequence upper sequence the third episode was centred on the atlantic coast and gave rise to a dense coastal dyke swarm and local lavas which are now only locally preserved by downfaulting the lavas are all tholeiitic basalts after an initial phase the two regional lava sequences of the first and second episodes show a similar vertical compositional zonation pattern a thin lower formation with variable composition is followed by a thick uniform formation which shows systematic compositional change with height from tio2 rich feti basalts to tio2 poor basalts and ending with a reversal to tio2 rich basalts each of these cyclic patterns apparently resulted from a temporary rifting episode and much of the compositional variation found can be explained by magma development in open magma chambers the dykes and lavas of the third episode of activity have chemical affinities to ocean floor basalts and their tio2 p2o5 ratios indicate formation at a spreading ridge centre the pattern of two failed rifting episodes and one event that produced oceanic crust can be correlated with stages in the complicated initiation of seafloor spreading in the region and the volcanism itself is closely related to this process

location and analysis of acoustic infrasound pulses in lightning acoustic vhf and electrostatic measurements throw new light onto the origin and production mechanism of the thunder infrasound signature 10 hz from lightning this signature composed of an initial compression followed by a rarefaction pulse has been the subject of several unconfirmed theories and models the observations of two intracloud flashes which each produced multiple infrasound pulses were analyzed for this work once the variation of the speed of sound with temperature is taken into account both the compression and rarefaction portions of the infrasound pulses are found to originate very near lightning channels mapped by the lightning mapping array we found that none of the currently proposed models can explain infrasound generation by lightning and thus propose an alternate theory the infrasound compression pulse is produced by electrostatic interaction of the charge deposited on the channel and in the streamer zone of the lightning channel

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

formation mechanisms of illite chlorite and mixed layer illite chlorite in triassic volcanogenic sediments from the southland syncline new zealand clay minerals from the three principal kinds of zeolitic sediments from the type area for zeolite facies alteration the triassic murihiku supergroup southland new zealand have been studied by tem bentonitic tuff consists largely of smectite and heulandite with minor illite they occur as replacements of glass shards and are inferred to be direct alteration products of tuff alteration both analcime and laumontite rich tuffs contain chlorite illite and mixed layer illite chlorite including 1 1 mixed layer sequences subhedral to euhedral phyllosilicate crystal shapes and other textural features imply that phyllosilicates crystallized from solution derived in part by dissolution of precursor smectite intralayer transitions involving illite and chlorite are inferred to be products of crystallization rather than direct alteration and replacement petrographically similar bentonitic and analcimized tuffs overlap each other in the stratigraphic section supporting earlier observations that there is no systematic change in smectite relative to the illite plus chlorite derived from smectite in sections up to 8 5 km thick the data imply that smectite may be metastable relative to illite plus chlorite permeability and fluid chemistry are inferred to be as significant as temperature in promoting reactions in clay minerals as well as zeolites during burial metamorphism

transition from the zeolite to prehnite pumpellyite facies in the karmutsen metabasites vancouver island british columbia

geology and geochemistry of paleosols developed on the hekpoort basalt pretoria group south africa the hekpoort paleosols comprise a regional paleoweathering horizon developed on 2 224 0 021 ga basaltic andesite lavas at the top of the hekpoort formation of the pretoria group transvaal supergroup south africa in five separate profiles from outcrops along road cuts near waterval onder and the daspoort tunnel and in three drill cores from the bank break area bb3 bb8 and bb14 the top of the paleosol is a sericite rich zone the sericite zone grades downward into a chlorite rich zone in core bb8 and in the road cut at the daspoort tunnel we sampled the underlying or parent basaltic andesite into which the chlorite zone grades we did not obtain samples of the parent material at waterval onder and in cores bb3 and bb14 but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core bb8 and at the daspoort tunnel the presence of apparent rip up clasts of the paleosol in the overlying ironstones of the strubenkop formation in the cores from bank break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at waterval onder point to a subaerial weathering origin very little if any al ti zr v or cr moved a discernible distance during weathering of any of the five profiles the vertical distribution of fe mg mn ni and co indicates that these elements were largely removed from the top of the soil during weathering the overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an fe 2 rich smectite the loss of fe from the top of the soil during weathering of the hekpoort paleosols indicates that atmospheric p o 2 was less than 8 x 10 4 atm about 2 22 ga fe 2 rich smectite should only precipitate during soil formation if atmospheric p co 2 is less than or equal to 2 x 10 2 atm rye kuo and holland 1995 ca and na were largely lost during weathering some na was apparently added to the sericite zone in cores bb3 bb8 and bb14 after weathering all five profiles are enriched in k and rb and most are enriched in ba the distribution of these elements indicates that they all were added during post weathering hydrothermal metasomatism rb sr analysis of the paleosol at the daspoort tunnel indicates that metasomatism last affected that profile 1 925 0 032 ga macfarlane and holland 1991

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

carbon 14 study of groundwater in the sedimentary rocks at the tono study site central japan isotopic investigations using 14c of groundwater were carried out to understand the hydraulic conditions in the sedimentary rocks at the tono study site central japan 14c activities of groundwater observed range from 2 to 32 modern carbon pmc measured 14c activities of groundwater are corrected by the isotopic mass balance model based on 14c activities 13c values concentrations of the dissolved inorganic carbon dic and 13c values of non active carbon dissolved into the groundwater from carbonate minerals and organics assuming that the groundwater reservoir is comparable to the piston flow situation the relative 14c ages of groundwaters were calculated from the corrected 14c activity the relative 14c age suggests that the groundwater infiltration from the upper part of the sedimentary rocks to the lower part takes several thousands of years or that the groundwater in the lower part of sedimentary rocks is derived from long distance flow from the surface through the unconformity between the sedimentary rocks and basement granite the flow rate calculated by relative 14c ages shows similar values to those estimated by computer simulation using hydraulic pressure and conductivity data hydraulic conditions at the tono study site inferred from 14c activity agree with those suggested from hydrogeological analyses isotopic approaches using 14c activity can be applied as geochemical evaluation for interpretations from the hydraulic study

the pantelleria caldera geothermal system data from the hydrothermal minerals abstract this paper proposes on the basis of petrographic and mineralogic data on cutting and cores from two deep wells pantelleria 1 and pantelleria 2 the first model of the active hydrothermal system of the island of pantelleria phyllosilicates were studied in detail because they are considered key minerals in the identification of hydrothermal processes the results of these studies emphasize differences between the intracaldera and pericaldera areas of the island within the 45 ka caldera there is a high temperature 240 260 c at 600 800 m depth active hydrothermal system with five zones of characteristic alteration minerals with increasing depth rocks are unaltered to a depth of 200 m contain smectite and mixed layer chlorite smectite c s between 200 and 380 m chlorite illite chalcedony and quartz from 380 to 500 m albite adularia and saponite from 500 to 680 m mixed layer biotite vermiculite from 680 m to the depth drilled 1100 outside the caldera but near the rim a low temperature and low permeability

symmetric conjugation of continent ocean boundary structures along the norwegian and east greenland margins abstract a characteristic structural feature of the norwegian continental margin that has been described from multichannel seismic data as well as dsdp and odp drilling is a major buildup of layered extrusive basaltic rocks forming wedges that dip seaward along the entire margin models for their origin describe them as either products of a late stage intra continental rift phenomenon with the volcanic rocks overlying attenuated continental crust or as an integral component of the oceanic crust formed during the first few million years of seafloor spreading in the norwegian greenland sea from studies of the norwegian margin alone it was not possible to unequivocally distinguish between the two proposed models so an investigation of the conjugate portions of the east greenland margin was undertaken which used two ship multichannel seismic acquisition as its focus we found that the wedges were not only present on the east greenland margin but that details of their along strike variability are mirrored on both margins together with their spatial relationship to the oldest magnetic lineation pattern the wedges are relatively small in the northern part of the margin where they occur almost entirely landward of lineation 24 moving south we see that the wedges broaden encroach into the pattern of lineation 24 then develop into two separate wedges the seaward of which is associated with lineation 23 lineations 24 and 23 on both margins are distorted when associated with wedges we believe that these data lend strength to a tectonic association of the wedges with nascent plate boundary processes their observation in many margins throughout the world suggest that a prolific volcanic phase may be commonly associated with the inception of a divergent plate boundary and we believe that the most likely mechanism to generate the excess volcanism is the convective partial melting scheme recently proposed by mutter and buck 1986 and mutter et al in press

mineralization and alteration of a modern seafloor massive sulfide deposit hosted in mafic volcaniclastic rocks tinakula is the first seafloor massive sulfide deposit described in the jean charcot troughs and is the first such deposit described in the solomon islands on land or the seabed the deposit is hosted by mafic basaltic andesitic volcaniclastic rocks within a series of cinder cones along a single eruptive fissure extensive mapping and sampling by remotely operated vehicle together with shallow drilling provide insights into deposit geology and especially hydrothermal processes operating in the shallow subsurface on the seafloor mostly inactive chimneys and mounds cover an area of 77 000 m2 and are partially buried by volcaniclastic sand mineralization is characterized by abundant barite and sulfide rich chimneys that formed by low temperature 250 c venting over 5 600 years barite rich samples have high sio2 pb and hg contents the sulfide chimneys are dominated by low fe sphalerite and are high in cd ge sb and ag few high temperature chimneys including zoned chalcopyrite sphalerite samples and rare massive chalcopyrite are rich in as mo in and au up to 9 26 ppm locally as visible gold below the seafloor the mineralization includes buried intervals of sulfide rich talus with disseminated sulfides in volcaniclastic rocks consisting mainly of lapillistone with minor tuffaceous beds and autobreccias the volcaniclastic rocks are intensely altered and variably cemented by anhydrite with crosscutting sulfate minor sulfide veins fluid inclusions in anhydrite and sphalerite from the footwall to 19 3 m below seafloor m b s f have trapping temperatures of up to 298 c with salinities close to but slightly higher than that of seawater 2 8 4 5 wt nacl equiv these temperatures are 10 to 20 c lower than the minimum temperature of boiling at this depth 1 070 1 204 m below sea level m b s l suggesting that the highest temperature fluids boiled below the seafloor the alteration is distributed in broadly conformable zones expressed in order of increasing depth and temperature as 1 montmorillonite nontronite 2 nontronite corrensite 3 illite smectite pyrite 4 illite smectite chamosite and 5 chamosite corrensite zones of argillic alteration are distinguished from chloritic alteration by large positive mass changes in k2o enriched in illite smectite mgo enriched in chamosite and corrensite and fe2o3 enriched in pyrite associated with illite smectite alteration the 18o and d values of clay minerals confirm increasing temperature with depth from 124 to 256 c and interaction with seawater dominated hydrothermal fluids at high water rock ratios leaching of the volcanic host rocks and thermochemical reduction of seawater sulfate are the primary sources of sulfur with 34s values of sulfides from 0 8 to 3 4 and those of sulfate minerals close to seawater sulfate from 19 3 to 22 5

lightning leader stepping k changes and other observations near an intracloud flash 1 an intracloud lightning flash in central new mexico began with the initiation of a negative stepped leader at an altitude of 8 2 km above sea level as this leader propagated eastward and upward at 9 1 km above sea level it passed about 200 m to the north of a balloon borne electric field change instrument esonde after the first leader stopped a second negative stepped leader began near the point of origin of the first leader but it propagated away from the esonde from the changes in the electric vectors and the locations of impulsive radio frequency sources detected by a lightning mapping array lma we conclude the following 1 the first negative stepped leader was not preceded by any significant charge rearrangement due to positive leaders 2 each step of the first negative leader had both a forward going wave and a step recoil wave that propagated simultaneously backwards away from the leader tip along the existing channel the presence of a step recoil wave during each step leads to an explanation for the existence of stepping 3 after the first nearby leader stopped step recoil waves from the second distant leader may have found their way onto the channel formed by the first leader 4 after the second leader stopped waves carrying negative charge propagated along the channel of the first leader producing strong k changes in the electric field at the esonde and providing a good record of the wavefront shapes

early proterozoic weathering processes under low o2 conditions reconstructed from a 2 45 ga paleosol in pronto canada we have examined a paleosol in pronto canada which formed at 2 45 ga and under very low o 2 conditions to reconstruct ancient weathering processes chlorite which replaced biotite in parent granite consists of almost complete chlorite layers as revealed by high resolution transmission microcopy chlorite grains were fragmented gradually with increased intensity of weathering the fragmented chlorite grains were partly or largely replaced by sericite formed from k metasomatism which strongly suggests that almost complete chloritization of biotite preceded sericitization in the upper part of the paleosol chlorite biotite mixed layers formed but the formation of these layers cannot be explained by mere chloritization and sericitization which are usually considered to occur concurrently during post weathering events our observations and analyses suggest that the chlorite biotite mixed layers were formed as follows chlorite with no or little biotite was formed from biotite in parent granite prior to weathering chlorite was then weathered by dissolution and fragmentation at 2 45 ga and chlorite vermiculite or smectite mixed layers were formed by layer by layer transformation in the weathering profile note that vermiculite is not actually observed in the pronto paleosol following burial of the weathering profile the vermiculite layers in the chlorite vermiculite mixed layers were converted to biotite layers by means of k metasomatism to form the chlorite biotite mixed layers the chlorite biotite mixed layers in the pronto paleosol were therefore chlorite vermiculite mixed layers at the time of weathering

estimates of atmospheric o 2 in the paleoproterozoic from paleosols abstract a weathering model was developed to constrain the partial pressure of atmospheric o 2 p o 2 in the paleoproterozoic from the fe records in paleosols the model describes the fe behavior in a weathering profile by dissolution precipitation of fe bearing minerals oxidation of dissolved fe ii to fe iii by oxygen and transport of dissolved fe by water flow in steady state the model calculates the ratio of the precipitated fe iii oxyhydr oxides from the dissolved fe ii to the dissolved fe ii during weathering as a function of p o 2 an advanced kinetic expression for fe ii oxidation by o 2 was introduced into the model from the literature to calculate accurate p o 2 relationships the model s validity is supported by the consistency of the calculated p o 2 relationships with those in the literature the model can calculate p o 2 for a given paleosol once a value and values of the other parameters relevant to weathering namely ph of porewater partial pressure of carbon dioxide p co 2 water flow temperature and o 2 diffusion into soil are obtained for the paleosol the above weathering relevant parameters were scrutinized for individual paleoproterozoic paleosols the values of temperature ph and p co 2 were obtained from the literature on the paleoproterozoic paleosols the parameter value of water flow was constrained for each paleosol from the mass balance of si between water and rock phases and the relationships between water saturation ratio and hydraulic conductivity the parameter value of o 2 diffusion into soil was calculated for each paleosol based on the equation for soil o 2 concentration with the o 2 transport parameters in the literature then we conducted comprehensive p o 2 calculations for individual paleoproterozoic paleosols which reflect all uncertainties in the weathering relevant parameters consequently robust estimates of p o 2 in the paleoproterozoic were obtained 10 7 1 10 5 4 atm at 2 46 ga 10 5 0 10 2 5 atm at 2 15 ga 10 5 2 10 1 7 atm at 2 08 ga and more than 10 4 6 10 2 0 atm at 1 85 ga comparison of the present p o 2 estimates to those in the literature suggests that a drastic rise of oxygen would not have occurred at 2 4 ga supporting a slightly rapid rise of oxygen at 2 4 ga and a gradual rise of oxygen in the paleoproterozoic in long term

investigating the origin of continual radio frequency impulses during explosive volcanic eruptions volcanic lightning studies have revealed that there is a relatively long lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning this very high frequency signal is referred to as continual radio frequency crf due to its long lasting nature the discharge mechanism producing this signal was previously hypothesized to be caused by numerous small 10 100m leader forming discharges near the vent of the volcano to test this hypothesis a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of sakurajima volcano in japan was collected from may to june 2015 our observations show that a single crf impulse has a duration on the order of 160ns giving an upper limit on discharge length of 10m and is distinct from near vent lightning discharges that were on the order of 30m in length crf impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field lightning mapping data and infrared video observations of the eruption column showed that crf impulses originated from the gas thrust region of the column these observations indicate that crf impulses are not produced by small leader forming discharges but rather are more similar to a streamer discharge likely on the order of a few meters in length plain language summary this paper investigates the origin of a radio frequency rf signal previously termed continual rf that has been detected from the ash plumes of explosive volcanic eruptions continual rf had been hypothesized to be caused by many very small lightning like discharges on the order of 100m in length occurring at the vent of the volcano to test this hypothesis we conducted a multiparametric observational experiment at sakurajima volcano in japan we measured continual rf during eruptions of sakurajima in 2015 and found that continual rf is a collection of short duration rf impulses on the order of 160ns in duration these rf impulses are distinct from those typically produced by lightning we also observed small 30 m lightning discharges occurring near the volcanic vent that were distinct from the source of continual rf our observations show that continual rf is caused by an electrical discharge that is more simple than even a very small approximate to 100m lightning discharge we conclude that continual rf is caused by numerous small electrical discharges similar to streamer discharges on the order of a few meters in length

kulkeite a new metamorphic phyllosilicate mineral ordered 1 1 chlorite talc mixed layer kulkeite occurs as platy colorless porphyroblastic single crystals up to 2 mm in size in a low grade dolomite rock associated with a triassic meta evaporite series at derrag tell atlas algeria it is associated with sodian aluminian talc unusual chlorite polytypes and both k and na phlogopite kulkeite is optically biaxial negative nx 1 552 ny 1 5605 nz 1 5610 2vz 24 obs based on microprobe analysis the empirical formula is na0 38k0 01ca0 01 mg8 02al0 99 al1 43si6 57o20 oh 10 with some variation in na si and tetrahedral al the crystals are monoclinic with a 5 319 1 b 9 195 2 c 23 897 10 a 97 1 3 z 2 the calculated density is 2 70 g cm 3 the four strongest lines in the x ray powder pattern are d i hkl 7 90 100 003 1 533 100 060 7 42 80 002 3 38 80 007 the 001 reflection with 23 7 a has intensity 10

iib trioctahedral chlorite from the barberton greenstone belt crystal structure and rock composition constraints with implications to geothermometry iib trioctahedral chlorite in the barberton greenstone belt bgb metavolcanic rocks was formed during pervasive greenschist metamorphism the chem ical composition of the chlorite is highly variable with the fe fe mg ratio ranging from 0 12 to 0 8 among 53 samples the chemical variation of the chlorite results from the chemical diversity of the host rock especially the mgo content of the rock but major details of the variation pattern of the chlorite are due to the crystal structure of the chlorite all major cation abundances in the chlorite are strongly correlated with each other sil icon increases with mg and decreases with fe while aliv and alvi decrease with mg and increase with fe2 a complex exchange vector explains over 90 of the chlorite compositional variation mg4sife2 3alvi 1 aliv 1 which has 3 parts fe mg substitution coupled with one part tschermakite substitution this ratio is required to maintain the charge and site balances and the dimensional fit between the tetrahedral and octahedral sheets the subtle change in al substitution in chlorite implies that alvi is preferentially ordered in the m 4 site and about 84 of the alvi present is in the m 4 sites when they are nearly filled with alvi based on 47 analyzed chlorite bearing rock samples chlorite chl composition is strongly correlated with the mgo content of the host rock calculated correlation coefficients are 0 91 for sio2chl mgorock 0 87 for al2o3chl mgorock 0 89 for mgochl mgorock and 0 85 for feochl mgorock only weak correlations have been found between chlorite oxides and other oxides of rock between same oxides in chlorite and rock sio2 0 67 al2o3 0 59 feo 0 41 however mgochl is saturated at about 36 wt in rocks that have mgo above 22 wt the mgochl is about 5 wt when the host rock approaches 0 wt of mgo this implies that mg substituting into the chlorite is approximately limited to 1 5 9 2 mg atoms per formula unit and 1 0 3 2 aliv chlorite geothermometers can not be applied to all bgb samples however the empirical chlorite geothermometer based on aliv of chlorite may be applicable to chlorites formed under metamorphic conditions because it can predict the chemical composition of the chlorite from basaltic and dacitic samples in this study an estimated temperature of about 320 c for the greenschist metamorphism of the greenstone belt through this geothermometer is consistent with that obtained by other geothermometers

isotopic evidence for channeled fluid flow in low grade metamorphosed jurassic accretionary complex in the northern chichibu belt western shikoku japan the low grade metamorphosed jurassic accretionary complex of the northern chichibu belt hijikawa area western shikoku is divided into two units the hijikawa and kanogawa units that are separated by an out of sequence thrust oost the ozu kawabegawa fault the kanogawa unit south of the ozu kawabegawa fault consists mainly of sandstone shale broken formation of alternating sandstone and shale greenstone chert and pelitic melange while the hijikawa unit is characterized by a stack of subunits separated by small scale thrusts the subunits are mainly made up of basic pelitic and psammitic semischists schistose pelitic melange and chert petrological and mineralogical constraints suggest peak metamorphic conditions of 204 247 c at 1 3 kbar in the kanogawa unit and 228 289 c at 3 5 6 kbar in the hijikawa unit quartz and quartz calcite veins are widely developed in the study area especially in the hijikawa unit regional variations in stable isotopic data show that the 18oquartz and 18ocalcite values in veins tend to increase towards the ozu kawabegawa fault the 18owhole rock values are remarkably high in some subunits close to oosts within the hijikawa unit oxygen isotopic compositions from vein quartz indicate that a higher 18o fluid migrated upward from depth along the ozu kawabegawa fault within the accretionary prism during prehnite pumpellyite facies metamorphism the fluid source is inferred to be pelitic rocks at higher temperatures and greater depths within the accretionary prism

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

the initial streamer of intracloud lightning flashes the initial development of four vertical intracloud lightning flashes has been studied using time resolved measurements of the electric field change from 7 8 ground locations at kennedy space center florida the initial field changes of the flashes were analyzed with a unidirectional piecewise linear streamer model in an attempt to determine the direction and sign of the initial charge transfer the results indicate that the discharges were initiated by an upward propagating negative streamer rather than by a downward propagating positive streamer the initial streamer appeared to progress upward at speeds between 1 and 3 105 m s for durations of 10 30 ms and deposited 1 to 4 coulombs per kilometer of extent these results disagree with those of earlier studies which used the shape of the overall electric field change to infer the sense of the streamer and which gave relatively low values for progression speeds 104 m s the results agree with observations of vhf radiation source locations by proctor in south africa

the smectite chlorite transition in drillhole nj 15 nesjavellir geothermal field iceland xrd bse and electron microprobe investigations abstract in well nj 15 of the nesjavellir geothermal field iceland the transition of discrete smectite into discrete chlorite has been studied from drill cuttings recovered at depths of less than 1714 m and over a continuous range of temperatures between 60 and 300 c at temperatures below 180 c the clay fractions contain mixtures of di and trioctahedral smectites whose layer charge increases with depth between 200 and 240 c discrete smectites have transformed into smectite rich randomly interstratified chlorite and smecite r0 c s because the abundance of chlorite interlayers in this c s is generally 20 its presence can be detected only by electron microprobe techniques and not by x ray diffraction between 245 and 265 c both regularly r1 and randomly interstratified c s are the predominant layer silicates discrete chlorite first appears at approximately 270 c and coexists with minor amounts of r0 c s at higher temperatures r0 and r1 c s form a nearly complete compositional series between trioctahedral saponite and discrete chlorite end members the interlayer cation and si content of smectites and c s decrease with increasing temperature the mg mg fe content of smectite c s and chlorite is unrelated to temperature the percentage of chlorite in c s as determined by electron microprobe analyses increases continuously with increasing temperature except for occurrences of smectite rich c s in fresh basaltic dykes which have not thermally equilibrated with the higher grade country rocks

corrensite and mixed layer chlorite corrensite in metabasalt from northern taiwan tem aem empa xrd and optical studies many chloritic minerals in low grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties expand slightly upon glycolation expandable chlorite and or have excess alvi relative to aliv as well as significant ca k and na contents chloritic minerals with these properties fill vesicles and interstitial void space in low grade metabasalt from northern taiwan and have been studied with a combination of tem aem empa xrd and optical microscopy the chloritic minerals include corrensite which is an ordered 1 1 mixed layer chlorite smectite and expandable chlorite which is shown to be a mixed layer chlorite corrensite corrensite and some mixed layer chlorite corrensite occur as rims of vesicles and other cavities while later formed mixed layer chlorite corrensite occupies the vesicle cores the tem observations show that the mixed layer chlorite corrensite has ca 20 and the corrensite has ca 50 expandable smectite like layers consistent with xrd observations and with their abnormal optical properties the aem analyses show that high si and ca contents high alvi aliv and low fevi fe mg vi ratios of chlorites are correlated with interstratification of corrensite or smectite like layers in chlorite the aem analyses obtained from 200 500 a thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low aliv siiv and low fevi fe mg vi while chlorite has high aliv siiv and high fevi fe mg vi this implies that the trioctahedral smectite like component of corrensite has significantly lower aliv siiv and fevi fe mg vi the ratios of fevi fe mg vi and aliv siiv thus decrease in the order chlorite corrensite smectite the proportions of corrensite or smectite like layers relative to chlorite layers in low grade rocks are inferred to be controlled principally by fe mg ratio in the fluid or the bulk rock and by temperature compositional variations of chlorites in low grade rocks which appear to correlate with temperature or metamorphic grade more likely reflect variable proportions of mixed layered components the assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases such as chlorite corrensite corrensite smectite or chlorite corrensite smectite a model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1 1 ordered mixed layer chlorite smectite

denudation history of the high t p ryoke metamorphic belt southwest japan constraints from chime monazite ages of gneisses and granitoids chime chemical th u total pb isochron method monazite ages were determined for gneisses and granitoids from the eastern and western parts of the ryoke belt separated by about 500 km the monazite ages for the gneisses are concentrated between 102 and 98 ma and are interpreted as the time of monazite formation under lower amphibolite facies conditions the peak metamorphism seems to be contemporaneous with the emplacement of the geologically oldest plutons that are dated at c 95 ma in both the eastern and western parts in the eastern part plutonism continued from c 95 ma to c 68 ma at intervals of 2 10 ma whereas in the western part it ceased at c 85 ma the chime monazite ages agree well with the relative age of granitoids derived from intrusive relationships of granitoids in both parts these lines of evidence are incompatible with a current view that the plutonometamorphism in the ryoke belt becomes younger towards the east the chime monazite ages coupled with available data on the depth at which the ryoke metamorphism took place and the emplacement of individual plutons show that the western part was eroded more rapidly about 1 5 mm year 1 than the eastern part about 0 8 mm year 1 over the time span from 91 to 85 ma the denudation rates agree well with those in active orogenic belts like the alps and himalayas

contribution of long term hydrothermal experiments for understanding the smectite to chlorite conversion in geological environments the smectite to chlorite conversion is investigated through long duration experiments up to 9 years conducted at 300 c the starting products were the wyoming bentonite mx80 79 smectite metallic iron and magnetite in contact with a na ca chloride solution the predominant minerals in the run products were an iron rich chlorite chamosite like and interstratified clays interpreted to be chlorite smectite and or corrensite smectite accompanied by euhedral crystals of quartz albite and zeolite the formation of pure corrensite was not observed in the long duration experiments the conversion of smectite into chlorite over time appears to take place in several steps and through several successive mechanisms a solid state transformation significant dissolution of the smectite and direct precipitation from the solution which is over saturated with respect to chlorite allowing the formation of a chamosite like mineral the reaction mechanisms are confirmed by x ray patterns and data obtained on the experimental solutions ph contents of si mg na and ca because of the availability of some nutrients in the solution total dissolution of the starting smectite does not lead to 100 crystallization of chlorite but to a mixture of two dominant clays chamosite and interstratified chlorite smectite and or corrensite smectite poor in smectite the role of fe fe mg in the experimental medium is highlighted by chemical data obtained on newly formed clay particles alongside previously published data the newly formed iron rich chlorite has the same composition as that predicted by the geothermometer for diagenetic to low grade metamorphic conditions and the quartz fe chlorite albite experimental assemblage in the 9 year experiment is close to that fixed by water rock equilibrium

isotopic and morphological features of fracture calcite from granitic rocks of the tono area japan a promising palaeohydrogeological tool this study aimed to develop a methodology for assessing the hydrochemical evolution of a groundwater system using fracture filling and fracture lining calcite fracture calcite in deep to ca 1000 m granitic rocks of the tono area central japan was investigated by optical and electron microscopy and chemical and isotopic analysis coupled with geological evidence these new data imply 3 main origins for the waters that precipitated calcite 1 relatively high temperature hydrothermal solutions precipitating calcite distinguished by 18osmow from 3 to ca 10 and with 13cpdb from ca 18 to 7 2 seawater probably partly of miocene age which precipitated calcite distinguished by 13cpdb of ca 0 and 18osmow ca 20 3 fresh water with a variable 13cpdb composition but which precipitated calcite distinguished by 13cpdb that was significantly ca 17 data for 14c suggest that at least some of the fresh water calcite formed within the last 50 ka the present day hydrogeological regime in the tono area is also dominated by fresh groundwater however the marine calcite of probable miocene age found at depth has shown no evidence for dissolution and many different calcite crystal forms have been preserved studies of other groundwater systems have correlated similar crystallographic variations with variations in the salinity of coexisting groundwaters when this correlation is applied to the tono observations the calcite crystal forms imply a similar range of groundwater salinity to that inferred from the isotopic data thus the present study suggests that even in presently low salinity groundwater systems calcite morphological variations may record the changing salinity of coexisting groundwaters it is suggested that calcite morphological data coupled with isotopic data could provide a powerful palaeohydrogeological tool in such circumstances

source of iron for sulfidation and gold deposition twin creeks carlin type deposit nevada this study was undertaken to determine the source of iron in comus formation sedimentary rocks that were sulfidized during deposition of gold in the megapit area of the twin creeks carlin type deposit sedimentary rocks in and near the megapit contain ferroan dolomite largely as overgrowths on iron poor dolomite iron to form these overgrowths appears to have been released from mafic volcanic rocks that are interlayered with the sedimentary rocks these igneous rocks have undergone two stages of hydrothermal alteration the first stage involved formation of albite and iron rich chlorite possibly caused by interaction with seawater the second stage involved destruction of the iron rich chlorite by illite or sericite which released iron to form ferroan dolomite in the sedimentary rocks comparisons show that transfer of iron from the igneous rocks to the sedimentary rocks can account for the present distributions of iron in these rocks relative to basalts comus formation igneous rocks are enriched in iron and potassium these results suggest that ferroan dolomite in sedimentary rocks is not solely a product of diagenetic processes and can form when iron is released from adjacent iron bearing igneous rocks recognition of this additional mechanism for formation of ferroan dolomite expands the range of geologic settings that can be favorable for formation of gold deposits formed by sulfidation

fine scale chlorite muscovite association in low grade metapelites from nurra nw sardinia and the possible misidentification of metamorphic vermiculite chlorite muscovite porphyroblasts occur in the low grade metapelites from nurra nw sardinia although actually heterogeneous and built up by two different intermixed minerals the porphyroblasts strongly simulate optical homogeneity and produce microprobe analyses that are typical for metamorphic vermiculite transmission and scanning electron microscopy combined with analytical facilities leads to a deeper characterization of the porphyroblasts that actually consist of a random association of chlorite and muscovite

phase relations among smectite r1 illite smectite and illite a variety of smectitic and illitic clays were studied by tem and aem following ex pansion by l r white resin to define phase relations for clay minerals undergoing di genesis and low grade metamorphism samples included a prograde shale sequence from the gulf coast a hydrothermal bentonite from zempleni hungary and shales from the nankai trough japan michigan and the welsh sedimentary basin all samples were dominated by various proportions of only three kinds of clay minerals smectite having no 10 alayers r1 illite smectite i s 50 illite and illite with only small proportions of smectite like interlayers mixed layer phases with intermediate ratios of i s were observed only as minor components of other layer sequences lattice fringe images show that the common layer spacing of r1 i s is 21 aand that it has 0 7 0 8 k pfu its properties are not an average of those of smectite and illite which is consistent with the uniqueness of the r1 i s structure a prograde sequence of clay mineral transitions in the studied samples can be charac terized by five stages with different combinations of the three major phases i e smectite r1 i s and illite corresponding to different grades the sequence from low to high grade is 1 pure smectite 2 smectite with small proportions of discrete r1 i s and illite 3 r1 i s with small proportions of smectite and illite 4 illite with some r1 i s and smectite and 5 illite common exceptions to this scheme are inferred to be caused by the inherent metastability of all phases in occurrences that are rate or path dependent

microstructures and mixed layering in intergrown wonesite chlorite talc biotite and kaolinite post pond volcanics vermont transmission electron microscopy and diffraction the chlorite occurs in intergrown 1 layer and disordered polytypes the wonesite occurs in 1 layer 2 layer 3 layer and disordered forms and the biotite occurs as 1 layer and 2 layer polytypes with minor stacking disorder modified journal abstract

from static alteration to mylonitization a nano to micrometric study of chloritization in granitoids with implications for equilibrium and percolation length scales strain accommodation in upper crustal rocks is often accompanied by fluid mediated crystallization of phyllosilicates which influence rock strength and shear zone formation the composition of these phyllosilicates is frequently used for pressure temperature time constraints of deformation events although it is often highly heterogeneous even in mylonites this study investigates the reactions producing a phyllosilicate chlorite in and below grenschist facies conditions and the variations in chlorite composition along a strain gradient in the variscan bielsa granitoid axial zone pyrenees compositional maps of chlorite including iron speciation are compared to nanostructures observed by transmission electron microscopy in increasingly strained samples and related to mechanisms of fluid percolation in the bielsa granitoid altered at the late variscan alpine age shear zones are found with high strain gradients the undeformed granitoid exhibits local equilibria pseudomorphic replacement and high compositional heterogeneities in chlorite this is attributed to variable reaction mechanisms at nanoscale and element supply little interconnected intra and inter grain nanoporosity and isolation of fluid evolving in local reservoirs in samples with discrete and mm sized fractures channelized fluid triggered the precipitation of homogeneous alpine chlorite in fractures preserving late variscan chlorite within the matrix in low grade mylonites where brittle ductile deformation is observed micro and nanocracks and defects allows the fluid percolating into the matrix at the scale of hundreds of m this results in a more pervasive but incomplete replacement of late variscan chlorite by alpine chlorite despite the high strain in studied granitoids deformed under greenschist facies conditions local equilibria and high compositional heterogeneities in phyllosilicates as chlorite are therefore preserved according reaction mechanisms and element mobility controlled by i matrix fracture porosity contrasts at nanoscale and ii the location and interconnection of nanoporosity between crystallites of phyllosilicates this preservation influences our ability to reconstruct the pre and syn kinematic metamorphic history of granitic rocks in low grade units of orogens

the smectite to chlorite transition in the chipilapa geothermal system el salvador clay mineralogical x ray diffraction and electron microprobe studies have been carried out on separated 2 m fractions from cutting and core material from three wells in the chipilapa geothermal system in el salvador the data indicate that the smectite to chlorite transition is prevalent but a secondary smectite to illite transition is also present at depths approximately 750 m smectite with very minor chlorite mixed layers approximately 15 is dominant and has a composition midway between a di and tri smectite at 750 m there is a very clear distinction and sharp transition into discrete chlorite with very minor smectite mixed layers approximately 10 corrensite is recorded only as a rare and minor phase smectite occurs in abundance at temperatures up to 200 c and the transition from a smectitedominant to chlorite dominant assemblage takes place over a narrow temperature range 150 to 200 c the stability range of smectite is very similar to that recorded in other geothermal systems whereas the smectite to chlorite transition differs greatly from that recorded in other systems the transition does not involve continuous chlorite smectite mixed layering but a marked step it is the sharpest and most discontinuous stepped sequence of this mineralogical transition recorded

a basaltic ferrobasaltic granulite association oonagalabi gneiss complex central australia magmatic variation in an early proterozoic rift extremely fractionated basaltic to ferrobasaltic amphibolites and granulites comprise two spatially associated mafic tholeiitic suites deformed sills within the early proterozoic oonagalabi basement gneiss complex harts range central australia the metatholeiites are characterised by high to very high feo tio2 and p2o5 contents and variable depletion in cao and al2o3 despite similar zr nb ratios the rocks from the two suites show different degrees of enrichment in lree and other immobile incompatible elements the basaltic melts which were parental to the two mafic suites were not comagmatic and the rocks cannot be related simply by fractionation of realistic assemblages of low pressure fractionating phases

the smectite to chlorite transition in a fossil seamount hydrothermal system the basement complex of la palma canary islands the hydrothermal metamorphism of a sequence of pliocene aged seamount extrusive and volcanoclastic rocks on la palma includes a relatively complete low p t facies series encompassing the zeolite prehnite pumpellyite and greenschist facies the observed mineral zonations imply metamorphic gradients of 200 300 c km 1 the transition from smectite to chlorite in the la palma seamount series is characterized by discontinuous steps between discrete smectite corrensite and chlorite which occur ubiquitously as vesicles and to a much lesser extent vein in fillings trioctahedral smectites mg fe mg 0 4 0 75 occur with palagonite and na ca zeolites such as analcime and a thompsonite natrolite solid solution corrensite mg fe mg 0 5 0 65 first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite discrete chlorite mg fe mg 0 4 0 6 becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases although random interstratifications of these phases have not been observed although smectite occurs as both low and high charge forms the la palma corrensite is a compositionally restricted 1 1 mixture of low charge trioctahedral smectite and chlorite electron microprobe analyses of coarse grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations calcium average 0 20 cations formula unit is the dominant interlayer cation with lesser mg k and na the absence of randomly interlayered chlorite smectite in the la palma seamount series may reflect high time integrated fluid fluxes through the seamount sequence this is consistent with the ubiquity of high variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples

hydrothermal alteration of deep fractured granite effects of dissolution and precipitation abstract this paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite a fracture accompanied by an alteration halo and filled with clay was found at a depth of 200 m in a drill core through toki granite gifu central japan microscopic observation xrd xrf epma and sxam investigations revealed that the microcrystalline clays consist of illite quartz and pyrite and that the halo round the fracture can be subdivided into a phyllic zone adjacent to the fracture surrounded by a propylitic zone in which fe phyllosilicates are present and a distinctive outer alteration front characterized by plagioclase breakdown the processes that result in these changes took place in three successive stages 1 partial dissolution of plagioclase with partial chloritization of biotite 2 biotite dissolution and precipitation of fe phyllosilicate in the dissolution pores 3 dissolution of k feldspar and fe phyllosilicate and illite precipitation associated with development of microcracks these hydrothermal alterations of the granite proceed mainly by a dissolution precipitation process resulting from the infiltration of hydrothermal fluid along microcracks such infiltration causes locally high mobility of al and increases the ratio of fluid to rock in the alteration halo these results contribute to an understanding of how granitic rock becomes altered in orogenic fields such as the japanese island arc

rocket and wire triggered lightning in 2012 tropical storm debby in the absence of natural lightning 1 lightning mapping array source locations channel base currents and electric field waveforms are presented for a lightning flash triggered in the rainbands of 2012 tropical storm debby the national lightning detection network reported no natural cloud to ground discharges within 60 km of the north florida triggering site for at least 20 h before and 8 h after the triggered flash additionally local electric field mill and wideband antenna networks show no close cloud or cloud to ground flashes the triggering rocket was launched with negative charge overhead producing an electric field at the ground of 5 kv m 1 and in coordination with x band dual polarimetric radar observations of streamers of enhanced precipitation descending from the melting level as they approached the site the debby flash consisted of an initial stage is followed by eleven leader return stroke sequences the flash exhibited all the processes of normal triggered and natural cloud to ground lightning leader return stroke sequences continuing currents k events and m components additionally the flash exhibited several exceptional characteristics three return stroke peak currents greater than 25 ka one very long 352 ms continuing current that transferred about 35 c of charge to ground and a relatively short 202 ms is containing no initial continuous current pulses following a near vertical upward positive leader attaining 2 8 km height the is branched and propagated horizontally at 3 5 km altitude the flash exhibiting strokes and continuing current then ascended to and propagated horizontally at 5 5 km extending about 25 km south and 15 km east the 0 c level was near 4 5 km above sea level it follows from the above that clouds that are not producing natural lightning can represent a triggered lightning hazard to launch vehicles and aircraft

textural and mineralogical changes associated with the incipient hydrothermal alteration of glassy dacite at the submarine pacmanus hydrothermal system eastern manus basin variably altered dacite from the pacmanus vent field in the eastern manus back arc basin papua new guinea was studied to determine the textural and mineralogical characteristics of hydrothermal alteration taking place in the immediate subsurface of this modern seafloor hydrothermal system detailed textural investigations show that fluid flow through the glassy dacite has been strongly controlled by the primary volcanic textures quench fractures and networks of interconnected perlitic cracks linking vesicles provided pathways for hydrothermal fluids flowing up to the seafloor hydrothermal alteration along these pathways resulted in the formation of pseudoclastic textures textural evidence suggests that alteration of the glassy dacite has not been sustained the samples have been affected by incipient hydrothermal alteration that is typically not preserved in ancient volcanic rock hosted massive sulfide deposits interaction of the glassy dacite with hydrothermal fluids primarily resulted in the conversion of volcanic glass to dioctahedral smectite only minor amounts of trioctahedral smectite were formed destruction of the volcanic glass and the formation of smectite caused pronounced changes in the chemistry of the dacite samples in particular a decrease in the sio2 whole rock content and the na2o k2o ratio the two alkali elements behaved differently during hydrothermal alteration due to preferential incorporation of k into the interlayer position of the newly formed dioctahedral smectite smectite formation occurred under rock dominated conditions although the addition of mg was required to form trioctahedral smectite from the silicic volcanic glass primary plagioclase was resistant to hydrothermal alteration highlighting the fact that the destruction of volcanic glass and feldspar are not necessarily contemporaneous in massive sulfide forming hydrothermal systems incipient alteration of the glassy dacite close to the seafloor occurred at temperatures below 150 c in an environment that allowed the development of steep temperature gradients comparison of the new data to the findings of deep drilling during odp leg 193 suggests that the smectite rich alteration in the immediate subsurface of the pacmanus hydrothermal vent field represents the low temperature equivalent of illite and chlorite rich alteration associations forming in the upflow zones of the hydrothermal fluids in the deeper portion of the volcanic sequence

interlayering and interlayer slip in biotite as seen by hrtem partial interlayers of brucite like sheets which form with the adjacent talc like layers of the mica single chlorite layers interstratified in the mica structure brucite interlayering is interpreted as a brucitization of an interlayer level of the mica where partial slip or cleavage has previously occurred example of a chemical process at the atomic scale favored by deformation microstructures modified journal abstract

ammonium vermiculite in schists from the betic cordillera spain nh 4 bearing phases from pre permian schists of the internal zones of the betic cordillera spain have been characterized by x ray diffraction differential thermal analysis and thermogravimetry infrared spectroscopy and transmission analytical electron microscopy the content and distribution of nh 4 in these phases have been estimated by combining elemental analysis of n with mineral quantification based on x ray diffraction whole rock composition and electron microprobe data the obtained results indicate that the nh 4 content in vermiculite ranges between 0 5 and 1 0 wt leading to terms with nh 4 k in the interlayer the nh 4 content is 4 contents 0 04 wt through the complete sequence we interpret that initially contained in low grade dioctahedral mica nh 4 was incorporated in the structure of the trioctahedral phases formed at increasing metamorphic conditions the entry of nh 4 in the interlayer was favored in chlorite vermiculite mixed layered structures and transitional phases with vacancies in the a site vermiculite and weak cohesion between layers nh 4 appears to favor the formation of intermediate phases instead the direct transformation of chlorite to biotite

eocene to miocene igneous activity in ne greenland northward younging of magmatism along the east greenland margin radiometric dating by the 40 ar 39 ar incremental heating method was carried out on lavas sills dykes and a central intrusion from ne greenland eighteen samples gave acceptable crystallization ages lavas of both lower and upper plateau lava series gave ages in the range 55 5 53 5 ma and cannot be constrained to better than 56 53 ma sills and dykes from traill o to shannon with compositions fairly similar to those of the lavas gave ages of 55 1 51 3 ma contemporaneous with and slightly younger than the lavas alkaline lavas on inland nunataks have ages of 53 50 ma and the kap broer ruys intrusive centre has an age of 48 7 0 5 ma an alkaline sill on hvalroso is much younger at 20 3 0 1 ma there are no pre breakup lavas onshore ne greenland we surmise that the hot mantle of the iceland plume arrived and melted extensively beneath the northern basins only at the time of breakup around 55 ma post breakup intrusive events in ne greenland coincided with plate tectonic events such as reorganization uplift and opening in the north the hvalroso sill represents a local small melting event that may be related to coeval opening of the lena trough supplementary materials details of the source data results and the compositions and locations of the dated samples are available at www geolsoc org uk sup18738

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher