microscale isotopic zonation in graphite crystals evidence for channelled co influx in granulites abstract coarse graphite in association with cordierite and quartz within a vein in a metapelite locality at chittikara cht in southern india illustrates precipitation of graphite from co 2 rich fluids carbon isotope traverses within individual graphite crystals using a microsampling technique reveal strong isotopic zonations in graphite crystal from the vein with 13 c values oscillating between 13 in the core and 8 5 in the rim co 2 trapped within fluid inclusions in the cordierite shows 13 c 5 suggesting isotopic equilbrium with the core composition of the graphite a graphite crystal from the metapelite immediately adjacent to the vein is also zoned with a smooth rimward increase in 13 c disseminated graphite flakes in the host metapelites ca 1 m from the vein are however unzoned and possess strongly negative 13 c values 34 4 the rimward increase in 13 c the absence of other carbon bearing phases and the sluggish exchange rates for carbon in graphites preclude diffusive re equilibration and suggest that the different zoning patterns in the coarse graphite flakes within and adjacent to the vein assemblage at cht have resulted from precipitation in different parts of a highly channelled fluid regime where fluids are non wetting and move episodically by a hydraulic fracture mechanism our study provides the first unambiguous insight into graphite precipitation mechanisms and has potential implications for the nature of fluid interconnectivity and co 2 transport and equilibration length scales within the crust

cyclostratigraphic and δ13c record of the lower cretaceous adriatic platform croatia assessment of milankovitch forcing abstract the 700 m thick hauterivian to albian section from the interior of the large adriatic platform is exposed on mljet and korcula islands croatia the cyclic platform consists of meter scale parasequences bundled into parasequence sets superbundles and then into breccia bounded depositional sequences spectral analysis of time series cycle number vs cycle thickness shows peaks in the short term eccentricity 95 to 130 kyr bands and 160 to 200 kyr bands isotope samples from micrite matrix of mudstone and wackestone have 13c values generally from 1 5 to 2 vpdb and 18o from 1 to 3 5 vpdb adriatic platform 13c values are shifted 2 vpdb more negative than marine pelagic values a 13c and 18o meteoric signal is limited to just beneath sequence boundaries suggesting that the isotopic shift is due mainly to marine phreatic and synorogenic burial diagenesis major excursions on the 5 point smoothed 13c profile of the adriatic platform tied biostratigraphically to 13c curves from pelagic sections include the oceanic anoxic events oae1a 1b and 1c time series constructed from 13c values unsmoothed data vs stratigraphic position show peaks in the milankovitch band especially short term eccentricity most positive peaks are near parasequence set boundaries 50 to 60 and regressive parts of parasequences 20 although diagenetically shifted the 13c record retains a highly clipped memory of astronomically driven global 13c fluctuations albeit modified by platform water restriction during cyclic deposition

footwall progradation in syn rift carbonate platform slope systems early jurassic northern apennines italy abstract the so called umbria marche domain of northern apennines represents a vast depositional system also stretching across the adriatic sea subsurface that was characterized by dominantly pelagic sedimentation through most of its jurassic to oligocene early miocene history the pelagic succession is underlain by hettangian shallow water carbonates calcare massiccio fm constituting a regional carbonate platform that was subjected to tectonic extension due to rifting of the adria african plate in the earliest jurassic while tectonic subsidence of the hangingwalls drove the drowning of the platform around the hettangian sinemurian boundary the production of benthic carbonate on footwall blocks continued parallel to faulting through a sequence of facies that was abruptly terminated by drowning and development of condensed pelagites in the early pliensbachian by then rifting had ceased so that the pliensbachian to early cretaceous hangingwall deposits represent a post rift basin fill succession onlapping the tectonically generated escarpment margins of the highs during the early phases of syndepositional faulting the carbonate factories of footwall blocks were still temporarily able to fill part of the accommodation space produced by the normal faults by prograding into the incipient basins in this paper we describe for the first time a relatively low angle

carbonate silicate inclusions in garnet as evidence for a carbonate bearing source for fluids in leucocratic granitoids associated with granulites of the southern marginal zone limpopo complex south africa abstract we present a study of carbonate bearing polyphase inclusions in garnets from leucocratic granitoids intruding metapelitic granulites of the southern marginal zone smz of the neoarchean limpopo high grade complex south africa during the post peak stage 2710 2650 ma u pb ages for zircons and monazites ternary feldspar thermometry suggests that the granitoid magma cooled from temperatures 800 900 c at a pressure of ca 6 5 kbar abundant co2 fluid inclusions in quartz and t xco2 phase equilibria modeling via perple x imply action of an essentially carbonic fluid in the granitoids cores of almandine rich garnet grains from the granitoids contain polyphase carbonate bearing inclusions with a distinct negative crystal shape the major carbonate in the inclusions is a strongly zoned magnesite siderite variety whereas pyrophyllite is the predominant silicate phase raman spectra of unexposed inclusions revealed a presence of co2 as well as ch4 and h2o the carbonate bearing inclusions coexist with larger polyphase inclusions composed of biotite quartz k feldspar plagioclase sillimanite which are interpreted as relics of granitic melts modeling the mineral assemblage preserved within the carbonate bearing inclusions shows that their present mineral and chemical compositions are a product of interaction of the trapped aqueous carbonic fluid with host garnet during cooling below 400 c despite strong modifications the inclusions bear evidence for initial saturation of the fluid with mg carbonate this is taken as an evidence for an origin of the fluids by devolatilization of the mg rich carbonate bearing ultrabasic greenstone rocks of the kaapvaal craton that were buried under the smz being generated at temperatures between 650 and 700 c the fluid subsequently participated in anatexis and coexisted with the granite magma during exhumation and interaction of the smz granulites with cratonic rocks

the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

composition and source of fluids in high temperature graphite bearing granitoids associated with granulites examples from the southern marginal zone limpopo complex south africa abstract p t conditions fluid regime and carbon isotope composition of graphite and fluid inclusions from garnet sillimanite bearing leucocratic tonalites trondhjemites and granites associated with orthopyroxene bearing granulite metapelites in the southern marginal zone smz of the limpopo complex south africa are presented in the paper re integrated compositions of perthitic alkali feldspars and antiperthitic plagioclase as well as p t and t xco2 phase equilibria modeling using perple x software indicate that the granitoids began to crystallize at temperatures of 900 940 c and pressures of 7 9 kbar and were equilibrated with a fluid phase with xco2 0 5 0 6 as is recorded in dense fluid inclusions in quartz a small fraction of a saline fluid accumulated during cooling only average 13cpdb values for graphite 6 52 to 8 65 and fluid inclusions 2 50 to 5 58 from the granitoids differ substantially from the values which have been obtained in previous studies for graphite from the surrounding smz metapelites isotope data thus indicate that fluids associated with the granitoid magmas of the smz originated from a source unrelated to the host metapelites in terms of the heavy isotope signatures of carbon the granitoids might carry fluids which have been produced during devolatilization of mafic rocks amphibolites interlayered with hydrothermal carbonate veins in the adjacent granite greenstone successions of the kaapvaal craton that have been buried underneath the smz granulites during their exhumation the cratonic rock could serve as a source for the trondhjemite magmas intruding the smz granulites in this scenario the studied granitoids crystallized from these magmas variously contaminated by metapelitic material graphite precipitated via reduction of co2 rich fluid as the result of dissolution of pyrrhotite rich metapelites in the magmas

the ellipsactinia limestones of the marsica area central apennines a reference zonation model for upper jurassic intra tethys reef complexes abstract this study presents a new and innovative distribution model of the main reef builders that thrived on bioconstructed margins of upper jurassic intra tethys platforms the proposed model is based on the zonation of an upper jurassic reef complex presently exposed in the central apennines excellent exposures allow the reconstruction of the reef profile across the platform margin biota are mainly represented by corals and calcified demosponges distributed with different amounts and aggregating structures along the reef complex microencrusters represent a secondary but important component that actively contributes to the reef construction process reef builders are distributed in variable quantities and with variable aggregating structures along the reef complex revealing a strong reef zonation like the biota the sedimentary features grain size sorting and reworking degree bioerosion cement crusts and cavities show a distinctive distribution along the reef complex three main zones have been recognized along the studied reef complex an internal more protected and deeper zone corresponding to a relatively deep back reef lagoon is dominated by corals and chaetetids a central zone reef flat where well preserved coral bioconstructions give rise to a true but discontinuous framework and a more external zone corresponding to the reef crest characterized by the shallowest depths recorded across the reef complex and dominated by stromatopores the latter forms mound shaped structures playing a role essential for the zoned character of the reef complex these structures actively contribute to the construction of a moderately high topographic relief in the reef crest

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

fault controlled dolomite bodies as palaeotectonic indicators and geofluid reservoirs new insights from gargano promontory outcrops the upper jurassic to lower cretaceous platform slope to basinal carbonate strata cropping out in gargano promontory southern italy are partly dolomitized fieldwork and laboratory analyses petrographic petrophysical and geochemical allowed the characterization of the dolomite bodies with respect to their distribution within the carbonate succession their dimensions geometries textural variability chemical stability age porosity genetic mechanisms and relation with tectonics the dolomite bodies range from metres to kilometres in size are fault related and fracture related and probably formed during the early cretaceous at 500 m burial depths and temperatures 50 c the proposed dolomitization model relies on mobilization of early cretaceous seawater that flowed downward and then upward along faults and fractures and was modified in its isotopic composition moving through triassic and jurassic strata that underlie the studied dolomitized succession despite the numerous cases reported in literature this study demonstrates that hydrothermal and or high temperature fluids are not necessarily required for fault controlled dolomitization distribution and geometries of dolomite bodies can be used for palaeotectonic reconstructions as they partly record the characteristics size attitude and kinematics of the palaeo faults even if not preserved that controlled dolomitization in gargano promontory dolomites record early cretaceous palaeo faults from metres to kilometres long striking north west south east to east west and characterized by normal to strike slip kinematics dolomitization increases the matrix porosity by up to 7 and therefore can improve the geofluid storage capacity of tight platform slope to basinal limestones the results have a great significance for characterization of geofluid for example hydrocarbons reservoirs hosted in similar dolomitized carbonate successions distribution size and shapes of reservoir rocks i e dolomite bodies could be broadly predictable if the characteristics of the palaeo fault system present at the time of dolomitization are known this article is protected by copyright all rights reserved

transverse versus longitudinal extension in the foredeep peripheral bulge system role of cretaceous structural inheritances during early miocene extensional faulting in inner central apennines belt this study reports on the rocca di cave extensional fault system which is located in the prenestini mountains central italy of the apennines fold and thrust belt and presently represents the oldest exposure of early orogenic foreland fault system of the apennines this fault system was oriented perpendicular to the strike of the foredeep peripheral bulge system indicating that the onset of convergence was marked by a foredeep parallel extension instead of the commonly observed foredeep perpendicular stretching associated with lithosphere flexuring the studied fault system is formed by a 10 km long and 2 km wide e w elongated area that includes two mutually orthogonal sets of faults oriented about e w and n s respectively e w and mainly n s striking faults developed during a preorogenic santonian to campanian in age e w oriented extension kinematics which caused first uplift and erosion and then drowning of the cretaceous carbonate platform and the onset of a pelagic environment both fault sets were later reactivated in the early miocene when the area was forming part of the foreland region ahead of the eastward migrating apennines fold and thrust belt and was undergoing local n s oriented i e foredeep parallel stretching this extensional stage implied the sedimentation of hundreds of meters of synkinematic strata in the northern block of the rocca di cave fault system coevally with episodes of subaerial erosion in areas of the southern block further extensional and right lateral reactivation of inherited faults occurred in the late miocene during the progressive incorporation of the area into the apennines belt

age and tectonic evolution of neoproterozoic ductile shear zones in the southern granulite terrain of india with implications for gondwana studies 1 the high grade rocks of the southern granulite terrain sgt of peninsular india are bounded to the north by the archean dharwar craton another high grade terrane the mesoproterozoic eastern ghats occurs to the northeast of the sgt the tectonic relationship between these crustal domains is complex we present new geochronological and structural data that indicate a continuation of the dharwar craton into the southern granulite terrain as far south as a newly identified neoproterozoic shear zone here named the karur kamban painavu trichur shear zone kkptsz south of the kkptsz mesoproterozoic dates of the sgt are similar to those recorded in the eastern ghats and the two domains may have been conterminous thirty three new u pb th single zircon and monazite dates of samples from six structural transects across the regional shear zones indicate that the sgt has experienced at least seven thermo tectonic events at 2 5 ga 2 0 ga 1 6 ga 1 0 ga 800 ma 600 ma and 550 ma and two distinct episodes of metasomatism charnockitization between 2 50 2 53 and between 0 55 0 53 ga deformation along a number of major shear zones in the sgt is neoproterozoic to earliest paleozoic in age with an early phase d2 concentrated between 700 800 ma and a later phase d3 between 550 and 600 ma major charnockitization 530 550 ma post dates d3 and is in turn overprinted by granitization retrogression and uplift between 525 and 480 ma the kkptsz active between 560 and 570 ma is either a terrane boundary or a tectonized decollement between cover and archean basement rocks represented by predominantly paragneisses to the south and orthogneisses to the north respectively other regional neoproterozoic shear zones do not appear to separate allochthonous terranes as previously suggested on the basis of nd model ages and rb sr biotite whole rock dates the neoproterozoic cambrian tectonothermal history of the sgt and eastern ghats is similar to that recorded in parts of madagascar east africa and antarctica and is used to reconstruct parts of central gondwana here named the deccan continent with more robust confidence

active intraplate deformation within adria examples from the adriatic region abstract recent seismicity recorded in the adriatic region suggests that active deformation occurs within the adria plate earthquakes are common in the adjoining chains and in particular along the northern apennines in the southern alps and along the dinaric albanian hellenic thrust fronts in addition medium to low grade seismicity also affects the foreland and is clustered along two main transects through the centre of the adriatic region the two zones of active deformation correspond to the mid adriatic ridge and the gargano region and approximately trend nw se and e w respectively several interpretations have been proposed to explain the deformation observed within the adriatic foreland including a variety of contrasting kinematic and geodynamic models we attempted to unravel the complicated structural evolution of the central adriatic region by interpreting industrial and ministerial shallow and deep seismic profiles and the recent seismicity recorded in the adriatic the subsurface study allowed us to better understand the structural style timing and rates of deformation affecting the mid adriatic ridge and the gargano region and to unravel the relationships of active deformation with respect to the adjacent chains the results of our study indicate that the structural setting and type of seismicity of the central adriatic can be explained in terms of active intraplate deformation with the reactivation of inherited discontinuities

facies associations and evolution of pelagic carbonate platform basin systems examples from the italian jurassic abstract during the structural and sedimentological evolution of rifted continental margins in carbonate dominated settings a characteristic stage is commonly reached when pelagic carbonate sedimentation occurs in association with complex fault block systems an integrated study of the ammonite biostratigraphy and sedimentology of jurassic pelagic rocks in the umbria marche apennines central italy and in the sila mountains north east calabria southern italy has revealed three distinctive facies associations which can be related to specific structural and depositional settings the condensed pelagic facies association is the constituent of condensed usually discontinuous sequences with numerous hiatal surfaces the normal and resedimented pelagic facies association is typical of thicker sequences comprising gravity flow and rockfall deposits the composite pelagic facies association is one in which rockfall deposits are found associated with condensed sequences containing minor or no gravity flow deposits palaeotopographical highs are dominated by the condensed pelagic facies association and constitute the pelagic carbonate platform pcp structurally the pcp can be coincident with the top of a horst or central high block or the crestal area of a tilted block in the latter case the sediment surface of the pcp slopes gently maximum of 1 3 in this the shallowest area of a pelagic carbonate ramp pcps can have erosional bypass rare and depositional margins stepped margins also exist as subparallel rows of erosional and bypass margins trends from erosional to depositional margins are usually seen as a response to basin filling and burial of submarine tectonic escarpments by pelagic deposits in late synrift or early post rift times this is apparent from progradation of pcp facies deposits beyond the structural boundaries of the pcp palaeoenvironmental analysis in pelagic carbonate platform deposits of the umbria marche apennines suggests that drowning of ancestral peritidal carbonate platforms in pliensbachian time was followed first by a moderate deepening and then by shallowing in the tithonian

a noble gas study of a granulite sample from the nilgiri hills southern india implications for granulite formation the he and ar isotopic composition of several mineral separates from a 2 5 ga old enderbite sample from the nilgiri hills southern india were analyzed the sample contains abundant high density carbonic fluid inclusions which have been well characterized in previous studies 1 2 on this particular sample garnet contains synmetamorphic primary fluid inclusions while quartz and plagioclase contain re equilibrated secondary inclusions the noble gases were extracted by crushing or heating of the minerals all measured 3he 4he ratios are above the typical value of old crustal rocks which is about 0 01 0 02 times the atmospheric ratio ra fluid inclusions from the crushed garnet sample contain helium with the highest 3he 4he ratio of 2 34 0 36 ra the he excess is mantle derived and cannot be explained by a cosmogenic or nucleogenic 3he rich component the elemental and isotopic ratios of he ne and ar in all minerals can be explained by a combination of elemental fractionation during diffusional loss of noble gases production of radiogenic nucleogenic4he 21ne 22ne and40ar and atmospheric contamination depending on the assumptions made for the evolution of the he trapped in the garnet fluid inclusions we obtain mixing ratios between mantle derived he and crustal he ranging from 1 5 5 to essentially pure mantle he however probably pure mantle he was trapped in the minerals 2 5 ga ago these data suggest that the enderbite sample represents a former mantle derived tonalitic magma which exsolved its volatiles upon crystallization in the lower crust liberation of a huge amount of co2 by similar intrusions together with the heat provided by them might be responsible for the dehydration of the former amphibolite facies rocks to the north bordering the nilgiri hills

carbon isotope compositions of fluid inclusions in charnockites from southern india models for the formation of crustal granulites which include the metamorphism of anhydrous lithologies1 2 the extraction of hygroscopic granite melts3 4 and fluxing by co25 7 constrain the thermal and geochemical evolution of the lower crust and its interaction with mantle derived volatiles here we present abundances and carbon isotope compositions of co2 in fluid inclusions in quartz and garnet from gneiss granulite pairs from the incipient char nockite quarries of southern india determined by a stepped combustion thermal decrepitation carbon extraction technique which quantifies problematic sample contamination and allows precise lithological control the results show that the co2 in incipient charnockite is more abundant and isotopically heavier than the co2 in associated gneiss providing evidence for the influx of co2 rich fluids during their formation the inferred carbon isotope compositions of these fluids are consistent with a mantle source and at ponmudi the isotopic composition of coexisting graphite and co2 implies fluid rock volume ratios in excess of 0 15

carbonate platform margin architecture and its influence on cambrian ordovician reef shoal development tarim basin nw china abstract six types of carbonate platform marginal slope have been identified in the cambrian ordovician of tarim basin these include a progradational carbonate ramp platform a progradational carbonate rimmed platform an aggradational rimmed carbonate platform a retrogradational rimmed carbonate platform an aggradational margin on an isolated carbonate platform and a retrogradational margin on a submerged carbonate platform various platform margin architectures and reef shoal characteristics occur in different areas of the tarim basin a progradational carbonate ramp platform margin began in the early cambrian in the tarim basin a progradational rimmed platform margin developed in the middle cambrian time in the northern tarim basin whereas contemporaneously a progradational ramp platform margin developed in the southwestern and central tarim basin a retrogradational rimmed carbonate platform developed in the northern tarim basin whereas an aggradational rimmed carbonate platform occupied the central tarim basin in the early ordovician time an aggradational margin on an isolated platform and a retrogradational margin on a submerged platform developed mainly during the late ordovician in the central tarim basin platform margin slopes migrated continually throughout the cambro ordovician the broad platform area western tarim platform that occupied most of the northwestern and central tarim basin in the early cambrian time was split by an east west oriented shelf seaway that began to develop along the eastern and western margins of the platform in the early ordovician time and completely transected the platform by late ordovician time the resultant central tarim basin platform area was much reduced elongate east west around the central tarim paleo uplift and terminated eastward towards region of the late ordovician basinal deposition across the eastern tarim basin affected by platform margin structure climate and paleodepth algal reefs and shoals developed mainly in the cambrian and intraclastic shoals developed mainly in the early ordovician followed by reef building of framestone or bafflestone in the late ordovician

landslide tsunami vulnerability in the ligurian sea case study of the 1979 october 16 nice international airport submarine landslide and of identified geological mass failures summary the ligurian sea at the france italy boarder of the mediterranean sea has experienced in the past numerous submarine landslides within its very near continental slope the continental shelf being very narrow the most recent occurred on the 1979 october 16 near nice international airport and generated tsunami waves of order 3 m of amplitude in some specific locations more ancient landslides are also easily identified through bathymetric surveys of the seafloor for the 1979 event we propose two distinct tsunamigenic landslides based on identified scars observable on the seafloor the first one corresponds to the volume vol1 that slid at the airport in shallow water while the second one corresponds to the more substantial volume vol2 that has been localized at the slope former studies indicate that only the combination of the two slides may explain the event we complement these studies by asserting that when the two slides are taken separately they already explain a significant although not a total part of the event vol1 explains partly the tsunami observations in the vicinity of the airport while vol2 contributes to explain the ones away from the area in particular at antibes where the highest wave has been observed the modelling effort is then extended to evaluate the tsunamigenesis of selected but representative former landslides having a clear scar signature the vulnerability of the area to landslide triggered tsunami is then proposed to discussion along with possible mechanisms that can be responsible for local wave amplification

seismic modelling of outcrop carbonate systems an application to the cretaceous platform to basin system of the maiella mountain central apennines italy

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust

lithospheric bulges recorded by regional unconformities the case of mesozoic tertiary apulia abstract cyclic shallow water carbonate sequences in the cretaceous of southern italy are punctuated by regional unconformities associated with bauxites and palaeokarst features direct and indirect evidence strongly suggests that despite their apparent plate interior position tectonics rather than eustasy was responsible for subaerial exposure long enough to form bauxites in plane stress related lithospheric arching caused by orogenic deformation along the distant active margins of apulia is invoked to explain the vertical stacking of a series of regional unconformities one of them marked by bauxites on land and under the sea the case history of apulian bauxites associated with a turonian arching allows a first estimate of the duration of a stress related distant perturbation of a subsiding passive continental margin

stratigraphy and tectonics offshore of puglia italy southern adriatic sea abstract the structural and stratigraphic framework of puglia offshore between the gargano promontory and the town of brindisi southern adriatic sea has been analysed based on 1700 km of multichannel seismic profiles and 10 exploratory wells the area includes two different geodynamic settings 1 part of the undeformed apenninic foreland apulian carbonate platform consisting mainly of shallow water mesozoic carbonates and 2 part of the southern adriatic basin which represents the foredeep of the hellenic thrust system a mesozoic slope buried by tertiary clastics and corresponding to the edge of the apulian carbonate platform is observed on seismic data the present physiography of the escarpment is the result of an erosional retreat mainly developed during the tertiary and related to the subsidence of the south adriatic basin at the same time carbonate facies belts as evidenced by well data seem to suggest that in some sectors of the margin the original mesozoic physiography has been preserved and fossilized three seismostratigraphic units separated by regional or local unconformities have been distinguished in the neogene clastic sequence of the south adriatic basin significant deformations in the sedimentary cover are represented by various antiforms one of these antiforms named the gondola ridge is an elongated positive structure deforming the pre tertiary basement the western sector of the gondola ridge belongs to a major e w strike slip lineament extending on land in the gargano promontory in the eastern part of the area in question some tectonic features resembling pop up like and thrust antiforms are arranged along an arcuate pattern named here grifone trend the grifone trend structures indicate a post pliocene tectonism probably related to the late stages of the dinaric hellenic orogenesis the recent westward migration of the hellenic fold and thrust belt can be demonstrated by the south adriatic foredeep shift during the last 5 6 million years

the ombrina rospo plateau apulian platform evolution of a carbonate platform and its margins during the jurassic and cretaceous abstract in this paper we analyze the jurassic and cretaceous evolution of the buried northwards stretch of the apulia platform southern italy ombrina rospo plateau orp and adjacent adriatic basin exploration wells indicate that inner platform carbonate facies across the orp in the jurassic and lower cretaceous are capped along a subaerial exposure surface by oligocene miocene carbonates a nw trending intra platform basin casalbordino corridor was infilled with shallow to deeper water sediments in the late early to late cretaceous interval while platform margins were experiencing tectonic reactivation the orp to basin transitional belt formed a corner defining a nw and a ne margin the nw margin was essentially stationary a syn and early post rift platform toe bypass wedge formed when late hettangian sinemurian extension produced the platform basin relief export of platform material coupled with a halt of faulting made the platform slope profile continuous in the late early or early middle jurassic possibly across an ooidal rim late jurassic ellipsactinia coral reefs passed downdip into bioclastics the maiolica fm displays two cycles m1 m2 where m2 onlaps the slope built by m1 in the aptian with lithospheric arching a high angle fault rejuvenated the margin off this margin a narrow basin locked between the orp and a pelagic carbonate platform was largely infilled with turbidites sourced by the orp but the high hampered the dispersal of the sand fraction the ne margin displays prograding ooidal to bioclastic clinoforms middle and upper jurassic downlapping onto the rift basin in the lower cretaceous the platform recovered after a slow down of carbonate productivity m1 2 boundary the marne a fucoidi fm thickens at the toe of and seals a fault backstepping the margin further backstepping occurred 5 km platformwards along a cenomanian normal fault producing room for a rudist factory a retreating rocky shoreline sourced breccias while downdip the shallow water facies graded into the scaglia fm basin along a ramp like profile with low angle clinoforms merging with turbidites

carbon isotope stratigraphy in a single graphite crystal implications for the crystal growth mechanism of fluid deposited graphite a 2 cm long and 0 8 cm thick single graphite crystal embedded in quartz feldspar and orthopyroxene of a granulite facies metamorphic rock from southern india exhibits unique homogeneity in 13 c values along layers parallel to the 0001 surface and smooth unidirectional variation of about 1 along the c crystallographic axis the fluid precipitated graphite shows isotope homogeneity indicative of crystal growth along the 0001 plane the c isotope data along with the textural features suggest that the formation of graphite initiates in a layer perpendicular to the c axis possibly by a spiral growth mechanism the initial layer is followed layer after layer until the final stages of graphite growth a second stage of graphite growth unrestricted by surrounding minerals is inferred from the un deformed idiomorphic hexagonal form of the overgrown crystals the c isotope values in the overgrown rim of the crystal are lowered by about 2 suggesting a multistage precipitation morphologic and stable isotope studies thus confirm uniform crystal growth of graphite recording an isotope evolution pattern relating to fractionation from a fluid in an infinite reservoir during the main crystal formation spiral growth parallel to the 0001 face can explain the perfect uniformity of stable isotope composition in a single layer whereas the variation across the 0001 surface gives insights into the time integrated fluid evolution attending the crystal growth

3 d stratigraphic architecture sedimentary processes and controlling factors of cretaceous deep water resedimented carbonates gargano peninsula se italy abstract detailed geological mapping in 3 d supported by a lidar derived dom sedimentologic and biostratigraphic analyses and 3 d numerical modelling are used to characterise the stratigraphic architecture of deep water resedimented carbonate systems in the gargano peninsula se italy the base of slope succession spanning the upper aptian to danian p p was subdivided in five lithostratigraphic units that record the complex evolution and sedimentary dynamic along a segment of the apulian platform margin that was strongly influenced by syn sedimentary tectonic activity the characteristic location in a relay zone between the nw se trending platform margin and the e w oriented mattinata fault system favoured the existence of a transtentional zone from the upper aptian up to the end of the cretaceous the spatial distribution of the gravity flow deposits the stratal geometries the lateral facies changes and the biostratigraphic data demonstrate that the base of slope systems were sourced by distinct platform blocks characterised by different slope profiles abrupt to west and distally steepened to the north in this context the nature and origin of the resedimented carbonate material were controlled by the fracturation of the margin the response of the carbonate factory to relative sea level changes but were also strongly influenced by the slope profile this study demonstrates the relevance of combining traditional field work with numerical tools to improve the understanding of ancient sedimentary systems notably by mapping the stratal architecture and lithologies in continuity and at various scales on doms and by reconstructing the paleo topographies in 3 d

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

understanding the geological record of carbonate platform drowning across rifted tethyan margins examples from the lower jurassic of the apennines and sicily italy abstract in the geological record a drowning process is documented by various types of shallow water to pelagic or shallow water to mixed benthic pelagic carbonate transitions drowning unconformities are paraconformities to disconformities to angular unconformities and their drowning surfaces range from planar to highly irregular morphologies drowning successions display a mix of products of both the benthic and pelagic carbonate factories these successions can be also bounded by unconformities drowning unconformities and drowning successions are contrasted through a description and discussion of examples of escarpment bounded platforms from the jurassic of the northern apennines and subordinately from sicily and other tethyan sectors the areal distribution of drowning unconformities and successions is discussed with reference to a complex depositional system whose architecture was the product of the rift induced fragmentation of a regional hettangian carbonate megabank the examples in this study show drowning unconformities to be exclusive to intrabasinal highs while drowning successions are found both on highs and in hangingwall basins drowning unconformities with their long associated hiatuses and drowning successions are often seen to merge laterally into one another over very short distances on the same intrabasinal high the deposits of the drowning succession are sometimes missing on the top of the platform while they are found forming clinoforms along its flanks evidence that sediment could be permanently swept from the highs in these depositional systems at this stage

isotopic evidence for involvement of c0 2 bearing magmas in granulite formation it has been suggested1 2 that co2 bearing magmas play an important part in the formation of granulites these magmas crystallize directly into granulites and also expel fluids which promote the development of granulite facies mineral assemblages in adjacent country rocks direct evidence for carbonic fluids remains elusive however as granulite facies aureoles adjacent to charnockitic intrusives1 may result either from the influx of carbonic fluids derived from the intrusives or simply from extraction of water into a vapour absent melt here we report results of a detailed study of carbon isotope compositions of graphite associated with a charnockite dyke from the ponmudi quarry of south india higher graphite abundances and an anomalously heavy carbon isotopic composition 13cgr 8 1 0 at the dyke margins indicate that externally derived co2 rich fluids were transported into the ponmudi paragneisses by the intrusive and precipitated nearly quantitatively as graphite on encountering reducing country rocks the occurrence of large orthopyroxene crystals along the dyke margins suggests that these fluids also served to dehydrate the country rocks this dyke may thus be representative of the widespread transport of carbonic fluids in this terrain by felsic magmas

thrust front segmentation induced by differential slab retreat in the apennines italy new seismic reflection data reveal that the south eastward prolongation of the apennine thrust front in the central adriatic sea is most likely located in a more external position with respect to the traditional interpretation in this new interpretation the apennine thrust front shows a segmented geometry in correspondence to the tremiti lithospheric transfer zone the available data suggest that the north eastward flexural retreat of the subducting adriatic lithosphere and the related frontal accretion of the apennine accretionary prism have acted during the last 5 ma and may be considered still lively in both the po plain and in the central adriatic domain north of the tremiti lineament by analysing the tectonic evolution of the apulo adriatic areas it may be argued that the differential slab retreat between the central and southern sectors of the subducting adriatic plate has been able to induce the segmentation of the apennine thrust front

control of differential compaction on the geometry of sediments onlapping paleoescarpments insights from field geology central apennines italy and numerical modeling basin strata onlapping pelagic carbonate platform margins in the central apennines commonly dip considerably as much as 20 30 toward the basin when platform strata calcare massiccio are retrodeformed to horizontal in order to undo the tilting related to apenninic compressional tectonics these angular relationships are commonly ascribed to normal drag associated with synsedimentary faulting we show that such angular relationships are fully consistent with results of numerical simulations that aim at modeling first order geometric features associated with sedimentation and compaction of deposits onlapping the escarpment at the margin of basins therefore growth of an underlying normal fault is not generally required to generate them this conclusion is also supported by field investigations of the contacts at pelagic carbonate platform margins and by paleoescarpment analysis which strongly suggest post early liassic tectonic quiescence

the messinian salinity crisis in the adriatic foredeep evolution of the largest evaporitic marginal basin in the mediterranean abstract the recent release of a large number of subsurface geological data by the italian minister of economic development including boreholes and seismic profiles provided the occasion for a new assessment of the deposits associated with the messinian salinity crisis msc in the adriatic foreland basin system and a new integration with the outcropping successions of the apennines in particular the study of the messinian evaporites allowed to reconstruct a new detailed palaeogeographic and palaeobathymetric framework for all the stages of the crisis we identified the largest evaporitic marginal basin ever described for the mediterranean hosting the precipitation of the primary shallow water gypsum deposits plg primary lower gypsum during the first stage of the crisis during the second and third stages of the crisis the plg basin underwent uplift and erosion and the evaporite accumulation moved to the deeper part of the basin and was characterized by the deposition of the resedimented lower gypsum unit including clastic evaporites recycling the plg ones primary halite and terrigenous deposits the distribution of the different evaporitic facies was the basis for an improved reconstruction of the upper miocene tectonic evolution of the apennines thrust belt our results show a clear separation between shallower depocenters located in the wedge top and in the adriatic foreland basins and characterized by msc stage 1 plg deposition and deeper water ones located in the adriatic foredeep and close to the calabrian arc where msc stage 2 terrigenous and gypsum bearing clastic deposits and primary halite accumulated

constraints on the application of carbon isotope thermometry in high to ultrahigh temperature metamorphic terranes nine marble horizons from the granulite facies terrane of southern india were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite the marbles in trivandrum block show coupled lowering of 13c and 18o values in calcite and heterogeneous single crystal 13c values 1 to 10 for graphite indicating varying carbon isotope fractionation between calcite and graphite despite the granulite facies regional metamorphic conditions the stable isotope patterns suggest alteration of 13c and 18o values in marbles by infiltration of low 13c 18o bearing fluids the extent of alteration being a direct function of the fluid rock ratio the carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated recrystallized in the presence of an externally derived co2 rich fluid and that the infiltration had occurred under high temperature and low fo2 conditions during metamorphism the onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining fluid calcite carbon reservoir following a rayleigh type distillation process within fluid rich pockets pathways in marbles resulting in the observed zonation the results suggest that calcite graphite thermometry cannot be applied in marbles that are affected by external carbonic fluid infiltration however marble horizons in the madurai block where the effect of fluid infiltration is not detected record clear imprints of ultrahigh temperature metamorphism 800 1000 c with fractionations reaching 1000 c and would be consistent with uht metamorphism

graphite bearing co2 fluid inclusions in granulites insights on graphite precipitation and carbon isotope evolution graphite in deep crustal enderbitic orthopyroxene garnet plagioclase quartz granulites 740 c 8 9 kb of nilgiri hills southern india were investigated for their spectroscopic and isotopic characteristics four types of graphite crystals were identified the first type gri which is interstitial to other mineral grains can be grouped into two subtypes gria and grib gria is either irregular in shape or deformed and rough textured with average 13c values of 12 7 0 4 n 3 a later generation of interstitial graphite grib shows polygonal crystal shapes and highly reflecting smooth surface features these graphite grains are more common and have 13c values of 11 9 0 3 n 14 both subtypes show well defined raman shifts suggesting a highly crystalline nature cores of interstitial graphite grains have on average lower 13c values by 0 5 compared to that of the rim the second type of graphite grii occurs as solid inclusions in silicate minerals commonly forming regular hexagonal crystals with a slightly disordered structure the third type of graphite griii is associated with solid inclusions up to 100 m that have decrepitation halos of numerous small 15 m satellite fluid inclusions of pure co2 with varying density 1 105 to 0 75 g cm3 the fourth type of graphite griv is found as daughter crystals within primary type co2 fluid inclusions in garnet and quartz these fluid inclusions have a range of densities 1 05 to 0 90 g cm3 but in general are significantly less dense than graphite free primary pure co2 fluid inclusions 1 12 g cm3 raman spectral characteristics of graphite inside fluid inclusions suggest graphite crystallization at low temperature 500 c the precipitation of graphite probably occurred during the isobaric cooling of co2 rich peak metamorphic fluid as a result of oxyexsolution of oxide phases the oxyexsolution process is evidenced by the magnetite ilmenite granular exsolution textures and the systematic presence of numerous micron sized rutile and other oxide inclusions in association with fluid inclusions within garnet plagioclase and quartz the carbon isotope compositions of coexisting co2 in fluid inclusions and graphite show a fractionation co2 gr co2 gr of 6 in garnet consistent with the existing theoretical estimates of co2 gr co2 gr at 800 c a subsequent generation of co2 inclusions trapped in matrix quartz and quartz segregation have higher 13c values 4 and 2 9 respectively graphite in quartz segregations also has higher 13c values 9 8 than those in enderbite 12 7 micro graphite crystals included in garnet quartz enderbite and quartz segregation have average 13c values of 11 1 10 4 and 8 7 respectively indicating progressive enrichment in 13c with a decrease in temperature of recrystallization of respective minerals this progressive enrichment is also observed in carbon isotope compositions of fluid inclusion co2 suggesting isotopic equilibrium during graphite precipitation from co2 fluids thus the carbon isotope record preserved in these rocks by the interstitial graphite co2 fluid in enderbite graphite microcrystals graphite in quartz segregation and co2 fluid in quartz segregation suggests a temperature controlled isotopic evolution this evolution is in accordance with a closed system rayleigh type graphite precipitation process which progressively enriched residual co2 in 13c

constraints on the timing of pan african granulite facies metamorphism in the kerala khondalite belt of southern india shrimp mineral ages and nd isotopic systematics abstract the supracrustal kerala khondalite belt kkb southern india constitutes an important but little understood terrain in the evolution of east gondwana here we report shrimp u pb zircon and titanite ages for a suite of metasedimentary rocks from the kkb metamorphic ages at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 530 2 pm 4 4 end document and documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd us

the cretaceous megabreccias of the gargano promontory apulia southern italy their stratigraphic and genetic meaning in the evolutionary framework of the apulia carbonate platform huge megabreccias occur at the eastern margin of the cretaceous apulia carbonate platform gargano promontory southern italy their stratigraphic and genetic meaning are controversial in the debated geological evolution of the apulia platform new stratigraphic analyses have revealed that three distinct megabreccia levels occur within the coarse debrites that were previously interpreted to be the result of repeated collapses of a scalloped platform margin during the late albian cenomanian each level has peculiar chronostratigraphic distribution geometry composition and genetic features they are the posta manganaro megabreccias late early aptian to late albian pp monte s angelo megabreccias early middle cenomanian and belvedere di ruggiano megabreccias middle turonian these deposits overlie regional tectonically enhanced unconformities of late early aptian late albian and late cenomanian age these megabreccias which were formed respectively during drowning prograding and exposure events of the apulia platform reflect important turning points in its cretaceous geodynamic evolution

the enigmatic ascent of ca sulphate rocks from a deep dense source layer evidences of hydration diapirism in the lesina marina area apulia southern italy in the lesina marina village area the cropping out gypsum rocks that rose up from the deep and thick upper trias burano fm anhydrite layer have been analyzed to investigate the trigger mechanism for their ascent in this regard we focus on the anhydrite to gypsum transformation starting from the deep source layer indeed petrographic observations of the widespread corroded anhydrite crystals embedded in these gypsum rocks revealed unequivocal evidences of the anhydrite to gypsum transformation in addition and referring to gypsum microstructural features indicate that ductile deformation mechanisms initially operated under higher temperature conditions this temperature should be close to 107 c namely the value of the upper temperature limit of stability of gypsum from lesina marina above which it starts to transform and dehydrate as revealed by microthermometry heating dehydration experiments combined with micro raman analyses all these evidences are in favor of the dramatic density decrease and volume increase due to anhydrite to gypsum transformation by hydration in the deep source layer these variations of physical conditions triggered by hydration promoted diapirism of the gypsum mass in other words hydration diapirism as revealed by seismic lines interpretation the diapirism which gave rise to the lesina diapir occurred during plio pleistocene and was genetically related to the lesina graben type structure hydration at depth was favored by the downward circulation of water rich fluids channeled in faults and the gypsum mass used the weakened zone of the southern fault to pierce the overlying mesozoic and tertiary sediments

carbon isotope constraints on volatile mixing and melt transport in granulite facies migmatites abstract migmatites at brattstrand bluffs east antarctica comprise granulite facies mineral assemblages produced by high temperature metamorphism of pelitic sediments these rocks preserve an advanced stage of partial melting with recrystallized melt accounting for 25 of outcrop area many of the melt veins contain cordierite which traps volatile molecules within open channels in its mineral framework and can be used to monitor the syn metamorphic volatile contents of the melts we have analysed the isotopic composition of cordierite channel co2 by step heating mass spectrometry channel co2 in cordierite from brattstrand bluffs has not been significantly affected by retrograde isotope exchange as it preserves high temperature carbon fractionations with coexisting graphite cordierite samples from the same locality have similar isotope compositions 0 6 reflecting efficient mixing of partial melt and dissolved volatiles on a metre scale however samples from different localities have distinct 13c values 10 to 20 and indicate that there was little mixing of melt or volatiles on a scale of 100 m despite the high degree of partial melting the 10 variation between localities reflects mixing of variable proportions of isotopically light biogenic carbon with carbon from a heavier reservoir although this mixing can be interpreted in terms of carbon influx from an external source co2 was not a driving force for granulite metamorphism in this case as granulite assemblages occur at all localities irrespective of isotope systematics co2 played a complex but passive role during metamorphism and melting at brattstrand bluffs where the dissolution of h2o into partial melt bodies was the dominant dehydration mechanism

multistage graphite precipitation through protracted fluid flow in sheared metagranitoid digana sri lanka evidence from stable isotopes abstract the digana metagranitoid situated within the digana shear zone a critical junction between the highland and wanni complexes of sri lanka hosts a variety of graphite types with structural evidence showing formation during different stages prior to and after deformational events affecting this terrain here we discuss their occurrence association and stable isotopes the carbon isotopes of graphite reported in this study from the sri lankan high grade metamorphic terrain differ significantly from the composition of graphite reported elsewhere in other precambrian terrains the stable isotope composition from random crystals depicts an enriched carbon isotopic composition in the range 1 6 to 8 suggesting precipitation by reduction from co2 rich fluids intracrystalline microscale traverses made on graphite crystals indicate the 13c composition of the rims becoming progressively lighter in 13c in metagranitoid hosted samples with the variation reaching up to 1 5 consistent with the changing fluid regimes induced by decreasing temperature during the graphite growth and shows the preservation of core at higher temperatures a highly enriched carbon isotopic composition 0 6 with a rimward enrichment of 13c observed in migmatites contrary to the values in metagranitoid indicates preferential enrichment of heavy isotopes as a result of the partial melting and dissolution reprecipitation of graphite the oxygen isotopic composition of a quartz calcite vein show values in the range 18 5 to 20 typical for recycled crustal source the tight constraint in the isotopic data from different graphite types studied indicates a homogeneous fluid source for the deposits prolonged fluid flow in this region is envisaged in this study which is related to the multistage deformation of the crustal scale shear zone

alkali granites with pan african affinities from kerala s india in the kerala region of the south indian shield alkali granite plutons ranging in age from 550 to 740 ma intrude precambrian charnockites and migmatites all of them are spatially related to regional fault lineaments their geochemistry is similar to pan african post kinematic plutons from the afro arabian shield they are of granitic to adamellitic composition with high sio 2 k 2 o up to 12 and na 2 o and low cao feo and mgo their major element composition together with a low 87 sr 86 sr i 0 703 from one pluton denote a type affinities however local charnockites have such low rb and radiogenic 87 sr that the granites could have formed by crustal melting their overall trace element characteristics are typical of alkaline granites in general but the details show that most resemble more recent volcanic arc granites and one pluton is typical of a within plate setting the presence of co 2 rich fluid inclusions supports the notion that the enrichment of rare earth an

basin analysis in the southern tethyan margin facies sequences stratal pattern and subsidence history highlight extension to inversion processes in the cretaceous panormide carbonate platform nw sicily abstract in the mediterranean the south tethys paleomargin experienced polyphased tectonic episodes and paleoenvironmental perturbations during mesozoic time the cretaceous shallow water carbonate successions of the panormide platform outcropping in the northern edge of the palermo mountains nw sicily were studied by integrating facies and stratal pattern with backstripping analysis to recognize the tectonics vs carbonate sedimentation interaction the features of the requienid limestone including geometric configuration facies sequence lithological changes and significance of the top unconformity highlight that at the end of the lower cretaceous the carbonate platform was tectonically dismembered in various rotating fault blocks the variable trends of the subsidence curves testify to different responses both uplift and downthrow of various platform blocks impacted by extensional tectonics physical stratigraphic and facies analysis of the rudistid limestone highlight that during the upper cretaceous the previously carbonate platform faulted blocks were subjected to vertical movements in the direction opposite to the displacement produced by the extensional tectonics indicating a positive tectonic inversion comparisons with other sectors of the southern tethyan and adria paleomargins indicate that during the cretaceous these areas underwent the same extensional and compressional stages occurring in the panormide carbonate platform suggesting a regional scale significance in time and kinematics for these tectonic events

microscale isotopic zoning in calcite and graphite crystals in marble chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes here i present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the hida metamorphic belt central japan showing isotopic zoning within individual crystals within 100 m of the calcite graphite grain boundary the 13c contents gradually decrease from the constant values of the crystal core to values 1 lower 18o contents in calcite decrease by up to 7 within 200 300 jim of the boundary at a calcite calcite grain boundary similar patterns of 13c and 18o depletions were found whereas the 13c contents of graphites remained constant except in a narrow zone at the calcite contact these isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13c and 18o these results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used and that isotopic zoning may provide another way to elucidate polymetamorphic processes

mineralization and wall rock alteration at the bogala graphite deposit bulathkohupitiya sri lanka the graphite mineralization in the bulathkohupitiya area was studied with an emphasis on the bogala deposit vein type mineralization occurs in the zones of deep seated fractures in supracrustal stratiform metasedimentary rocks resulting from the differential rise of subcrustal migmatites the mineralization at bogala comprises several veins of graphite and a large vein of syenite pegmatite mineralogical and geochemical study of the wall rocks reveals a well zoned alteration halo about the deposit chemical zoning in the altered wall rock and the relict mineral replacement textures indicate deep seated hydrothermal activity formation of vein graphite by decarbonation of carbonates and reduction of co 2 formed during the decarbonation reaction is indicated by the available carbon isotope data chemical zoning in the alteration halo may be a useful aid in the exploitation of known graphite deposits

graphite mineralization in paleoproterozoic khondalites of the north china craton a carbon isotope study abstract graphite mineralization in precambrian supracrustal rocks provide important information on the source characteristics of carbon and has been the focus of studies tracking primitive life in the early earth as well as a geochemical tracer in fluid rock interaction processes here we present results from a high precision carbon stable isotope study of the different associations of graphites from a graphite deposit in the paleoproterozoic khondalite belt of the north china craton our results show that disseminated graphite occurring as stratabound deposits along the compositional planes of the khondalites possess the lowest 13c values of ca 25 5 graphite in the massive ores also show identical composition with 13c values in the narrow range of ca 25 3 to 25 7 coarse graphite flakes in quartz pods and veins show slightly heavier values with 13c in the range of 19 1 to 20 9 such flakes with 13c composition of ca 20 6 were also deposited in some domains of the host khondalites the graphite in melt pockets within felsic leucosomes show the heaviest 13c values in the range of 15 8 to 16 8 micro sampling perpendicular to the c axis of the graphite crystals indicates a remarkable homogeneity of carbon isotopic composition within the individual graphite types the highly negative 13c values of the dominant graphite type in this deposit as well as similar values reported for those from other deposits in the region compare well with the isotopic signature of biogenic carbon occurring in other precambrian terranes and suggest that microbial life was flourishing in the paleoproterozoic oceans that closed during the final assembly of the north china craton the 13c enriched graphite in veins and melt pockets might have been deposited from mixed fluids derived through degassing of organic material during high grade metamorphism and externally derived co2 rich fluids

the early cretaceous drowning unconformities of the apulia carbonate platform gargano promontory southern italy local fingerprints of global palaeoceanographic events drowning successions which cap carbonate platforms and flanks bear palaeoenvironmental information which is useful for genetic stratigraphy they constitute predictive key markers in regional to global correlations an early cretaceous platform to basin transition has been investigated in apulia southern italy and two drowning unconformities dated as early valanginian and late early aptian have been documented they occur at the base of thick pelagic tongues wedging toward the platform and mark the base of two depositional sequences showing distinct transgressive regressive cycles timing of drowning processes based on biostratigraphy and dynamic stratigraphy allows the correlation of unconformities with global scale palae oceanographic events marked among others by positive spikes of well established 13c curves drowning signatures in the apulia carbonates fit the stratigraphic palaeoecological and possibly geochemical evidence found in global records at the same stratigraphic levels moreover it is proposed that the observed drowning events were caused by palaeoceanographic crises affecting factory productivity

melt related metasomatism in mafic granulites of the quetico subprovince ontario constraints from o sr nd isotopic and fluid inclusion data mafic granulites in the archean quetico subprovince north of manitouwadge ontario occur as isolated lenses or discontinuous layers in spatial association with tonalitic leucosomes in metasedimentary rocks and exhibit concentric zoning from a biotite rich margin to an orthopyroxene rich outer zone and a clinopyroxene rich central zone with internal orthopyroxene bearing leucosomes and rarely patches of relict amphibolites within the clinopyroxene rich zone microstructural and microchemical evidence suggests that the mafic granulites formed from amphibolites by combined infiltration diffusion processes in the presence of a p f bearing silicate melt p 2o5 melt 0 24 0 28 wt and ac o 2 rich hypersaline fluid the whole rock and mineral 18 o values of the mafic granulites 8 9 v smow indicate oxygen isotope equilibration between amphibolites 6 6 6 9 and associated tonalitic leucosomes 9 5 10 at 700 800 c strontium and nd isotope data and u pb zircon ages confirm isotopic homogenization at the leucosome amphibolite boundaries during the peak granulite facies metamorphism at about 2650 ma texturally early co2 rich fluid inclusions in quartz and garnet yield p t conditions similar to those of the peak granulite facies metamorphism hypersaline fluid inclusions occur in textural coexistence with the early co2 rich inclusions but are invariably low in homogenization temperatures 178 234 c this study shows that silicate melts not only provide a conduit for co2 rich fluids but also interact directly with country rocks for the formation of granulites also the o sr nd isotope data show that the documented mobility of rare earth elements in the quetico granulite zone is localized in scale and related to anatexis of local metasedimentary rocks during the granulite facies metamorphism resume les granulites mafiques dans la sous province de quetico archeenne au nord de manitouwadge en ontario apparaissent sous forme de lentilles isolees ou de couches discontinues associees spatialement a des leucosomes tonalitiques dans les roches metasedimentaires elles exhibent un zonage concentrique evoluant d une marge riche en biotite a une zone externe riche en orthopyroxene et a une zone centrale riche en clinopyroxene incluant des leucosomes internes contenant un orthopyroxene occasionnellement sont rencontrees des plages d amphibolites relictuelles dans la zone riche en clinopyroxene les analyses microstructurales et microchimiques suggerent que les granulites mafiques derivent d amphibolites transformees par les processus combines d infiltration diffusion en presence d un magma silicate contenant p et f p2o5 magma 0 24 0 28 par poids et d un fluide riche en co2 hypersalin

a mechanical model for complex fault patterns induced by evaporite dehydration and cyclic changes in fluid pressure complex fault patterns i e faults which exhibit a diverse range of strikes may develop under conditions where a regional tectonic stress field is weak or absent e g polygonal faults the present paper considers a complex system of synsedimentary faults in the umbria marche apennines italy geometrically similar to polygonal fault systems developed during an early jurassic extensional episode this particular fault pattern differs from many extensional fault systems as it lacks structures that are developed with a classical bimodal conjugate andersonian geometry a conceptual and mechanical model is proposed to explain the development and evolution of the complex fault pattern in which it is proposed that faulting is primarily controlled by the development of volumetric instability in triassic evaporites due to dehydration processes anhydritisation during burial the lithological architecture of the triassic evaporites comprising interbedded ca sulphate layers and dolostones played a fundamental role in controlling the deformation processes cyclic fluid overpressure build up release and the coexistence of brittle and brittle ductile flow processes led to horizontal isotropic and non plane extensional strain fields within the dehydrating rock mass which favoured the development of complex deformation patterns the mechanical model proposed shows that the studied fault pattern developed under a stress field consistent with almost homogeneous stress intensities within the horizontal plane the data presented show that local strain fields and transient fluid pressure conditions have been dominant over weak regional extensional tectonics the findings are relevant to many other areas where complex faulting patterns including polygonal faults occur in association with evaporite or clay rich sedimentary sequences

ore fluids associated with the wynad gold mineralization southern india evidence from fluid inclusion microthermometry and gas analysis abstract in southern india major gold deposits occur in the archean granite greenstone terrain of kolar hutti ramagiri and within proterozoic granulite terrain in wynad the wynad gold field wgf which is located within the moyar bhavani lineament a proterozoic transcrustal shear zone hosts gold within quartz veins which are emplaced along the mesoscopic faults and shears in the region the quartz veins cut the regional fabric of the country rocks suggesting that the veins were formed in post tectonic and post metamorphic episode of crustal shearing gold as visible specks or interstitial grains and veinlets are seen within quartz and associated sulfide minerals indicative of multiple mineralizing events fluid inclusion studies carried out on gold quartz veins showed the frequent occurrence of bi phase primary inclusions of h 2 o co 2 pseudosecondary inclusions of h 2 o co 2 and aqueous secondary inclusions microthermometric studies of different samples revealed a near pure co 2 composition associated with the aqueous phase with melting temperatures close to 56 6 c clathrate melting temperatures of primary and pseudosecondary inclusions show that the fluids were low to moderately saline 2 14 wt nacl equiv homogenization temperatures of primary and pseudosecondary inclusions range between 250 330 c and 230 300 c respectively the secondary aqueous inclusions have much lower homogenization temperatures between 130 and 220 c fluid densities calculated from the microthermometric data were between 0 8 and 1 0 g cm 3 the isochores pertaining to these fluid densities intercept the trapping temperatures within pressure ranges of 0 5 and 2 9 kbars fluid inclusion gas analyses were carried out on selected samples using a quadrupole mass spectrometer the analysis shows that the fluid inclusions were mainly of h 2 o and co 2 with minor quantities of n 2 and ch 4 which was in close correlation with our visual analytical data we envisage that the fluids responsible for the wynad gold mineralization evolved from an h 2 o co 2 fluid and precipitated gold at temperatures of 300 350 c due to the sudden pressure and temperature decrease as the fluids entered the shear zone

a dominant tectonic signal in high frequency peritidal carbonate cycles a regional analysis of liassic platforms from western tethys abstract meter scale peritidal carbonate cycles are a common feature of the geological record but debate continues about what processes lead to their formation three conceptual models or a combination thereof are commonly invoked to explain cycle formation eustasy tectonics or autocyclicity these three models are tested with a large new dataset from different early jurassic plate margins from western tethys study of seven logged sections from spain italy greece tunisia morocco and gibraltar enables an analysis of the possible roles of local versus regional patterns and controls on cyclicity within a sinemurian time slice cycle types are diverse and include shallowing upward cycles parasequences but also deepening upward and diagenetic cycles high frequency sequences and subtidal cycles numbers of cycles per section and cycle stacking patterns within this time slice vary from section to section statistical tests runs tests time series and bundling all indicate random stacking of cycles within sections and an absence of any bundling of thicknesses or of facies trends assessment of cycle types by their occurrence and stacking patterns indicates little support for either eustasy or autocyclicity being the dominant cycle forming mechanism however the variability in numbers of cycles per section thickness variations of the sections cycle type variability and randomness of stacking patterns all favor a pulsed tectonic control for the creation and filling of accommodation space this conclusion is further supported by evidence that has largely arisen during the course of this study of syndepositional extensional tectonics in the sinemurian on these rifted tethyan margins although tectonics appears to be the dominant control superimposed eustasy and or autocyclic processes cannot be discounted

chlorine stable isotope composition of granulites from lofoten norway implications for the cl isotopic composition and for the source of cl enrichment in the lower crust abstract the cl isotopic composition of lower crustal rocks as revealed from granulites from the lofoten islands northern norway centres around the value of standard mean ocean chloride smoc the investigated rocks and mineral separates of cl amphibole and cl biotite have 37 cl values 37 cl 35 cl normalized to smoc of 1 12 to 0 79 with most values concentrated in the range of 0 3 to 0 11 and an average of 0 15 samples from gabbroic and from dry granitic rocks magmatic mangerites and charnockites with highly cl enriched hydrosilicates and from a later amphibolite with low cl amphiboles show no distinct differences in their 37 cl values the results indicate that there was only minor involvement of mantle derived cl in fluid involving processes in the middle and lower crust assuming a 37 cl of 4 7 for the undegassed mantle 1 cl isotopic values of the granulites do not support the influx of significant amounts of mantle derived cl the maximum possible mantle contribution to the sample with the highest 37 cl is about 33 thus the common occurrence of cl enriched minerals in granulite facies terrains is regarded as a product of remobilized crustal cl either during magmatism or during later fluid activity the results support the hypothesis that the crust can be regarded as a reservoir with cl isotopic values very similar to smoc

fluid rock history of granulite facies humite marbles from ambasamudram southern india an extensive humite bearing marble horizon within a supracrustal sequence at ambasamudram southern india was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics at peak metamorphic temperatures of 775 73 c based on calcite graphite carbon isotope thermometry the mineral assemblages suggest layer by layer control of fluid compositions clinohumite calcite bearing assemblages suggest xco2 0 9 at 790 c and local wollastonite scapolite grossular bearing zones formed at xco2 of c 0 3 retrograde reaction textures such as scapolite quartz symplectites after feldspar and calcite and replacement of dolomite diopside or tremolite dolomite after calcite forsterite or calcite clinohumite are indicative of retrogression under high xco2 conditions calcite preserves late proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting isotopic zonation of calcite and graphite grains was likely produced by localized co2 fluid infiltration during retrogression contrary to the widespread occurrence of humite marbles related to retrograde aqueous fluid infiltration the ambasamudram humite marbles record a prograde to peak metamorphic humite formation and retrogression under conditions of low xh2o

regional carbonate alteration of the crust by mantle derived magmatic fluids tamil nadu south india regional carbonate alteration of the crust associated with major shear zones provides direct evidence for co 2 rich fluid mobility a good example occurs within the attur lineament one of numerous proterozoic shear zones which crosscut charnockitic gneisses and other lithologies of the southern indian craton at this locality widespread carbonate alteration of silicate rocks has involved growth of ankerite and other carbonate minerals which replace preexisting silicates some of the ankerite was subsequently recrystallized to fine grained calcite and iron oxide accompanied by sericitization of feldspar carbon oxygen and strontium isotope analyses of samples of ankerite and calcite together with some of the coexisting silicate minerals have been used to constrain the conditions of formation of the carbonate alteration and the origin of the fluids involved delta 13 c values of ankerite are relatively homogeneous ranging between 6 5 and 3 9 with a mean of 5 3 delta 18 o is also

u pb lu hf and ree in zircon from 3 2 to 2 6 ga archean gneisses of the repulse bay block melville peninsula nunavut abstract combined in situ u pb and lu hf isotope and ree analyses of zircons from the tonalite trondhjemite granodiorite ttg type gneisses and granitoids within the repulse bay block rbb of melville peninsula nunavut reveal that the block is composed of ca 2 86 ga and 2 73 2 71 ga granitoids that formed by reworking of a 3 25 3 10 ga basaltic crust the interpretation is supported by initial hf values for ca 2 86 ga and ca 2 73 2 71 ga gneisses of 2 7 to 0 7 and 4 8 to 2 3 respectively and the preservation of high uranium xenocrystic cores at 3 15 0 05 ga neoarchean plutonism also occurred at ca 2 69 2 66 ga and is characterized by two pyroxene bearing charnockite enderbite and hornblende biotite granitoid intrusions that yield initial hf values that range from 7 1 to 1 0 demonstrating that they were derived from juvenile magmas with significant assimilation of the existing crust the pyroxene and non pyroxene bearing granitoids also contain elevated lree in zircon a feature that is interpreted to reflect metasomatism of the source this study also demonstrates that in the rbb the results of lu hf isotopes in zircon combined with in situ u pb geochronology from inherited zircon cores differ from the results of whole rock sm nd isotopes

slab bending syn subduction normal faulting and out of sequence thrusting in the central apennines in the central apennines a tertiary present eastward vergent fold and thrust belt thrusting mainly occurred in sequence cutting across a mesozoic to early neogene succession deposited in rifted early jurassic to passive continental margin to foredeep late miocene conditions however the simbruini mts were characterized by the occurrence of regional out of sequence thrusts the vallepietra filettino monte ortara thrust fault and oftertiary prethrusting normal faults associated with the deposition of thick breccia deposits brecce della renga tortonian early messinian a direct link between these two features is here proposed evidence for a prethrusting normal faulting origin for the brecce della renga is amply discussed although evidence for subduction related normal faulting is growing in the apennines literature nowhere in the region are known extensional systems so vast and their syn tectonic deposits so thick as in the simbruini area we propose that the simbruini prethrusting normal faults were subduction related i e they developed in the foreland due to anomalous bending of the lithosphere subducting in late tertiary time under the apennines in the simbruini mts area the associated breccia deposits were subsequently deformed during the development of the simbruini mts thrust front we speculate that the prethrusting normal faults allowed the penetration of fluids within the subducting crust and possibly also in the mantle weakening this part of the subducting plate as a consequence the weaker plate was anomalously down bent leading to a subcritical state of the apennines wedge the regional scale out of sequence thrust faults developed in order to bring the apennines wedge back to the critical state

carbon isotope stratigraphy and carbonate production during the early middle jurassic examples from the umbria marche sabina apennines central italy abstract the carbon isotopic signature of carbonates depends on secular variations of organic carbon and carbonate carbon production burial rates a decrease in carbonate productivity makes the organic carbonate carbon ratio unstable up to the point that even minor variations in the organic carbon reservoirs can provoke carbon isotopic shifts the 13c positive shifts of the middle carixian early pliensbachian and the early bajocian recorded in the umbria marche sabina domain represent a good example of this mechanism both sedimentology and lithostratigraphy of pelagic platform basin carbonate systems in this area show that important changes in the source of carbonates correspond to the observed isotopic shifts the middle carixian event is in fact well correlatable to the drastic reduction of benthic carbonate production on rift related intrabasinal highs which then became pelagic carbonate platforms the early bajocian event is concomitant with the beginning of a long hiatus on the pelagic carbonate platforms and with a drop of the biodiversity of calcareous organisms followed by the onset of biosiliceous sedimentation in basins

pelagic carbonate platforms in the geologic record their classification and sedimentary and paleotectonic evolution drastic differences in thickness and abrupt lateral facies changes in synrift and postrift pelagic sequences usually indicate structural control over deposition although the highs and the basins in pelagic carbonate systems have long been recognized in ancient rifted continental margins relatively little detailed information has been available on facies transitions between the two and on the geometries of pelagic sediment bodies outcrops in the umbria marche apennines central italy provide new constraints for jurassic paleogeographic reconstructions allowing for the development of models for these depositional systems pelagic carbonate platforms pcps are submarine highs that are drowned fragments of an ancestor regional peritidal carbonate platform pcps can be horsts or crests of rotated blocks the extensional regime and drowning history exert a major control over the pcp type and over the composition of sediment which fills inter pcp basins given the very low rates of pelagic sedimentation a few mm 1000 yr the effects of faulting on submarine topography are drastic block tilting is of great importance creating pelagic carbonate ramps that are the source area of most of the gravity flow deposits in half grabens excessively rapid tilts cause nondeposition in horst and graben settings on the other hand basins are sediment starved and there are comparatively only minor gravity flows ma s transport there is mostly in the form of collapse of platform margins the margins of pcps are erosional during most of pcp history becoming depositional when adjacent basins are filled stepped margins develop through fault induced reduction of the pcp area back stepping

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

the upper cretaceous carbonates of the gargano murge region southern italy a model of platform to basin transition the outcrops in gargano murge region are good examples of the upper cretaceous carbonate systems of the peri adriatic area they enable the architecture and the processes of the platform to basin transition to be studied in detail the platform carbonates are juxtaposed to the deeper marine carbonates by the intermediary of a faulted scarp the base of slope is characterized by bioclastic and conglomeratic aprons interbedded with pelagic mudstones the outer shelf domain which was the prolific source of rudistid bioclastic aprons is not preserved the platform is mainly built of mud dominated transgressive systems tracts whereas highstand systems tracts are developed as bioclastic base of slope aprons the volume of the resedimented bioclasts largely exceeds the volume of missing outer shelf indicating that carbonate production and sediment bypass are more critical for this stratigraphic response than carbonate erosion the lowstands which were controlled by tectonic deformations are characterized by base of slope breccia and blocks eroded from the shelf edge this erosion resulted in the progressive retreat of the shelf edge the best potentials for hydrocarbon reservoir are found in the bioclastic base of slope aprons formed during the cenomanian and maastrichtian highstands this model is considered as an analog for the hydrocarbon reservoirs formed by the deep marine deposits of cretaceous tamabra limestone in the gulf of mexico

arrested charnockite formation in southern india and sri lanka arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high grade terrains of southern india and sri lanka two major kinds of orthopyroxene producing reactions are recognized breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic granitic gray gneiss produced the regional orthopyroxene isograd manifest in charnockitic mottling and veining of mixed facies exposures as at kabbal karnataka and in the kurunegala district of the sri lanka central highlands chemical and modal analyses of carefully chosen immediately adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of cao mgo and feo and gains of sio2 and na2o rb and y are depleted in the charnockite another kind of charnockitization is found in paragneisses throughout the southern high grade area and involves the reaction of biotite and quartz garnet to produce orthopyroxene and k feldspar although charnockite formation along shears and other deformation zones at such localities as ponmudi kerala is highly reminiscent of kabbal close pair analyses are not as suggestive of open system behavior this type of charnockite formation is found in granulite facies areas where no prograde amphibole bearing gneisses exist and connotes a higher grade reaction than that of the orthopyroxene isograd metamorphic conditions of both kabbaltype and ponmudi type localities were 700 800 c and 5 6 kbar lower p h2o in the ponmudi type metamorphism was probably the definitive factor

fe 3 reduction during biotite melting in graphitic metapelites another origin of co 2 in granulites the fe 3 fetot of all fe bearing minerals has been analysed by mossbauer spectroscopy in a suite of biotite rich to biotite free graphitic metapelite xenoliths proxies of an amphibolite granulite transition through progressive biotite melting biotite contains 9 to 16 fe 3 fetot whereas garnet cordierite and ilmenite are virtually fe 3 free 0 1 fe 3 fetot in all samples regardless of biotite presence under relatively reducing conditions graphite bearing assemblages biotite is the only carrier of fe 3 during high temperature metamor phism therefore its disappearance by melting represents an important event of iron reduction during granulite formation because haplogranitic melts usually incorpo rate small amounts of ferric iron iron reduction is accompanied by the oxidation of carbon and the production of co2 according to the redox reaction 2fe2o bt 3 c gr 4feo crd grt ilm opx co fluid melt crd 2 depending on the nature of the peritectic fe mg mineral produced garnet cordierite orthopyroxene the co2 can either be present as a free fluid component or be completely stored within melt and cordierite the oxi dation of graphite by iron reduction can account for the in situ generation of co2 implying a consequential ra ther than causal role of co2 in some granulites and migmatites this genetic model is relevant to graphitic rocks more generally and may explain why co2 is present in some granulites although it is not required for their formation

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

structural architecture of the central apennines interpretation of the crop 11 seismic profile from the adriatic coast to the orographic divide 1 we present an interpretation of the eastern half portion of the crop 11 line a deep reflection seismic profile 265 km long that cuts across the central apennines from the tyrrhenian coast to the adriatic coast in the study area the line cuts across a pile of thrust sheets that underwent tectonic transport between the messinian and the pleistocene in its easternmost part the line runs through the plio pleistocene deposits of the adriatic foredeep in the foreland region the crop 11 line integrates previous information on the crustal structure derived from petroleum exploration and from deep seismic sounding refraction experiments in particular the crop 11 line confirms the existence of a very thick sedimentary sequence underlying the mesozoic tertiary carbonates of the apulia platform interpreted as the paleozoic triassic sedimentary cover of a pre cambrian crystalline basement in the mountain chain where the base thrust of the orogenic wedge reaches a depth of about 25 km this sedimentary sequence appears to be the deepest geological unit incorporated in the thrust system this interpretation of the crop 11 profile suggests an unusual thin skin tectonic style implying the detachment from the original basement and the incorporation in the post tortonian tectonic wedge of a very thick paleozoic triassic sedimentary sequence possibly affected by low grade metamorphism in the lower part other new suggestions from the crop 11 seismic data concern the origin of the fucino basin one of the most remarkable plio pleistocene intramontane basins the normal faults bordering this structural depression as other important normal faults present in the central apennines e g the caramanico fault system in the majella region seem to have been controlled by gravitational collapse processes driven by uplift during crustal shortening rather than by a generalized extension subsequent to the apennine compression as usually reported in the geological literature if this interpretation is correct the strong seismic activity in correspondence to the apennine watershed may be related to the very recent increase in the structural relief caused by an out of sequence propagation of the active thrusts

immiscibility between carbonic fluids and granitic melts during crustal anatexis a fluid and melt inclusion study in the enclaves of the neogene volcanic province of se spain in the restitic crustal enclaves in the neogene volcanics of el hoyazo and mazarron se spain associations of fluid and silicate melt inclusions indicative of immiscibility are frequently observed in the bt poor crd rich graphitic metapelites these occurrences extremely rare for anatectic crustal rocks have been studied by microthermometry micro raman spectroscopy and emp analysis both at el hoyazo and mazarron the immiscible fi and mi are hosted in plagioclase and cordierite with microstructures that suggest primary trapping the fi hosted in cordierite are monophase whereas they may contain crystals of calcite when hosted in plagioclase indicating fluid host reaction during cooling decrepitation microstructures have not been observed the mi contain fresh glass of peraluminous felsic rhyolitic composition typical of anatectic s type melts in all samples the fluids are co2 dominated n85 mol with minor amounts of n2 and ch4 and traces of co and h2 the nucleation of graphite induced by the laser beam in some inclusions demonstrates that the fluids are graphite saturated large scatter in microthermometric behaviour of fi indicates significant density variations only in one sample from el hoyazo are fluid densities compatible with the estimated p tconditions of trapping 5 7 kbar 850 50 c whereas in the remaining samples the extremely low densities suggesting trapping pressures b1 kbar are in contrast with the microstructural indications of primary entrapment and little evidence of decrepitation in addition although some measured compositions are compatible with c o h n fluid speciation at the estimated p t conditions of anatexis the lack of h2o in all fi is inconsistent with the slightly hydrated character of coexisting glasses the possible mechanisms accounting for departure of densities and compositions of fi from expected values are discussed and leakage of h2o suggested as the most plausible

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

heterozoan carbonate deposition on a steep basement escarpment late miocene almeria south east spain heterozoan temperate water carbonates mixed with varying amounts of terrigenous grains and muddy matrix azagador limestone accumulated on and at the toe of an inherited escarpment during the late tortonian early messinian late miocene at the western margin of the almeria nijar basin in south east spain the escarpment was the eastern end of an uplifting antiform created by compressive folding of triassic rocks of the betic basement channelized coralline algal bryozoan rudstone to coarse grained packstone together with matrix supported conglomerate are the dominant lithofacies in the higher outcrops comprising the deposits on the slope these sediments mainly fill small canyon shaped half graben depressions formed by normal faults active before during and after carbonate sedimentation roughly bedded and roughly laminated coralline algal bryozoan rudstone to coarse grained packstone are the main lithofacies forming an apron of four small kilometre scale lobes at the toe of the south eastern side of the escarpment almeria area channelized and roughly bedded coralline algal bryozoan rudstone to coarse grained packstone conglomerates packstone and sandy silt accumulated in a small channel lobe system at the toe of the north eastern side of the escarpment las balsas area carbonate particles and terrigenous grains were sourced from shallow water settings and displaced downslope by sediment density flows that preferentially followed the canyon shaped depressions roughly laminated rudstone to packstone formed by grain flows on the initially very steep slope whereas the rest of the carbonate lithofacies were deposited by high density turbidite currents the steep escarpment and related break in slope at the toe favoured hydraulic jumps and the subsequent deposition of coarse grained low transport efficiency skeletal dominated sediment in the apron lobes accelerated uplift of the basement caused a relative sea level fall resulting in the formation of outer ramp carbonates on the apron lobes which were in turn overlain by lower messinian coral reefs this is the first known example of a base of slope apron within temperate water carbonate systems this article is protected by copyright all rights reserved

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

partial melting and the formation of granulite facies assemblages in namaqualand south africa abstract dehydration melting reactions in which water from a hydrous phase enters the melt leaving an anhydrous solid assemblage are the dominant mechanism of partial melting of high grade rocks in the absence of externally derived vapour equilibria involving melt and solid phases are effective buffers of ah2 o the element partitioning observed in natural rocks suggests that dehydration melting occurs over a temperature interval during which for most cases ah2o is driven to lower values the mass balance of dehydration melting in typical biotite gneiss and metapelite shows that the proportion of melt in the product assemblage at t 850 c is relatively small 10 20 and probably insufficient to mobilize a partially melted rock body granulite facies metapelite biotite gneiss and metabasic gneiss in namaqualand contain coarse grained discordant unfoliated anhydrous segregations surrounded by a finer grained foliated matrix that commonly includes hydrous minerals the segregations have modes consistent with the hypothesis that they are the solid and liquid products of the dehydration melting reactions bt sil qtz pi grt crd kfs l metapelite bt qtz pl opx kfs l biotite gneiss and hbl qtz opx cpx pl l metabasic gneiss the size shape distribution and modes of segregations suggest only limited migration and extraction of melt growth of anhydrous poikiloblasts in matrix regions development of anhydrous haloes around segregations and formation of dehydrated margins on metabasic layers enclosed in migmatitic metapelites all imply local gradients in water activity also they suggest that individual segregations and bodies of partially melted rock acted as sinks for soluble volatiles the preservation of anhydrous assemblages and the restricted distribution of late hydrous minerals suggest that retrograde reaction between hydrous melt and solids did not occur and that h2o in the melt was released as vapour on crystallization this model combined with the natural observations suggests that it is possible to form granulite facies assemblages without participation of external fluid and without major extraction of silicate melt

metamorphism of reduced granulites in low co 2 vapour free environment pervasive flooding of co2 has been proposed as the cause of granulite facies metamorphism that is capable of producing many distinctive characteristics of the deep continental crust reduced water activity orthopyroxene bearing assemblages depletion of large ion lithophile lil elements and dehydration1 6 the calculations presented here of c o h fluid composition for conditions of granulite facies metamorphism show that oxygen fugacity f o2 estimates from many terranes are sufficiently low that the addition of co2 rich fluid causes graphite to precipitate for values of pressure p and temperature t common to granulites and with f o2 slightly below the quartz fayalite magnetite buffer qfm the addition of co2 sufficient to grow 10 vol orthopyroxene requires the precipitation of 1 5 vol graphite as 0 1 vol graphite is readily recognizable but is not reported in most low f o2 granulites these rocks have not been flooded by co2 and low f h2o is probably due to extraction of a magma or recrystallization of an already dry rock7 8 granulite terranes may thus result from a combination of these three processes and the dominance of any one cannot now be demonstrated on a regional basis

vein graphite deposits geological settings origin and economic significance graphite deposits result from the metamorphism of sedimentary rocks rich in carbonaceous matter or from precipitation from carbon bearing fluids or melts the latter process forms vein deposits which are structurally controlled and usually occur in granulites or igneous rocks the origin of carbon the mechanisms of transport and the factors controlling graphite deposition are discussed in relation to their geological settings carbon in granulite hosted graphite veins derives from sublithospheric sources or from decarbonation reactions of carbonate bearing lithologies and it is transported mainly in co2 rich fluids from which it can precipitate graphite precipitation can occur by cooling water removal by retrograde hydration reactions or reduction when the co2 rich fluid passes through relatively low fo2 rocks in igneous settings carbon is derived from assimilation of crustal materials rich in organic matter which causes immiscibility and the formation of carbon rich fluids or melts carbon in these igneous hosted deposits is transported as co2 and or ch4 and eventually precipitates as graphite by cooling and or by hydration reactions affecting the host rock independently of the geological setting vein graphite is characterized by its high purity and crystallinity which are required for applications in advanced technologies in addition recent discovery of highly crystalline graphite precipitation from carbon bearing fluids at moderate temperatures in vein deposits might provide an alternative method for the manufacture of synthetic graphite suitable for these new applications

charnockite formation at ponmudi in southern india charnockites constituents of most precambrian high grade terrains1 2 are essential for understanding the evolution of the early continental crust the arrested development of charnockite in shear veins at kabbaldurga3 in the state of karnataka in india suggests flow of co2 rich water deficient fluids through deep seated rocks as a mechanism of granulite grade metamorphism4 5 we report here an occurrence of arrested charnockite formation well south of kabbaldurga in the khondalite belt of southern kerala where rocks with amphibolite facies give way to the vast southern india sri lanka charnockite terrain indicating that metamorphism due to co2 rich fluids carbonic metamorphism may have operated over a large area in southern india if such localities prove to be widespread the present level of exposure throughout much of the high grade terrain probably does not extend far beyond an isofacial surface marking the boundary between upper and lower crust in the late archaean

mineralogical characterization of graphite deposits from thodupuzha kanjirappally belt madurai granulite block southern india abstract graphite from deposits occurring in the high grade metamorphic rocks and their larteritized equivalents of the thodupuzha kanjirappally belt in madurai granulite block southern india is structurally fully ordered crystallite size lc 002 ranging from 469 to 749 a possess high degree of graphitization dg value ranging from 105 to 267 a and reflect crystallization at high temperature 700 100 c raman spectra of graphite display profiles corresponding to high crystallinity and high structural ordering the high temperature crystallinity characteristics of graphite were not obliterated during retrogression of granulites to amphibolite facies gneisses preliminary carbon stable isotope results show a spread in isotope values from 11 8 to 26 8 which suggest more than one sources for carbon the lighter carbon isotope values are suggestive of biogenic origin whereas the heavier ones are probably fluid precipitated graphite

dehydration and incipient charnockite formation a phase equilibria and fluid inclusion study from south india a 3 m traverse across a charnockite lens in a biotite garnet graphite gneiss quarry from southern india has provided mineral equilibria that indicate charnockite formation occurred under fluid conditions of x h 2 o 0 2 to 0 3 at p 5 5 pm 1 9 kb and t 700 to 750 c dehydration of biotite loss of garnet and growth of orthopyroxene are related to a decrease in x h 2 o in the fluid phase within the charnockite lens isotopic analysis of the fluid entrapped in quartz from the charnockite indicates delta 13 c 8 2 0 3 0 heavier than delta 13 c values from smaller volumes of co 2 entrapped in quartz from the gneiss although the increase in fluid inclusion abundance in the charnockite can be related to oxidation of graphite without influx of co 2 an external source of co 2 is required in order to account for the shift to heavier carbon isotope values observed in both graphite and entrapped co 2 within the charnockite carbon isotope data across the gne

arrested charnockite formation at kottavattam southern india at kottavattam southern kerala india late proterozoic homogeneous leptynitic garnet biotite gneisses of granitic composition have been transformed on a decimetric scale into coarse grained massive charnockite sensu stricto along a set of conjugate fractures transecting the gneissic foliation charnockitization post dates the polyphase deformation regional high grade metamorphism and anatexis and evidently occurred at a late stage of the pan african tectonothermal history geothermobarometric and fluid inclusion data document textural and chemical equilibration of the gneiss and charnockite assemblages at similar p lith t conditions 650 700 degrees c 5 6kbar in the presence of carbonic fluids internally buffered by reaction with graphite and opaque mineral phases x co2 0 7 0 6 x h2o 0 2 0 3 x n2 0 1 logf o2 l7 5 mineralogical zonation indicates that charnockitization of the leptynitic gneiss involved first the breakdown of biotite and oxidation of graphite in narrow outward migrating transition zones adjacent to the gneiss followed by the breakdown of garnet and the neoblastesis of hypersthene in the central charnockite zone compared to the host gneiss the charnockite shows higher concentrations of k na sr ba and zn and lower concentrations of mg fe ti v y zr and the hree with a complementary pattern in the narrow transition zones of biotite breakdown the p lith t x h2o data and chemical zonation patterns indicate charnockitization through subsolidus dehydration reaction in an open system subsequent residence of the carbonic fluids in the charnockite resulted in low grade alteration causing modification of the syn charnockitic elemental distribution patterns and the properties of entrapped fluids we favour an internally controlled process of arrested charnockitization in which during near isothermal uplift the release of carbonic fluids from decrepitating inclusions in the host gneiss into simultaneously developing fracture zones led to a change in the fluid regime from fluid absent in the gneiss to fluid present in the fracture zones and to the development of an initial fluid pressure gradient triggering the dehydration reaction

depositional geometries and facies associations in an upper cretaceous prograding carbonate platform margin orfento supersequence maiella italy abstract although progradation of platform margins is a well documented process its timing with respect to sea level cycles is controversial this outcrop study was designed to test the relation between prograding stratal patterns and sea level cycles using a sequence stratigraphic analysis and direct investigation of the sedimentological facies associations the upper campanian maastriehtian orfento supersequence in the maiella platform margin is an outstanding outcrop example of a large scale prograding carbonate wedge composed of smaller scale vertically and laterally stacked sequences the evolution of the orfento supersequence was characterized by an initial phase of aggradation followed by progradation at the scale of the supersequence basinal aggradation preceded progradation of hallower water facies because excess relief had to be buried prior to progradation seven depositional facies were distinguished on the basis of depositional geometries stratal patterns and sedimentary features these facies record different depositional environments on a low angle ramp ranging from deep water pelagic wackestones to wave dominated upper shoreface grainstones facies distributions record the overall transition from pelagic sediments turbidites and megabreccias into progressively shallower water shoreface complexes the prograding units consist of shingled offlapping sigmoidal complexes composed of rudstones and grainstones deposited in shallow wave dominated environments and their deeper water equivalents sigmoidal sequences are separated by erosive unconformities which bring upper shoreface facies into direct contact with underlying lower shoreface or outer shelf facies indicating a sea level fall forced regression meteoric diagenesis associated with the unconformities also supports lowering of relative sea level depositional facies patterns within sequences record a relative rise and highstand of sea level repetitive downward shifts bring the shoreline successively farther basinward indicating long term lowering of sea level during the late stages of progradation producing downstepping progradation our data suggest that changes in relative sea level acting on a low angle ramp control the overall architecture of sequence distribution whereas changes in sediment supply con rol changes in facies association within each sequence

stable isotopic signatures of superposed fluid events in granulite facies marbles of the rauer group east antarctica the role of volatiles in the stabilization of the lower granulite facies crust is contentious opposing models invoke infiltration of co2 rich fluids or generally vapour absent conditions during granulite facies metamorphism stable isotope and petrological studies of granulite facies metacarbonates can provide constraints on these models in this study data are presented from metre scale forsteritic marble boudins within archaean intermediate to felsic orthogneisses from the rauer group east antarctica forsteritic marble layers and associated calcsilicates preserve a range of 13c and 18o depleted calcite isotope values 13c 9 9 to 3 0 pdb 18o 4 0 to 12 1 smow a coupled trend of 13c and 18o depletion 2 5 respectively from core to rim across one marble layer is inconsistent with pervasive co2 infiltration during granulite facies metamorphism but does indicate localized fluid rock interaction at another locality more pervasive fluid infiltration has resulted in calcite having uniformly low carbonatite like 18o and 13c values a favoured mechanism for the low 18o and 13c values of the marbles is infiltration by fluids that were derived from or equilibrated with a magmatic source it is likely that this fluid rock interaction occurred prior to high grade metamorphism other fluid rock histories are not however ruled out by the available data coupled trends of 13c and 18o depletion are modified to even lower values by the superposed development of small scale metasomatic reaction zones between marbles and internally folded mafic interlayers the timing of development of these layers is uncertain but may be related to archaean high temperature 1000dc granulite facies metamorphism