petrology and geochemistry of potassic and ultrapotassic volcanism in central italy petrogenesis and inferences on the evolution of the mantle sources major trace element sr isotopic and mineral chemical data are reported for mafic volcanic rocks mg value 65 from the northern central sector of the potassic volcanic belt of central italy the rocks investigated range from potassic series ks and high k series hks to lamproitic lmp and kamafugitic kam through a transitional series trans thus covering the entire compositional spectrum of potassic and ultrapotassic magmas kam rocks are strongly silica undersaturated and compared with the other rock series have low sio2 al2o3 na2o sc and v and high cao k na na k al ks and hks have high al2o3 cao and variable enrichment in k2o and incompatible elements lmp rocks are saturated in silica and have high sio2 k2o k2o na2 mgo ni and cr and low al2o3 cao na2o sc and v trans rocks display intermediate compositional characteristics between lmp and ks all the rocks under study have fractionated hygromagmaphile element patterns with high lil hfs element values and negative anomalies of ti ta nb and ba negative sr anomalies are observed in the lmp and trans rocks lil elements show overall positive correlations with k2o whereas different trends of sr and hfse vs k2o are defined by lmp trans and ks hks kam 87sr 86sr range from about 0 710 to 0 716 ks hks and kam rocks have similar 87sr 86sr values clustering around 0 710 lmp and trans rocks have the highest 87sr 86sr values geochemical and isotopic data reported for the most primitive italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of italian potassic magmatism simple mass balance calculations exclude however an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of central italy volcanics underwent contamination with fluids and or melts released by upper crustal material previously brought into the mantle by subduction processes different trends of incompatible elements vs k2o observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of lmp rocks fluids or melts rich in ca sr and with high lile hfse value and sr isotopic composition around 0 710 are the most likely contaminant of the source region of ks hks and kam volcanics variations in cao na2o and ferromagnesian element abundances and ratios suggest that in some zones the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism

potassic dyke swarm in the sapucai graben eastern paraguay petrographical mineralogical and geochemical outlines abstract the western side of the parana basin of brazil extends to central paraguay where repeated and widespread magmatic activity developed from lower cretaceous to oligocene associated with late mesozoic crustal extension trending ne sw in central paraguay this trend is characterized by a zone of nw se normal faults which formed the asuncion sapucai graben up to 45 km wide and 200 km long where alkaline rocks occur as volcanic domes complexes lava flows and dykes these rocks 128 ma aged are dominantly potassic and ne normative a swarm of at least 200 mainley nw se trending dykes occurs in the sapucai region and seems to be formed by two main lineages tephrite to phonolite and peralkaline phonolite and alkali basalt to trachyphonolite they are characterized by ubiquitous diopside to ferrosalite consistently yielding al enrichment trends common olivine fo 81 69 in tephrites and alkaline basalts and up to fo 65 in phonolites zoned megacrysts of hastingsitic hornblende core to kaersutite rim associated with accessory groundmass pargasite in tephrites and phonotephrites k rich hastingsite and k rich ferroan pargasite in the phonolites accessory groundmass mica falls in the annite phlogopite range and consistently yields insufficient si al to satisfy the expected t site occupancy of 8 00 a f u fe ti oxides are ti magnetite rarely ilmenite or haematite phenocrystal i e xenocrystal plagioclase is an 70 20 and an 74 42 in the tephrites and phonolites respectively coexisting groundmass microlites are an 22 14 associated with sodasanidine and sanidine feldspathoids include analcimized leucite and nepheline accessories ti andradite and sphene the two main lineages recognized by distinctive mineralogical variations are consistent with the petrochemical variations complex interaction of discrete and independently evolving magma batches are indicated by intra and or interphase chemical variations suggesting multiple equilibrations of the crystallizing phases under shallow level volcanic pressure regime the observed geochemical trends are quite similar to those of roman region type magma with the same negative anomalies of ta nb zr and ti the most likely mantle source is a garnet peridotite characterized by different enrichment in incompatible elements and which suffered low degree of partial melting 3 7 which has geochemical and isotopic features distinct from those of the adjoining tholeiitic basalts 130 ma and nephelinites 61 39 ma the similarities of the sapucai dyke suite with barton s roman region type magma supports the view that this magma type may not be formed as a result of orogenic and or subduction driven activity in this region therefore a causal relationship of the latter activity with roman region type magma is not supported and remains questionable

laboratory model of a planetary eastward jet the concentration of eastward planetary currents into strong wavy jets is a major feature of the atmospheric general circulation for example the jet stream and of oceanic currents for example the gulf stream east of cape hatteras these strongly nonlinear jets are however not well understood here we describe experiments in which we have produced similar jets in a rotating annulus with mechanical forcing the coriolis force acting on fluid pumped radially inward from a ring of sources to a ring of sinks results in a strong eastward jet for a wide range of parameters the jet has a robust wavy shape as shown in fig 1 the wave velocity and wavelength of these rossby waves are accounted for by simple scaling arguments experiments with dye injected into the fluid show that the jet acts as a barrier to tracer transport see fig 1e much as the southern polar night jet may act as a barrier to the transport of ozone from lower latitudes into the polar region1 our observations are insensitive to the details of the arrangement of the sinks and sources

pressure transients within mcs mesohighs and wake lows by animating enhanced coarse surface pressure observations of 12 1985 preliminary regional experiment for storm scale operational research meteorology pre storm mesoscale convective systems mcss the authors exposed 92 transitory highs and lows living within virtually all of the systems mesohighs and wake lows a quasi lagrangian feature following not material following analysis of the pressure fields produced five primary results first these transients with magnitudes of a few millibars horizontal dimensions of order 100 km and average lifetimes of about 2 h collectively composed spatial and temporal envelopes that contributed at least part of the total pressure field within mesohighs and wake lows transients did not apparently favor formation or dissipation in any location of the envelopes second as the mcss matured the difference between each complex s transitory highs mean pressure and transitory lows mean pressure increased in 78 of the conclusive cases apparently one frequent role of mcss is locally to magnify storm scale pressure gradients third transient paths reflect the frequent symmetric to asymmetric metamorphoses of the mcss fourth the temporal fluctuations of the numbers and apparent sizes of transients within a composite mcs partially support theories of mcs upscale evolution finally the composite s transient numbers and apparent sizes varied almost identically with time in a pattern that closely resembles the fluctuation of stratiform and convective volumetric rain rates of mcss

petrology and isotope geochemistry of san vincenzo rhyolites tuscany italy two groups of rhyolites have been recognized at san vincenzo tuscany italy group a rhyolites are characterized by plagioclase quartz biotite sanidine and cordierite mineral assemblages they show constant mgo and variable cao and na2o contents initial87sr 86sr ratios in group a samples range between 0 71950 and 0 72535 whereas the nd isotopic compositions are relatively constant 0 51215 0 51222 group b rhyolites are characterized by orthopyroxene and clinopyroxene as additional minerals and show textural mineralogical and chemical evidence of interaction with more mafic magmas the sr and nd isotopic ratios range between 0 71283 0 71542 and 0 51224 0 51227 respectively magmatic inclusions of variable size 1 mm to 10 cm were found in groups b rhyolites these inclusions consist mainly of diopsidic clinopyroxene and minor olivine and biotite they are latitic in composition and represent blobs of hybrid intermediate magmas entrained in the rhyolitic melts these magmatic inclusions have relatively high sr contents 996 1529 ppm and sr and nd isotope ratios of 0 70807 0 70830 and 0 51245 0 51252 respectively 87sr 87sr data on minerals separated from both group a and b rhyolites and magmatic inclusions reveal strong isotopic disequilibria due to the presence of both restitic and newly crystallized phases in group a rhyolites and due to interaction of rhyolites with a mantle de rived magma in group b rhyolites isotopic data on whole rocks and minerals allow us to interpret the group a rhyolites as representative of different degrees of melting of an isotopically fairly homogeneous pelitic source conversely group b rhyolites underwent interactions with a mantle derived magma the crustal source as inferred from isotopic systematics would be characterized by87sr 86sr and143nd 144nd ratios close to 0 7194 and 0 51216 respectively the sub crustal magma would have sr isotopic composition close to 0 7077 and a143nd 144nd ratio greater than or equal to 0 51252 these isotopic features are different from those reported for the parental magmas postulated for vulsini and alban hills in the nearby roman magmatic province and are similar to those of the vesuvius and ischia magmas

the geochemistry of potassic lavas from vulsini central italy and implications for mantle enrichment processes beneath the roman region major and trace element and 143nd 144nd 0 51209 0 51216 and 87sr 86sr 0 70879 0 71105 isotope analyses are presented on a representative group of lavas from the vulsini district of the roman magmatic province three distinct series are identified the high k and low k series are similar to those described from other italian volcanoes while the third is represented by a group of relative ly undifferentiated leucite basanites which are thought to be near primary mantle melts major and trace element variations within the high k series are consistent with fractional crystallisation from a parental magma similar to the most magnesian leucitites crustal contamination resulted in an increase in 87sr 86sr with increasing fractionation but it was superimposed on magmas which had already inherited a range of incompatible element and isotope ratios from enrichment processes in the sub continental mantle these are reviewed using the available results from vulsini roccamonfina and ernici transition element abundances and ta yb ratios indicate that the pre enrichment mantle was similar to that of e type morb and that these elements were not mobilised by the enrichment process mixing calculations suggest that three components were involved in the enrichment process mantle comparable with the source of morb and two other components rich in trace elements one the low k component had high sr nd th ta and ba nb and no europium anomaly while the second had lower sr nd a negative europium anomaly and very high th ta it was also characterised by low nb ba and high rb ba ratios similar to those reported from phlogopite rich peridotite xenoliths the trace element enrichment processes are therefore thought to have occurred in the mantle wedge above a subduction zone with the trace element characteristics of the high k end member reflecting the subduction of sediments and the stabilisation of mantle phlogopite

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

homogenization of potential vorticity in planetary gyres the mean circulation of planetary fluids tends to develop uniform potential vorticity q in regions where closed time mean streamlines or closed isolines of mean potential vorticity exist this state is established in statistically steady flows by geostrophic turbulence or by wave induced potential vorticity flux at the outer edge of the closed contours the expelled gradients of q are concentrated beyond this transition lies motionless fluid or a different flow regime in which the planetary gradient of q may be dominant the homogenized regions occur where direct forcing by external stress or heating within the closed isoline is negligible upon the potential density surface under consideration in the stably stratified ocean such regions are found at depths greater than those of direct wind induced stress or penetrative cooling in channel models of the atmosphere we again find constant q when mesoscale eddies cause the dominant potential vorticity flux in the real atmosphere the results here can apply only where internal heating is negligible the derivations given here build upon the prandtl batchelor theorem which applies to non rotating steady two dimensional flow supporting evidence is found in numerical circulation models and oceanic observations

u pb ages sr nd isotope geochemistry and petrogenesis of kimberlites kamafugites and phlogopite picrites of the alto paranaiba igneous province brazil abstract the kimberlites kamafugites and phlogopite picrites of alto paranaiba igneous province apip southern brazil span a range between 91 and 78 ma with new in situ more tightly constrained u pb ages the kimberlites show porphyritic texture with olivine xeno and phenocrysts plus phlogopite fe ti cr oxides and perovskite microcrysts set in a carbonate rich matrix the kamafugites are feldspar free rocks represented by ugandites and mafurites ugandites and mafurites are porphyritic and contain olivine and clinopyroxene phenocrysts in a fine grained groundmass composed by clinopyroxene perovskite apatite magnetite phlogopite leucite and or analcime in ugandites and by olivine clinopyroxene amphibole phlogopite perovskite magnetite kalsilite and ba zeolites in mafurites phlogopite picrites have a pseudo fluidal porphyritic texture with olivine phenocrysts and abundant phlogopite microcrysts in a groundmass composed by olivine spinel apatite perovskite calcite and rare garnet new in situ sr and nd isotopic data on perovskites 87 sr 86 sr i 0 70467 0 70565 and 143 nd 144 nd i 0 51222 0 51233 fall within the known ranges of apip rocks 87 sr 86 sr i 0 70431 0 70686 143 nd 144 nd i 0 51205 0 51280 the apip magmas derived from a source assemblage made up of an old metasomatized mica carbonate garnet lherzolite that did not suffer interaction with convective mantle nor with any hypothetical melts derived from a trindade mantle plume geochemical modelling show that low degree melting f 0 5 2 of such a source can produce compositions resembling the apip rocks the geochemical and isotopic composition of the magmas the calculated degrees of partial melting the composition of the calculated source and the absence of a hot spot track from goias to alto paranaiba igneous provinces can be explained with the presence of chemically and mineralogically heterogeneous mantle sources that melted at different pressures

observations of zonal flow created by potential vorticity mixing in a rotating fluid received 3 may 2002 revised 17 july 2002 accepted 18 july 2002 published 24 september 2002 1 we present an experimental and numerical study of a rotating fluid with a zonal flow produced from small scale eddies a common feature of many planetary systems the apparatus consists of a water filled annular tank with a sloped bottom flow is forced mechanically at small nonaxisymmetric scales potential vorticity is materially conserved and well mixed this implies the existence of nonzero axisymmetric vorticity and therefore of zonal flow which has three zones in this case the strength of zonal flow has an upper bound imposed by complete depletion of the beta plane potential vorticity reservoir index terms 5707 planetology fluid planets atmospheres structure and dynamics 5734 planetology fluid planets magnetic fields and magnetism 5744 planetology fluid planets orbital and rotational dynamics citation aubert j s jung and h l swinney observations of zonal flow created by potential vorticity mixing in a rotating fluid geophys res lett 29 18 1876 doi 10 1029 2002gl015422 2002

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

a numerical study of the along line variability of a frontal squall line during pre storm despite considerable progress in the understanding of two dimensional structures of squall lines little attention has been paid to the along line variability of these convective systems in this study the roles of meso and larger scale circulations in the generation of along line variability of squall lines are investigated using an 18 h prediction of a frontal squall line that occurred on 26 27 june 1985 during pre storm preliminary regional experiment for stormscale operational research meteorology it is shown that the canadian regional finiteelement rfe model reproduces reasonably well a number of surface and vertical circulation structures of the squall system as verified against available network observations these include the initiation propagation and dissipation of the squall system surface pressure perturbations and cold outflow boundaries a midlevel mesolow and an upper level mesohigh a front to rear ftr ascending flow overlying an intense rear to front rtf flow and a leading convective line followed by stratiform precipitation regions it is found that across line circulations at the northern segment of the squall line differ significantly from those at its southern segment including the different types of precipitation the absence of the rtf flow and midlevel mesolow and the early dissipation of organized convection in the northern part the along line variability of the squall s circulations results primarily from the interaction of convectively generated perturbations with a midlevel baroclinic trough the large scale trough provides an extensive rtf flow component in the southern portion of the squall system and an ftr flow component in the north whereas the midlevel mesolow tends to enhance the rtf flow to the south and the ftr flow to the north of the mesolow during the mature to decaying stages the along line variability of the squall s circulations appears to be partly responsible for the generation of different weather conditions along the line such as the development of an upper level stratiform region in the southern segment and a midlevel cloud region in the northern portion of the squall line

crystal chemistry of trioctahedral micas in the top sequences of the colli albani volcano roman region central italy abstract trioctahedral mica crystals are frequently found in the volcanoclastic products emplaced during the final stages of the activity of the colli albani volcano roman region central italy in the youngest phreatomagmatic deposits mica is found either as a minor mineral phase in holocrystalline ejecta scoriae and coherent pyroclastics or as loose phenocryst in incoherent pyroclastics based on optical and electron microscope investigations as well as crystal chemical and structural data the micas selected for this study were divided into two groups the first one encompassing brownish fe rich crystals type a phlogopites hereafter referred as t a with 0 68 from a petrological point of view the textural and chemical variations of t a phlogopites are compatible with fractional crystallization processes taking place within the magma chamber t b phlogopites show evidence of a ti oxy substitution mechanism thus suggesting high fo2 conditions textural and paragenetic features observed in t b phlogopite bearing rock samples indicate a genesis by thermal metamorphism of a siliceous dolomitic limestone with the input of a variable amount of a potassic magma possibly the same from which the t a phlogopites formed with the exception of one sample for which a different parental magma is suggested indeed there is an almost continuous spectrum of crystal chemical and structural parameters starting from t b and evolving towards t a phlogopites the t a phlogopites displays complex apparently meaningless relationships in their crystal chemical parameters thus indicating interplay of several substitution mechanisms they possibly formed in polybaric conditions since their cell volumes differ but the total size of the cations hosted in the octahedral sheet is the same

dolomite calcite textures in early carbonatites of the kovdor ore deposit kola peninsula russia their genesis and application for calcite dolomite geothermometry in early calcite carbonatites of the kovdor ore deposit four morphological types of dolomite are represented in the first type dolomite microcrystals occur as lamellae enclosed by optically continuous calcite in the second dolomite microcrystals occur as segmented rods plates and xenomorphic grains enclosed by optically discontinuous calcite and in the third dolomite is represented by grains of various morphologies situated along calcite grain boundaries the fourth type of dolomite occurs as a fine grained aggregate which develops along grain boundaries and cleavage cracks of calcite from microscopic scanning electron microscope and microprobe studies of these different types of dolomite microcrystals as well as the calcite associated with them it can be concluded that the first type of dolomite was exsolved from magnesian calcite during cooling the second and the third types of dolomite microcrystals were formed by recrystallization the fourth type of dolomite was formed by metasomatic dolomitization as the result of these two processes recrystallization and metasomatic dolomitization early dolomite microcrystals seldom occur the composition of the early formed primary magnesian calcite yielded temperatures of exsolution of dolomite from magnesian calcite between 665 and 700 c

geochemistry and geodynamic implications on the source of parana etendeka large igneous province evidenced by the 128 ma rosario 6 kimberlite southern brazil abstract the rosario 6 is a non diamondiferous hypabyssal kimberlite located above the rio de la plata craton and near the south eastern edge of the parana basin in southern brazil it is petrographically an inequigranular texture macrocrystal kimberlite fresh and the groundmass exhibits a microporphyritic texture and round megacrysts of olivine which are derived from disaggregated mantle xenoliths olivine is also present as macrocrysts microphenocrysts and in the groundmass together with phlogopite and apatite these microphenocrysts are immersed in a groundmass of olivine monticellite phlogopite catio3 perovskite apatite mg chromite and mg ulvospinel and melilite a mesostasis assemblage of phlogopite melilite soda melilite akermanite and calcium carbonate is segregated from the groundmass its geochemical signature is similar to those of transitional kimberlites of kaapvaal craton south africa and the u pb ages of 128 ma on perovskite reveal that rosario 6 kimberlite post dates the main pulse of volcanism in the parana etendeka large igneous province lip the high ti content of some minerals such as mg chromite mg ulvospinel phlogopite and melilite and the presence of perovskite suggest a ti rich source the petrographic geochemical and isotopic data indicate that the rosario 6 kimberlite source is a depleted mantle metasomatized by h2o rich fluids co2 rich and silicate melts derived from the recycling of an ancient subducted oceanic plate eclogite before the south atlantic opening although several authors indicate the influence of tristan da cunha plume for the generation of alkaline magmatism associated to the parana etendeka flood basalts our data demonstrates that tristan da cunha plume has no chemical contribution to the generation of rosario 6 kimberlite except by its thermal influence

bebedourite from its type area salitre i complex a key petrogenetic series in the late cretaceous alto paranaiba kamafugite carbonatite phoscorite association central brazil abstract bebedourite is a cumulate rock composed of variable but roughly equant amounts of diopside apatite magnetite phlogopite and a ca ti phase mostly perovskite more rarely titanite and or ti garnet other minerals may be modally important such as olivine and k feldspar in the least and most evolved members of the bebedourite series respectively the magmatic evolution in bebedourites is accompanied by a progressive increase in sio2 activity which results in the transformation of perovskite into titanite and titanite into ti garnet although the sio2 increase may in some cases result from crustal contamination it seems to be a localized effect and cannot account for the evolution of the whole bebedourite series crystal fractionation is supported by the chemical variation of key mineral phases such as pyroxene and phlogopite the salitre complex is an ultrapotassic carbonatite and phoscorite bearing plutonic complex belonging to the late cretaceous alto paranaiba igneous province apip and consisting of three main bodies salitre i ii and iii the complex is composed mainly of bebedourite with lesser amounts of carbonatite and phoscorite in its central north portion a particular type of bebedourite where the main ca ti phase is ti garnet dominates the southern part of salitre i and also occurs as dikes crosscutting older bebedourites suggesting that ti garnet bebedourites form an independent intrusion sr and nd isotopic data indicate that the parental magmas to the bebedourites in the salitre complex originated in a metasomatized sub continental lithospheric mantle similar to that involved in the origin of the rest of the apip

alkaline rocks from continental brazil abstract the present literature review on brazilian alkaline rocks stresses mainly the petrographic and geologic aspects at least eight different rock associations are represented agewise four groups are found among southern brazilian outcrops an older one about 240 m y only that is still poorly known the massifs clustered around jacupiranga about 130 m y old a few occurrences 100 110 m y old tunas itapirapua and the youngest and most important one with an age spread from about 80 m y to about 53 m y recent research shows a clear tectonic control both on local and on regional scales of alkaline occurrences in southern brazil alkaline magmatism was set off by pre drift and drift activity and is at its onset geologically related to basaltic activity emplacement of many massifs is also locally controlled by old lineaments e g in the minas gerais goias belt as is emphasized by geophysical data on a petrographic and chronologic basis several alkaline provinces are distinguished in southern brazil preliminary data on the cambrian precambrian rocks from southern bahia state a province with undersaturated syenites and litchfieldites and from cratonic areas in northern brazil are also presented

the catalao i niobium deposit central brazil resources geology and pyrochlore chemistry abstract the catalao i alkaline carbonatite phoscorite complex contains both fresh rock and residual weathering related niobium mineralization the fresh rock niobium deposit consists of two plug shaped orebodies named mine ii and east area respectively emplaced in carbonatite and phlogopitite together these orebodies contain 29 mt at 1 22 wt nb2o5 measured and indicated in closer detail the orebodies consist of dike swarms of pyrochlore bearing olivine free phoscorite series rocks nelsonite that can be either apatite rich p2 unit or magnetite rich p3 unit dolomite carbonatite dc is intimately related with nelsonite natropyrochlore and calciopyrochlore are the most abundant niobium phases in the fresh rock deposit pyrochlore supergroup chemistry shows a compositional trend from ca na dominant pyrochlores toward ba enriched kenopyrochlore in fresh rock and the dominance of ba rich kenopyrochlore in the residual deposit carbonates associated with ba sr enriched pyrochlore show higher 18osmow than expected for carbonates crystallizing from mantle derived magmas we interpret both the 18osmow and pyrochlore chemistry variations from the original composition as evidence of interaction with low temperature fluids which albeit not responsible for the mineralization modified its magmatic isotopic features the origin of the catalao i niobium deposit is related to carbonatite magmatism but the process that generated such niobium rich rocks is still undetermined and might be related to crystal accumulation and or emplacement of a phosphate iron oxide magma

incorporating diagnosed intercept parameters and the graupel category within the arps cloud analysis system for the initialization of double moment microphysics testing with a squall line over south china abstractin this study a new set of reflectivity equations are introduced into the advanced regional prediction system arps cloud analysis system this set of equations incorporates double moment microphysics information in the analysis by adopting a set of diagnostic relationships between the intercept parameters and the corresponding mass mixing ratios a reflectivity and temperature based graupel classification scheme is also implemented according to a hydrometeor identification hid diagram a squall line that occurred on 23 april 2007 over southern china containing a pronounced trailing stratiform precipitation region is used as a test case to evaluate the impacts of the enhanced cloud analysis scheme the results show that using the enhanced cloud analysis scheme is able to better capture the characteristics of the squall line in the forecast the predicted squall line exhibits a wider stratiform region and a more clearly defined transition zone between the leading convection and the trailing str

the dynamics of circulations within the trailing stratiform regions of squall lines part i the 10 11 june pre storm system abstract a dynamic version of the two dimensional kinematic cloud model of rutledge and houze has been developed to investigate the effects of microphysics on circulations within the stratiform regions of mesoscale convective systems the design of the model allows for specified inputs of hydrometeors water vapor and heat from the convective line the stratiform region of the 10 11 june 1985 pre storm squall line is simulated with initialization based upon appropriate soundings heat budgets and id cumulonimbus model results the model accurately simulates the evolution of the stratiform rain area significant ascent occurs in the stratiform region where in situ condensate production contributes increasingly to the surface rainfall reaching 65 of the total in the mature stage and averaging 44 over the entire simulation the ratio of condensate produced within the mesoscale updraft to that advected from the convective line generally agrees with water budgets from other studies simulated horizontal

contemporaneous alkaline and tholeiitic magmatism in the ponta grossa arch parana etendeka magmatic province constraints from u pb zircon baddeleyite and 40ar 39ar phlogopite dating of the jose fernandes gabbro and mafic dykes abstract we report the first high precision id tims u pb baddeleyite zircon and 40ar 39ar step heating phlogopite age data for diabase and lamprophyre dykes and a mafic intrusion jose fernandes gabbro located within the ponta grossa arch brazil in order to constrain the temporal evolution between early cretaceous tholeiitic and alkaline magmatism of the parana etendeka magmatic province u pb dates from chemically abraded zircon data yielded the best estimate for the emplacement ages of a high ti p sr basaltic dyke 133 9 0 2 ma a dyke with basaltic andesite composition 133 4 0 2 ma and the jose fernandes gabbro 134 5 0 1 ma a 40ar 39ar phlogopite step heating age of 133 7 0 1 ma from a lamprophyre dyke is identical within error to the u pb age of the diabase dykes indicating that tholeiitic and alkaline magmatism were coeval in the ponta grossa arch although nearly all analysed fractions are concordant and show low analytical uncertainties 0 3 0 9 ma for baddeleyite 0 1 0 4 ma for zircon 2 pb loss is observed in all baddeleyite fractions and in some initial zircon fractions not submitted to the most extreme chemical abrasion treatment the resulting age spread may reflect intense and continued magmatic activity in the ponta grossa arch

petrological characterization of the mantle source of mediterranean lamproites indications from major and trace elements of phlogopite lamproites are among the most enigmatic mantle generated melts and are typically abundant in phlogopite we investigated the major and trace element chemistry of phlogopite crystals from mediterranean lamproite occurrences in spain serbia and turkey the most primitive lamproite samples were selected in order to evaluate the generation of the different phlogopite populations in their distinct mantle setting s phlogopite hosted in mediterranean lamproites can be grouped into different compositional arrays on the basis of their major element chemistry using al2o3 feot and tio2 concentrations contents of cr f and presumably ti allow discrimination of the macrocrysts into phlogopite phenocrysts which are liquidus and near liquidus phases and mantle xenocrysts further distinction among different populations of mantle derived phlogopite can be achieved considering trace element and isotopic ratios the latter also distinguish between crustal and asthenospheric imprints on the source of the lamproitic parental melt

major and trace element compositional variation of phlogopite from kimberlites and carbonatites as a petrogenetic indicator abstract ferromagnesian trioctahedral micas are a common macrocryst phenocryst phase in kimberlites and carbonatites we explored the possibility of using the chemistry of ferromagnesian micas to discriminate between these rocks in order to assess their economic potential we determined the extent of major and trace element variations of micas from 14 selected kimberlite and carbonatite localities worldwide representing several different kimberlite fields and alkaline carbonatite provinces phlogopite macrocrysts from kimberlites follow two principal evolutionary trends primary macrocrystic involving an increase in ba al ti cr zr nb and sr contents at decreasing mg towards the rim and transitional macrocryst groundmass trend involving an increase in kinoshitalite component at decreasing fe ti and cr contents micas from dolomite calcite carbonatites cover a much greater compositional range than those from kimberlites defining evolutionary trends towards annite tetra ferriphlogopite and kinoshitalite our data confirm that macrocrystic micas from kimberlites cannot be reliably distinguished from carbonatitic phlogopite on the basis of their major element compositions exceptions are fe al rich fe fe mg 0 2 and na rich 0 3 wt na 2 o micas that seem to be virtually restricted to carbonatites the generally higher levels of na in carbonatitic micas relative to those from kimberlites can be explained by the lower na abundances in the latter relative to carbonatites our data indicate that the trace element composition of mica determined by la icp ms can be used as a reliable petrogenetic indicator kimberlitic phlogopite is characteristically enriched in cr up to 12030 ppm ni up to 1600 ppm and co 40 70 ppm and depleted in mn 280 ppm nb 28 ppm sr 55 ppm sc 8 ppm zr 12 ppm and to some extent cs 7 ppm and ta 3 ppm with respect to carbonatitic micas 315 ppm cr 470 ppm ni 34 ppm co up to 17200 ppm mn 1080 ppm nb 830 ppm sr 80 ppm sc 105 ppm zr 27 ppm cs and 19 ppm ta with the exception of zr the observed differences in trace element composition of mica probably reflect the contrasting trace element geochemistry of kimberlitic and carbonatitic magmas the depletion of kimberlitic phlogopite in zr and possibly nb ta can be explained by sequestration of these elements in the earlier crystallized ilmenite variations in ba rb and v contents are similar in mica from both rock types and cannot be used as a petrogenetic indicator

titanium aluminum and interlayer cation substitutions in biotite from high grade gneisses west greenland detailed electron microprobe study pelitic to mafic metamorphic rocks from two localities higher ti k k na and possible k na similar al iv and lower al vi in granulite vs amphibolite grade samples modified journal abstract

the brazilian mineral resources abstract the activity of the first generation of brazilian geologists began in the early sixties systematic exploration work since then has evidenced some important new mineral reserves in brazil the most important examples are the 18 10 9 tons of high grade iron ore carajas district formed by supergene enrichment on iron formations older than 1800 m y the 2 5 10 9 tons of bauxite and similar reserves of kaolinite as residual enrichment in cenozoic sediments in the amazonas basin oriximina capim the potash and magnesium rich evaporites near aracaju sergipe the large residual concentrations of phosphate anatase pyrochlore and rare earths related to cretaceous alkaline complexes with carbonatites and some garnierite and asbestos deposits related to ultramafic rocks in the states of goias and piaui

crystal chemistry and petrologic significance of fe3 rich phlogopite from the tapira carbonatite complex brazil this contribution deals with the crystal chemistry of phlogopite and fe3 rich phlogopite from the tapira alkaline carbonatite complex brazil to assess the petrological significance and genetic conditions of these rocks the tapira complex consists of a layered intrusion composed mainly of ultramafic rocks dunite wehrlite clinopyroxenite bebedourite garnet magnetitite perovskite magnetitite and glimmerite with subordinate carbonatite the wide range of textural optical and crystal chemical characteristics of ph logopite is related to the variation of 102 ah20 and ac02as well as magma bulk chemical composition during fractional crystallization phlogopite from alkaline silicate rocks ranging from dunite to bebedourite is characterized by fairly constant al content moderate 4 fe3 substitution and variable amounts of ti the 4 fe3 substitution accompanied by crystals showing reverse pleochroism increases during fractional crystallization these features correspond to crystallization at low pressure and high 102 and ah20 in the presence of moderate saturation in ti bearing phases al203 in the magma or both phlogopite from silicate carbonatite rocks classified as ferriphlogopite on the basis of strong reverse pleochroism related to 4 fe3 tetrahedral substitution also presents low to very low ai fe2 and ti contents these features suggest very high 102 h20 and c02 conditions in the presence of strong saturation in ti bearing phases as well as very low al203 content in the liquid the crystal structure refinements of tapira phlogopite show that fe3 substitutes for si in tetrahedral sites fe distribution is completely disordered so the resulting space group is c21m the octahedral site composition is similar to that of phlogopite the octahedral sites being preferentially occupied by mg the presence of fe3 in the tetrahedral sheet enlarges the whole structure this enlargement is reflected by an increase in cell edge lengths and a decrease in b angle values the increase in distortion of the tetrahedral ring a angle up to 11 is necessary for the tetrahedral and octahedral sheets to fit together

stable isotope composition of minerals in the belaya zima plutonic complex russia implications for the sources of the parental magma and metasomatizing fluids abstract the belaya zima alkaline carbonatite complex in the east sayan mountains russia is a multiphase concentric intrusion which comprises diverse alkaline silicate rocks and carbonatites melteigites are the earliest products of crystallization and they are followed by ijolites urtites nepheline syenites and finally calcite calcite dolomite and ankerite carbonatites in this paper we present new geochronological data ar ar method chemical and stable isotope h c and o compositions of the main rock forming minerals in carbonatites and the silicate rocks of the complex the ar ar dating of phlogopite from ankerite carbonatites is consistent with the age of syenite emplacement and implies that the silicate rocks and carbonatites are likely to be comagmatic the evolutionary trends of pyroxene fluorapatite amphibole and phlogopite are consistent with fractional crystallization from a single parental magma primary nb mineralization is represented by pyrochlore whereas columbite fe is a replacement product of pyrochlore at the post magmatic hydrothermal stage at that stage interaction of calcite carbonatites with hydrothermal fluids resulted in the formation of hydrothermal paragenesis comprising dolomite ankerite monazite ce ancylite ce minerals of burbankite group and ca ree fluorcarbonates the hydrothermal processes were also responsible for cation leaching from pyrochlore the replacements of phlogopite by tetraferriphlogopite and early ca rich pyroxene by aegirine the stable isotope data suggest that the rocks crystallized from a 18o depleted magma shifts toward higher 18o values relative to the primary compositions are commonly observed in minerals from carbonatites which is attributed to hydrothermal processes

compositional variations major and trace elements of clinopyroxene and ti andradite from pyroxenite ijolite and nepheline syenite alno island sweden compositional variations major and trace elements of clinopyroxene and ti andradite from pyroxenite ijolite and nepheline syenite alno island sweden

phlogopite and tetra ferriphlogopite from brazilian carbonatite complexes petrogenetic constraints and implications for mineral chemistry systematics abstract the results of a mineral chemistry study of phlogopite and tetra ferriphlogopite in carbonatites and associated alkaline silicate rocks from the brazilian carbonatite complexes of jacupiranga tapira and catalao are presented a wide textural variety of mica is found ranging from primary magmatic crystals to late stage metasomatic phases primary micas from the carbonatites and from the associated plutonic silicate rocks follow distinct evolution paths with magma differentiation in all three complexes micas from the silicate rocks evolve from phlogopite towards annite although in jacupiranga they are more al rich among the micas crystallising from carbonatite liquids those from jacupiranga are typically al and mg rich while in tapira and catalao they are extremely al poor metasomatic micas bridge the gap between primary micas from silicate rocks and from carbonatites the complete phlogopite tetra ferriphlogopite series is reported from the catalao and tapira complexes this study shows that micas from carbonatite complexes may span a wide compositional range largely overlapping the fields of micas from several types of alkaline ultrapotassic rocks especially regarding ti and al contents the use of phlogopite composition and evolution to discriminate between different types of alkaline rocks should be undertaken with caution

electrification of stratiform regions in mesoscale convective systems part ii two dimensional numerical model simulations of a symmetric mcs abstract model simulations of a symmetric mesoscale convective system mcs observations discussed in part i were conducted using a 2d time dependent numerical model with bulk microphysics a number of charging mechanisms were considered based on various laboratory studies the simulations suggest that noninductive ice ice charge transfer in the low liquid water content regime characteristic of mcs stratiform regions is sufficient to account for observed charge density magnitudes and as much as 70 of the total charge in the stratiform region the remaining 30 is contributed by charge advection from the convective region the strong role of in situ charging is consistent with previous water budget studies which indicate that roughly 70 of the stratiform precipitation results from condensation in the mesoscale updraft thus both in situ charging and charge advection the two previously identified hypotheses appear to be important contributors to the electrical budget of the stratiform region the

thermodynamic properties of mesoscale convective systems observed during bamex dropsonde observations from the bow echo and mesoscale convective vortex experiment bamex are used to document the spatiotemporal variability of temperature moisture and wind within mesoscale convective systems mcss onion type sounding structures are found throughout the stratiform region of mcss but the temperature and moisture variability is large composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the mcs the calculated air vertical velocity helped identify subsaturated downdrafts it was found that lapse rates within the cold pool varied markedly throughout the mcs layered wet bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions it was also found that lapse rate transitions across the 0 c level were more common than isothermal melting layers the authors discuss the implications these findings have and how they can be used to validate future high resolution numerical simulations of mcss

phoscorites of the salitre i complex origin and petrogenetic implications abstract the salitre i complex is a kidney shaped alkaline carbonatite phoscorite complex part of the late cretaceous alto paranaiba igneous province central brazil this complex is a key example where the phoscorite carbonatite association was preserved from metasomatism by late stage fluids and thus provides an opportunity to address the genesis of phoscorites salitre i is composed of two main coalescing intrusions a a northern one dominantly containing perovskite bebedourites b1 with swarms of ring dykes of carbonatites and phoscorites and b a southern one containing melanite bebedourites b2 salitre i phoscorites can be subdivided into p1 and p2 based on modal abundance mineral texture chemistry and mode of emplacement p1 phoscorites contain essential olivine phlogopite and apatite with accessory magnetite and traces of perovskite whereas p2 phoscorites are composed of the same essential phases but also contain carbonate rich pockets accessory pyrochlore and rare phlogopite carbonate c o isotopes and whole rock sr nd show that salitre i phoscorites crystallized from mantle derived parental magmas similar to other apip carbonatite complexes however chemical and textural discrepancies between p1 and p2 suggest derivation from different magma sources and through distinct processes for instance p1 al and ti rich phlogopite accessory perovskite and general trace element geochemical behaviour can be associated with the evolution of b1 perovskite bebedourites i e genesis through fractional crystallization from a bebedourite magma p2 phoscorites on the other hand have their evolution linked to a magmatic phase that underwent melt immiscibility as suggested by trace element fractionation additionally p2 contains pyrochlore which is generally lacking in bebedourites therefore whereas p1 phoscorites might have derived from a bebedourite magma p2 phoscorites were generated from a carbonated magma enriched in phosphate and iron oxides

mineralogical petrological and geochemical aspects of alkaline and alkaline carbonatite associations from brazil abstract a general description of mesozoic and tertiary fortaleza brazilian alkaline and alkaline carbonatite districts is presented with reference to mineralogy petrology geochemistry and geochronology it mainly refers to scientific results obtained during the last decade by an italo brazilian research team alkaline occurrences are distributed across brazilian territory from the southern piratini rio grande do sul state to the northeastern fortaleza ceara state regions and are mainly concentrated along the borders of the parana basin generally coinciding with important tectonic lineaments the most noteworthy characteristics of these alkaline and alkaline carbonatite suites are i prevalence of intrusive forms ii abundance of cumulate assemblages minor dunites frequent clinopyroxenites and members of the ijolite series and iii abundance of evolved rock types many data demonstrate that crystal fractionation was the main process responsible for magma evolution of all brazilian alkaline rocks a hypothesis is proposed for the genesis of carbonatite liquids by immiscibility processes the incidence of ree and trace elements for different major groups of lithotypes belonging both to carbonatite bearing and carbonatite free districts are documented sr and preliminary nd isotopic data are indicative of a mantle origin for the least evolved magmas of all the studied occurrences mantle source material and melting models for the generation of the brazilian alkaline magma types are also discussed

single crystal x ray studies of trioctahedral micas coexisting with dioctahedral micas in metamorphic sequences from western maine a crystal chemical study of thirteen biotite twelve of 1 m polytype and one of 2 m 1 polytype and four muscovite samples was made the biotite coexists with the muscovite samples are from metamorphic terranes and from granitic and granodioritic bodies occurring in three areas of western maine the metamorphic mineral zones identified by mineral compatibilities are in order of increasing metamorphic grade the lower sillimanite zone lsz the upper sillimanite zone usz and the k feldspar sillimanite zone k sz the muscovite compositions cluster near ideal muscovite and display a small celadonite substitution and a small but variable paragonite substitution the biotite composition has values of vimg2 vi mg2 fe2 ranging from 0 26 to 0 54 and significant octahedral al content 0 48 vial 0 72 apfu in metamorphic biotite samples 0 51 vial 0 67 in those from granites in trioctahedral micas from western maine and especially in those with graphite there are a greater number of interlayer vacancies than in common micas interlayer vacancies have an increase in interlayer cation basal oxygen atom distances and a decrease in tetrahedral flattening angle thus suggesting a reduced interlayer charge with a few exceptions tetrahedral rotation angle is related to crystallization temperature in particular decreases with a temperature increase and is also related to octahedral chemical substitutions results tentatively suggest for micas from metamorphic environments a direct influence of genetic parameters t and f o2 on mica crystal structure and not just chemical composition

a synthesis and new perspective on the petrogenesis of kamafugites from west qinling china in a global context we discuss the overall characteristics of a recently recognized kamafugite province in west qinling china using field observations and geochemical data we discuss the petrogenesis of the kamafugites using new bulk rock major and trace element data and sr nd isotope compositions of representative samples together with the literature data in chinese and comparing them with type kamafugite suites from italy brazil and uganda all these four kamafugite suites show oib like rare earth element ree patterns but are much more enriched than oib in the progressively more incompatible elements the west qinling kamafugite samples resemble closely the ugandan and brazilian suites in having a negative anomaly of k p and ti and a positive nb ta anomaly yet the italian suite shows conspicuously a negative nb ta anomaly the four kamafugite suites have different 8nd t values and 87sr 86sr1 ratios implying their distinct sources and source histories we consider that the ideal sources for kamafugite magmas are most likely metasomatized sub continental lithosphere with components of ancient seafloor subducted calcareous terrigenous sediments the close association of kamafugite with carbonatite worldwide including the west qinling suite is consistent with both being derived from a single co2 rich silicate parental magma segregated during ascent as a result of decompression induced immiscibility in terms of both sources or source histories and processes our simple interpretation can effectively explain the petrogenesis of all the apparently different kamafugite suites suggests that the petrogenesis of kamafugites may actually be simple further effort should aim to test whether our interpretation is indeed valid globally c 2013 elsevier ltd all rights reserved

substitution mechanisms and solubility of titanium in phlogopites from rocks of probable mantle origin previously proposed substitution mechanisms for ti in phlogopites based on experimental studies and crystal chemistry have been examined using data for 81 phlogopites from mantle derived rocks primarily as nodules in kimberlites and also from alkali basalts lamprophyres and carbonatites 49 phlogopites from high k rocks with basaltic affinities and from 32 phlogopites crystallized in high pressure experiments mainly on high k rock compositions for the majority of phlogopites from the kimberlite group and for all those crystallized in the experimental studies the substitution of ti can be represented by a combination of the mechanisms represented by 2mg vi ti vi vi and mg vi 2si iv ti vi 2al iv some phlogopites in ultrapotassic rocks have only the former substitution mechanism the ti contents of phlogopites generally increase with decreasing octahedral site occupancy and decreasing si al vi for the phlogopites crystallized in the experiments on high k rocks the solubility of ti increases with increasing fo2 and temperature and possibly with decreasing pressure at constant fo2 the effect of the composition of the liquids used in the experimental studies from which these phlogopites have crystallized has only minor effect on either the substitution mechanism or the solubility of ti in phlogopites this suggests that phlogopite in high k rocks may be a potential geothermometer and possibly a geobarometer