identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

brittle frictional mountain building 2 thermal structure and heat budget this paper describes a simple thermal model of an actively deforming critically tapered fold and thrust belt the model determines the steady state temperature distribution and heat flow as well as the pressure temperature time histories of rocks that outcrop at the surface the main parameters controlling the thermal structure are the accretion and erosion rates the undisturbed geothermal gradient at the toe and the amount of frictional heating both shear heating on the decollement fault and internal strain heating within the deforming brittle wedge are incorporated in a mechanically consistent manner and they dominate the effect of radiogenic heating except in fold and thrust belts with significantly overpressured pore fluids the mean stresses temperatures and surface heat flow all increase with an increase in the basal and internal coefficients of friction and this dependence is used to constrain the level of friction on the decollement fault beneath the steady state fold and thrust belt in taiwan rocks outcropping in the core of the central mountain range of taiwan experience maximum theoretical temperatures in excess of 400 c and maximum mean pressures in excess of 500 mpa if the coefficient of basal friction is b 0 5 qualitatively these conditions are in good agreement with the observed high greenschist facies metamorphism the theoretical surface heat flow which increases from 95 mw m2 at the front of the fold and thrust belt to 240 mw m2 at the rear is in excellent agreement with the results of a recent geothermal survey of taiwan and theoretical cooling histories are in good agreement with fission track and other geochronologic studies taken together these results provide strong evidence that sliding on the basal decollement fault beneath taiwan is governed by a coefficient of friction in the range of typical laboratory measurements b 0 5 0 2 approximately 35 of the total surface heat flux of 3 gw is heat conducted into the base of the wedge from the top of the basal decollement fault and somewhat more than 30 is heat advected into the toe by accretion the remaining heat is generated internally about 25 by internal strain heating and about 10 by radiogenic heating either an increase in the coefficient of basal friction b or a reduction in the pore fluid pressure ratio b leads to an increase in the surface heat flow because of the increased frictional heating within the wedge and on the basal decollement fault the overall balance of energy in a steady state fold and thrust belt is described by the equation e w g q where is the rate at which both mechanical and heat energy are added from external sources w g is the rate at which work is performed against gravitational body forces in a reference frame attached to the overriding plate and q is the rate at which waste heat flows out of both the upper and lower boundaries the total power input into the taiwan fold and thrust belt is approximately 4 2 gw the mechanical work being done on the base and front of the fold and thrust belt accounts for 3 of these 4 2 gw in addition 0 9 gw of heat are being advected from the subducting plate into the toe by accretion the remaining 0 3 gw are being supplied by in situ radiogenic heating the outgoing energy is dominated by the 3 gw of heat conducted out the top in the surface heat flow however another 0 8 gw are conducted down beneath the rear portion of the basal decollement fault to heat the underlying subducting slab only 0 4 of the incoming 4 2 gw do useful mechanical work against gravity within the wedge the efficiency of brittle frictional mountain building in taiwan is therefore 10

40ar 39mineral ages from the scituate granite rhode island implications for late palaeozoic tectonothermal activity in new england j i gil ibarguchi abstract the alkalic scituate granite was emplaced into crystalline sequences within the new england esmond dedham terrane in the late devonian c 370 ma variably recrystallized amphibole iron rich hastingsite hastinpitic hornblende from four variably deformed samples of the pluton record south westerly younging ar ar plateau ages ranging between 276 and 263 ma these are interpreted to date diachronous cooling through temperatures appropriate for intracrystalline retention of argon following late palaeozoic orogenic activity iron rich biotite concentrates from the samples record only slightly younger ages and therefore suggest relatively rapid post metamorphic cooling the ar ar ages indicate that the late palaeozoic tectonothermal overprint was much more regionally pervasive than was previously considered the apparent timing of this activity is similar to previous estimates for the chronology of high grade metamorphism throughout the adjacent hope valley terrane and for phases of ductile movement on the intervening lake char honey hill fault system

silurian orogenesis in the western penobscot bay region maine new 40ar 39ar mineral ages from rocks collected west of penobscot bay maine indicate this region was regionally deformed metamorphosed to amphibolite facies conditions and intruded by plutons in silurian times rather than in the devonian as previously assumed disturbed hornblende age spectra along with the presence of some devonian felsic plutons and extensive retrograde metamorphic textures do suggest however that these rocks were subsequently affected by low grade devonian thermal events in sharp contrast rocks west of the sennebec pond thrust fault a major tectono stratigraphic boundary in this region lack a significant silurian tectono thermal signature and instead record the effects of intense devonian deformation and high grade regional metamorphism the data suggest the two regions experienced very different pre devonian histories and were most likely juxtaposed by the sennebec pond thrust fault in latest silurian to early devonian time rocks now exposed east of the sennebec pond faul

the petrogenesis and emplacement of the new hampshire plutonic suite a longstanding problem associated with the acadian orogeny in new england is whether or not the orogeny involved a redistrubution of mass and energy within the midcrust without the addition of magmas and or anomalous heatfrom the mantle and or lower crust several closed system models suggest the new hampshire plutonic suite nhps resulted from essentially in situ partial melting of the metasedimentary rocks of the central maine terrane cmt at midcrustal levels crustal thickening models shear heating along the decollement and the presence of u enriched metasedimentary rocks have been suggested as heat sources for anatexis while applicable to numerous nhps plutons there are several difficulties with these models as explanations for the nhps as a whole 1 the syntectonic bethlehem kinsman and spaulding members are too cao and na 2 o rich to have been derived from the exposed metapelites deeper seated metagraywackes may account for some of the nhps source rocks but not for the metaluminous spaulding tonalite and other more mafic nhps rocks 2 some nhps 1 8 o nd and sr isotopic values are outside the range of cmt and bronson hill terrane metasedimentary rocks requiring a more primitive mantle like component 3 the temperatures of the kinsman and the spaulding magmas were higher than those attained during regional metamorphism associated with crustal thickening greater than 850 c 4 magmatic epidote and hornblende geobarometry for the winnipesaukee pluton of the spaulding tonalite suggest intratelluric crystallization initially at pressures 6 kbars deeper than the inferred decollement between the allochthonous cmt terrane metasedimentary rocks and underlying basement these data suggest that while the nhps contains a significant component from the cmt metasedimentary rocks the metaluminous spaulding rocks mafic enclaves in the kinsman and mafic rocks in northeastern vermont western maine and southeastern new hampshire provide evidence of heat and mass beyond that associated with closed midcrustal system processes

el ventorrillo a paleostructure of popocatepetl volcano insights from geochronology and geochemistry volcan popocatepetl mexico was constructed over the remains of a volcanic paleostructure based on fieldwork 40ar 39ar dating u pb dating and geochemistry we have determined the age chemistry and location of this paleostructure and named it el ventorrillo most remnants of el ventorrillo are covered by deposits from subsequent activity of popocatepetl except for the el abanico scarp and the barranca de nexpayantla where the stratigraphy of el ventorrillo eruptive products can be investigated inception of volcanism at el ventorrillo occurred at 331 10 ka with emission of the nexpayantla andesitic lavas and continued with extrusion of the yoloxochitl 267 31 ka and microwave 227 6 ka domes intrusion of dikes occurred at 298 94 and 230 3 ka activity at el ventorrillo continued with the emission of lavas that built the el abanico scarp 193 29 to 96 8 ka and continued until the tutti frutti eruption destroyed the cone 14 1 kyr ago el ventorrillo magmas produced rocks divided into two mineralogical groups the first group contains biotite amphibole rich rocks and the second group consists of biotite amphibole free lavas the rocks that contain biotite and amphibole are older than 198 13 ka whereas the rocks with no hydrous phases are younger than 227 6 ka and contain skarn and granodiorite xenoliths we interpret the change to an anhydrous mineral assemblage and the occurrence of skarn and granodiorite xenoliths as evidence for the formation of a new shallower reservoir a granodiorite xenolith was chosen for 40ar 39ar dating and u pb zircon analyses the u pb method yielded an age of 540 110 ka and the 40ar 39ar an age of 109 24 ka these ages are interpreted to indicate granodiorite crystallization 540 110 ka which metamorphosed the calcareous basement beneath popocatepetl into skarn and an influx of magma 109 24 ka that reheated the granodiorite major and trace elements sr nd and pb isotopic compositions and textural analyses of plagioclase show that el ventorrillo magmas were moderately modified by mixing with more mafic magmas and that assimilation of the calcareous basement was negligible

late proterozoic and devonian plutonic terrane within the avalon zone of rhode island the u th pb radiometric age of zircons demonstrates that much of rhode island consists of a late proterozoic plutonic complex that subsequently was intruded by a large devonian alkalic to subalkalic igneous complex two groups of late proterozoic rocks can be recognized 1 the esmond granite and related plutonic rocks in northern rhode island ranging in composition from gabbro to granite and yielding an upper concordia intercept of 621 8 m y and 2 quartz rich recrystallized gneissic rocks ten rod granite gneiss and hope valley alaskite gneiss in southern rhode island giving an upper concordia intercept age of 601 5 m y the lower intercept of the zircon discordia for the gneissic rocks indicates the isotopic systems were disturbed during the late paleozoic alleghanian orogeny whereas zircons from the esmond granite and related plutonic rocks have been subjected mainly to loss of lead attributable to recent dilatancy rocks determined to be of devonian age include the scituate granite and plutonic rocks of the east greenwich plutonic suite the quincy granite of quinn 1971 in northeastern rhode island may be of a similar devonian age or it may be slightly younger zircon data from these rocks fall upon a chord that gives an upper concordia intercept of 370 7 m y and a lower intercept close to the origin collectively these rocks form a composite pluton with an area 700 km 2 the devonian rocks exhibit petrologic characteristics distinct from slightly older acadian orogenic rocks that occur in lithostratigraphic zones to the west and are more comparable to anorogenic ordovician to devonian alkalic granitoids that trend north northeast across massachusetts and the gulf of maine the new age determinations confirm that much of rhode island contains plutonic rocks intruded during the avalonian orogeny but that a hertofore unrecognized major devonian plutonic episode also occurred the distinctly different ages probably had gone unrecognized because of generally similar lithologic and textural features exhibited by the late proterozoic and devonian rocks we present new petrologic and geochemical criteria that should assist in distinguishing the rocks of different ages as additional mapping and geologic study proceeds

timing of intrusion of the narragansett pier granite relative to deformation in the southwestern narragansett basin rhode island the pennsylvanian sediments of the narragansett basin rhode island were deformed during the al leghanian orogeny and record the effects of alleghanian deformation in southeast new england without the complication of earlier structures during this deformation the basin was intruded at its southwestern corner by the narragansett pier granite which has a crystallization age of 273 ma mapping of basin metasediments along the narragansett bay shore in the southwestern portion of the basin reveals features formed by several episodes of deformation two generations of isoclinal folds along north trending axes f1a and f1b are the earliest structures in the area followed by a set of small closed folds f2 also on north trending axes the fla f1b and f2 folds are the result of east west closure of the basin minor sinistral and more significant dextral motion on faults within the beaverhead shear zone produced local east trending crenulations s3 and open folds with north trending axes f4 in the study

precipitation of rutile and ilmenite needles in garnet implications for extreme metamorphic conditions in the acadian orogen u s a we report the discovery of oriented needles of rutile and ilmenite in garnet crystals from granulite facies metapelitic rocks of the merrimack synclinorium connecticut and present a precipitation model for their origin the rocks were strongly metamorphosed and deformed during the devonian acadian orogeny the needles are primarily elongated parallel to in garnet rutile has anomalous extinction angles as great as 35 cf griffin et al 1971 rutile and ilmenite needles are typically a few hundred nanometers to several micrometers in diameter and are several tens of micrometers to nearly a millimeter long other oxide inclusions that may be present include submicrometer to micrometer scale twinned rutile bicrystals as well as srilankite and a crichtonite group mineral some garnet cores have unusual box shaped quartz inclusions which coexist with ti fe oxide needles and commonly contain micrometer scale rods of f oh cl apatite negative garnet crystal pores are also widespread ti fe oxide needles are restricted to garnet core regions rims have a distinctly different inclusion population dominated by granulite facies minerals including sillimanite spinel cordierite and k feldspar consequently the garnet core regions represent an earlier distinct period of growth relative to the rims garnet cores contain 25 35 pyrope and a host of minor and trace constituents including tio2 0 07 0 6 wt cr2o3 0 01 0 10 wt na2o 0 01 0 03 wt p2o5 0 01 0 09 wt and zro2 up to 150 ppm na2o and zro2 correlate positively with tio2 titanium zoning is preserved in some garnets zoning profiles and two dimensional chemical mapping show that ti and to a lesser degree cr are depleted around ti fe oxide inclusions therefore we conclude that the needles are precipitates that formed from ti bearing garnet during exhumation and cooling garnet contained sufficient ti to form precipitates no ti source external to garnet was necessary titanium bearing garnets that contain oriented ti fe oxide needles are known primarily from ultrahigh pressure metamorphic rocks mantle peridotites and pyroxenites and high pressure granulites thus the presence of needle bearing garnets in connecticut strongly suggests that a previously unrecognized domain of extreme pressure and or temperature metamorphism exists in the acadian orogen

thermophysical properties of the earth s crust in situ measurements from continental and ocean drilling knowledge of the variation of thermal conductivity and heat production with depth is critical to understanding the thermal state of the crust continental and oceanic drill holes provide unique opportunities for the calibration of empirical and theoretical models relating crustal thermal properties to physical and chemical properties these calibrations are based on more than 30 000 well log measurements of acoustic velocity both compressional and shear density porosity radioelement concentrations k u th and major element chemistry al si ca fe s mg na in formations ranging in age from 5 to 620 ma and in composition from granitic to gabbroic the mineralogical data available from induced gamma ray spectroscopy logs when combined with known mineral thermal conductivities in a model for the thermal conductivity of a crystalline aggregate enable the in situ application of a laboratory estimation technique and yield continuous conductivity profiles however mineralogy based conductivity models cannot account for the anisotropic conductivity observed in foliated metamorphic rocks a phonon conduction model which utilizes acoustic velocity and bulk density measurements is accurate within 15 in both isotropic and anisotropic formations of the upper continental crust and in oceanic crustal layers 2c and 3 in oceanic crustal layers 2a and 2b however the effects of fracturing on compressional and shear velocities lead to inaccurate results the heat flow heat production relationship which provides one method of determining subsurface heat production has well documented limitations allis 1979 and rybach and buntebarth 1982 1984 on the basis of laboratory measurements have proposed quantitative relationships between heat production and rock compositional and physical properties the well log k u and th data indicate that heat production can be predicted from compositional data within a factor of 2 or 3 predictions of heat production from acoustic velocity and bulk density measurements are only accurate to within an order of magnitude three factors account for these results 1 the natural variability of velocity and density for a given rock composition 2 the tendency of u and th to associate with secondary rather than primary minerals and 3 u and th redistribution through fluid flow and metamorphism thus seismic velocity based heat production profiles can at best be taken as first order estimates which may misrepresent the complexity of the continental crust however the correlation of formations of known heat production with subsurface structures when combined with a suite of existing techniques for estimating heat production may lead to more accurate results

quaternary geology of eastern germany saxony saxon anhalt south brandenburg thuringia type area of the elsterian and saalian stages in europe abstract the characteristic feature of the quaternary geology of eastern germany location map fig 1 is a sequence of more than 50 horizons and complexes of glacial laminated clays tills glaciofluvial sediments and periglacial river gravels gelifluction sheets alluvium loess facies in the period between the younger tertiary and the first elsterian continental glaciation at least four gravel terraces were built up under cold climate conditions the youngest of these gravel bodies lacks scandinavian rocks and is interbedded with elsterian glaciolacustrine deposits pre elsterian temperate periods have been recorded at a number of places i e zeuchfeld untermassfeld voigtstedt sussenborn two major ice advances with additional minor oscillations have been identified of elsterian and saalian ages complete eemian and holsteinian sequences are represented showing vegetational development through each interglacial cycle cool temperate warm cool the weichselian glacial stage in eastern germany is represented by thick periglacial sedimentation including gravels gelifluction sheets alluvium debris covers and loess within these sediments is a wide variety of glaciotectonic structures and periglacial soil structures including classical involutions and ice wedge casts an outline of the present state of knowledge of the quaternary of eastern germany is given in tables 1 3 while table 4 presents a stratigraphical comparison with the neighbouring regions and countries the palaeogeography of the region during the periods of the european continental glaciation is depicted in fig 2

fluid geochemistry and soil gas fluxes co2 ch4 h2s at a promissory hot dry rock geothermal system the acoculco caldera mexico abstract the acoculco caldera has been recognized by the mexican federal electricity company cfe as a hot dry rock geothermal system hdr and could be a potential candidate for developing an enhanced geothermal system egs apart from hydrothermally altered rocks geothermal manifestations within the acoculco caldera are scarce close to ambient temperature bubbling springs and soil degassing are reported inside the caldera while a few springs discharge warm water on the periphery of the caldera in this study we infer the origin of fluids and we characterize for the first time the soil degassing dynamic chemical and isotopic 18o d analyses of spring waters indicate a meteoric origin and the dissolution of co2 and h2s gases while gas chemical and isotopic compositions n2 he 3he 4he 13c 15n reveal a magmatic contribution with both morb and arc type signatures which could be explained by an extension regime created by local and regional fault systems gas geothermometry results are in agreement with temperature measured during well drilling 260 c 300 c absence of well developed water reservoir at depth impedes re equilibration of gases upon surface a multi gas flux survey including co2 ch4 and h2s measurements was performed within the caldera using the graphical statistical analysis gsa approach co2 flux measurements were classified in two populations population a representing 95 of measured fluxes is characterized by low values mean 18 g m 2 day 1 while the remaining 5 fluxes belonging to population b are much higher mean 5543 g m 2 day 1 this low degassing rate probably reflects the low permeability of the system a consequence of the intense hydrothermal alteration observed in the upper 800 m of volcanic rocks an attempt to interpret the origin and transport mechanism of these fluxes is proposed by means of flux ratios as well as by numerical modeling measurements with co2 ch4 and co2 h2s flux ratios similar to mass ratios of sampled gases were considered as reflecting advective transport a numerical model of co2 migration in the subsoil system under fully water and gas saturated conditions was performed using the tough2 code in order to reproduce semi quantitatively field measurements the main results show that high flux values produced by advective geothermal degassing can be very localized and that low and heterogeneous permeability conditions can induce low advective co2 flux values therefore in this case the populations discriminated by the gsa method should not be interpreted in terms of origin and or transport mechanism but rather in terms of permeability conditions

horizontal subduction and truncation of the cocos plate beneath central mexico 1 based on analysis of data from a trans mexico temporary broadband seismic network centered on mexico city we report that the subducting cocos plate beneath central mexico is horizontal and tectonically underplates the base of the crust for a distance of 250 km from the trench it is decoupled from the crust by a very thin low viscosity zone the plate plunges into the mantle near mexico city but is truncated at a depth of 500 km probably due to an e w propagating tear in the cocos slab unlike the shallow slab subduction in peru and chile there is active volcanism along the trans mexican volcanic belt tmvb that lies much further inland than regions to either side where subduction dip is not horizontal geodynamical modeling indicates that a thin weak layer such as imaged by the seismic experiment can explain the flat subduction

three decades of geochronologic studies in the new england appalachians over the past 30 years both isotope geochronology and plate tectonics grew from infancy into authoritative disciplines in the geological sciences previously mountain systems like the appalachians had been viewed almost entirely in the context of the classical geosyncline implying a gradualism in stratigraphic and structural change throughout the orogen age control determined largely from distant fossiliferous strata was unabashedly carried to high grade metamorphic rocks based only on lithological correlations with the new concepts in tectonics came the realization that abrupt breaks in stratigraphy and structure occur in many cases at the boundaries of lithotectonic zones fortunately the new techniques of isotope geochronology could be brought to bear directly on the rocks of the immediate study area this paper chronicles some of the major contributions to the geology of the new england appalachians that resulted from these efforts during the past three decades in tracing the history of geochronologic research one encounters an increasingly sophisticated approach to the analytical and interpretive aspects of the discipline today the geochronologist can under optimum conditions constrain the age of stratigraphic units igneous activity deformation and metamorphism with accuracy that is capable of resolving fine structure within individual orogenic pulses he participates in full partnership with other colleagues of the science in unravelling the mysteries of mountain building several of the topical problems of new england geology in which geochronology played a key role include 1 the recognition and delineation of avalonia as a late proterozoic eastern basement distinct from more western terranes 2 the dating of the white mountain plutonic volcanic suite a mesozoic igneous event spanning 100 m y and 3 the temporal and spatial separation of structural and metamorphic features imprinted by the taconic and acadian orogenies the existing geochronology is summarized into a map and table emphasizing the temporal construction of the new england appalachians by using lithotectonic zones as the building blocks of the orogen seven such zones are defined in terms of pre syn and post assembly geologic history from west to east these lithotectonic zones are 1 berkshire green mountain 2 rowe hawley 3 connecticut valley 4 bronson hill 5 kearsarge central maine 6 tatnic hill nashoba and 7 avalonia avalonia is further divided into three subzones hope valley esmond dedham and penobscot bay which themselves may have had distinct origins and assembly histories the boundaries between these zones are faults in most cases some of which may have had recurring movement to further complicate any plate tectonic scenario a delineation of underlying grenvillian chain lakes and avalonian basement is also attempted which now can make use of isotopes in igneous rocks as petrogenetic indicators to supplement the rare occurrences of basement outcrop within mobile zones of the orogen the belt of permian thermal disturbance within the kearsarge central maine zone is hypothesized to reflect rapid rebound following compressional thickening of underlying avalonian basement during the alleghanian orogeny

u pb isotopic and geologic evidence for late paleozoic anatexis deformation and accretion of the late proterozoic avalon terrane southcentral connecticut

pioneer vegetation as an indicator of the geochemical parameters in abandoned mine sites using hyperspectral airborne data a general problem that is associated with open pit mining is the total displacement of the former landscape s geocomponents overburden conveyor bridges have an irreversible impact on the environment the consequence of this is a completely new system the so called post mining landscapes these are characterized by extreme geochemical milieus especially acidity which is caused by weathering processes acid mine drainage these extreme environments are often left to natural succession because of the enormous costs and poor prospects of a successful reclamation this study investigated the relationship between pioneer vegetation e g calamagrostis epigejos and the geochemical properties of heap material using hyperspectral airborne hymap data in the west bohemian lignite district near sokolov czech republic thus a fully constrained linear spectral unmixing algorithm was applied to link the geochemical parameters with fractional abundances due to the limitation of pure surfaces in the data set of such fragmented and mixed areas a three stage semiautomated endmember extraction was developed the first stage included the selection of pure surface types using a decision tree with a self developed narrow band and normalized difference indices the second stage extracted the potential endmembers using the sequential maximum angle convex cone algorithm the third stage identified the final endmembers and eliminated the spectral outliers by comparing the extractions to field laboratory spectral libraries the abundance fraction image of the pioneer vegetation which was generated by the linear spectral unmixing showed the spatial distribution and density of the vegetation a linear regression model was used to calibrate the abundance image against the ph value the regression model successfully predicted the ph values of the soil r 2 0 67 rpd 1 42 this method demonstrated that hyperspectral remote sensing data could be used for ecological medium and long term monitoring as well as for spatial assessments in post mining areas in addition this approach works with a small amount of geochemical measurements and the sparse availability of endmembers

40ar 39ar ages from the narragansett basin and southern rhode island basement terrane their bearing on the extent and timing of alleghenian tectonothermal events in new england pennsylvanian sedimentary rocks record the effects of progressive barrovian metamorphism and polydeformation in the narragansett basin of rhode island whole rock phyllite samples from low grade portions of this terrane display internally concordant 40 ar 39 ar age spectra with plateau ages of 248 to 258 m y four samples biotite from higher grade rocks records plateau ages of 240 to 248 m y eight samples similar 40 ar 39 ar biotite ages are displayed westward across the southern rhode island basement terrane 239 to 250 m y nine samples although coexisting hornblende records slightly older plateau ages of 255 m y two samples the 40 ar 39 ar plateau ages are interpreted to date times of post metamorphic cooling through temperatures required for argon retention in the various mineral phases examined the ages suggest that a distinct late paleozoic alleghenian thermal event affected much of southern rhode island together with the depositional ages of the variably metamorphosed pennsylvanian rocks westphalian b stephanian a or b the 40 ar 39 ar data permit calibration of the sequence of alleghenian tectonothermal events recorded in the narragansett basin the controls suggest a permian event lasting about 40 to 50 m y between initial barrovian regional metamorphism and synchronous d 1 d 2 ductile deformation between 295 and 275 m y and post d 3 cooling below argon retention temperatures between 250 and 240 m y

deformation induced reconstitution and local resetting of mineral equilibria in polymetamorphic gneisses tectonic and metamorphic implications a sequence of at least three al2sio5 bearing mineral assemblages are preserved in successively overprinted ductile shear zones in the willimantic window connecticut the ductile deformation localized at and near the boundary between the putnam nashoba terrane and underlying avalon terrane is characterized by a network of anastomozing shear zones that outline metre scale tectonic blocks of migmatitic kfs sil gt bi pg qtz ilm ru gneiss these assemblages record acadian or older metamorphic conditions of 6 kbar 700d c mylonitic gneisses in shear zones that define block margins were formed by reconstitution and recrystallization of the migmatitic gneiss the reconstituted rocks exhibit relict ky st grt pl bt qtz rt ilm assemblages and require a minimum pressure for the ky str grade metamorphism of 8 5 kbar kyanite in block margins is widely replaced by sillimanite and locally by andalusite during a period of post alleghanian ductile deformation the interiors of blocks do not record this sequence of polymorphs the pattern of reconstitution is accounted for by localization of strain along block margins within a regionally extensive terrane bounding fault zone strain provided the activation energy for recrystallization and retrograde mineral reactions the p t conditions of post alleghanian ductile deformation evolved from 600d c and 6 kbar to 550d c and 3 kbar the occurrence of ky str bearing assemblages overprinting acadian kfs sil bearing assemblages and subsequently overprinted by alleghanian sillimanite and andalusite bearing assemblages along with reset hornblende 40ar 39 ar mineral ages from mississippian to permian requires a prograde alleghanian metamorphism of rocks previously metamorphosed during the acadian thus mineral assemblages from gneisses in the willimantic fault zone retain evidence of a protracted tectonothermal evolution that included high grade acadian orogenesis tectonic loading resulting from alleghanian collision of avalon with north america and tectonic exhumation in permo triassic time the c 3 kbar pressure decrease between prograde and retrograde alleghanian metamorphic conditions corresponds to 10 km of crust that must have been tectonically excised from the base of the putnam nashoba terrane cover sequence following alleghanian orogenesis in south eastern new england

permian bulk shortening in the narragansett basin of southeastern new england usa pennsylvanian age sediments within the narragansett basin allow the effects of alleghanian deformation to be distinguished from the taconic and acadian orogenies that affected the rocks to the west three dimensional microstructural analyses of both matrix foliations and structures preserved in porphyroblasts define two extended periods of deformation and metamorphism about two differently trending foliation intersection inflection axes in porphyroblasts fias ssw nne trending fias set 1 formed first followed by wsw ene trending fias set 2 the ssw nne fia trends from the south central zone lie parallel to regional folds in the entire southern graben the changes in fia trends reveal that the direction of maximum bulk shortening changed from wnw ese to nnw sse during amphibolite facies metamorphism within the central zone of the basin they reveal a more varied history than the simple kinematic framework of solely w e directed bulk shortening that was previously suggested

early paleozoic paleogeography and accretionary history of the newfoundland appalachians new paleomagnetic results were obtained from several units in the central mobile belt of the north central newfoundland appalachians combined with recently published data the results place important limits on interpretations of early paleozoic paleogeography and evolution of the appalachian caledonian orogen the ordovician appalachian margin of north america located at low paleolatitudes and facing roughly south was separated from the southern margin of iapetus avalon armorica by 3500 km primary directions in pillowed volcanic rocks of the moreton9s harbour group that are part of an early ordovician island arc show that these rocks were formed near the north american margin at a paleolatitude of 12 s early to middle ordovician volcanic rocks of the roberts arm chanceport and summerford groups on the other hand were extruded at paleolatitudes of 30 40 s unconformably overlying volcanics of the silurian botwood group were extruded subaerially at a paleolatitude of 24 s combined with tectonostratigraphic data these results suggest the following tectonic history in early ordovician time northerly subduction of the main iapetus basin was accompanied by the formation of a volcanic arc and a back arc basin near the north american margin middle ordovician emplacement of ophiolites on the north american margin reflects the closure of this back arc basin iapetus i and continued northerly subduction in silurian time closed the main basin iapetus ii

monazite u pb dating of staurolite grade metamorphism in pelitic schists a study of the occurrence of and relations between rare earth element ree minerals in pelitic schists indicates that monazite forms at or near the p and t of the staurolite isograd samples at staurolite grade from the silurian perry mountain formation in the rumford quadrangle of maine yield monazite in sufficient quantities to permit accurate dating of the metamorphic events forming the monazites the bulk chemistry of the metapelites as seen in the major element abundances and ree patterns does not vary significantly across the study area thus the appearance and disappearance of ree phases is assumed to reflect changes in metamorphic grade in a sample from the biotite zone scanning electron microscope and microprobe studies show allanite and monazite intimately associated on a 10 m scale the texture suggest that metastable detrital monazite breaks down distributing its ree components to allanite from samples below staurolite grade in which monazite is not present our observations suggest that rees are partitioned into allanite at or near the staurolite isograd monazite forms as a metamorphic mineral initiating its role as a geochronometer garnet biotite geothermometry on samples at this grade from this and other studies places constraints on the minimum temperature necessary to form monazite 525 c 25 c at 3 1 0 25 kbar a total of 15 separates from nine schist samples ranging up to sillimanite grade have been dated each date is remarkably concordant even though petrologic and textural studies by previous workers have shown that the rocks in the area have been affected by at least three metamorphic episodes calculations indicate insignificant th disequilibrium in these monazites the conditions associated with the metamorphic events suggest that monazite remains closed to lead loss provided that subsequent metamorphisms are at or below sillimanite grade two distinct metamorphic events are resolved one at around 400 ma and one at about 370 ma the latter was due to thermal effects of a nearby pluton that yields concordant monazite ages of 363 ma this work suggests that in addition to dating plutonism and high grade metamorphism monazite should be viewed as a reliable geochronometer for moderate metamorphism of pelitic schists

early rifting in the narragansett basin massachusetts rhode island evidence from late devonian bimodal volcanic rocks abstract the basal wamsutta formation of the narragansett basin massachusetts rhode island contains 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 373 pm 2 end document ma rhyolite that is unexpectedly 60 m yr older than sedimentary strata containing late pennsylvanian floras higher in the basin fill the transitional alkalic geochemistry of the rhyolite and associated basalt signifies late devonian rifting pre dating major basin subsidence surface rifting was accompanied by voluminous alkalic intrusions of the 380 370 m

a crystal chemical basis for pb retention and fission track annealing systematics in u bearing minerals with implications for geochronology this study develops an empirical crystal chemical framework for systematizing the kinetics of pb loss and fission track annealing in u bearing minerals ionic porosity z the fraction of a mineral s unit cell volume not occupied by ions potentially accounts for kinetic behavior by monitoring mean metal oxygen bond length strength various tests of a general kinetics porosity relationship are presented based upon diverse mineral data including 1 pb diffusion parameters 2 measured closure temperatures tc for fission track annealing and 3 retentivities of both pb and fission tracks from apparent age data every kinetic parameter including tc and mineral age for both the u pb and fission track systems is inversely correlated with z within the sub assemblage zircon z 29 titanite 34 and apatite 38 assuming a diffusional closure model pb isotopic transport phenomena are described by a tc z scale calibrated with field based tc data for titanite 680 20 c and apatite 500 c extrapolation of this scale yields tc estimates for the following minerals staurolite tc 1060 c z 25 garnet 1010 c 26 5 zircon 900 c monazite xenotime and epidote 750 c 32 and ca clinopyroxene 670 30 c 34 1 depending on composition these empirical results imply that a u pb pb date for staurolite or garnet records the time of mineral growth not post growth isotopic closure as also concluded in recent field studies because z systematizes fission track annealing this recrystallization process like volume diffusion must also be rate limited by the strength of chemical bonds the extent to which other recrystallization processes are likewise rate limited is important to u pb geochronology because they potentially compete with diffusion as mechanisms for pb isotopic resetting in nature

archean inheritance in zircon from late paleozoic granites from the avalon zone of southeastern new england an african connection abstract in southeastern new england the narragansett pier granite locally intrudes carboniferous metasedimentary rocks of the narragansett basin and yields a monazite u pb permian emplacement age of 273 2ma zircon from the narragansett pier granite contains a minor but detectable amount of an older inherited component and shows modern loss of lead zircon from the late stage aplitic westerly granite exhibits a more pronounced lead inheritance permitting the inherited component to be identified as late archean such old relict zircon has not been previously recognized in proterozoic to paleozoic igneous rocks in new england and may be restricted to late paleozoic rocks of the avalon zone we suggest that the archean crustal component reflects an african connection in which old archean crust was underplated to the avalon zone microplate in the late paleozoic during collision of gondwanaland with avalonia

age and setting of the bronson hill magmatic arc a re evaluation based on u pb zircon ages in southern new england new u pb zircon ages of selected rocks from the bronson hill anticlinorium in southern new england are as follows microcline gneiss of the dry hill gneiss in the pelham dome believed to be metamorphosed alkali rhyolite is confirmed as late proterozoic yielding an age of 613 3 ma another sample shows strong evidence of zircon inheritance with a minimum mean age of 1402 ma plagioclase rich gneisses with associated amphibolites swanzey pauchaug monson and fourmile gneisses now believed to represent metamorphosed intrusive igneous rocks yield ages from 454 to 442 3 2 ma thus ranging from early late through latest ordovician consistent with other absolute ages of the oliverian plutonic series in the region quartz phyric rhyolite from the upper member of the ammonoosuc volcanics and rhyolite tuff from the partridge formation are dated at 453 2 ma and 449 3 2 ma respectively indicating that eruption of felsic lavas in the overlying volcanic section spanned an interval of approximately 4 m y additional zircon ages are reported from a crosscutting but deformed tonalite dike in the swanzey gneiss 381 3 ma and a coarse grained gabbro from the prescott intrusive complex 407 3 2 ma intrusive into the partridge formation metamorphic overprinting of the region during both the acadian and alleghanian orogenies is indicated by u pb titanite ages of 357 5 ma and 292 5 ma from a tonalite gneiss on prescott peninsula and the dry hill gneiss respectively the above ages and other zircon ages as well as petrography and geochemistry of the fourmile monson swanzey pauchaug and other plagioclase rich gneisses of the bronson hill anticlinorium suggest that they represent the plutonic root of a calc alkaline magmatic arc at least 250 km long that was produced partly or entirely on a continental margin in late ordovician time ca 454 442 ma the physically overlying cover sequence of chemically different tholeiitic arc volcanic and sedimentary rocks of the ammonoosuc volcanics and partridge formation previously thought to rest unconformably on the plagioclase rich plutonic gneisses is now shown to have had a magmatic history overlapping with them the zircon ages in the plutonic gneisses and the cover sequence indicate that both are the same age or slightly younger than the late ordovician caradocian emplacement of the giddings brook slice of the taconian allochthons and too young to have formed above an early and medial ordovician subduction zone

analyses and monitoring of lignite mining lakes in eastern germany with spectral signatures of landsat tm satellite data abstract coal mining activities cause an increased acidity and an associated decrease of the ph value in mine waters this process is also known as acid mine drainage amd due to amd lakes that were formed in the post mining landscapes in the lignite mining area of central germany are characterized by specific limnological development changes remote sensing is a time and cost saving technique that enables the observation of the hydrological and limnological development of the lakes ranging from a small to a mid size scale the current research was based on landsat tm5 etm 7 satellite data collected between 1999 and 2004 in combination of satellite data surface waters of the post mining lakes in central germany were sampled and analyzed for their physicochemical properties the objective of this approach was to evaluate the environmental conditions and to develop a monitoring system on the other hand the research was conducted to assess the potential of the use of satellite data and to calibrate its content for monitoring the geochemistry of mining lakes correlation of hydrochemical parameters of lake water to spectral signatures detected by satellites was performed with multivariate statistical analysis methods the five determined clusters of spectral partitions described the actual data ground truth data within the visible range the statistically identified clusters were combined with expert knowledge in limnology geology and water chemistry of large scale lakes in open cast mining areas in order to analyze the spectral information of the satellite images scientifically the utilization of spectral signatures revealed an acceptable classification of hydrological and hydrochemical properties of mining lakes and established the basis for further investigation of open cast lignite mining concerning the environmental impact particularly in areas where lignite mining lakes usually form

petrologic diversity in mount st helens dacites during the last 4 000 years implications for magma mixing mount st helens has explosively erupted dacitic magma discontinuously over the last 40 000 years and detailed stratigraphic data are available for the past 4 000 years during this last time period the major element composition of the dacites has ranged from mafic 62 64 wt sio2 to felsic 65 67 wt sio2 temperature has varied by about 150 c 770 920 c and crystallinity has ranged between 20 and 55 water content of these dacites has also fluctuated greatly although the source for the dacitic magmas is probably partial melting of lower crustal rocks there is strong physical evidence such as banded pumices thermal heterogeneities in single pumices phenocryst disequilibrium contrasts between compositions of glass inclusions and host matrix glass and amphibole reaction rims that suggests that magma mixing has been prominent in the dacitic reservoir indeed we suggest that the variations in major and trace element abundances in mount st helens dacites indicate that magma mixing between felsic dacite and mafic magma has controlled the petrologic diversity of the dacitic magmas magma mixing has also controlled the composition of andesites erupted at mount st helens and thus it appears that the continuum of magmatic composition erupted at the volcano is controlled by mixing between felsic dacite or possibly rhyodacite and basalt the flux of the felsic endmember to the reservior appears to have been relatively constant whereas the flux of basalt may have increased in the past 4 000 years as suggested by the apparently increased abundance of mafic dacite and andesite erupted in this period

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

evidence for extensive hercynian metamorphism in western maine 40 ar 39 ar release spectrum ages for five hornblendes from two acadian plutons in western maine and petrologic observations for nearby metamorphic rocks are interpreted to indicate that high grade k feldspar sillimanite metamorphism occurred during carboniferous time not devonian time as previously believed the metamorphism was closely associated in time with the emplacement of the sebago batholith 325 ma petrologic data suggest that rocks as far as 30 km north of the sebago batholith were affected release spectrum ages for hornblendes from the songo pluton indicate that by 300 ma high grade metamorphic conditions had ended and cooling through 500 c had occurred

crustal thickening by tectonic wedging of the ganderian rocks southern new england usa evidence from cataclastic zircon microstructures and u pb ages abstract zircon grains in granites from avalonian and ganderian rocks in southern new england host brittle internal structures that are interpreted here to show the host rocks to be allochthonous significant among these structures are inherited cores that are commonly fractured and even dismembered this intense fracturing is interpreted as reflecting an important cataclastic event the maximum age of fracturing is constrained to be younger than the age of the youngest broken magmatic core 360 4 ma the minimum age must be older than the oldest zircon rim that heals these fractures that is early permian the occurrence of cataclastic zircon requires that these rocks were relatively cold i e in the upper crust during the carboniferous and therefore were not involved in the pervasive high grade acadian metamorphism the present map pattern of inter tonguing high grade and low grade slices of peri gondwanan rocks shows that they were assembled by crustal scale tectonic wedging the consequent thickening ultimately led to anatexis in the lower slices during the permian thus evidence for cataclasis of zircon grains from the avalon and gander terranes of southern new england suggests that these peri gondwanan terranes remained outboard of laurentia during the well documented early devonian acadian orogeny and were first fully accreted to north america during the alleghanian permian orogeny

the distribution style and intensity of alleghanian metamorphism in south central new england petrologic evidence from the pelham and willimantic domes abstract alleghanian metamorphism in south central new england is characterized by late pennsylvanian 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 mathrm kyanite mathrm muscovite mathrm staurolite end document grade heterogeneous reconstitution of migmatitic documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepack

sulfur isotope studies to quantify sulfate components in water of flooded lignite open pits lake goitsche germany abstract a system of connected lignite mining pits part of the former goitsche mining complex germany was flooded with river water between 1999 and 2002 a considerable accumulation of acid associated with oxidized sulfides in sediments was seen as a critical point for the development of the lake water to characterize the components contributing to the supply of dissolved lake water so4 hydro chemical and isotope investigations with respect to groundwater pore water in the sulfide bearing sediments river water and lake water were performed 34s of pore water so4 that was dominated by oxidized pyrites ranges around 25 vcdt and differs strongly from river water so4 with about 4 4 thus interactions between lake water and sediments were particularly pronounced during the first phase of flooding for this period a more quantitative estimation of the so4 components in the lake water was difficult because of the heterogeneous so4 distributions between the different sub basins of the lake and according to the flooding process itself later a component separation was attempted following mixing of the whole lake which first occurred in spring 2002 a very heterogeneous groundwater environment with respect to highly variable so4 concentrations and 34s values and changing interaction with the forming lakes proved to be one of the most important limitations in the calculations of the mixing

structural implications of some radiometric ages of igneous rocks in southeastern new england u th pb zircon rb sr whole rock and k ar hornblende isotopic ages reveal two major episodes of igneous activity in southeastern new england one in late proterozoic z time 600 650 m y ago and the other in devonian to ordovician time 375 450 m y ago the dated rocks are discussed in the context of several individual structural provinces that evolved more or less independently of each other prior to middle to late paleozoic assembly these provinces generally are bounded by major faults and or abrupt changes in metamorphic grade and from east to west include i the milford dedham zone ii the putnam nashoba zone iii the merrimack synclinorium and iv the bronson hill zone from the present and other recently published studies reasonably accurate ages representative of the two major episodes can now be assigned to many of the igneous rocks other units remain less well constrained but probably may be placed into one or the other of the general age groupings case by case examination of the geochronologic data makes us cautious in accepting some apparent fine structure age resolution within each grouping until factors such as inherited zircon and metamorphic overprinting can be better evaluated with the above mentioned qualifications in mind igneous rock ages summarized according to structural province are as follows i milford dedham zone a late proterozoic z dedham granite and related rocks 630 15 m y 595 15 m y 612 646 m y milford granite 630 15 m y 591 50 m y hope valley alaskite gneiss and scituate granite gneiss ages uncertain unnamed granite near assonet 600 650 m y b devonian to ordovician alkalic rocks including quincy cape ann and peabody granites wenham monzonite and nahant gabbro ii putnam nashoba zone a late proterozoic z no plutonic rocks identified but may include some metavolcanic rocks b devonian to ordovician sharpners pond diorite 430 5 m y andover granite 408 22 m y 450 22 m y muscovite granite near west berlin age uncertain preston gabbro 424 5 m y ill merrimack synclinorium a late proterozoic z granitic orthogneiss unit of the massabesic gneiss complex 600 620 m y metavolcanic unit of the massabesic gneiss complex 646 m y or older b devonian to ordovician fitchburg complex at maiden hill 402 11 m y fitchburg complex at rollstone quarry 390 15 m y newburyport complex 450 15 m y ayer granite 433 5 m y chelmsford granite age uncertain muscovite biotite granite at millstone hill 372 7 m y canterbury gneisses 395 10 m y 392 9 m y iv bronson hill zone a late proterozoic z dry hill gneiss of the pelham dome 600 m y b devonian to ordovician monson gneiss 440 10 m y these distinctive age patterns together with contrasts in petrography and texture of the igneous rocks in stratigraphy of the country lock and in metamorphic grade accentuate the separate geologic development of each structural province no correlation involving preassembly geology should be attempted across province boundaries without due consideration of the exotic character of each province

evidence for the influence of fch 4 on the crystallinity of disseminated carbon in greenschist facies rocks rhode island usa disseminated carbon has been extracted from 19 samples of arkosic rocks from the chlorite biotite and garnet zones in the narragansett basin and analysed by x ray diffraction xrd and scanning electron microscopy sem xrd of these samples yields only the 002 peak which may be as much as four times wider than the silicon internal standard peak and is always skewed to low angles 2 all 002 peaks were digitized and the four moments calculated the results suggest that width at half height w1 2 provides a poorer estimate of peak shape than coefficients of skewness and kurtosis the positive correlation of these coefficients with grain size determined by sem in the range of 0 1 100 m suggest a direct relationship between peak shape and grain size

partitioning of deformation along an orogen and its effects on porphyroblast growth during orogenesis an identical succession of foliation inflection intersection axis trends in porphyroblasts fias is present in three separate areas affected by acadian deformation and metamorphism along 130 kms of the appalachians from east central vermont to north central massachusetts the fias trend successively nw se sw ne w e nnw sse and ssw nne and appear to have formed during the same succession of deformations which have been dated in se vermont as follows not yet dated pre 425 ma 425 to 404 ma 404 to 385 ma and 385 to 360 ma respectively the two areas that are furthest apart in east central vermont and north central massachusetts have strikingly similar total distributions of fias in garnet porphyroblasts that show a somewhat inverse relationship to those observed in the chester athens dome area of se vermont that separates them that is the number of samples containing the first formed fia set is greatest for the two regions lying furthest apart and decreases in younger sets whereas the number of samples containing the first fia set is the least in the central region and increases for more recently developed sets partitioning of deformation into zones of progressive shearing and shortening has been demonstrated to control the sites of development of differentiated crenulation cleavage versus porphyroblast growth and sites of porphyroblast growth on one limb of a regional fold versus the other we argue that partitioning of the deformation around competent feldspathic gneiss bodies at an orogen scale produced the variation in the number of samples containing the various fia sets between the central and outer areas described above porphyroblasts most commonly grew during sw ne directed shortening to the north and south of the chester athens dome region of the appalachians but only rarely grew in the latter region this suggests that deformation at this time partitioned around an outlier of competent basement feldspathic gneiss that underlies the chester athens dome region and this protected the rocks above and in the strain shadow to the nw and se from the effects of the great bulk of the deformation that occurred over the period of time during which nw se trending fias formed we attribute the increase in the number of samples containing progressively younger fias in the chester athens dome area during subsequent periods of nw se n s wsw ene and wnw ese directed shortening to the rise in temperature and pressure recorded in the rocks above the chester athens dome with peak conditions occurring during the development of the nnw sse oriented fia set between 404 and 385 ma as the temperature and pressure increased the gneiss below would have become less competent allowing the deformation associated with the succession of fia sets to partition more pervasively through the dome core this provided more sites for porphyroblast nucleation and growth and hence the number of samples recording these fia sets increased the concomitant decrease in the number of samples in which porphyroblasts grew in the rock within the areas to the north and south with successive fias possibly resulted from a progressive increase in competency of these rocks as the number of porphyroblasts increased

the acoculco caldera complex magmas genesis evolution and relation with the acoculco geothermal system abstract the acoculco caldera complex acc is located in the eastern part of the trans mexican volcanic belt mexico the acc was formed 2 7 ma and since then volcanic activity has persisted until 0 06 ma through the emission of domes cinder cones fissure lava flows and two ignimbrite eruptions dated at 1 2 and 0 65 ma the pervasive hydrothermal alteration in the central part of the acc has motivated considerable geothermal exploration however none of it assessed the relation between the magmatic heat supply and the evolution of magmas including their reservoir depth magmatic processes were investigated with petrography major oxides trace element geochemistry mineral chemistry and isotopic analysis in addition we performed a series of hydrothermal experiments in order to constrain the storage depth for the magma tapped 1 2 ma during a reactivation of the caldera we investigated the origin of magmas tapped during the eruptive history of the acc and the magmatic processes magma mixing assimilation and crystallization that modified these magmas after the caldera collapse 2 7 ma the local stress field was probably modified and allowed the ascent of peralkaline magmas through new plumbing systems such magmas mixed with calc alkaline magmas and formed the post caldera volcanism influx of new magma is considered as the probable heat supply that maintains the active magmatic system whereas assimilation has been negligible but yields insights about the depth at which processes have occurred our work suggests that there are either shallow storage zones 200 500 bars where magmas crystallize and either erupt or stall and cool or there are intrusive magmas unrelated to the acc suite that have accumulated nearby and heat the reservoir magmas

geochronologic studies in central new england i evidence for pre acadian metamorphism in eastern vermont sup 40 ar sup 39 ar geochronology on hornblendes from central new england reveals a grenvillian cooling age 1026 plus minus 12 ma along the eastern margin of the green mountain massif acadian ages in east central vermont 350 397 ma and along the bronson hill anticlinorium in new hampshire and massachusetts 407 280 ma and late ordovician to silurian ages 440 451 ma along a belt in eastern vermont and central massachusetts these ages indicate a minimal acadian overprint in eastern vermont the highest degree of acadian overprint being located along the axis of the domes in the connecticut valley synclinorium these data suggest that the formation of the domes occurred in the acadian moreover the late ordovician to silurian cooling ages in eastern vermont suggest that much of the metamorphic mineralogy and fabric observed in the connecticut valley synclinorium may be pre silurian in age

carboniferous u pb age of the sebago batholith southwestern maine metamorphic and tectonic implications two phases pink and white granite of the sebago batholith of southwestern maine have been dated by the u pb zircon method identical upper concordia intercepts of both rocks indicate an intrusive age of 325 3 m y for the batholith the lower intercept of the pink phase sample 114 13 m y is inferred to represent episodic lead loss due to the intrusion of the nearby cretaceous pleasant mountain stock the lower intercept of the white phase sample 18 21 m y suggests only modern dilatancy lead loss monazites have ages of 272 m y pink and 282 m y white which are thought to be cooling ages rb sr whole rock data have low initial 87 sr 86 sr ratios of 0 7031 pink and 0 7053 white these data in conjunction with published 40 ar 39 ar rb sr k ar and fission track ages suggest that little or no uplift occurred in this part of new england until the permian and that the uplift rate from 275 m y to 225 m y was 3 times as rapid as was the rate for 225 m y to the present the carboniferous age of the sebago batholith suggests that currently accepted metamorphic and tectonic interpretations for southwestern maine and for east central new hampshire require revision

u s geological survey deep seismic reflection profile across the gulf of maine deep seismic reflection and magnetic data suggest that the gulf of maine is underlain by four crustal blocks of differing reflection and magnetic character two of these blocks the gulf of maine fault zone and adjacent central plutonic zone can be correlated with avalonian rocks in southern new england and new brunswick the boundary between them the fundy fault projects onshore near the ponkapoag fault in southeastern massachusetts in a region where no major crustal boundary has yet been identified a third block called the southern plutonic zone is interpreted as avalonian although the reflection and magnetic data are ambiguous the fourth block along the rifted continental margin is correlated with meguma rocks of nova scotia the late paleozoic variscan front crosses the gulf of maine within the gulf of maine fault zone and indicates significant compressional movement rather than strike slip the moho surface throughout the region is essentially flat and may have been produced by mesozoic crustal extension associated modification of the lower crust was minimal in the northern gulf and may have been moderate in the central and southern gulf the franklin rift basin formed by reactivation of the inferred avalon meguma boundary beneath georges bank as a low angle detachment

monitoring of hydrochemical parameters of lignite mining lakes in central germany using airborne hyperspectral casi scanner data active and abandoned coal mines have a huge impact on the environment the most challenging problem is caused by acid mine drainage amd using traditional methods such as single point measurements to determine and analyze mining lakes over the period of a few years is difficult due to the lakes high dynamic and inner differentiation to overcome this difficulty a new method has been successfully tested to additionally monitor residual lakes using a manifold data set like images from the hyperspectral airborne scanner casi ground truth data spectral field and laboratory measurements the optical properties reflection absorption and scattering of acid mining lakes were defined for the first time ever furthermore hydrochemical parameters in quality and quantity were ascertained in a two stage process first optical properties of the mining lakes were analyzed and defined for each of the limnological stages of development second based on the lakes optical properties algorithms for classification of the hydrochemical parameters evolved and were reliably utilized the new algorithms enable the monitoring of mining lakes from acidic to alkaline as well as the quantification of the hydrochemical properties inside the lake water

p t t paths and differential alleghanian loading and uplift of the bronson hill terrane south central new england late paleozoic u pb ages of sphene and 4 0 ar 3 9 ar cooling ages of amphibole and muscovite from rocks of the bronson hill terrane in connecticut and central massachusetts reflect a late paleozoic alleghanian overprinton acadian metamorphic rocks prograde alleghanian sphenes crystallized during the late pennsylvanian and eliminate the possibility that amphibole ages reflect delayed permian cooling from devonian acadian metamorphism fourteen new amphibole ages from connecticut form a north to south trend of decreasing age from 294 to 245 ma while in massachusetts four new amphibole ages together with three others from the literature produce a random carboniferous pattern seven new muscovite ages support existing data indicating uniform cooling throughout the bronson hill terrane through 350 c in the early triassic the rate of permian cooling defined by amphibole muscovite pairs increases from 4 c my in northern connecticut to 50 c my near long island sound hinged loading and hinged but delayed exhumation in the southern part of the bronson hill terrane with the hinge in central connecticut explain these ages and cooling rates as well as a southerly increasing metamorphic field gradient one dimensional thermal modeling indicates that loading of bronson hill rocks must have begun by the late mississippian the time of peak alleghanian metamorphic temperature decreases southward from early permian in northern connecticut to late permian to the south these results demonstrate that the metamorphic effects of the alleghanian orogeny are not restricted to the avalon terrane of southeastern new england on the contrary the alleghanian orogeny reset 4 0 ar 3 9 ar mineral ages recrystallized minerals partially melted felsic rocks and transposed fabrics at least as far west as the bronson hill terrane in south central new england

contrasting p t t paths thermochronologic evidence for a late paleozoic final assembly of the avalon composite terrane in the new england appalachians strongly contrasting pressure temperature time paths for the avalon composite terrane and the structurally overlying putnam nashoba zone in eastern new england obtained from thermochronologic and thermobarometric data are best explained by a late paleozoic underthrusting of cover rocks by the avalon composite terrane we present new ar and u pb thermochronologic data that show that in the southern hope valley zone permian 280 ma anatectic metamorphic conditions of 700 c and 6 kbar were quenched by relatively rapid cooling 12 c m y and exhumation 0 5 km m y for 40 m y in contrast peak metamorphic conditions in the putnam nashoba zone predate silurian intrusions and slower cooling 3 5 c m y began at about 400 ma one dimensional thermal modeling suggests that these two belts were not in thermal equilibrium during the permian metamorphism of the avalon composite terrane because of the absence of high grade alleghanian metamorphism in rocks overlying the avalon terrane we conclude that high grade alleghanian metamorphism in the avalon terrane occurred east of rocks now overlying it and that significant motion between avalon and this cover occurred after peak alleghanian metamorphism similarly contrasting metamorphic histories between avalon inliers willimantic window massabesic complex gneiss pelham dome and their cover rocks reveals the regional significance of this boundary the core rocks all show permian cooling but the cover rocks show post acadian cooling ages decreasing from east to west to the pelham area where hornblende ages in avalon and cover differ by only 35 rather than 80 m y model calculations show that thermal equilibrium between instantaneously thrusted blocks of rocks is generally obtained in tens of millions of years consequently underthrusting of avalon is constrained to be middle mississippian or younger because the leading edge of the underthrusting block would have been heated the longest and would have most closely approached thermal equilibrium with its cover core rocks of the pelham dome must have been relatively close to this leading edge thus carboniferous to permian underplating from a generally eastward direction best explains these thermochronologic relationships

oriented multiphase needles in garnet from ultrahigh temperature granulites connecticut u s a this study investigates distinctive oriented needle shaped multiphase inclusions found within cores of garnets from felsic granulites of the upper member of the bigelow brook formation and the brimfield schist northeastern connecticut u s a the rocks crop out in the southern end of the central maine terrane and thus are a part of the acadian neoacadian orogen the typical mineral assemblage is garnet sillimanite k feldspar plagioclase quartz cordierite biotite spinel the sillimanite is commonly pseudomorphous after kyanite the multiphase needle inclusions and associated exsolved needles of rutile and ilmenite are mostly oriented parallel to of garnet the multiphase needles contain various combinations of quartz micas chlorite rutile graphite a siliceous compositionally variable phase phase cv zn spinel apatite zircon and rare ilmenite we hypothesize that they represent inclusions of fluid that adhered to exsolving ti fe oxide needles mostly rutile or extended along zones of weakness in garnet this requires that multiphase needle formation occurred in response to cooling and or decompression the needles ultimately decrepitated during retrogression we note that micaceous needle shaped multiphase inclusions are rarely described the closest analogs of which we are aware are found in uhp garnets of the erzgebirge perchuk 2008 the brimfield schist in this area underwent ultrahigh temperature metamorphism uhtm of 1000 c at a minimum pressure of 1 gpa ague et al 2013 here we provide new temperature estimates for the adjacent upper member of the bigelow brook formation ternary feldspar reintegration using the activity model of benisek et al 2004 and zr in rutile thermometry tomkins et al 2007 give average temperatures of 990 and 1010 c respectively at 1 gpa for this unit therefore the recently discovered uht zone in the brimfield schist of northeastern connecticut extends to the east to include the upper member of the bigelow brook formation consequently the first confirmed regional uht locality in the united states is larger than initially recognized and is at least 25 km long and 5 10 km wide the oriented elongate multiphase inclusions and petrographically obvious oriented ti fe oxide needles may be useful indicators of extreme temperature and or pressure rocks in other field areas

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

tectonic implications of late paleozoic metamorphism in southeastern new england a map showing the distribution of pennsylvanian permian metamorphism in southern new england shows that the center of metamorphism is located substantially south and east of middle devonian acadian high grade metamorphism this suggests that the permian disturbance in southern new england is not related to delayed post acadian uplift the map is based on existing data within the pennsylvania basins and on a combination of published microstructures and apparent mineral ages in the surrounding rocks the distribution of metamorphism is however apparently related to major tectonic boundaries that were active during the late paleozoic and suggests that it may be the result of terrane accretion during the late paleozoic

use of gis to discover potential coalfields in yatagan milas area in turkey abstract the study was aimed to produce potential coalfield map using geographic information systems gis in the milas yatagan basin frequency ratio model was used to define the relationships between the coal occurrences and the selected variables which are significant for coal prospection formation geologic age lithology rock types depositional environment distance to fault and slope data of the study area were used as variables frequency ratio values of the variables were calculated and assigned to variable s class attributes all variable maps were summed according to the frequency ratio values of superposed pixels to calculate the probability index the probability index values of the potential map were classified into five classes as very high high medium low and very low probability areas finally the potential map was compared with known coalfields in the milas yatagan basin and calculated distribution of the known coalfields on the probable areas

identification of the scales of differential element mobility in a ductile fault zone two fundamentally different scales of element mobility have been identified in the upper amphibolite facies hunts brook fault zone of south central connecticut usa field relations mineral chemistry and 80 bulk rock analyses provide overwhelming evidence that the blastomylonitic schists and gneisses of the fault zone were derived from the enclosing granodioritic rope ferry orthogneiss two sample mass balance calculations between the rope ferry gneiss and fault rocks strongly suggest that the rope ferry gneiss was segregated into biotite rich schists and quartz plagioclase rich gneisses through the centimetre scale transfer of si al ca na ba and zr from schists to gneisses three and four sample mass balance calculations provide convincing evidence that al ca na and ba were lost and si and k gained by the entire fault zone both scales of metasomatism have been identified at two localities separated by 20 km implying that the metasomatic processes were pervasive throughout the fault zone from the mass balance calculations an apparent disparity in k mobility arises k appears to be gained by the entire fault zone but is immobile during the centimetre scale segregation this is because mass balance calculations can only detect differential element mobility differential element mobility requires that the mechanism of metasomatism produces chemical potential gradients therefore the identification of differentially mobile elements provides insight into the mechanisms of metasomatism the immobility of k during segregation of schists and gneisses implies that the segregation was not achieved through the extraction of partial melt however the element mobility is reconcilable with deformation driven metamorphic differentiation the gains of si and k and losses of ca na al and ba for the entire fault zone are also inconsistent with the intrusion or extraction of partial melt but may reflect the infiltration of a metasomatizing aqueous fluid

hyperspectral remote sensing monitoring of pyrite mine wastes a record of climate variability pyrite belt spain monitoring of mine waste on sulphide deposits through hyperspectral remote sensing data contributes to predicting surface water quality quantitatively estimating acid drainage and metal contamination on a yearly basis the mineralogy of surface crusts loaded with highly soluble salts is a record of available humidity and temperature along the year a temporal monitoring of salt efflorescence on mine wastes at a mine site in the iberian pyrite belt spain has been mapped in this work using hyperspectral airborne hymap data climate change estimations are made based on oxidation stages derived from well known sequences of minerals tracing sulphides oxidation intensity using archive spectral libraries therefore mine waste weathering products of sulphide mapped from airborne hyperspectral remote sensing data can be used as a short term record of climate change providing a useful tool for assessing environmental geoindicators in semi arid areas

a tectonic model for the late paleozoic of southeastern new england hornblende and biotite sup 40 ar sup 39 ar age spectra from rocks in south central connecticut help define a permian triassic cooling curve for the area together with petrologic and structural information a time temperature pressure strain path is established similar data for the narragansett basin in rhode island and massachusetts allow correlation of the late paleozoic histories of the two areas together these data suggest that in the late paleozoic south central new england was part of a fold thrust belt and the narragansett basin was a retroarc foreland basin nw se compression during the final assembly of pangaea resulted in se directed thrusting causing the development of clastic wedges in adjacent rhode island and massachusetts in the late carboniferous early permian a clockwise rotation of this deformation from nw to nne led to northward underthrusting and concomitant uplift of both eastern connecticut and rhode island in the permian and triassic

the massabesic gneiss complex new hampshire a study of a portion of the avalon terrane geochemical data from the 625 ma massabesic gneiss complex of southern new hampshire show strong affinities for other avalonian rocks of southern new england and suggest continental rifting in the late proterozoic migmatized paragneiss the dominant rock type in the complex has major and trace element compositions that are compatible with graywackes from continental arcs the para gneiss also has strong lithologic metamorphic and isotopic similarities to the rocks of the hope valley zone of connecticut avalon suggesting a possible hope valley massabesic correlation at 625 ma the paragneiss end values are similar to avalonian crust in other locations of the orogen two types of amphibolite are present in minor amounts in the paragneiss of the massabesic gneiss complex the first type is a paramphibolite and consists of calc silicate layers in the massabesic paragneiss the second type is metaigneous major and trace element abundances reveal that the protoliths of the orthoamphibolites range from continental rift alkaline basalts and tholeiites to n type morbs orthoam phibolite end 625 ma values range from 2 4 to 4 as expected of rift related magmas derived from partial melting of a depleted mantle source and have the same values as iapetus ocean floor rocks of similar age orthoamphibolite major and trace element geochemical characteristics overlap those of the middlesex fells amphibolites of the esmond dedham zone of eastern massachusetts avalon which range from alkaline to transitional basalts erupted in a continental rift setting the compositions of orthoam phibolites define a potential magmatic continuum produced by batch partial melting of the mantle initiated during continental rifting and proceeded to ocean basin forma tion the inferred continuity of mafic magmatism from the esmond dedham mid dlesex fells formation to the massabesic gneiss complex and hope valley zone suggests that these zones are not distinct lithotectonic zones but are parts of a single landmass massachusetts avalon esmond dedham represents the continental section of avalon where the alkaline to transitional magmas of the early rifting stages are preserved according to our tectonic reconstruction the massabesic gneiss complex is the oceanward continental margin represented by volcanoclastic sediments with the morbs representing the initiation of ocean basin development the leading edge of this landmass of which the massabesic gneiss complex is the only observable remnant collided with laurentia during the acadian orogeny the inboard thicker more continental trailing edge that is platform avalon esmond dedham collided later during the alleghanian orogeny

u pb monazite geochronology of granitic rocks from maine implications for late paleozoic tectonics in the northern appalachians crystallization ages of monazites from peraluminous granites and granitic pegmatites in southwestern maine constrain the timing of final ductile motion of a major shear zone to approximately 280 ma u pb monazite ages of granite at brunswick 278 pm 2 ma and evolved granitic pegmatites in topsham 275 269 ma provide evidence that synkinematic intrusion was followed by final emplacement at the end of ductile deformation these granitic rocks were evidently generated during the final high temperature event experienced by this portion of the appalachian orogen during this time the host rocks record initial rapid cooling c 16 c m y followed by slower cooling c 4 c m y into the mesozoic the similarity of ages of granite in brunswick and pegmatites in topsham permit the rocks to be related to the same magmatic system the spatially associated sebago batholith the largest exposed pluton in new england has a concordant u pb monazite age of 293 pm 2 ma thus the sebago batholith cannot be

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

thermal history of the acoculco geothermal system eastern mexico insights from numerical modeling and radiocarbon dating abstract acoculco is a geothermal prospective area hosted by a volcanic caldera complex in the eastern trans mexican volcanic belt surface manifestations are scarce and consist of gas discharges co2 rich and acid sulfate springs of low temperature whereas hydrothermal explosive activity is profusely manifested by meter scale craters and mounds of hydrothermal debris and breccias silicic alteration extends for several square kilometers around the zone with gas manifestations and explosive features affecting surficial volcanic rocks primarily tuffs and breccias in the subsurface an argillic alteration zone ammonium illite extends down to a depth of 600 m and underneath it a propylitic zone epidote calcite chlorite occurs down to 1000 m thermal logs from an exploratory borehole eac 1 drilled in 1995 down to 1810 m showed a conductive heat transfer regime under high geothermal gradient 140 c 1000 m in contrast the thermal profile established from temperatures of homogenization of fluid inclusions measured on core samples from the same drill hole suggests that convection occurred in the past through the upper 1400 m of the geothermal system a drop in permeability due to the precipitation of alteration minerals would have triggered the cessation of the convective heat transfer regime to give place to a conductive one with the purpose of determining when the transition of heat transfer regime occurred we developed a 1d model that simulates the time depth distribution of temperature according to our numerical simulations this transition happened ca 7000 years ago this date is very recent compared to the lifespan of the geothermal system in addition radiocarbon chronology indicates that the hydrothermal explosive activity postdates the end of the convective heat transfer regime having dated at least three explosive events at 4867 5295 1049 1417 and 543 709 y cal bp therefore hydrothermal explosions arise from the self sealing of the acoculco geothermal system involving a natural hazard that could affect future geothermal power infrastructure

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated