u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

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

prolonged acadian orogenesis revelations from foliation intersection axis fia controlled monazite dating of foliations in porphyroblasts and matrix numerous phases of garnet growth are revealed by detailed studies of foliation inflection intersection axes preserved in porphyroblasts fias in acadian metamorphic rocks in the chester dome region of vermont u s a a regionally consistent succession of four different fia tends in garnet porphyroblasts has been dated by analyzing monazite inclusions with an electron microprobe these monazite inclusions which lie within the various foliations that define the fias provide absolute ages for multiple periods of deformation and episodic phases of garnet growth the monazite inclusions reveal a progression in foliation ages from 431 2 to 349 3 million years within porphyroblasts and from 366 3 to 327 5 million years in pervasive matrix foliations three samples of schist reveal ages ranging through 75 to 70 million years from the cores of porphyroblasts through the medians to the rims and then into the matrix ages determined from monazite grains within garnet porphyroblasts link directly to periods of multiple deformation and episodic garnet growth defined by the fias the four fia sets began forming prior to 424 3 405 6 386 6 and 366 4 million years ago respectively thus multiple stages of garnet growth occurred throughout acadian deformation and metamorphism in vermont and orogenesis was far more prolonged than previously thought invariably garnet growth occurred early in the accompanying deformation event dating of monazite inclusions without careful separation of phases of garnet growth by fia studies will lead to a spread of ages that will confuse rather than elucidate the metamorphic and structural history analysis of monazite grains in the matrix alone will likely only present ages for the youngest events these ages can be amalgamated from grain to grain to yield apparently precise ages but such ages reveal nothing about the deformation and metamorphic processes operating during orogenesis or the overall continuity of the deformation and metamorphism that accompanies plate motion fia and microstructural studies of inclusion trail successions allow numerous phases of garnet growth to be distinguished and then dated using monazite that has dissolved and regrown many times as multiple successive foliations developed this in turn allows very long and involved metamorphic histories to be fully integrated with similarly complex structural histories

fortnightly and monthly variability of the exchange through the strait of gibraltar the fortnightly and monthly variability of the exchange through the strait of gibraltar has been studied from two simultaneous five month long moored datasets at camarinal sill and the east section the study focuses on the msf and mm tidal components and their role for the subinertial exchange a significant monthly signal is observed in the upper layer transport also a significant fortnightly signal is observed in the lower layer transport which minimum maximum flow toward the atlantic takes place approximately on spring tides in consequence the net transport has both signals with maximum taking place during neap tides and a small monthly inequality fortnightly and monthly variability in the interface depth is also observed at camarinal sill the interface being deeper on neap and shallower on spring tides at the east section the interface depth signals are not significant the subinertial variability of the transports is separated in two contributions the first one is called quasistatic transport and arises from the subinertial fluctuations of currents the second contribution called tidally rectified transports arise from the non linear correlation of currents and interface depth at tidal frequencies the tidally rectified transports are important at camarinal but not at the east section an apparent contradiction between the fortnightly signals of the subinertial currents and subinertial transports is resolved when the fortnightly signal of the tidally rectified transports are considered the fortnightly signal of the quasistatic and tidally rectified transports mutually cancel in the upper layer but not in the lower layer where the rectified transports dominate a simple model for the spring tide mixing forcing accounts for the fortnightly variability of the lower layer quasistatic transports but underestimates it for the upper layer finally the observed lower layer transport is compatible with the hydraulic control condition at camarinal sill except for certain periods during intense spring tides 2006 elsevier ltd all rights reserved

pressure temperature fluid evolution in eburnean metabasites and metapelites from tamanrasset hoggar algeria abstract tamanrasset central hoggar algeria is part of the 2000 ma eburnean terrane in which spectacular examples of granulite grade metapelites and metabasites occur reactional textures in metabasites supplemented by geothermobarometry fluid inclusions and mineral equilibria indicate a complex metamorphic history characterized by a strong decompression during postpeak uplift peak metamorphic pressure temperature pt conditions of 800 c and 10 kbar respectively were followed by rapidly decreasing pressure to 700 c and 6 kbar at nearly constant temperature during which time the rocks acquired their present mineral assemblages and textures garnet pyroxenites this isothermal decompression path was followed by nearly isobaric cooling throughout this history water activity remained consistently low documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usep

tides in the strait of gibraltar the strait of gibraltar is where the transition occurs between two distinct tidal regimes the north atlantic where tidal ranges are in excess of 2 m and the western mediterranean where tidal ranges are less than 1 m within the strait the tide is principally semidiurnal observations indicate that on average 96 of the bottom pressure and 74 of the current variability are contained in the semidiurnal band 2 cpd the structure of the local cotidal chart of the m2 tidal constituent is complicated but can be explained in terms of the along and across strait momentum balances along the strait the pressure gradient is mainly balanced by the acceleration of the flow although friction can be of appreciable magnitude corresponding to a decay time scale of 3 16 hours across the strait the momentum balance appears mostly geostrophic but better observations would be required to explain residual terms available observations indicate that the m2 tide has no net energy flux through the strait at the sill the tidal transport in the upper layer exceeds that in the lower layer by nearly a factor of 2 at the eastern end of the strait between algeciras and ceuta the tidal transport is larger in the lower layer this apparent shift in the location of maximum tidal transport is explained in terms of the kinematics of the interface between atlantic and mediterranean waters a mean transport of 0 21 sv due to subinertial and tidal flows carries atlantic water through the strait compensated by an approximately equal return in the lower layer

geochronologic studies in central new england ii post acadian hinged and differential uplift sup 40 ar sup 39 ar analyses of muscovite biotite and k feldspar from central new england reveal a remarkable pattern of mineral ages the ages are progressively younger from central to western new hampshire and rise sharply near the vermont border to ages more typical of post acadian cooling this distribution is attributed to differential uplift via isostatic rebound of an anomalously thickened crust at the bronson hill anticlinorium this explanation requires that between 6 and 8 km of normal fault motion has occurred on structures in western new hampshire not previously recognized to have accommodated this kind or magnitude of displacement this hinged differential uplift occurred from approximately 360 170 ma and is consistent with a time constant for rebound of approximately 80 m y

a model for garnet and plagioclase growth in pelitic schists implications for thermobarometry and p t path determinations numerical models of the progressive evolution of pelitic schists in the ncmnkfmash system with the assemblage garnet biotite chlorite staurolite plagioclase muscovite quartz h2o are presented with the goal of predicting compositional changes in garnet and plagioclase along different p t paths the numerical models support several conclusions that should prove useful for interpreting the p t paths of natural parageneses i garnet may grow along p t vectors ranging from heating with decompression to cooling with compression p t paths deduced from garnet zoning that are inconsistent with these growth vectors are self contradictory ii there is a systematic relation between garnet and plagioclase composition and growth such that for most p t paths garnet growth requires plagioclase consumption furthermore mass balance in a closed system requires that as plagioclase is consumed the remaining plagioclase becomes increasingly albitic inclusions of plagioclase in the core of garnet should be more anorthitic than those near the rim and zoned matrix plagioclase should have rims that are more albitic than the cores complex plagioclase textures may arise from the local variability of growth and precipitation kinetics iii a decrease of fe fe mg in a garnet zoning profile is a reliable indicator of increasing temperature for the assemblage modelled however there is no single reliable p monitor and inferences about p can only be made by considering plagioclase and garnet together iv consumption of garnet during the production of staurolite removes material from the outer shell of a garnet and may make recovery of peak metamorphic compositions and p t conditions impossible low peak temperatures typically recorded by staurolite bearing assemblages may reflect this phenomenon v diffusional homogenization of garnet affects the computed p t path and results in a clockwise rotation of the computed p t vector relative to the true p t path

a near uniform basin wide sea level fluctuation of the mediterranean sea abstract a new basin wide oscillation of the mediterranean sea is identified and analyzed using sea level observations from the ocean topography experiment topex poseidon satellite altimeter and a numerical ocean circulation model more than 50 of the large scale nontidal and non pressure driven variance of sea level can be attributed to this oscillation which is nearly uniform in phase and amplitude across the entire basin the oscillation has periods ranging from 10 days to several years and has a magnitude as large as 10 cm the model suggests that the fluctuations are driven by winds at the strait of gibraltar and its neighboring region including the alboran sea and a part of the atlantic ocean immediately to the west of the strait winds in this region force a net mass flux through the strait of gibraltar to which the mediterranean sea adjusts almost uniformly across its entire basin with depth independent pressure perturbations the wind driven response can be explained in part by wind setup

a calculated petrogenetic grid for ultramafic rocks in the system cao feo mgo al2o3 sio2 co2 h2o at low pressures calculated phase equilibria among the minerals amphibole chlorite clinopyroxene orthopyroxene olivine dolomite magnesite serpentine brucite calcite quartz and fluid are presented for the system cao feo mgo al2o3 sio2 co2 h2o caf masch with chlorite and h2o co2 fluid in excess and for a temperature range of 440 c 600 c and low pressures the minerals chosen in cafmasch represent the great majority of phases encountered in metamorphosed ultramafic rocks the changes in mineral compositions in terms of femg 1 and mg fe sial 1al 1 are related to variations in the intensive parameters for example equilibria at high x text co text 2 in the presence of chlorite involve minerals which are relatively aluminous compared with those at low x text co text 2 the calculated invariant univariant and divariant equilibria are compared with naturally occurring greenschist and amphibolite facies ultramafic mineral assemblages the correspondence of sequences of mineral assemblages and the compositions of the minerals in the assemblages is very good

two stage decompression in garnet bearing mafic granulites from sostrene island prydz bay east antarctica mafic garnet bearing granulites from sostrene island 150 km southwest of davis station on the coast of prydz bay east antarctica exhibit two stage symplectic coronas on garnet formed after peak metamorphic conditions m1 an outer corona of opx mg66 pl an94 97 minor hbl mantles a finer grained inner corona of opx mg67 pl an95 96 spl mg36 both symplectites contain minor ilmenite magnetite intergrowths the finer grained symplectite also occurs along a fracture cleavage in the garnet the outer corona originated during a second metamorphic event m2 via the reaction grt cpx hbl sio2 opx pl 1 whereas the inner corona formed later in response to decompression and minor deformation resulting in the fracture cleavage in the garnet according to the reaction grt opx pl spl 2 the grossular content of the garent xgrs 0 168 is almost exactly that which is required for the stoichiometric breakdown by reaction 2 calculated xgrs 0 167 the mafic rocks are silica undersaturated and the sio2 for reaction 1 was most probably derived externally from the surrounding felsic gneisses preferred p t estimates for m1 based on garnet core prp40alm42grs17sps1 matrix opx cpx hbl pairs are c 10 kbar at 980 c the fine grained symplectite formed post peak m2 at c 7 kbar and 850 c the enclosing felsic gneisses yield pressure estimates of between 5 and 7 kbar which compare with conditions of c 6 kbar and 775 c in the nearby bolingen islands these lower p t estimates are considered to be representative of the widespread 1100 ma metamorphic event recognized in outcrops along the prydz bay coast the high p high t estimates derived from the garnet relics provide evidence for an earlier possibly archaean high grade metamorphic event

pan african displaced terranes in the tuareg shield central sahara concepts developed in the recently published model of the air region eastern tuareg shield niger africa as a college of three displaced terranes integrated in a single geodynamic model lead us to propose a terrane map of the tuareg shield 500000 km 2 the 23 terranes recognized have their own lithological metamorphic magmatic and tectonic characteristics and are separated by subvertical strike slip megashear zones that can be traced for hundreds of kilometres or by major thrust fronts some of these boundaries have ophiolitic assemblages or molassic deposits the tuareg shield was shaped and partly accreted during the pan african orogeny 750 550 ma but not as a homogeneous body

ultrahigh temperature mafic granulites from panrimalai south india constraints from phase equilibria and thermobarometry abstract the panrimalai area constitutes part of the granulite facies rocks of the madurai block in the southern granulite terrain sgt india garnet bearing mafic granulites in panrimalai occur as small enclaves within charnockite the common stable assemblage during peak metamorphism contains hornblende garnet orthopyroxene clinopyroxene quartz and plagioclase the resorption of garnet in various reaction textures and the development of spectacular orthopyroxene plagioclase and hornblende plagioclase symplectites characterize the subsequent stages of metamorphism application of multi equilibrium calculation procedures for mineral core compositions of the early assemblage yields near peak conditions at 900 c at 9 kbar these estimates are the highest yet reported in mafic granulites from the madurai block the post peak p t path is constructed for the mafic granulites based on observed microstructural relations and thermobarometric results is characterized by a steep clockwise decompressional p t segment from 9 to

the effect of mediterranean exchange flow on european time mean sea level using a suite of ocean model simulations and a set of dedicated twin experiments we show that the exchange flow between the mediterranean and the north atlantic leads to a drop in time mean european coastal sea level along the atlantic coast north of gibraltar the drop is about 7 cm along the portuguese coast and remains apparent though reduced as far north as the norwegian coast we also show that mediterranean time and spatial mean sea level is about 9 cm lower than it would be without the exchange flow but assuming a small supply from the atlantic to balance evaporation each of these relationships makes possible an estimate of the magnitude of the exchange flow based on sea level measurements and estimates of 0 8 and 0 91 sverdrups are made consistent with previous determinations based mainly on current measurements in the strait of gibraltar

supplemental material zircon and monazite geochronology in the palmer zone of transpression south central new england usa constraints on timing of deformation high grade metamorphism and lithospheric foundering during late paleozoic oblique collision in the northern appalachian orogen analytical methods for zircon u pb and monazite th pb sims geochronology zircon u pb la icp ms geochronology data tables and supporting previous work

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

atlantic to mediterranean sea level difference driven by winds near gibraltar strait observations and numerical simulations show that winds near gibraltar strait cause an atlantic ocean to mediterranean sea sea level difference of 20 cm peak to peak with a 3 cm standard deviation for periods of days to years theoretical arguments and numerical experiments establish that this wind driven sea level difference is caused in part by storm surges due to alongshore winds near the north african coastline on the atlantic side of gibraltar the fraction of the moroccan coastal current offshore of the 284 m isobath is deflected across gibraltar strait west of camarinal sill resulting in a geostrophic surface pressure gradient that contributes to a sea level difference at the stationary limit the sea level difference is also caused in part by the along strait wind setup with a contribution proportional to the along strait wind stress and to the length of gibraltar strait and adjoining regions and inversely proportional to its depth in the 20 360 day band average transfer coefficients between the atlantic alboran sea level difference and surface wind stress at 36 n 6 5 w estimated from barometrically corrected ocean topography experiment topex poseidon data and ncep ncar reanalysis data are 0 10 0 04 m pa 1 with 1 5 day lag and 0 19 0 08 m pa 1 with 5 4 day lag for the zonal and meridional wind stresses respectively this transfer function is consistent with equivalent estimates derived from a 1992 2003 high resolution barotropic simulation forced by the ncep ncar wind stress the barotropic simulation explains 29 of the observed atlantic alboran sea level difference in the 20 360 day band in turn the alboran and mediterranean mean sea level time series are highly correlated 0 7 in the observations and 0 8 in the barotropic simulation hence providing a pathway for winds near gibraltar strait to affect the mean sea level of the entire mediterranean

winds in the strait of gibraltar summary automated meteorological observations were made from october 1985 to september 1986 in the narrows of the strait of gibraltar additional surface and upper air measurements were made in the strait from may to july 1986 the main wind events in summer were mostly mesoscale levanters winds from the east through the strait and a lesser number of synoptic scale levanters and westerlies during mesoscale levanters the wind speed increased and the pressure decreased from gibraltar downstream through the narrows as far as tangier a mesoscale low and the highest winds were found over the axis of the strait north of tangier high velocity 20 m s winds occurred only under 1 km height the air temperature profile became progressively warmer moving from gibraltar towards tangier a weak air temperature inversion decreased in height to the west of the narrows venturi flow as an explanation for the downstream increase of the low level winds during a levanter is inconsistent with observations a new model is proposed to explain the wind field associated with levanter winds in the strait that includes some orographic blocking and low level convergence into the narrows some west side divergence due to drag over water and leeside heating that generates a leeside mesoscale low pressure the surface low accelerates the surface winds to their maximum strength well downstream of the narrows a similar flow regime has been observed recently in the sea level channel between hawaii and maui

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

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

low frequency fluctuations in the strait of gibraltar from medalpfx sea level data abstract thirtten months of hourly sea level data from four stations in the strait of gibraltar along with appropriate atmospheric pressure data are used to investigate tidal and low frequency fluctuations in the strait apparent recording errors in the data weaken a study of the tides on their own but low passed and complex demodulated at m2 time series show that nonastronomical variations in the alongstrait m2 sea level slope are correlated with the varying phase lag from tarifa to gibraltar more importantly regression of the low passed sea level difference across the strait on the varying tidal amplitude suggests that the mean surface inflow is only about 10 different from what it would be in the absence of tides correlation and cross spectral analyses also show significant connections between the three time series representing the slowly varying surface inflow subsurface pressure gradient along the strait and atmospheric pressure gradient along the strait correlation between the first and

an example of ultrahigh temperature metamorphism orthopyroxene sillimanite garnet sapphirine quartz and spinel quartz parageneses in al mg granulites from in hihaou in ouzzal hoggar quartz al mg granulites exposed at in hihaou in ouzzal nw hoggar preserve an unusual high grade mineral association stable at temperatures up to 1050 c involving the parageneses orthopyroxene sillimanite garnet quartz sapphirine quartz and spinel quartz the phase relationships within the fmas system show that a continuum exists between the earlier prograde reaction textures and those of the later decompressive event the following mineral reactions involving sillimanite are deduced 1 grt qtzopx sil 2 opx silgrt spr qtz 3 grt sil qtzcrd 4 grt silcrd spr 5 grt sil sprcrd spl 6 grt silcrd spl 7 grt crd silspl qtz and 8 grt silspl qtz minerals in quartz al mg granulites display compositional variations consistent with the observed reactions the mg mg fe2 range of the main minerals is as follows cordierite 0 81 0 97 sapphirine 0 77 0 88 orthopyroxene 0 65 0 81 garnet 0 33 0 64 and spinel 0 23 0 56 the reaction textures and the evolution of the mineral assemblages in the quartz al mg granulites indicate a clockwise p t trajectory characterized by peak conditions of at least 10 kbar and 1050 c followed by decompression from 10 to 6 kbar at a temperature of at least 900 c

microstructure and crystallographic preferred orientation of polycrystalline microgarnet aggregates developed during progressive creep recovery and grain boundary sliding abstract optical microscopy electron probe microanalysis and electron backscatter diffraction methods have been used to examine a broad range of garnet microstructures within a high strain zone that marks the western margin of a major transpression zone in the southern new england appalachians garnet accommodated variable states of finite strain expressed as low strain porphyroclasts type 1 high strain polycrystalline aggregates type 2 and transitional morphologies type 3 that range between these end members type 1 behaved as rigid porphyroclasts and is characterized by four concentric ca growth zones type 2 help define foliation and lineation are characterized by three ca zones and possess a consistent bulk crystallographic preferred orientation of 100 symmetrical to the tectonic fabric type 3 show variable degrees of porphyroclast associated with aggregate where porphyroclasts display complex compositional zoning that corresponds to lattice distortion low angle boundaries and subgrains and aggregate cpo mimics porphyroclast orientation all aggregates accommodated a significant proportion of greenschist facies deformation through grain boundary sliding grain rotation and impingement and pressure solution which lead to a cohesive behavior and overall strain hardening of the aggregates the characteristic cpo could not have been developed in this manner and was the result of an older phase of partitioned amphibolite facies dislocation creep recovery including chemical segregation and recrystallization of porphyroclasts this study demonstrates the significance of strain accommodation within garnet and its affect on composition under a range of pt conditions and emphasizes the importance of utilizing ebsd methods with studies that rely upon a sound understanding of garnet

monazite geochronology in central new england evidence for a fundamental terrane boundary monazite crystallization ages have been measured in situ using sims and emp analysis of samples from the bronson hill anticlinorium in central new england in west central new hampshire each major tectonic unit nappe displays a distinctive p t path and metamorphic history that requires significant post metamorphic faulting to place them in their current juxtaposition and monazite ages were determined to constrain the timing of metamorphism and nappe assembly monazite ages from the low pressure high temperature fall mountain nappe range from c 455 to 355 ma and y zoning indicates that these ages comprise three to four distinct age domains similar to that found in the overlying chesham pond nappe the underlying skitchewaug nappe contains monazite ages that range from c 417 to 307 ma 40 ar 39 ar ages indicate rapid cooling of the chesham pond and fall mountain nappes after 350 ma which is believed to represent the time of emplacement of the high level chesham pond and fall mountain nappes onto rocks of the underlying skitchewaug nappe garnet zone rocks from western new hampshire contain monazite that display a range of ages c 430 340 ma both the metamorphic style and monazite ages suggest that the low grade belt in western new hampshire is continuous with the vermont sequence to the west rocks of the big staurolite nappe in western new hampshire contain monazite that crystallized between c 370 and 290 ma and the same unit along strike in northern new hampshire and central connecticut records ages of c 257 300 ma conspicuously absent from this nappe are the older age populations that are found in both the overlying nappes and underlying garnet zone rocks these monazite ages confirm that the metamorphism observed in the big staurolite nappe occurred significantly later than that in the units structurally above and below these data support the hypothesis that the big staurolite nappe represents a major tectonic boundary along which rocks of the new hampshire metamorphic series were juxtaposed against rocks of the vermont series during the alleghanian

frictional processes in straits friction and mixing can be dynamically significant in straits as in many oceanographic situations for weak time dependent homogeneous flows geostrophy friction and acceleration can all play roles in limiting the flow through a strait and the ratio of the geostrophic elevation difference across the strait to the frictional difference along the strait may be of importance in more general situations a specific question for quasi steady exchange flows through straits concerns the influences of friction and entrainment on hydraulic control within the context of layered models these effects tend to drive a flow towards hydraulic criticality in the downstream direction and to shift control points downstream however friction and entrainment also induce vertical gradients in velocity and density rendering layered models dubious in such situations the conditions for hydraulic control have been uncertain even for a homogeneous fluid there is an apparent contradiction between control conditions based on a similarity assumption for the velocity profile on the one hand and on the speed of long waves on the other the resolution of this contradiction is discussed it seems that if the frictional forces only involve local flow properties then inviscid long waves are arrested at the control section though this is shifted from its location for inviscid flow but that if flow derivatives along the channel are involved the condition changes for a homogeneous flow with shear internal friction and bottom friction the control section is shifted downstream partway to where it would be for a slab flow with bottom friction while the parameterization of bottom friction actually seems to be reasonably well established the nature and quantification of internal and lateral frictional processes are uncertain in a rotating system secondary cross strait flows are expected to be driven by the vertical gradient of the vertical reynolds stress and can provide estimates of the magnitude of bottom and internal friction

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

deformation induced garnet zoning compositional zoning patterns in garnet porphyroblasts from kyanite bearing samples of the devonian littleton formation north central massachusetts reveal complex patterns of growth that are related to multiple deformation and metamorphic events garnet porphyroblasts exhibit asymmetrical and irregular zoning patterns in xmn xca and fe fe mg zoning reversals in mn and fe fe mg and patch distribution in ca appear to occur around the boundaries of the textural zones also the compositions of the garnet at the textural boundaries are variable for all traverses these observations suggest that the garnet zoning was not only modified from diffusion processes but was also influenced by pre existing microfabrics through the effects of preferential dissolution and resorption in partial disequilibrium relationships between chemical and textural truncations indicate that the zoning patterns of garnet were strongly modified from preferential dissolution and precipitation during the development of successive foliations that occurred in zones of high strain stress cleavage seams and zones of low strain stress respectively

raman spectroscopic characterization of h2o in co2 rich fluid inclusions in granulite facies metamorphic rocks abstract water h2o has been identified during raman analyses at 150 200 c of fluid inclusions from granulites that were previously thought to contain pure co2 at room temperature h2o in a co2 rich fluid inclusion forms an optically unresolvable liquid wetting the inclusion walls during heating the h2o phase evaporates into the co2 phase to produce a homogeneous h2o co2 fluid throughout the inclusion volume and the h2o raman peak at 3640 cm 1 is clearly resolvable at elevated temperatures to test and confirm the method synthetic h2o co2 fi of known composition 87 5 mol and 95 mol co2 were also analyzed previously studied granulite samples from the adirondack mountains usa and from the kerala khondalite belt sittampundi complex and sevitturangampatti india were tested for the presence of h2o in co2 rich fluid inclusions traces of h2o were found in co2 rich fluid inclusions in quartz crystals from the adirondacks and from the kerala khondalite belt h2o was not detected in co2 rich secondary fluid inclusions in garnet from the sittampundi complex and from sevitturangampatti rather hydrogarnet was detected along the walls of inclusions in garnet as evidenced by a peak at 3661 cm 1 the hydrogarnet is interpreted to be a step daughter phase that formed by reaction of the h2o in the fluid inclusion with the garnet host during retrogression these observations confirm the presence of an h2o bearing co2 rich fluid at some time during granulite petrogenesis but do not resolve the question of whether these co2 rich fluids were trapped at peak metamorphic conditions or during retrogression or whether the fluid inclusions have reequilibrated following entrapment

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

combining compositional zoning and foliation intersection axes fias in garnet to quantitatively determine early p t t paths in multiply deformed and metamorphosed schists north central massachusetts usa quantitative compositional and microstructural analysis of garnet porphyroblasts in kyanite staurolite garnet grade rocks from the northeastern flank of the pelham dome north central massachusetts distinguishes the effects of acadian deformation and metamorphism from extensive overprinting alleghanian shearing the p t conditions and the metamorphic path during the acadian were determined using samples preserving well defined stages in a lengthy tectonic history revealed by a succession of five foliation intersection axis trends preserved within porphyroblasts fias this acadian succession extends at least 120 km to the north into rocks where no evidence has been found of an alleghanian overprint for each sample where garnet first nucleated during one of these stages in the tectonic history the pt of core growth was determined by plotting the intersection of the mn fe and ca isopleths calculated for the core composition on a p t pseudosection for that sample using thermocalc combining the pt data from all these samples indicates that the temperature and pressure increased throughout acadian orogenesis causing episodic garnet growth during the alleghanian locally intense shearing especially against the margin of the pelham dome formed the dominant schistosity which truncated all foliations defined by inclusion trails in porphyroblasts and obliterated all remains of acadian deformation and metamorphism in the rock matrix shearing was accompanied by near complete homogenization of the compositional zoning in garnet porphyroblasts and an associated apparent increase in the temperature of the matrix to 700 c in those rocks lying directly adjacent to the pelham dome and resulted from the rocks of the northfield syncline being thrust a large distance southwards over the gneisses in the dome

geothermometry and geobarometry a discussion geothermometric and geobarometric methods are considered under two groupings directly calibrated methods and internally consistent data set methods emphasis is placed on the importance of error propagation calculations they allow the calculation of model uncertainties on temperatures and pressures due to the quantifiable uncertainties involved in the calibration and application of methods the possibility of systematic errors due to the unquantifiable effects of the assumptions and approximations involved must be evaluated using the criterion of geological reasonableness the advantages of the internally consistent data set approach are expounded and an appropriate error propagation procedure developed

a two dimensional tidal model for the mediterranean sea the tidal propagation in the mediterranean sea is described through a high resolution two dimensional hydrodynamic model forced by the equilibrium tide and the incoming tide at the strait of gibraltar the four most significant constituents m2 s2 k1 and o1 are included in the model good agreement with a set of 63 coastal gauges is achieved the significance of the equilibrium tide and the forcing at the open boundary is investigated the incoming wave from the strait of gibraltar is important in tuning the tides in the whole of the mediterranean for the north aegean sea the solution without the forcing at gibraltar results in a doubling of the amplitudes of the semidiurnal tides the estimated energy dissipation due to bottom friction is 8 8 108 w the major area of dissipation is the gulf of gabes energy fluxes through the major straits are calculated

apparent oxygen isotope equilibrium during progressive foliation development and porphyroblast growth in metapelites implications for stable isotope and conventional thermometry the assumption of oxygen isotope and major element equilibrium during prograde metamorphism was tested using staurolite grade pelitic schists that have undergone sequential porphyroblast growth and multiple episodes of recrystallization of matrix minerals and foliation development textural relationships are used to infer a metamorphic history that involves garnet growth followed by staurolite growth with each porphyroblast growth event followed by at least one period of recrystallization of matrix minerals conventional geothermobarometry using qtz grt pl ms bt st equilibria yields peak p t conditions of c 625 c at 9 11 kbar consistent with kmnfmash petrogenetic grid predictions for stability of the assemblage grt st bt qtz grt oxygen isotope fractionations yield apparent temperatures of c 590 c and qtz st fractionations yield an apparent temperature of c 595 c diffusional modelling indicates that quartz isotopic compositions were reset by c 30 c via retrograde isotopic diffusional exchange with micas the isotopic temperatures appear to be in excellent agreement with one another and suggest oxygen isotope equilibrium was attained between garnet and staurolite at c 625 c however the agreement of qtz grt and qtz str isotopic temperatures is not consistent with petrographic observations garnet grew before staurolite and petrogenetic grid constraints that predict that garnet grows over a temperature interval of c 525 550 c given that i oxygen diffusion rates in staurolite and garnet are slow enough to render an individual porphyroblast effectively closed to exchange after it forms and ii matrix minerals are able to exchange isotopes via recrystallization during each period of deformation garnet and staurolite could not have simultaneously achieved oxygen isotope equilibrium with each other or with minerals in the recrystallized matrix thus the qtz grt fractionations which yield apparent temperatures that are in apparent agreement with peak metamorphic temperature and apparent temperatures for qtz st fractionations cannot be fractionations resulting from equilibrium isotopic exchange instead they are apparent fractionations between porphyroblasts formed at different temperature and times in the prograde p t d path and quartz that recrystallized and exchanged with micas and plagioclase during several phases of deformation

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

evidence for extension at the willimantic dome connecticut implications for the late paleozoic tectonic evolution of the new england appalachians

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

how well known are the thermodynamics of fe mg ca garnet evidence from experimentally determined exchange equilibria many thermodynamic calculations relating to metamorphic rocks hinge on the thermodynamic parameters of garnet though some models are widely used it is not clear whether their underlying premise is correct that a single set of equations can be written for the activities of the end members of garnet covering the whole compositional range a voluminous body of data can be used to constrain the thermodynamics of garnet namely fe mg exchange experimental data involving garnet and another mineral particularly clinopyroxene orthopyroxene and olivine however examination of these data reveals inconsistencies apparently stemming from differences between the thermodynamics of low ca and high ca garnets with a boundary of about xgca 0 15 in the two regions for the high p t of the experimental data the thermodynamics follow the regular model with values for the interaction parameters in the low ca region of about wgfemg 50r and wafe wgmgca 1300r in which r is the gas constant and in the high ca region of about wgfemg 1100r and wgcafe wgmgca 2200r using the subregular rather than the regular model does not remove the discrepancy the cause of the discrepancy needs to be identified if reliable calculations on rocks are to be made

textural and rb sr isotopic evidence for late paleozoic mylonitization within the honey hill fault zone southeastern connecticut a petrographic and rb sr isotopic study of rocks within and near the honey hill fault zone places important constraints on its history of movement rb sr apparent ages for micas and plagioclase from these rocks have been reset and range from permian to triassic considerably younger than the minimum stratigraphic age ordovician of the rocks studied or of acadian devonian regional metamorphism permian rb sr ages of dynamically recrystallized muscovite date the development of mylonite fabric an older age is precluded by the excellent preservation of unrecovered quartz which indicates that these rocks did not experience temperatures high enough to anneal quartz or thermally reset rb sr isotopic systems in muscovite since the time of mylonitization metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist lower amphibolite grade conditions during permian to triassic time collectively these results indicate that the honey hill fault zone was active during the late paleozoic and that ductile deformation and metamorphism associated with the alleghanian orogeny extend well into southern connecticut an alleghanian age for mylonitization within the honey hill fault zone suggests it should be considered as a possible site for the major late paleozoic strike slip displacementsmore inferred from paleomagnetic studies for parts of coastal new england and maritime canada less

comparison of conventional and garnet aluminosilicate quartz o isotope thermometry insights for mineral equilibration in metamorphic rocks oxygen isotope thermometry based on fractionations among quartz garnet kyanite sillimanite and potassium feldspar in amphibolite to granulite facies schists and gneisses was compared to thermometry based on mineral equilibria conventional thermometry the former approach takes advantage of the exchange between quartz and more refractory minerals such as garnet and the aluminosilicates and their potential for preserving peak oxygen isotopic fractionations although isotopic thermometry using these phases is potentially an approach for circumventing the problem in slowly cooled rocks of retrograde oxygen isotopic exchange with micas and feldspars and of fe and mg exchange between garnet and biotite the results are accurate or geologically meaningful in only certain settings in most cases the results of isotopic thermometry must be evaluated with the aid of quantitative forward models for calculating the amount of retrograde diffusive exchange among micas feldspars and quartz two models used here predict quartz isotopic compositions that differ by only 0 1 per mil and in most cases reproduce to within 0 2 per mil the measured isotopic composition of quartz excellent agreement between isotopic and conventional thermometry is obtained for mid to upper amphibolite facies rocks that have experienced one period of recrystallization and mineral growth and if they are coarse grained or cooled in the absence of a hydrous fluid phase isotopic temperatures of 850 degrees c are in excellent agreement with conventional thermometry in migmatitic granulite facies metapelites if cooling occurred under anhydrous conditions in other cases isotopic temperatures in granulite facies rocks are higher than conventional temperatures a reasonable result in view of the tendency for retrograde cation exchange between garnet and biotite in samples that have undergone multiple periods of recrystallization or metamorphism isotopic temperatures from coexisting quartz garnet and aluminosilicates may be modified by diffusional exchange of quartz with micas and feldspars aided by recrystallization by retrograde reactions involving the latter phases or by open system interaction with externally derived fluids external fluid infiltration combined with recrystallization of quartz and aluminosilicate may result in isotopic reversals between garnet and matrix phases conventional thermobarometry in such complex rocks based in large part on mineral equilibria involving garnet may be erroneously assigned geological significance in the absence of insights provided by oxygen isotope analysis

a mechanism for preferential h 2 o leakage from fluid inclusions in quartz based on tem observations preferential leakage of h2o from fluid inclusions containing multiple gas components has been suspected in natural metamorphic rocks and has been demonstrated experimentally for synthetic h2o co2 rich inclusions in natural quartz knowledge of the physical and chemical characteristics of the leakage mechanism which may be very complex increases the value of natural fluid inclusions to metamorphic geology it is proposed that crystal defects play a major role in nondecrepitative preferential h2o leakage through quartz and remain effective during metamorphism inclusions with either an internal overpressure or underpressure produce strain in the adjacent quartz crystal via the nucleation of many dislocations and planar defects like dauphine twin boundaries these defects allow preferential loss of h2o from h2o co2 rich inclusions at supercritical conditions the transport capacity of this leakage mechanism is enhanced by nucleation of small bubbles on defect structures the nucleation of these bubbles seems to be a recovery process in strained crystals solubility gradients of quartz in water in a crystal with internally underpressurized inclusions may result in optical visible implosion halos in a three dimensional spatial arrangement caused by the growth of small bubbles at the expense of the larger original fluid inclusion natural fluid inclusions from naxos greece are always associated with numerous interlinked dislocations these dislocations may have been produced by plastic derormation or by crystal growth related processes e g crack healing the presence of small bubbles on these dislocations indicates that a similar leakage mechanism for h2o must have occurred in these rocks

the flow of atlantic water through the strait of gibraltar abstract we describe and analyze observations of the water exchange through the strait of gibraltar the primary observations were taken in april 1986 and included data from moored recording instruments at four locations in the strait together with an intensive survey by ship these measurements included extensive ctd profiling acoustic doppler current profiling numerous profiles from expendable instruments and imaging using a high frequency echo sounder the analysis focuses on the internal hydraulics of the strait and in particular the presence of hydraulic controls and their influence on the exchange our observations during april 1986 show that the maximal exchange condition in which a subcritical flow is bounded by supercritical flow at both ends of the strait did occur although with various subtleties not explicitly incorporated in our previous theoretical developments the atlantic water moving east along the surface encounters a control at tarifa narrows in the eastern part of the strait the mediterranean water passes through controls both at camarinal sill and at spartel sill further west at our westernmost mooring at spartel the outflowing mediterranean water is continuously supercritical with little tidal variability the control at camarinal sill is periodically lost due to tidal action and reappears on a reverse flow during a falling spring tide tangier basin bounded by camarinal and spartel sills acts as an internal reservoir for the outflowing mediterranean water the interface rising and falling through each tidal cycle during spring tides the tangier basin interface rises high enough to flood the control at camarinl sill and produces a reverse flow of the lower layer when control is lost at camarinal sill a travelling bore is released this bore may modify the location of the control acting on the surface layer in tarifa narrows the atlantic water enters the alboran sea as a jet which may have a well defined northern boundary where it separates from the european coast this boundary may be identified by the presence of a slick although the internal jump west of camarinal sill is almost certainly an area of intense mixing frictional effects do not appear to be dominant in the subcritical portion of the flow

monazite ages in the chesham pond nappe sw new hampshire u s a implications for assembly of central new england thrust sheets four distinct generations of monazite growth have been identified in samples from the chesham pond nappe and three monazite compositional domains 2 3 and 4 have been correlated with both temperature and mineral assemblage domain 1 cores were interpreted previously to be detrital relics or vestiges of an earlier acadian metamorphism the four monazite domains have been dated by in situ isotope and chemical methods the following are chemical ages of each domain weighted average 2 standard errors of the mean 400 10 ma domain 1 381 8 ma domain 2 372 6 ma domain 3 352 14 ma domain 4 heating and cooling rates derived from combining monazite ages monazite thermometry and 40ar 39ar closure temperatures are approximately 10 15 c m y for heating from 470 to 740 c approximately 8 c m y for cooling from 740 to 375 c and approximately 1 2 c m y for cooling from 375 to 150 c temperature time paths calculated with monazite ages and monazite thermometry indicate that 1 plutonism at ca 400 ma was the likely heat source for the formation of monazite domain 1 and 2 monazite domains 2 4 were produced during a regional low pressure high temperature metamorphism active between 380 350 ma the regional metamorphism is ascribed to lithospheric mantle delamination followed by asthenospheric mantle upwelling which heated a wide area of the merrimack basin southwestern new hampshire central massachusetts central connecticut to temperatures in excess of 725 c monazite ages in the chesham pond nappe and adjacent structural units to the west constrain the commencement of nappe overthrusting to roughly 355 ma