sr ca and δ18o in a fast growing diploria strigosa coral evaluation of a new climate archive for the tropical atlantic this study provides the first monthly resolved 41 year record of geochemical variations 18o and sr ca in a fast growing diploria strigosa brain coral from guadeloupe caribbean sea linear regression yields a significant correlation of coral sr ca 18o with instrumental sea surface temperature sst on both monthly and mean annual scales e g r 0 59 for correlation between simple ocean data assimilation soda sst and sr ca and r 0 66 for 18o mean annual scale p 0 0001 the generated coral sr ca 18o sst calibration equations are consistent with each other and with published equations using other coral species from different regions moreover a high correlation of coral sr ca and 18o with local air temperature on a mean annual scale r 0 78 for sr ca r 0 73 for 18o p 0 0001 demonstrates the applicability of geochemical proxies measured from diploria strigosa corals as reliable recorders for interannual temperature variability both coral proxies are highly correlated with annual and seasonal mean time series of major sst indices in the northern tropical atlantic e g r 0 71 for correlation between the index of north tropical atlantic sst anomaly and sr ca and r 0 70 for 18o mean annual scale p 0 001 furthermore the coral proxies capture the impact of the el nino southern oscillation on the northern tropical atlantic during boreal spring thus fast growing diploria strigosa corals are a promising new archive for the atlantic ocean

origin and metamorphic history of an early cretaceous polybaric granulite terrain fiordland southwest new zealand regionally extensive two pyroxene granulites in fiordland southwest new zealand are products of metamorphism of a suite of anhydrous magmas which crystallized two pyroxenes the granulite protolith igneous charnockitic rock synkinematically intruded metasediment and other orthogneiss in an early cretaceous subduction related magmatic arc and during cooling experienced deformation induced recrystallization to form granoblastic gneiss the granulites occur side by side with coeval rocks of amphibolite facies mineral zoning and textural relationships in both granulites and amphibolite facies rocks provide evidence of two distinct periods of crystallization 1 an early high temperature comparatively low pressure event accompanying magmatic intrusion andalusite sillimanite facies series recorded locally in the country rock followed by 2 high pressure metamorphism under conditions of 650 700 c at 12 13 kbar garnet granulite locally overprinted earlier formed two pyroxene granulite during the latter event the pressure increase 6 kbar between the two events is attributed to crustal thickening by overthrusting and is equivalent to unloading of a 20 km thick slab over rocks already buried at mid crustal depths both events occurred over a 20 m y interval between the time of magmatic emplacement of the granulite protolith and uplift controlled final cooling of the terrain the phanerozoic granulites in fiordland share some petrologic similarities with precambrian granulite terrains suggesting that at least some aspects of the former may serve as a useful model for development of the latter

a deep crustal shear zone exposed in western fiordland new zealand an approximately 180 km long deep crustal shear zone in western fiordland new zealand has been shown to have formed during continental extension between 116 and 100 ma the western fiordland shear zone forms a major tectonic boundary between two sets of gneisses with unrelated deformation histories a detailed study of the northern part of the shear zone has revealed that the shear zone formed at depths of 40 km approximately 12 kbar and 680 c and was originally very gently dipping or subhorizontal prior to subsequent upright folding the current thickness postfolding of the shear zone is 3 4 km abundant asymmetric structures in the shear zone indicate noncoaxial deformation and a top to the ne sense of shear unlike ductile shear zones in metamorphic core complexes from elsewhere in the world there is no evidence that decompression of the shear zone rocks or foot wall rocks occurred during the active life of the shear zone suggesting that displacement along the shear zone by noncoaxial deformation must have been largely horizontal this shear zone provides important evidence for the nature of deep crustal deformation occurring during continental extension

evidence of early cretaceous collisional style orogenesis in northern fiordland new zealand and its effects on the evolution of the lower crust structural metamorphic and kinematic data from a well exposed section of lower crustal rocks in northern fiordland new zealand reveal a history of intense contractional deformation and high p metamorphism at the roots of a convergent orogen high p 14 kbars granulite facies garnet clinopyroxene bearing reaction zones occur adjacent to anorthositic veins within gabbroic and dioritic gneiss these veins and reaction zones were variably deformed by two phases of high p granulite facies deformation quantitative kinematic analyses conducted using systems of rotated veins and reaction zones indicate that the first phase produced steeply dipping shear zones within a sinistral pure shear dominated flow regime wk 0 69 this deformation occurred at conditions of p 14 0 1 3 kbars and t 676 34 c and resulted in subhorizontal arc parallel ne sw stretching and up to 60 subhorizontal shortening in high strain zones of the lower crust at depths 45 km the second phase of deformation occurred at p 14 1 1 2 kbars and t 674 36 c and produced vertically stacked gently dipping ductile thrust faults that accommodated arc normal nw directed displacement these features reflect major tectonic thickening of the crust oblique convergence and high p metamorphism during the collision of the roots of a convergent orogen represented by plutons of the median tectonic zone in eastern fiordland with the paleo pacific margin of gondwana represented by western fiordland distinctive kinematic styles suggest that this collision resulted in a partitioning of the arc parallel ne sw and arc normal nw se components of oblique convergence onto sinistral strike slip and ductile thrust faults respectively at lower crustal levels

thermomechanical evolution of the crust during convergence and deep crustal pluton emplacement in the western province of fiordland new zealand 1 fiordland new zealand contains exposures of high pressure p 12 14 kbar granulite facies rocks that form one of earth s largest exposed lower crustal roots of an early cretaceous magmatic arc these exposures allowed us to examine the mechanisms and processes that controlled crustal thickening and large vertical displacements at the deepest levels of a deforming arc system we present structural and metamorphic data that show how the root of this arc was tectonically thickened by imbricate granulite facies thrust zones during and after the emplacement of sheeted plutons into the middle and lower crust the imbricate thrust zones form part of a well exposed 12 km wide two sided fold thrust belt that preferentially developed in crust that was thermally softened by magmatism changes in metamorphic mineral assemblages and microstructural data from the contact aureole of a composite arc batholith called the western fiordland orthogneiss record thrust and pluton emplacement conditions of p 7 9 kbar paleodepths of 25 30 km these data show that thrust imbrication and tectonic loading at 30 km depth is a viable mechanism of large vertical displacements and crustal thickening at the deepest levels of magmatic arcs this mechanism produced a characteristic up pressure metamorphic history that is similar to that observed in many other large magmatic belts worldwide

moho vs crust mantle boundary evolution of an idea abstract the concept that the mohorovicic discontinuity moho does not necessarily coincide with the base of the continental crust as defined by rock type compositions was introduced in the early 1980s this had an important impact on understanding the nature of the crust mantle boundary using information from seismology and from deep seated samples brought to the surface as xenoliths in magmas or as tectonic terranes the use of empirically constrained p t estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment the xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere and revealed that the crust mantle boundary in off craton regions commonly is transitional over a depth range of about 5 20 km early seismic reflection data showed common layering near the moho correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust mantle boundary developments in seismology petrophysics and experimental petrology have refined interpretation of lithospheric domains the expansion of in situ geochronology especially zircon u pb ages and hf isotopes os isotopes of mantle sulfides has defined tectonic events that affected whole crust mantle sections and revealed that the crust mantle boundary can change in depth through time however the nature of the crust mantle boundary in cratonic regions remains enigmatic mainly due to lack of key xenoliths or exposed sections the observation that the moho may lie significantly deeper than the crust mantle boundary has important implications for modeling the volume of the crust mapping the crust using seismic techniques alone without consideration of the petrological problems may lead to an overestimation of crustal thickness by 15 30 this will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust formation processes and the composition of the convecting mantle

processes controlling vertical coupling and decoupling between the upper and lower crust of orogens results from fiordland new zealand the pre cenozoic configuration of western new zealand allows determination of the effects of magmatism and a changing lower crustal rheology on the evolution of a cretaceous orogen from upper to lower crustal levels 10 50 km beginning at 126 ma a composite batholith dominated by diorite was emplaced into the lower crust during emplacement deformation was partitioned into zones weakened by magma and heat leading to the development of two layer parallel shear zones at the upper and lower contacts of the batholith transient vertical decoupling of the crust above and below the batholith occurred from 126 ma until 120 ma as magma was emplaced into and moved through a weak thick lower crust by 116 ma however much of the batholith had crystallized and the lowermost crust had cooled from 750 c t 850 c to t 650 700 c cooling was aided by the juxtaposition of pre existing crust against hot new crust and by the efficient extraction of partial melts out of the lower crust cooling together with dehydration of the lower crust and mafic compositions led to the development of a strong dry lower crustal root by 116 ma a strong lower crust resulted in high degrees of vertical coupling between the upper and lower crust during contraction from 116 to 105 ma even as magma continued to be emplaced into the mid upper crust a narrow focused orogenic style in the upper crust at this time reflected a highly viscous lower crust through which compressional stresses were transferred vertically the results imply that changes in plate boundary dynamics rather than the thermal weakening of thick lower crust during convergence controlled the onset of regional extension at 108 105 ma

regional granulite facies metamorphism in the ivrea zone is the mafic complex the smoking gun or a red herring one widely accepted paradigm for the development of continental lower crust is that regional granulite facies metamorphism is caused by intrusion of mafic magma beneath or into the crust magmatic accretion the amphibolite to granulite facies supracrustal section exposed in the ivrea zone southern alps northern italy is commonly cited as a classic example establishing this postulated genetic relationship our interpretation of the pattern of metamorphic isograds compositional trends in high grade metasedimentary rocks and textural evidence in metapelite however indicates that final emplacement of the mafic plutonic rocks the mafic complex occurred subsequent to the regional thermal maximum field and petrographic relations suggest that a spatially restricted contact melting event in crustal rocks accompanied the emplacement of the mafic complex this inference is consistent with leucosome compositions in migmatites and a low pressure high temperature metamorphic overprint recorded by mineral assemblages in wall rocks proximal to the intrusion therefore evidence of anatexis and metamorphism of crustal rocks associated unequivocally with emplacement of the mafic complex is found only within an 2 km wide contact aureole overlying the intrusion the narrow aureole associated with emplacement of the mafic complex demonstrates that in some cases emplacement of large volumes of mafic magma within the crust does not inexorably lead to regional scale granulite facies metamorphism and large ion lithophile element depletion by melt loss

crustal thickening of the early cretaceous paleo pacific gondwana margin abstract the cause of 7 to 25 km of early cretaceous thickening of parts of the new zealand gondwana margin has been argued to be due to tectonic or magmatic processes new insights into this event have been gained from examination of the grebe mylonite zone an extensive amphibolite facies early cretaceous ductile shear zone that separates volcanic arc rocks of the outboard median batholith from metasedimentary and intrusive rocks of the western province inboard median batholith at lake manapouri in southwest new zealand ar ar and u pb geochronology shows that here exhumation of the outboard median batholith began 128 ma syn kinematic magmatism was taking place at 121 ma and measurable displacement had ceased by 116 ma although the mylonite zone is currently subvertical a combination of thermochronological cooling profiles lineation orientations and back rotation of tilted tertiary unconformities indicate that it most likely formed as an oblique sinistral reverse fault that dipped 60 e and therefore displaced the outboard median batholith over the margin of the western province however the high original angle of this and other compressional shear zones in analogous structural positions the apparent absence of a regional thrust or nappe sheet s and the subtly different ages of thickening for different areas indicate that tectonic loading can have played only one part in the crustal thickening event another factor was the contemporaneous emplacement of 30 000 km 3 of mafic to felsic magma which was likely accommodated by vertical depression of the middle and lower crust tectonic and magmatic processes leading to crustal thickening were therefore not mutually exclusive

granulite formation during continental extension in fiordland new zealand the formation of the high pressure high temperature rocks known as granulites has traditionally been attributed to metamorphism in the deeper parts of continental collision zones and magmatic arcs1 3 more recently greater consideration has been given to the possibility of granulite formation during continental rifting4 6 and in particular4 to whether granulites are forming today beneath the north american basin and range province here we report thermobarometric data and single zircon u pb ages for an analogous but much more deeply exhumed extensional terrain in fiord land new zealand7 8 where early cretaceous granulites underwent renewed granulite facies metamorphism at significantly shallower crustal levels following the extensional collapse of magmatically thickened continental crust our data show that granulite facies metamorphism can take place during continental extension and demonstrate that in western new zealand it was accompanied at higher structural levels by the emplacement of one or more metamorphic core complexes7 9 in keeping with the model postulated4 for the basin and range province

the giant marine gastropod campanile giganteum lamarck 1804 as a high resolution archive of seasonality in the eocene greenhouse world

tempo of burial and exhumation within the deep roots of a magmatic arc fiordland new zealand the u pb thermochronology of titanite apatite and rutile from a crustal profile through a mesozoic magmatic arc in fiordland new zealand is used to constrain the timing and duration of significant vertical movements during arc construction and evolution titanite data from deep crustal 12 13 kbar basement and cover rocks of central fiordland imply that contractional arc thickening 25 km occurred by 111 1 113 4 ma within a few million years of a major phase of mid to deep crustal magmatism this finding suggests that this cycle of magmatism arc thickening and high grade metamorphism occurred in 6 2 m y in contrast to rapid burial significant unroofing of the central fiordland gran ulites was more protracted requiring an additional 40 45 m y these new data are con sistent with continued residence of the granulites in thickened arc crust for 15 20 m y with subsequent major unroofing recorded by rutile cooling to 450 8c by ca 70 ma such temporal constraints are essential for comprehensive models of the growth modifi cation and unroofing of magmatic arc systems

three stage evolution of lower crustal gneiss domes at breaksea entrance fiordland new zealand 1 new structural analyses reveal the presence of several kilometer scale gneiss domes and many subdomes within an exhumed section of cretaceous lower crust in sw fiordland the domes are defined by complex nearly concentric trajectories of foliations and steep high strain zones in migmatitic granulite and eclogite facies orthogneiss structural patterns combined with evidence of deformation that was synchronous with partial melting and high grade metamorphism steep mineral lineation orientations sense of shear indicators and near isothermal decompression suggest that buoyancy driven diapiric flow of hot partially molten crust aided initial dome formation mafic intermediate magmatism appears to have enhanced this process superimposed on all high grade structures are upper amphibolite facies shear zones that record a change in the style and conditions of lower crustal flow lineation orientations sense of shear evidence of cooling with decompression and other patterns suggest that the retrograde shear zones record bulk horizontal flow and crustal thinning driven by regional tectonic forces a preferred sequence begins with the initial emplacement of mafic intermediate magma into the lower crust at depths up to 70 km d1 diapirism and initial dome formation occurred during a period of waning arc magmatism and episodic partial melting and high grade metamorphism d2 following melt crystallization dominantly horizontal flow of a cooler strain hardened lower crust occurred during late cretaceous continental extension d3 this example highlights the interplay between mechanisms of horizontal and vertical flow at the root of a continental arc and illustrates their roles in the formation of gneiss domes

successive hydration and dehydration of high p mafic granofels involving clinopyroxene kyanite symplectites mt daniel fiordland new zealand three texturally distinct symplectites occur in mafic granofels of the arthur river complex at mt daniel fiordland new zealand these include symplectic intergrowths of clinopyroxene and kyanite described here for the first time pods of mafic granofels occur within the contact aureole of the early cretaceous western fiordland orthogneiss batholith the pods have cores formed entirely of garnet and clinopyroxene and rims of pseudomorphous coarse grained symplectic intergrowths of hornblende and clinozoisite that reflect hydration at moderate to high p these hornfelsic rocks are enveloped by a hornblende clinozoisite gneissic foliation s1 narrow garnet reaction zones in which hornblende and clinozoisite are replaced by garnet clinopyroxene assemblages developed adjacent to fractures and veins that cut s1 fine grained symplectic intergrowths of 1 clinopyroxene and kyanite and 2 clinozoisite quartz kyanite and plagioclase form part of the garnet reaction zones and partially replace coarse grained s1 hornblende and clinozoisite the development of the garnet reaction zones and symplectites was promoted by dehydration most probably following cooling of the contact aureole maps of oxide weight percent and cation proportions calculated by performing matrix corrections on maps of x ray intensities are used to study the microstructure of the symplectites

shrimp monazite and zircon geochronology of high grade metamorphism in new zealand ion microprobe dating of zircon and monazite from high grade gneisses has been used to 1 determine the timing of metamorphism in the western province of new zealand and 2 constrain the age of the protoliths from which the metamorphic rocks were derived the western province comprises westland where mainly upper crustal rocks are exposed and fiordland where middle to lower crustal levels crop out in westland the oldest recognisable metamorphic event occurred at 360 370 ma penecontemporane ously with intrusion of the mid palaeozoic karamea batholith c 375 ma metamorphism took place under low pressure high temperature conditions resulting in upper amphibolite sillimanite grade meta morphism of lower palaeozoic pelites greenland group orthogneisses of younger cretaceous age formed during emplacement of the rahu suite granite intrusives c 110 ma and were derived from protoliths including cretaceous separation point suite and devonian karamea suite granites in fiordland high grade paragneisses with greenland group zircon age patterns were metamorphosed m1 to sillimanite grade at 360 ma concomitant with crustal thickening and further granite emplace ment m1 mineral assemblages were overprinted by higher pressure kyanite grade metamorphism m2 at 330 ma it remains unclear whether the m2 event in fiordland was primarily due to tectonic burial as suggested by regional recumbent isoclinal folding or whether it was due to magmatic loading in keeping with the significant volumes of granite magma intruded at higher structural levels in the formerly contiguous westland region metamorphism in fiordland accompanied and outlasted emplacement of the western fiordland orthogneiss wfo at 110 125 ma the wfo equilibrated under granulite facies conditions whereas cover rocks underwent more limited recrystallization except for high strain shear zones where conditions of lower to middle amphibolite facies were met the juxtaposition of palaeozoic kyanite grade rocks against cretaceous wfo granulites resulted from late mesozoic extensional defor mation and development of metamorphic core complexes in the western province

non ideal mixing in the phlogopite annite binary constraints from experimental data on mg fe partitioning and a reformulation of the biotite garnet geothermometer the existing experimental data ferry and spear 1978 perchuk and lavrent eva 1983 on mg fe partitioning between garnet and biotite are disparate the underlying assumption of ideal mg fe exchange between the minerals has been examined on the basis of recently available thermochemical data using the updated mixing parameters for the pyrope almandine asymmetric regular solution as inputs ganguly and saxena 1984 hackler and wood 1984 thermodynamic analysis points to non ideal mixing in the phlogopite annite binary in the temperature range of 550 c 950 c the non ideality can be approximated by a temperature independent one constant margules parameter the retrieved values for enthalpy of mixing for mg fe biotites and the standard state enthalpy and entropy changes of the exchange reaction were combined with existing thermochemical data on grossular pyrope and grossular almandine binaries to obtain geothermometric expressions for mg fe fractionation between biotite and garnet t in k begin gathered text t hw 20286 0 text 0193p 2080 x text mg text gt text text 2 text 6350 x text fe text gt text text 2 hfill text 13807 x text ca text gt text 1 x text mn text gt text 8540 x text fe text gt text x text mg text gt text 1 x text mn text gt text hfill text 4215 x text ca text gt text x text mg text gt text x text fe text gt text 4441 text 2x text mg text bt text 1 mathord left vphantom text 2x text mg text bt text 1 text 13 text 138 right kern nulldelimiterspace text 13 text 138 hfill text 8 text 3143 ink text d text 6 text 276 x text ca text gt text 1 x text mn text gt hfill text t gs 13538 0 text 0193p 837 x text mg text gt text 2 text 10460 x text fe text gt 2 hfill text 13807 x text ca text gt 1 text x text mn text gt text 19246 x text fe text gt text x text mg text gt text 1 x text mn text gt hfill text text 5649 x text ca text gt text x text mg text gt text x text fe text gt text 7972 2x text mg text bt text 1 mathord left vphantom text 5649 x text ca text gt text x text mg text gt text x text fe text gt text 7972 2x text mg text bt text 1 text 6 text 778 right kern nulldelimiterspace text 6 text 778 hfill text 8 text 3143ink text d text 6 text 276 x text ca text gt 1 text x text mn text gt hfill end gathered the reformulated geothermometer is an improvement over existing biotite garnet geothermometers because it reconciles the experimental data sets on fe mg partitioning between the two phases and is based on updated activity composition relationship in fe mg ca garnet solid solutions

western fiordland orthogneiss early cretaceous arc magmatism and granulite facies metamorphism new zealand u pb isotopic analyses of zircons from a distinctive suite of previously undated granulite facies metaplutonic rocks here termed the western fiordland orthogneiss wfo in fiordland southwest new zealand indicate synkinematic magmatic emplacement between 120 and 130 ma ago these rocks were previously interpreted as possibly being of precambrian age initial pb and sr ratios are consistent with arc subduction related magmagenesis with little or no involvement of ancient continental crust subsequent high pressure 12 kb metamorphism of the wfo may reflect a major collision event involving crustal thickening by overthrusting of a 15 km thick sequence metamorphism ceased 116 ma ago based on206pb 238u ages of zircon from a retrogressed granulite u pb isotopic analysis of apatite along with previously published rb sr mineral ages indicate that final uplift and cooling to 300 400 c was largely completed by 90 ma the average uplift rate during this period is inferred to have been in excess of 1 mm yr unmetamorphosed gabbronorites of the darran complex in eastern fiordland inferred by some investigators to be the granulite protolith yield concordant u pb zircon ages of 137 1 ma u pb ages of apatite and previously published k ar mineral ages indicate that these rocks experienced a rapid and simple cooling history lasting only a few million years the high grade wfo and unmetamorphosed darran complex are now separated by a profound structural break however the ages and similarities in initial pb and sr isotopic ratios suggest that both suites are products of the same early cretaceous cycle of subduction related magmatism the timing of early cretaceous magmatism and metamorphism collision and resultant crustal thickening and subsequent great uplift and erosion in fiordland has important implications for terrane accretion and the evolution of relative plate motions along the new zealand segment of the gondwana margin

cretaceous high p granulites at milford sound new zealand metamorphic history and emplacement in a convergent margin setting granulite facies orthogneiss of the arthur river complex arc at milford sound western fiordland records a complex early cretaceous magmatic and orogenic history for the pacific gondwana margin that culminated in the emplacement and burial of a dioritic batholith the western fiordland orthogneiss wfo enstatite bearing mafic to intermediate protoliths of the arc and wfo intruded the middle to upper crust the early deformation history of the arc is preserved in the pembroke granulite where two pyroxene s1 assemblages that reflect p 750 c were only patchily recrystallized during later deformation s1 is cut by garnet bearing leucogabbroic to dioritic veins which are cut by distinctive d2 fractures involving anorthositic veins and garnet diopside plagioclase bearing reaction zones these zones are widespread in the arc and wfo and record conditions of p 14 kbar and t 750 c garnet clinopyroxene bearing corona reaction textures that mantle enstatite in both the arc and wfo reflect early cretaceous burial by approximately 25 km of continental crust most of the arc is formed from the milford and harrison gneisses which contain steeply dipping s4 assemblages that envelop the pembroke granulite and involve garnet hornblende diopside clinozoisite rutile and plagio clase with or without kyanite the p t history of rocks in western fiordland reflects pronounced early cretaceous convergence related tectonism and burial possibly related to the collision and accretion of island arc material onto the pacific gondwana margin

medium high pressure metamorphic rocks of the tuhua orogen western new zealand as lower crustal analogues of the lachlan fold belt se australia abstract lower palaeozoic rocks are widely distributed in the western province of new zealand they include 1 ordovician greywackes slates and minor paragneiss in the buller terrane 2 weakly metamorphosed subgreenschist to greenschistfacies cambrian mafic volcanics ordovician limestones and silurian siliciclastic rocks in the takaka terrane and 3 higher grade rocks mainly in fiordland which include 350 380 ma amphibolite facies metasediments held to be more highly metamorphosed equivalents of the buller and takaka terranes metamorphic rocks derived from late precambrian protoliths may also be present together with the buller and takaka terranes these fiordland rocks were regionally metamorphosed and deformed during the mid palaeozoic tuhua orogeny before late mesozoic continental rifting and breakup of the pacific margin of gondwana they were part of a much more extensive palaeozoic orogen which included the lachlan fold belt and extended from southern new south wales through victoria and tasmania into new zealand and antarctica victoria land in common with the lachlan fold belt regional metamorphism in the western province occurred largely under low pressure high temperature conditions andalusite sillimanite facies series such that in fiordland and the higher grade parts of the western province low pressure 0 3 0 5 gpa sillimanite and sillimanite potash feldspar cordierite assemblages developed in rocks of appropriate bulk chemical composition higher pressure 0 7 0 9 gpa rocks in which kyanite is the dominant aluminosilicate polymorph are almost entirely confined to fiordland and represent the deepest exposed crustal levels within the western province at these levels migmatized pelitic schists containing kyanite and garnet are interstratified with calc silicate and quartzofeldspathic rocks tonalitic gneisses metamorphosed anorthosites and granite orthogneisses these rocks were exhumed from depths of 25 30 km and offer useful insights into the nature and composition of the continental crust beneath what was once part of eastern gondwana exhumation itself was brought about by late mesozoic crustal extension combined with more recent transpression along the mid tertiary alpine fault assuming plate reconstructions for gondwana during the palaeozoic are valid the lower to middle crustal rocks of fiordland may give some indication as to what lies at depth beneath the lachlan fold belt

two new geobarometers for garnet amphibolites with applications to southeastern vermont two new geobarometers for the assemblage garnet hornblende plagioclase quartz have been calibrated on the basis of the equilibrium 6 anorthite 3 tremolite 2 grossular 1 pyrope 3 tschermakite 6 quartz and its fe end member equivalent data representing 37 natural samples that equilibrated at conditions of 2 5 to 13 kbar and 500 to 800 c were fitted to the general equation rt in keq a bt p i c by using a weighted least squares method multiple correlation coefficients are high 0 98 and 0 97 lines of constant keqhave extremely shallow slopes in p t space 2 to 8 bars per degree suggesting that pressures may be deduced precisely even where temperatures are only poorly constrained typical analytical errors and temperature imprecisions propagate to very small errors in pressure about 500 bars caution is advised in applying the barometers outside the range of calibrant mineral compositions application of the calibrations to samples from southeastern vermont near the strafford chester and athens domes documents relatively high pressure metamorphism 7 to 10 kbar for these structures

autochthonous inheritance of zircon through cretaceous partial melting of carboniferous plutons the arthur river complex fiordland new zealand tims and shrimp u pb analyses of zircons from milford orthogneiss metadiorite p 1 1 4 gpa t 750 c of the arthur river complex of northern fiordland reveal a bimodal age pattern zircons are predominantly either paleozoic 357 0 4 2 ma and prismatic with oscillatory zoning or cretaceous 133 9 1 8 ma and ovoid with sector or patchy zoning the younger age component is not observed overgrowing older grains most grains of both ages are overgrown by younger cretaceous 120 ma metamorphic zircon with very low u and th u 0 01 we interpret the bimodal ages as indicating initial igneous emplacement and crystallisation of a dioritic protolith pluton at 357 ma followed by early cretaceous granulite facies metamorphism at 134 ma during which a significant fraction 60 of the zircon grains dissolved and subsequently reprecipitated effectively in situ in partial melt pockets the remaining 40 of original paleozoic grains were apparently not in contact with the partial melt remained intact and show only slight degrees of pb loss sector zoning of the cretaceous grains discounts their origin by solid state recrystallisation of paleozoic grains the alternative explanation that the paleozoic component represents a 40 inherited component in an early cretaceous transgressive dioritic magma is considered less likely given the relatively high solubility of zircon in magma of this composition the absence of 134 ma overgrowths the single discrete age of the older component equivalent time integrated 177hf 176hf compositions of both age groups and the absence of the cambrian proterozoic detrital zircon that dominates regional cambro ordovician metasedimentary populations similar bimodal carboniferous early cretaceous age distributions are characteristic of the wider arthur river complex 8 of 12 previously dated dioritic samples have a paleozoic component averaging 51 furthermore the age and chemical suite affinity of these and several more felsic rocks can be matched with those of the relatively unmetamorphosed carboniferous plutonic terrane along the strike of the mesozoic margin in southern fiordland also supporting the in situ derivation of the carboniferous inherited component

tracking the influence of a continental margin on growth of a magmatic arc fiordland new zealand using thermobarometry thermochronology and zircon u pb and hf isotopes 1 geothermobarometric radiogenic isotopic and thermochronologic data are used to track the influence of an ancient continental margin western province on development of an adjacent carboniferous cretaceous magmatic arc outboard median batholith in fiordland new zealand the data show a record of complicated mesozoic gondwana margin growth paragneiss within the outboard median batholith is of carboniferous to jurassic age and records burial to middle crustal depths in late jurassic early cretaceous during subduction related plutonism and arc thickening in contrast western province metasedimentary rocks in the area of study immediately west of the outboard median batholith are late cambrian early ordovician in age recrystallized at the amphibolite facies in the late devonian early carboniferous and exhibit no evidence for mesozoic textural or isotopic reequilibration a phase of deformation between 128 and 116 ma deformed exhumed and cooled the outboard median batholith to greenschist facies temperatures while large parts of the western province underwent 9 kbar metamorphic conditions zircon grains from mesozoic inboard plutons are isotopically more evolved hf t 2 3 to 4 0 than those in the outboard median batholith hf t 9 4 to 11 1 the contrasting zircon hf isotope ratios absence of s type plutons or proterozoic early paleozoic inherited zircon and the apparent absence of early paleozoic metasedimentary rocks indicates that the outboard median batholith is unlikely to be underlain by the western province continental lithosphere the new data are consistent with the outboard median batholith representing an allochthonous although not necessarily exotic arc that was juxtaposed onto the gondwana continental margin along the intervening grebe mylonite zone

granulite facies thermal aureoles and metastable amphibolite facies assemblages adjacent to the western fiordland orthogneiss in southwest fiordland new zealand in southwest new zealand a suite of felsic diorite intrusions known as the western fiordland orthogneiss wfo were emplaced into the mid to deep crust and partially recrystallized to high p 12 kbar granulite facies assemblages this study focuses on the southern most pluton within the wfo suite malaspina pluton between doubtful and dusky sounds new mapping shows intrusive contacts between the malaspina pluton and adjacent palaeozoic metasedimentary country rocks with a thermal aureole 200 1000 m wide adjacent to the malaspina pluton in the surrounding rocks thermobarometry on assemblages in the aureole indicates that the malaspina pluton intruded the adjacent amphibolite facies rocks while they were at depths of 10 14 kbar similar p t conditions are recorded in high p granulite facies assemblages developed locally throughout the malaspina pluton palaeozoic rocks more than 200 1000 m from the malaspina pluton retain medium p mid amphibolite facies assemblages despite having been subjected to pressures of 10 14 kbar for 5 myr these observations contradict previous interpretations of the wfo malaspina pluton as the lower plate of a metamorphic core complex everywhere separated from the metasedimentary rocks by a regional scale extensional shear zone doubtful sound shear zone slow reaction kinetics lack of available h2o lack of widespread penetrative deformation and cooling of the malaspina pluton thermal anomaly within c 3 4 myr likely prevented recrystallization of mid amphibolite facies assemblages outside the thermal aureole if not for the evidence within the thermal aureole there would be little to suggest that gneissic rocks which underlie several 100 km2 of southwest new zealand had experienced metamorphic pressures of 10 14 kbar similar high p metamorphic events may therefore be more common than presently recognized

transformation of two pyroxene hornblende granulite to garnet granulite involving simultaneous melting and fracturing of the lower crust fiordland new zealand granulite facies gabbroic and dioritic gneisses in the pembroke valley milford sound new zealand are cut by vertical and planar garnet reaction zones in rectilinear patterns in gabbroic gneiss narrow dykes of anorthositic leucosome are surrounded by fine grained garnet granulite that replaced the host two pyroxene hornblende granulite at conditions of 750 uc and 14 kbar major and trace element whole rock geochemical data indicate that recrystallization was mostly isochemical the anorthositic veins cut contacts between gabbroic gneiss and dioritic gneiss but change in morphology at the contacts from the anorthositic vein surrounded by a garnet granulite reaction zone in the gabbroic gneiss to zones with a septum of coarse grained garnet surrounded by anorthositic leucosome in the dioritic gneiss the dioritic gneiss also contains isolated garnet grains enclosed by leucosome and short planar trains of garnet grains linked by leucosome partial melting of the dioritic gneiss mostly controlled by hornblende breakdown at water undersaturated conditions is inferred to have generated the leucosomes the form of the leucosomes is consistent with melt segregation and transport aided by fracture propagation limited retrogression suggests considerable melt escape dyking and melt escape from the dioritic gneiss are inferred to have propagated fractures into the gabbroic gneiss the migrating melt scavenged water from the surrounding gabbroic gneiss and induced the limited replacement by garnet granulite

sm nd and rb sr isotopic and geochemical systematics in phanerozoic granulites from fiordland southwest new zealand sm nd and rb sr isotopic analyses are reported for granulite facies orthogneisses from fiordland southwest new zealand whole rock samples define a rb sr isochron age of 120 15 ma and an initial 87sr 86sr ratio of 0 70391 4 nd values at 120 ma show a relatively wide range of from 0 4 to 2 7 indicating decoupling of sr nd isotope systems associated ultramafic rocks have initial 87sr 86sr ratios of from 0 70380 to 0 70430 and nd values of from 0 1 to 3 0 the different initial ratios suggest that the various intrusions although contemporaneous were not derived through fractionation of a single parent magma a metasedimentary enclave incorporated during emplacement of the granulitic rocks preserves a proterozoic isotopic signature with a measured nd 0 value of 10 2 87sr 86sr ratio of 0 73679 and a tnd provenance age of 1490 ma the rb sr whole rock age of the granulites is the same as obtained from recent u pb zircon dating mattinson et al 1986 and is interpreted as the time of magmatic emplacement and essentially contemporaneous granulite facies metamorphism rb sr and sm nd analyses of mineral systems indicate that the terrain had cooled below 300 c by 100 ma providing further evidence that high grade metamorphism was of exceptionally short duration

high pressure metamorphism caused by magma loading in fiordland new zealand cretaceous granulite facies metamorphism in the fiordland area of new zealand has distinctive mineralogical textural and structural features that set it apart from most other regional metamorphic belts the metamorphism developed over a 30 150 km area and the consequence of a 20 km thick increment to crustal thickness is closely associated in space and time with a large plutonic complex the western fiordland orthogneiss wfo although temperatures and pressures as high as 700 c and 12 kbar were attained the metamorphic overprint on earlier low pressure assemblages is weak and incomplete little strain accompanied the metamorphism the temperature threshold at which metamorphic recrystallization is recorded is over 500 c zoned garnets are preserved at unusually high temperatures indicating duration of metamorphism on the order of 10 times shorter than in most other regional terranes this pattern of features bears close similarity to metamorphism in the coast plutonic complex in north america where a mechanism of magma loading has been invoked in fiordland the high pressure metamorphism can be explained by depression of country rock under a crustal zone that is inflated by intrusion of the wfo regional structure of the wfo as a horizontally sheeted complex suggests that the pluton was emplaced by vertical displacement of country rock and supports the magma loading model

extension of thickened and hot lithospheres inferences from laboratory modeling 1 the extension of a previously thickened lithosphere is studied through a series of analogue experiments the models deformed in free and boundary controlled gravity spreading conditions that simulate the development of wide rift type and core complex type structures in models the development of structures mainly depends on boundary velocity and therefore on bulk strain rate wide rifts are of tilted block type at high strain rate and of horst and graben type at low strain rate the development of metamorphic core complex type structures is enhanced by low strain rates and by the presence of weak heterogeneities within the ductile crust core complexes result from a necking instability of the upper crust creating a graben which further widens allowing the rise and exhumation of a ductile layer dome an upward convex detachment flat on top of the dome and steeper on dome limb appears not to be the primary cause of the core complex development but its consequence

short lived orogenic cycles and the eclogitization of cold crust by spasmodic hot fluids collision tectonics and the associated transformation of continental crust to high pressure rocks eclogites are generally well understood processes but important contradictions remain between tectonothermal models and petrological isotopic data obtained from such rocks here we use 40ar 39ar data coupled with a thermal model to constrain the time integrated duration of an orogenic cycle the burial and exhumation of a particular segment of the crust to be less than 13 myr we also determine the total duration of associated metamorphic events to be 20 kyr and of individual heat pulses experienced by the rocks to be as short as 10 years such short timescales are indicative of rapid tectonic processes associated with catastrophic deformation events earthquakes such events triggered transient heat advection by hot fluid along deformation shear zones which cut relatively cool and dry subducted crust in contrast to current thermal models that assume thermal equilibrium and invoke high ambient temperatures in the thickened crust our non steady state cold crust model satisfactorily explains several otherwise contradictory geological observations the duration of the geological processes that shape the earth generates vigorous debate mountain building where crust is consumed continuously by burial and recycled as buried remnants rise to the surface is one process where new dating methods can resolve the issue high precision dating of rock remnants left by continental collision in the caledonides of southern norway shows that the entire cycle can happen quickly in about 13 million years in addition the rapid transport of hot fluid zones through the cold crust may explain many puzzling geological observations