calculated mineral equilibria for eclogites in cao na2o feo mgo al2o3 sio2 h2o application to the pouebo terrane pam peninsula new caledonia the high p medium t pouebo terrane of the pam peninsula northern new caledonia includes barroisite and glaucophane bearing eclogite and variably rehydrated equivalents the metamorphic evolution of the pouebo terrane is inferred from calculated p t and p t xh2o pseudosections for bulk compositions appropriate to these rocks in the model system cao na2o feo mgo al2o3 sio2 h2o the eclogites experienced a clockwise p t path that reached p 19 kbar and t 600 c the eclogitic mineral assemblages are preserved because reaction consequent upon decompression consumed the rocks fluid extensive reaction occurred only in rocks with fluid influx during decompression of the pouebo terrane

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

eclogites and blueschists of the pam peninsula ne new caledonia a reappraisal high p rocks of the pam peninsula ne new caledonia are divided into three zones 1 an uppermost ferroglaucophane lawsonite zone of cretaceous to eocene metasediments and metavolcanics of the diahot terrane that experienced peak conditions involving p 7 9 kbar and t 400 58 c 2 albite epidote omphacite zone diahot terrane rocks that experienced blueschist facies conditions of p 12 6 1 2 kbar and t 570 36 c 3 lowermost metabasic eclogites of uncertain age that form the pouebo terrane which experienced high p conditions of p 23 9 3 0 kbar and t 600 c eclogite occurs as metre to kilometre scale pods in coarse grained hydrous mineral rich glaucophanite formed during hydration and decompression of the pouebo terrane metamorphism and deformation were consequent to 44 51 ma eocene convergence when sedimentary and ophiolitic nappes were thrust over the eclogites in a sw direction white mica ages constrain metamorphism to have ended by 37 1 ma large steps in metamorphic grade are coincident with sw dipping and ne dipping faults that separate the three zones and were formed during two stages 1 comparatively slow uplift and hydration of the pouebo terrane before it was juxtaposed with the albite epidote omphacite zone at p 14 kbar 2 comparatively rapid uplift of both the pouebo terrane and the albite epidote omphacite zone to form a domal core of eclogite flanked by significantly lower grade rocks to the sw and ne

tectonic and metamorphic architecture of the hp belt of new caledonia abstract new caledonia includes a well exposed example of high pressure orogenic belt formed as a result of cenozoic plate tectonic reorganizations at the australia pacific plate boundary the metamorphic belt is relatively well accessible and has deserved extensive attention mainly for its metamorphic and petrological features the architecture of this belt however still lacks general consensus the aim of this paper is i to review the nature and origin of the main tectonic units of the belts and ii to revisit the available structural models describing its architecture and geodynamic evolution for that we integrate the available field petrological geochemical and geochronological data together with new results from large scale field survey and focused ar ar geochronological data all together these data allow proposing a new model for the tectonic and metamorphic architecture of the belt also comprising a newly established tectonostratigraphic unit this architecture resembles that characterizing alpine type metamorphic belts formed in non pacific settings and clearly differs from cordilleran type belts found in eastern pacific regions moreover the collected data also allow refining our understanding of the oceanic and transitional oceanic lithosphere involved in the eocene subduction and plausible analogies with hyper extended margins known in present day ocean continent transition zones

large scale structure of the eclogite blueschist belt of new caledonia abstract this paper considers the large scale geometry of the northern part of the eclogite blueschist belt of new caledonia based largely on classical style structural analysis but in consideration of modern concepts regarding crustal extension exhumation of high pressure rocks and uplift shear zones played an important role in the evolution of the region early shear zones and high pressure metamorphism appear to be associated with overthrusting of an ultramafic sheet middle stage shear zones are associated with large scale continental extension during which the high pressure rocks were exhumed the extended crust was subsequently folded during renewed compression producing an orogen scale antiform throughout the high pressure belt that folds all previously formed structures late stage shear zones formed when the orogen was once again thrown into extension relatively youthful normal faults caused late block faulting uplifting a regional peneplain and producing the present geomorphology previously published interpretations of the structure and geometry of the belt have suggested that the high pressure rocks are found in the core of a regionally developed antiform interpreted as a metamorphic core complex our structural mapping shows that allochthonous slices of high pressure rocks are draped over a younger unrelated foliation antiform lower grade retrogressed equivalent rocks are found within the core of the antiform thus the metamorphic core complex model is rejected

40ar 39ar dating of white micas from the epidote to the omphacite zones northern new caledonia tectonic implications an 40ar 39ar study of white micas from high pressure metamorphic rocks of northern new caledonia yielded cooling ages of 37 1 ma for both epidote and omphacite zone samples whole rock samples from the lawsonite zone yielded ages in the range 44 51 ma with complicated age spectra probably reflecting both detrital and newly grown micas the areal extent of the mica samples over 300 km2 suggests that the epidote and omphacite zone rocks cooled through the muscovite closure temperature about 350 c as a coherent cooling unit simple thermal modeling suggests that these rocks could have closed at similar times if the unroofing rate were greater than 2 10 mm a 1 lawsonite zone rocks occur structurally within about 0 5 km of garnet omphacite rocks suggesting the possibility of major postmetamorphic tectonic displacement

lawsonite composition and zoning as tracers of subduction processes a global review abstract lawsonite is an abundant hydrous mineral in oceanic crust sediments and metasomatic rocks at depths of 45 to 300 km in most subduction zones but it is rarely preserved in the geologic record because it commonly transforms to epidote and other minerals during prograde or retrograde metamorphism owing to the significance of lawsonite for water and element cycling in subduction zones occurrences of fresh lawsonite in blueschist and more rarely eclogite provide important opportunities to determine lawsonite composition zoning and inclusion suites and to use this information to reconstruct reaction history during subduction and exhumation in this review we use new and published data to document lawsonite composition in eight of the nine known lawsonite eclogite localities in which fresh lawsonite coexists with garnet omphacite in the rock matrix as well as the composition of lawsonite inclusions in six of seven known sites in which lawsonite occurs only as inclusions in garnet in eclogite facies rocks that lack matrix lawsonite as lawsonite blueschist is much more common than lawsonite eclogite we survey the composition of lawsonite in representative localities of blueschist including blueschist associated with eclogite lawsonite bearing epidote bearing and blueschist not associated with eclogite at current exposure levels included in this review are metabasaltic rocks silica and carbonate rich metasedimentary rocks metasomatic rocks and lawsonite rich veins this dataset demonstrates that lawsonite composition is a sensitive indicator of reaction history during subduction and exhumation and specifically of fluid rock interaction with implications for element cycling in subduction zones furthermore most exhumed lawsonite eclogite records slab surface conditions that correspond to the location where the slab mantle interface transitions from decoupled to coupled and therefore provides key insights into the thermal history and dynamics of subduction zones

the origin and p t evolution of peridotites and serpentinites of ne new caledonia prograde interaction between continental margin and the mantle wedge the pouebo and diahot terranes of ne new caledonia mostly comprise eclogite to blueschist facies metabasite and metasedimentary rocks that experienced c 40 ma metamorphism this eocene high p event has been linked with the sw directed obduction of the new caledonian ophiolite an extensive ultramafic nappe that dominates outcrop in the south of the island in the north ultramafic lithologies are found only as sheets or discrete lenticular masses interleaved with but separated from the eclogites and blueschists by foliated talc chlorite serpentine carbonate bearing rocks the base of the largest and best preserved ultramafic body at yambe is marked by a distinctive 2 m thick layer of high p mylonite that preserves evidence for early blueschist facies conditions s1 as inclusions in eclogite facies minerals textural evidence preserved in olivine bearing serpentinites and their bounding mafic mylonites suggest that the ultramafic bodies were emplaced within the structurally highest levels of the high p terrane as serpentinite tectonites sourced from hydrated mantle formerly in the hangingwall of the eocene subduction zone serpentinite emplacement accompanied burial of the ne new caledonian margin at t 500 c and p 16 kbar the ultramafic fragments were buried to depths of 50 60 km in the subduction zone where olivine was stable and coarse grained garnet omphacite rich assemblages developed in low strain domains within enclosing mylonites host metabasic and metasedimentary rocks from the structurally highest portions of the high p belt have a prograde record identical to that of the ultramafic tectonites the early emplacement and similar p t history of host rocks and ultramafic masses suggest that ne new caledonia preserves a fossil slab mantle wedge boundary reactivated during exhumation

understanding the contrasting north atlantic oscillation anomalies of the winters of 2010 and 2014 the present study investigates the two contrasting winters of 2010 and 2014 during which the north atlantic oscillation nao was mainly negative and positive respectively in the north pacific contrasting anomalies were also present with a straight zonal pacific jet in 2010 and a strong poleward deviation of the pacific jet in its exit region in 2014 using reanalysis data sets and adopting a nonlinear initial value approach with a quasi geostrophic model we show that the pacific north american anomalies are responsible for shaping synoptic wave trains propagating across north america this in turn largely determines the nature of wave breaking and the synoptic eddy feedback onto the mean flow in the north atlantic and finally the nao phase in such a proposed mechanism synoptic wave activity forms the cornerstone of the dynamical relationship between the north pacific and north atlantic large scale anomalies during the contrasting winters of 2010 and 2014

lawsonite omphacite bearing metabasites of the pam peninsula ne new caledonia evidence for disrupted blueschist to eclogite facies conditions

fractionation of bulk rock composition due to porphyroblast growth effects on eclogite facies mineral equilibria pam peninsula new caledonia chemically zoned porphyroblasts in metamorphic rocks indicate that diffusional processes could not maintain equilibrium conditions on a grain scale during porphyroblast growth or establish it afterwards an effect of this inability to maintain equilibrium is the progressive removal of elements forming garnet cores from any metamorphic reaction that occurs at the porphyroblast boundaries or in the matrix of the rock to examine this effect on mineral assemblages the bence albee matrix correction was applied to x ray intensity maps collected using eclogite samples from northern new caledonia in order to determine the chemical composition of all parts of the sample the manipulation of these element maps allows a quantitative analysis of the fractionation of the bulk rock composition between garnet cores and the matrix a series of calculated equilibrium volume compositions represents the change in matrix chemistry with progressive elemental fractionation as a consequence of prograde garnet growth under high p conditions pressure temperature pseudosections are calculated for these compositions in the cao na2o feo mgo al2o3 sio2 h2o system assemblages modal proportions and mineral textures observed in the new caledonian eclogites can be closely modelled by progressively removing elements forming garnet cores from the bulk rock composition the pseudosections demonstrate how chemical fractionation effects the peak metamorphic assemblage prograde textures and the development of retrograde assemblages

a potential method to confirm the previous existence of lawsonite in eclogite the mass imbalance of sr and lrees in multistage epidote ganghe dabie uhp terrane lawsonite is an important hydrous mineral that is stable at low temperature lt and high to ultrahigh pressure hp uhp conditions in subducted slabs the occurrence absence of lawsonite in eclogite is a significant constraint for the construction of the metamorphic tectonic and fluid melt evolution histories of an hp uhp terrane however lawsonite is very rarely preserved in natural eclogites and accurate judgment of its former existence is a significant challenge for petrologists at present whether lawsonite has ever existed in lawsonite absent eclogite is mainly judged by i pseudomorphs after lawsonite and ii phase equilibria modelling in this study major element and trace element distributions in multistage minerals were examined in the ganghe lawsonite absent uhp eclogite in the dabie uhp terrane eastern china this work demonstrates that the whole rock sr and light rare earth elements lrees are mainly dominated by epidote other minerals garnet omphacite quartz kyanite barroisite phengite and accessory minerals play a very limited role in the sr and lrees budgets two stages of epidote which have noticeably different sr and lrees contents were recognized in the eclogite i epidote porphyroblasts ep p core which are suspected to be the pseudomorphic mineral after lawsonite contain significantly high sr 7200 10 300 ppm and lrees 160 1300 ppm for la ii an earlier stage epidote ep in core occurs as inclusions in matrix omphacite or in omphacite inclusions in the suspected pseudomorphic minerals after lawsonite spmal this early epidote has significantly lower sr 990 1890 ppm average 1495 ppm n 17 and lrees contents 60 110 ppm for la average 91 ppm n 17 all of the existing early stage minerals predating the spmal have very low contents of sr and lrees and the total amounts of these elements in the early stage minerals do not balance those in the spmal this indicates that a missing ca al sr and lree rich mineral which was previously in equilibrium with the early stage minerals likely existed in the ganghe eclogite on the basis of the mineral geochemistry and phase equilibria modelling we confirm that the missing mineral cannot be anything but lawsonite this study indicates that examining the mass im balance of sr and lrees between multistage hp uhp epidote can be used as a potential method to confirm the previous existence of lawsonite in lawsonite absent eclogite

high pressure veins in eclogite from new caledonia and their significance for fluid migration in subduction zones abstract this paper describes the petrology and geochemistry of high pressure veins and associated metasomatic selvages that are hosted by eclogite in the pouebo eclogite melange of northern new caledonia isotopic and geochemical evidence indicates that the mafic host rock represents seafloor altered fractionated morb that underwent eclogite facies metamorphism in a subduction zone within the host rock are cm thick garnet quartz phengite veins that are enveloped by garnet poor omphacite rich selvages or bleach zones petrography thermometry oxygen isotope characteristics and mass balance calculations are used to show that the veins largely formed by fluid mediated mass transfer from the bleach zones during prograde metamorphism minerals in the veins are free of inclusions but the vein garnets preserve complex chemical zoning features that are not present in the host rock garnets vein garnets have mn and hree zoning patterns that are indicative of progressive garnet growth during prograde metamorphism whereas mg and ca contents reveal prominent sector zoning and fine scale intergrowth features we propose that the veins formed over a prolonged period during subduction by local circulation of fluid that was sourced from prograde dehydration of minerals in the host rock fluid circulation may have been driven by episodic microcracking sealing around garnet porphyroblasts which led to significant mass transfer and progressive vein growth mass balance calculations and phengite trace element compositions also require the additional of pelite derived components to the veins these components were probably introduced into the veins at conditions close to peak metamorphism via a relatively small external fluid flux this model for vein formation is consistent with previous studies that suggest fluid flow in deeply subducted oceanic crust is highly restricted in many cases the delay of fluid migration after hydrous mineral breakdown may provide an important source of water for arc magmas as free fluid is transported to deeper levels in subduction zones

permian magmatic sequences of the bilihe gold deposit in central inner mongolia china petrogenesis and tectonic significance abstract the bilihe gold deposit is located in the eastern section of the ondor sum yanji suture at the southern margin of the xing an mongolian orogenic belt xmob and the northern margin of the north china craton ncc central inner mongolia the magmatic rocks in the ore district are generally high k calc alkaline enriched in lree zr and hf and depleted in hree nb ta and p the magmatic evolution sequences are norite gabbro granodiorite porphyry granite or norite gabbro andesite dacite porphyry granodiorite which show a trend of decreasing tio2 feo mgo cao and p2o5 with increasing sio2 in the bilihe ore district hydrothermal processes were coeval with granitic magmatism for a period of 17 myr 272 255 ma the ages of the granite granodiorite porphyry granodiorite and dacite porphyry are 271 5 264 1 ma 269 8 255 8 ma 268 3 ma and 268 6 259 4 ma respectively the magmatic rocks contain magmatic hydrothermal and magmatic hydrothermal zircons the magmatic zircons have ce 4 la 2 5 the hydrothermal zircons have ce 3 ppm and smn lan

isotopic analysis of the super large shuangjianzishan pb zn ag deposit in inner mongolia china constraints on magmatism metallogenesis and tectonic setting abstract the super large shuangjianzishan pb zn ag deposit is a newly discovered deposit located in the huanggang ganzhuermiao polymetallic metallogenic belt of inner mongolia ne china the deposit s resource includes 0 026 mt ag 1 1 mt pb and 3 3 mt zn the deposit is controlled by a nw trending ductile shear zone and ne and nw trending faults in black pelite assigned to the lower permian dashizhai formation lree enrichment hree depletion nb ta p and ti depletion and zr and hf enrichment characterize felsic magmatic rocks in the shuangjianzishan pb zn ag district the ages of porphyritic monzogranite rhyolitic crystal vitric ignimbrite and porphyritic granodiorite are 254 252 169 and 130 ma respectively pyrite sampled from the mineralization has re os isochron ages of 165 7 ma which suggest the mineralization is associated with the ca 169 ma magmatism in the shuangjianzishan district zircons extracted from the porphyritic granodiorite yield e hf t values of 11 34 to 1 41 with t dm2 dates of 1275 1901 ma the e hf t values of zircons in the rhyolitic crystal vitric ignimbrite and the ore bearing monzogranite porphyry are 7 57 16 23 and 10 18 15 96 respectively and their t dm2 ages are 177 733 and 257 632 ma respectively partial melting of depleted mantle resulted in the formation of the ca 254 252 ma ore bearing porphyritic monzogranite and the ca 169 ma rhyolitic crystal vitric ignimbrite dehydration partial melting of subducted oceanic crust resulted in the formation of the ca 130 ma porphyritic granodiorite the porphyritic monzogranite was emplaced during the late stages of closure of the paleo asian ocean during the transformation from a collisional to extensional tectonic setting the ca 170 and ca 130 ma magmatism and mineralization in the shuangjianzishan district are related to subduction of the mongolia okhotsk ocean and subduction of the paleo pacific ocean plate respectively

very low temperature record of the subduction process a review of worldwide lawsonite eclogites abstract lawsonite eclogites preserve a record of very low temperature conditions in subduction zones all occur at active margin settings typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite matrix melange peak lawsonite eclogite facies mineral assemblages garnet omphacite lawsonite rutile typically occur in prograde zoned garnet porphyroblasts their matrix is commonly overprinted by higher temperature epidote bearing assemblages greenschist or amphibolite facies conditions erase former lawsonite eclogite relics various pseudomorphs after lawsonite occur particularly in some blueschist eclogite transitional facies rocks coesite bearing lawsonite eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low temperature ultrahigh pressure eclogites are known using inclusion assemblages in garnet lawsonite eclogites can be classified into two types l type such as those from guatemala and british columbia contain garnet porphyroblasts that grew only within the lawsonite stability field and e type such as from the dominican republic record maximum temperature in the epidote stability field formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation the earliest occurrences of lawsonite eclogite facies mineral assemblages are early paleozoic in spitsbergen and the new england fold belt of australia this suggests that since the phanerozoic secular cooling of earth and subduction zone thermal structures evolved the necessary high pressure temperature conditions buoyancy of serpentinite and oblique convergence with a major strike slip component may facilitate the exhumation of lawsonite eclogites from mantle depths

hydration of eclogite pam peninsula new caledonia garnet glaucophanite and greenschist facies assemblages were formed by the recrystallization of barroisite bearing eclogite facies metabasites in northern new caledonia the mineralogical evolution can be modelled by calculated p t and p xh2o diagrams for appropriate bulk rock compositions in the model system cao na2o feo mgo al2o3 sio2 h2o the eclogites having developed in a clockwise p t path that reached p 19 kbar and t 590 c underwent decompression with the consumption of free h2o as the volume of hydrous minerals increased eclogite is preserved in domains that experienced no fluid influx following the loss of this fluid garnet glaucophanite formed at p 16 kbar during semi pervasive fluid influx fluid influx after further isothermal decompression was focused in shear zones and resulted in chlorite albite bearing greenschist facies mineral assemblages that reflect p 9 kbar