quantitative remote sensing study indicates doubling of coastal erosion rate in past 50 yr along a segment of the arctic coast of alaska a new quantitative coastal land gained and lost method uses image analysis of topographic maps and landsat thematic mapper short wave infrared data to document accelerated coastal land loss and thermokarst lake expansion and drainage the data span 1955 2005 along the beaufort sea coast north of teshekpuk lake in the national petroleum reserve in alaska some areas have undergone as much as 0 9 km of coastal erosion in the past 50 yr land loss attributed to coastal erosion more than doubled from 0 48 km2 yr 1 during 1955 1985 to 1 08 km2 yr 1 during 1985 2005 coastal erosion has breached thermokarst lakes causing initial draining of the lakes followed by marine flooding although inland thermokarst lakes show some uniform expansion lakes breached by coastal erosion display lake expansion several orders of magnitude greater than inland lakes

zircon xenocrysts from the kambalda volcanics age constraints and direct evidence for older continental crust below the kambalda norseman greenstones abstract the hangingwall basalt at kambalda western australia contains zircons that have been shown by ion microprobe analyses to have very high u and th contents and a wide variety of crystallization ages nearly all of these zircons certainly are xenocrysts a few might relate to intrusive veinlets the age of the youngest xenocrysts 2693 50ma 2 shows that the eruptive age of the basalt cannot exceed 2743 ma this confirms that the apparent sm nd isochron giving 3200 ma 1 2 for kambalda mafic and ultramafic rocks is a mixing line 2 between unrelated components enriched and depleted in light rare earth elements mixing probably occurred at depth by erosion of 3200 3500 ma old felsic crust from the walls of the hwb conduits the zircon xenocryst ages are the first direct evidence for the presence of very old felsic crust in the eastern yilgarn block the latter implies that the kalgoorlie norseman greenstone sequences were formed in a continental rather than an oceanic environment

geochemistry and nd isotope systematics of archaean granites of the eastern goldfields yilgarn craton australia implications for crustal growth processes abstract the archaean granites and granitic gneisses of the eastern goldfields in the yilgarn craton western australia can be divided into two major groups high ca and low ca and three minor groups high hfse high field strength elements mafic and syenitic the high ca group 68 77 sio 2 with high al 2 o 3 na 2 o and sr and low y shares many features with typical archaean tonalite trondhjemite suites but has higher k 2 o rb and th contents the low ca group 70 76 sio 2 differs from the high ca group in having lower al 2 o 3 cao and na 2 o but higher k 2 o rb th zr y la and ce contents granites of the high hfse mafic and syenitic groups form a minor component 10 20 of the eastern goldfields granites the siliceous 74 77 sio 2 high hfse granites are restricted to a narrow nnw trending zone and are characterised by high tio 2 total feo mgo y zr and ce but only moderate rb th and pb contents the a type syenites 50 68 sio 2 are distinguished by their high total alkalies and mainly occur along tectonic lineaments the mafic group 55 70 sio 2 is lithologically diverse and exhibits a wide range of k 2 o rb th la and ce contents granite emplacement occurred between 2 69 and 2 60 ga contemporaneous with or post dating greenstone formation nd values for the high ca mafic and syenitic groups are similar mostly 0 0 to 2 5 whereas those for the low ca group show a pronounced polarity from 4 5 in the west to 2 0 in the east nd depleted mantle model ages for the low ca granites range from 3 2 ga in the west to 2 75 ga in the east model ages for the high ca group 2 75 2 9 ga overlap with ages for inherited zircons from these granites the high ca granites appear to have been derived at high pressures by partial melting of a mafic to intermediate source subducted oceanic crust crustal underplate or thickened crust or remelting of an older tonalitic source derived by such a process if the high ca granites were largely crust derived then their extensive source rocks must have formed less than 250 ma prior to granite formation the low ca granites appear to be the products of crustal reworking probably from a tonalitic to granodioritic protolith that was progressively younger towards the east perhaps in the order of several hundred million years younger or involved an additional younger component the localisation of the crustally derived high hfse granites suggests either geochemical zonation of the crust or specific tectonic processes such as rifting the mafic granites and possibly the syenites imply a significant mantle contribution and new crustal growth although the extent is equivocal the crust of the eastern goldfields appears to have been generated by both lateral and vertical accretion over a significant period from or before 3 0 ga until the time of granite emplacement

the p t record of synchronous magmatism metamorphism and deformation at petrel cove southern adelaide fold belt porphyroblastic schists in the thermal aureole of the victor harbor granite at petrel cove in the southern adelaide fold belt south australia preserve a record of sequential cordierite andalusite staurolite fibrolite chlorite and muscovite growth along with biotite plagioclase quartz ilmenite during progressive deformation a p t pseudo section appropriate to biotite saturated assemblages in kfmash shows that the sequence of mineral reactions records increasing pressure of at least 1 kbar from c 3 to c 4 kbar during cooling from around 580 c heating at pressures below c 3 kbar is inferred for growth of early formed cordierite porphyroblasts and is attributed in part to the thermal effects of granite emplacement while the pressure increase is attributed to tectonic burial accruing from ongoing deformation the anticlockwise p t path is consistent with convergent deformation being focussed as a consequence of heating as to be expected for a lithospheric rheology that is strongly temperature dependent

direction of arrival estimation of vhf signals recorded on the international space station and simultaneous observations of optical lightning we report an initial investigation of the new location method of a very high frequency vhf radiation source using signals recorded at the international space station a vhf interferometer vitf has two vhf sensors locating lightning with vhf bands is useful to locate the position of the charge distribution in the thunderstorm the location method of a radio source proposed used two direction of arrival estimation techniques one is the interferometric technique and another is based on the ionospheric propagation delay measurement of received signals the combination of the two techniques provides two angular positions of the radiation source when an altitude of a radiation source is assumed we can determine two possible positions one of the two positions was associated with the radiation source while the other was not in this paper we compared the position of lightning and sprite imager lsi data which are simultaneously captured during a lightning emission with the locating position near the emission the data set of the vitf within 100 ms of the optical lightning emission captured with the lsi was used the temporally simultaneous event seems to be associated with the same lightning event the estimated radiation positions were spatially in close agreement with the optical lightning positions captured with lsi under nighttime ionosphere conditions from statistical analysis the spatial difference of the standard deviation changed from 15 3 to 30 8 km depending on the installation direction of the vhf sensors the usefulness and limitations of the method are also discussed

geology and geochemistry of archaean granites in the kalgoorlie region of the eastern goldfields western australia a syn collisional tectonic setting abstract granites in the kalgoorlie region of the archaean yilgarn craton are predominantly biotite granodiorite and monzogranite with some hornblende bearing varieties granites are divided on the basis of field relationships petrography and chemical composition into five supersuites an older supersuite containing four suites pre dates regional folding and four supersuites post date regional folding the potassic composition of the mainly silica rich granites 68 sio2 suggest that the most appropriate source for the majority of supersuites is continental crust with a composition in the range tonalite to granodiorite most supersuites evolved by fractional crystallization mainly of biotite and plagioclase some suites contain synplutonic dykes and microgranite xenoliths that crystallized from enriched mantle derived magmas there was only limited and local chemical interaction between granite and mantle derived magmas geometric and temporal relationships between regional structures and granites indicate that the granites were emplaced during a major orogenic event however s type granites which are widespread in some modern syn collision settings are absent in the kalgoorlie region the predominance of high fo2 i type granites in the study area probably reflects the absence of large graphite bearing metasedimentary accumulations in the lower crustal source regions the distribution of suites and supersuites implies a common source region beneath the kalgoorlie and gindalbie granite greenstone terranes suggesting that they shared a common geological history dating back to late greenstone deposition

evolutionary cycles during the andean orogeny repeated slab breakoff and flat subduction tectonomagmatic similarities between the modern chilean flat slab region and pre neogene magmatic episodes suggest that they represent analogues to flat subduction evolutionary patterns in each magmatic suite include i increasing la yb ratios and sr and nd isotopic enrichment through time ii eastward migration of magmatism after periods of transpressional transtensional intra arc deformation and iii subsequent termination and virtual absence of main arc activity for 5 10 myr these patterns may reflect slab shallowing followed by flat subduction and thickening of the overlying crust if repeated they require interchanging episodes of slab steepening increasing convergence rates force slab kinking and eventual failure of the oversteepened slab followed by rebound of the slab tip owing to lack of further slab pull flat subduction and termination of subduction related magmatism rapid subduction leads to shallow overriding of the detached slab fragment eclogitization of the gradually steepening slab tip at depth and subsequent slab pull permits asthenospheric corner flow and subduction related magmatism

late archaean deep marine volcaniclastic sedimentation in an arc related basin the kalgoorlie sequence of the eastern goldfields superterrane yilgarn craton western australia abstract the kalgoorlie sequence 2658 ma is a 3000 m thick succession of volcaniclastic sedimentary rocks and subordinate rhyolite dacite andesite and basalt spatially and temporally associated with subvolcanic sills and dykes of rhyolite and dacite gabbro sills and i type granitoids although basalts are tholeiitic the felsic rocks have ttd affinity the sequence comprises mostly deep marine channel levee turbidite complexes and hemipelagites resedimented syneruptive volcaniclastic deposits are associated with coherent lavas but almost all of the sedimentary fill was recycled from prior cycle volcanic and volcaniclastic sources provenance was mainly dacitic rhyolitic with minor andesitic basaltic and polymictic compositions volcano bound and fault bound architectures and two styles of basin filling are identified progradational or aggradational transverse fans and slope aprons and retrogradational longitudinal fans of a linear trough retrogradation in longitudinal systems is consistent with basin lengthening and deepening six depositional sequences are grouped in four unconformity bounded tectonic stages that record uplift subsidence cycles coeval mafic and felsic magmatism indicate that the tectonic stages represent extensional tectonic settings whereas volcanogenic provenance spatially linked volcanism and plutonic magmatism and deep marine environments support an intra arc site cyclic uplift subsidence and basin lengthening are more consistent with strike slip controls on basin formation than with orthogonal extension the tectonic setting is interpreted to have been a pull apart basin associated with strike slip faulting and amalgamating arc related terranes similar to the modern philippines archipelago the strong similarity between archaean volcaniclastic and modern arc related volcaniclastic environments implies comparable tectonic settings and therefore comparable controlling tectonic factors

terrane amalgamation in the eastern goldfields superterrane yilgarn craton evidence from tectonostratigraphic studies of the laverton greenstone belt abstract tectonostratigraphic evolution of the laverton greenstone belt involves amalgamation of structural relics of sedimentary basins and continental fragments in the burtville terrane to the east prior to their accretion to the kurnalpi terrane to the west the burtville terrane records sedimentation and volcanism in a continental setting between 2758 ma and 2715 ma the kurnalpi terrane is dominated by 2715 2700 ma andesitic volcaniclastic rocks with erosional remnants of uplift of the margaret dome a granite gneiss cored batholith north of the laverton domain is interpreted to have been the main driving force for rapid deposition and burial of conglomeratic and turbiditic siliciclastic sequences in the lake carey basin a switch from submarine canyon deposits to deep water turbiditic rocks with time suggests extension and basin formation was initially driven by the uplift of the dome however basin development switched to a flexural phase with increasing sediment load and ongoing uplift to the north the 2663 ma maximum depositional age for the granny smith sequence indicates that active sedimentation may have been occurring contemporaneous with collisional orogeny the collisional orogeny comprises four main episodes of compressive deformation starting after either 2675 ma or 2665 ma and ending at 2650 ma d 1 involved development of n s upright to inclined km scale folds and axial planar foliation and inversion of pre collision extensional faults as reverse faults during east west directed compression d 2 involved reactivation of d 1 reverse faults as transcurrent faults and development of nw se directed dm scale folds with associated axial planar foliation that overprints the early n s foliation d 2 occurred under a ne sw directed compressive stress field to the west the celia fault records d 2 as its first deformation suggesting a westward migrating deformation front the celia fault zone records its second deformation episode d 3 as sinistral reactivation of the fault zone and locally influenced lode gold development d 3 occurred during wnw ese directed maximum compression the final compressive deformation event d 4 involved overprinting of the d 3 shear fabric by conjugate arrays of kink bands in the celia fault zone during a clockwise rotation of the compressive stress field into a nnw sse orientation the tectonic process responsible for such a rapid uplift and deposition of thick synorogenic sediments lateral to the deformation front and penecontemporaneous with collisional orogeny invites comparisons with modern arc related settings the present suture zone between the indo australian plate and the pacific plate in new guinea records active deposition of fluvial sediments laterally along the accretion zone and in thick deep water fans onto the bismarck sea floor

regional metamorphic controls on alteration associated with gold mineralization in the eastern goldfields province western australia implications for the timing and origin of archean lode gold deposits alteration assemblages associated with archean epigenetic gold mineralization in the menzies kambalda area of the yilgarn craton western australia vary systematically with regional metamorphic grade up to and including upper amphibolite facies rocks k metasomatism is recorded by the presence of muscovite biotite and k feldspar at progressively higher metamorphic grades high metamorphic grades are commonly developed in broad thermal aureoles around fate syntectonic granitic intrusions metamorphic recrystallization of alteration assemblages is common in the thermal aureoles these relations suggest broad contemporaneity among granitoid intrusion regional metamorphism and mineralization during the final stages of the tectonic evolution of the granite greenstone terrain late syntectonic granitoids acted as centers of heat and fluid flux in large scale synmetamorphic hydrothermal systems that deposited gold possibly from modified mantle derived fluids

constraints on archaean crustal composition and structure provided by deep seismic sounding in the yilgarn block abstract new seismic reflection data from the eastern goldfields and southern cross provinces coupled with results from earlier seismic refraction profiles recorded in the western southern cross province indicate that with the exception of the greenstone belts that occupy much of the surface of the eastern goldfields province the crust in the yilgarn block is composed predominantly of felsic material with only minor mafic material within the lowest part of the crust the greenstone belts themselves are shallow features and not deep rooted features as often proposed the transition from the crust to the mantle is sharp occurs over only a few kilometres and marks a significant change in composition and density the middle and lower crust along the section have no marked lateral change in reflection character between the greenstones terranes and the adjacent granite dominated terranes except that both the mid crustal and crust mantle boundaries have been bowed downwards by approximately 6 km under the greenstones the greenstone belts of the eastern goldfields province are 6 9 km thick they are superimposed on an otherwise uniform crust their base is planar and subhorizontal and appears to be block faulted in places the ida fault which defines the western boundary of the greenstone belts is planar dips to the east at 25 30 and can be traced to depths of approximately 25 km 8 s

precambrian tectonic evolution of part of gondwana southwestern australia southwestern australia has a long dynamic precambrian history of crustal fragmentation and aggregation by continental collision and accretion this interpretation contrasts with the widely held belief that most of australia was part of a proterozoic supercontinent in which all tectonic magmatic and metamorphic activity was intracontinental the pilbara and yilgarn cratons are two quite different fragments of archean continental crust that collided to form the capricorn orogen between 2000 and 1600 ma the albany fraser orogen formed along the southern margin of the yilgarn craton during another major continental collision at 1300 to 1100 ma rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 ma subsequent continental collision along this rifted margin formed the paterson orogen at 700 to 600 ma therefore the assembly of this considerable part of gondwana may not have been completed until about 600 ma

physical volcanology and geochemistry of a late archaean volcanic arc kurnalpi and gindalbie terranes eastern goldfields superterrane western australia abstract late archaean 2715 2704 ma calc alkaline volcanic complexes in the kurnalpi terrane are identical in facies and geochemistry to modern intra arc volcanic complexes preserved volcanic rocks and associated feldspathic sedimentary rocks represent proximal to medial submarine facies of submarine to locally emergent intra oceanic arc related volcanoes the least altered volcanic rocks are dominantly andesite but range from basalt and basaltic andesite to rare rhyolite and are the product of magmas similar in composition to those of modern arcs intermediate magmas were most likely derived from large ion lithophile element lile enriched mafic magmas by fractional crystallisation with or without assimilation processes the kurnalpi terrane thus provides an example of a late archaean volcanic arc in which hydrated mantle wedge melting was the main mechanism for magma genesis ttd suite volcanism derived from slab melting was either absent or played a subordinate role the adjacent gindalbie terrane contains younger 2692 2680 ma bimodal basalt rhyolite volcanic complexes with associated quartz rich sedimentary rocks and calc alkaline intermediate silicic volcanic complexes volcanosedimentary basement to the gindalbie volcanic sequences is deeply eroded equivalents of the calc alkaline volcanic complexes their associated sedimentary rocks and younger basaltic sequences found in the kurnalpi terrane gindalbie basalt rhyolite successions locally contain volcanic hosted massive cu zn mineral deposits rhyolites derived by low pressure fractional crystallisation or melting of andesites are more abundant than in the kurnalpi volcanic complexes facies associations and the local occurrence of distinctive incompatible element enriched mildly peralkaline a type rhyolites are consistent with rifting of a mature arc system the two terranes most likely represent volcanic evolution of the same late archaean volcanic arc but are different tectonic fragments that were welded together by 2660 ma

geochemistry and tectonic setting of two contrasting archaean felsic volcanic associations in the eastern goldfields western australia abstract archaean felsic volcanic rocks from two areas in the eastern yilgarn craton of western australia comprise dacite and rhyolite with subordinate basalt and andesite one suite from one of the areas black flag group is dominated by subaqueous dacite lava lobes and their reworked products the other suite from the other area melita and jeedamya volcanics consists of abundant rhyolitic and rhyodacitic pyroclastic deposits with less abundant dacitic lava flows both suites are intercalated with volumetrically subordinate basic and intermediate volcanic rocks black flag group dacites and rhyolites have steep ree patterns la yb cn about 40 and no eu anomaly high sr and al2o3 low nb and y hence high sr y melita and jeedamya dacites and rhyolites have flatter ree patterns la yb cn between 2 and 9 negative eu anomalies eu eu 0 4 0 6 and higher zr nb y and lower sr hence lower sr y on chemical grounds mafic rocks in both areas are genetically unrelated to felsic volcanic rocks black flag group andesites dacites and rhyolites are probably unrelated by fractional crystallization but resulted from 22 28 partial melting of amphibolite leaving a residual mineralogy of amphibole plagioclase garnet ilmenite clinopyroxene alternatively andesites may have been derived by partial melting of a metasomatised mantle source jeedamya rhyodacite could have been produced by 35 vapour absent melting of tonalite leaving a residual mineralogy of plagioclase orthopyroxene amphibole ilmenite the source would have had a slightly lree enriched pattern with a positive eu anomaly residual garnet in the source of black flag group rocks requires melting at depths greater than 35 km which is below the base of the present tectonically thinned crust the most likely source is subducted oceanic crust with black flag group rocks erupted in a back arc basin melita and jeedamya felsic volcanic rocks resulted from melting of thicker continental crust adjacent to the back arc

4d architecture and tectonic evolution of the laverton region eastern yilgarn craton western australia abstract the laverton region located in the eastern yilgarn craton eyc western australia is second only to the kalgoorlie region for gold endowment the integration of high density potential field data regional and camp scale seismic reflection data regional and mine scale structural analysis and geochronologically constrained stratigraphy provided new insights into the 4d architecture and tectonic evolution of laverton region at a regional scale the map patterns of laverton are dominated by the mt margaret dome in the northwest and the kirgella dome in the southeast these domes are flanked to the east and west by north northwest striking shear zones with the central zone between the two domes being dominated by north to north northeast striking sigmoidal shear zones these distinctly different strikes to the shear zones developed early in the tectonic evolution and resulted in a favourable architecture for late stage orogenic gold mineralisation a series of regional seismic reflection lines have imaged the sub surface architecture of the laverton region with a major crustal penetrating shear extending to the moho mapped as the laverton tectonic zone ltz the ltz consists of a basal fault the north northwest striking celia fault and a series of steeper faults for example the north to north northeast striking childe harold fault and far eastern fault which sole at depth into the celia fault beneath the laverton region lower angle faults imaged in the seismic reflection data develop parallel to granite gneiss domes that postdate the north northwest striking and north to northeast striking faults the construction and integration of the new 3d map with the structural stratigraphic and geochronological analysis has defined six main deformation events and their effects on the architectural evolution of the region this analysis suggests that early formed faults are genetically associated with late stage orogenic gold mineralisation regional and mine scale structural analysis at the wallaby and sunrise dam deposits indicate that gold deposition occurred synchronously during the d4b event in both deposits both mines are separated by the ltz which records sinistral and later d5 dextral movement the kinematic model which best describes the observed architecture is a restraining step over within a sinistral strike slip system a structural model consistent with analogue modelling of strike slip systems is proposed where two early extensional basement faults were reactivated during d4b northwest southeast contraction as low angle thrusts in a pop up zone this architecture has been mapped in 3d in the region between wallaby and sunrise dam where both deposits are located on the low angle thrusts on opposing sides of a sigmoidal structure developed during sinistral strike slip movement this strike slip step over architecture provided significant opportunity for dilation and fluid flow late dextral movement of the basement faults during northeast southwest contraction d5 reactivated the low angle thrusts at sunrise dam producing extensional movement and further dilation within the overall restraining step over this event is not significant at wallaby mine a detailed 3d stress analysis at sunrise dam revealed that the most favourable fault segments to reactivate during the d4b event were orientated at 30 towards 310 a comparison of the spatial distribution of gold defined from extensive production and resource estimation drilling with the favourably orientated segments of faults was confirmed the analysis also highlighted down dip extensions beyond the coverage of the drilling of favourably oriented segments which may provide additional targets during future near mine exploration the same approach was applied to the regional 3d map and new targets generated beneath the major salt lake between wallaby and sunrise dam

structural setting and geochemistry of archaean i type granites in the bardoc coolgardie area of the norseman wiluna belt western australia abstract regional structures in the bardoc coolgardie area of the archaean norseman wiluna greenstone belt in western australia developed during early large scale thrusting followed by a transpressional regime characterized by enewsw shortening and large scale sinistral strike slip faults structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history emplacement mechanisms include solid or liquid state diapirism forceful dilation of country rocks and passive stoping i type granites are common and include early and late tectonic intrusions the widespread occurrence of i type granodiorite and monzogranite probably derived by partial melting of lower continental crust or subducted oceanic crust suggests a continental margin setting for the belt alkalic quartz diorite occurs as rounded enclaves in granodiorite and is enriched in ba rb sr ce la p and f which suggests a mantle derived volatile component these quartz diorite melts may have formed by partial melting of metasomatized mantle or alternatively mantle degassing may have lowered solidus temperatures in the source region and thus induced melting emplacement of hot volatilerich quartz diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite recent models for archaean gold mineralization suggest that auriferous fluids contained co 2 derived from lower crustal or mantle sources in the bardoc coolgardie area co 2 may have been flushed out during partial melting of the lower continental crust however the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late stage event and took place over a considerably shorter time interval than the formation and emplacement of i type granites

late archean convergent margin tectonics and gold mineralization a new look at the norseman wiluna belt western australia on a world scale the most important hydrothermal gold deposits occur either in late archean ca 2700 ma greenstone belts or at late paleozoic to quaternary convergent plate boundaries in the latter environments epithermal and porphyry hosted deposits form during subduction related magmatism in volcanic arcs and deep level meso thermal deposits form during deformation in continental margin orogenic belts the mesothermal deposits are similar to archean gold deposits in greenstone belts such as the norseman wiluna belt in western australia we here suggest that this similarity exists because the norseman wiluna belt is an orogenic belt with a tectonic history similar to that of younger mineralized convergent margins such as the north american cordillera it is most likely that the norseman wiluna belt resulted from the interaction of lithospheric plates during the major period of continental growth and stabilization that occurred in the late archean the distribution of gold mineralization being controlled by convergent margin tectonics

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

age constraints on recycled crustal and supracrustal sources of archaean metasedimentary sequences eastern goldfields province western australia evidence from shrimp zircon dating abstract shrimp u pb zircon dating of sedimentary volcanic and subvolcanic intrusive rocks from unconformity bounded sequences in the eastern goldfields province defines maximum depositional ages for those sequences the kambalda sequence which records a backarc basin was deposited prior to 2700 ma and from at least 2715 ma the spargoville sequence which records an arc adjacent volcano bound basin was deposited between 2700 and 2683 ma the kalgoorlie sequence which records an intra arc rift basin comprises two tectonic stages with depositional ages of 2681 2670 and 2661 2655 ma deposition of the spargoville and kalgoorlie sequences overlapped with the intrusion of granitoids and subvolcanic porphyries thereby indicating that those granitoids were emplaced during crustal extension younger submarine fan kurrawang sequence and braided fluvial merougil and jones creek sequences deposits of a remnant ocean basin were deposited at when coupled to palaeocurrent data provenance dating of detrital zircon suites fingerprints southeast oriented amalgamation of felsic detritus from multiple sources within longitudinal depositional systems and longitudinal reworking of felsic detritus from single sourced transverse systems most felsic detritus was recycled from coeval volcanoplutonic arcs and the orogen to the remnant ocean basin sequences with zircon ages ranging from 2730 to 2660 ma older felsic sources with age ranges of 3570 3130 3030 2900 2870 2770 and 2760 ma could have been structural enclaves within the volcanoplutonic arcs or orogen but were more likely within a distant cratonic basement when coupled with stratigraphic data it is concluded that detrital zircon age distributions preserve evidence for the sedimentary recycling of coeval volcanoplutonic arc or orogenic sources uplifted basin floor and dissected arc successions and cratonic basement virtually all source terrains have apparently vanished presumably through the combination of tectonic and sedimentary recycling and tectonic severance increased use of detrital zircon suites from archaean sedimentary sequences is advocated in order to quantify the balance between sedimentary recycling of felsic rocks from contemporaneous volcanoplutonic sources which themselves document crustal growth in arc environments and from relict volcanoplutonic and crustal basement sources which document the degree of crustal recycling

late archaean felsic alkaline igneous rocks in the eastern goldfields yilgarn craton western australia a result of lower crustal delamination numerous felsic alkaline intrusions were emplaced in the granite greenstone terrain of the eastern goldfields yilgarn craton between c 2650 and 2630 ma intrusion coincided with the waning stages of voluminous regional granitic magmatism the alkaline rocks are localized along and adjacent to major crustal structures that separate lithostratigraphic greenstone terranes and are divided into four geographically and compositionally distinct suites viz the mount monger emu claypan and ninnis suites the rocks have features in common with a type granites including high total alkalis an anhydrous primary mineralogy an apparent anorogenic setting and enrichment in some hfse although they also have low concentrations of nb and y they show a range of features that together point to a crustal source e g the alkaline rocks are not associated with voluminous mafic magmatism they have high lile concentrations they carry zircon xenocrysts of similar age to whole rock sm nd model ages they show evidence for regional source heterogeneity suites have constant and distinct la y and nb y ratios and the rocks show many compositional similarities to the slightly older voluminous crust derived granites extreme enrichments in sr and ba in the mount monger suite however suggests that their source may have been metasomatized before or during melting intrusion of the alkaline rocks heralds a poorly recognized third tectonothermal event in the evolution of the eastern part of the yilgarn craton and was broadly synchronous with the intrusion of voluminous felsic fractionated granites crustal extension and widespread au mineralization the late archaean geology of the eastern goldfields shows many features in common with phanerozoic collisional belts thought to be profoundly influenced by processes of lithospheric delamination or convective thinning this newly recognized third tectonothermal event in the eastern goldfields may relate to the delamination or convective thinning of a dense garnet rich lower crust that resulted from extraction of earlier voluminous granite magma and it is possible that such processes have had a greater influence on late archaean crustal evolution than previously recognized

the wangkathaa orogeny an example of episodic regional d2 in the late archaean eastern goldfields province western australia abstract the eastern goldfields province egp is a late archaean orogenic belt located on the eastern margin of the yilgarn craton the egp is characterised by a prominent nnw trending tectonic grain developed largely during regional e w oriented shortening a simplistic sequence of largely progressive compressional deformation events d 1 to d 4 has been used by previous workers to explain the development of the egp regional d 2 was thought to be responsible for most of the finite strain and therefore a reliable marker event for correlating deformation histories across the region a re examination of the deformation history has shown that d 2 kalgoorlie orogen of weinberg et al precambrian res 120 2003 219 239 was not a single progressive event rather it was episodic and involved several stages of switching of the tectonic mode compression extension switching between 2665 and 2655 ma the sequence of events during d 2 was an early stage of e w shortening d 2a followed by extension with basin formation and normal fault movement d 2e and finally a second stage of e w compression d 2b we introduce this sequence of events as the wangkathaa orogeny more complex in tectonics and broader in geographical scope than the kalgoorlie orogen features of the wangkathaa orogeny are well illustrated by the geometry and geological relationships that occur in the kurnalpi terrane welcome well area and the kalgoorlie terrane ora banda kambalda and the boorara domains of the central and southern egp available geochronology indicates that this sequence of events was likely to have been diachronous across the entire egp and the eastern southern cross province of the yilgarn craton recognition of these separate episodic stages of e w oriented compression and extension is important in our understanding the tectonic evolution of the egp switching tectonic mode between compression and extension will change the state of mean stress in a rock mass e g from net dilation to net constriction and vice versa and is an effective method in transporting and trapping mineral rich fluids the paradox of the different timings established for d 2 across the province are explained by the wangkathaa orogeny especially if it were diachronous as different workers dated different phases of an episodic orogeny

gneiss domes and extensional deformation in the highly mineralised archaean eastern goldfields province western australia abstract the recognition of large areas of gneiss within granitic complexes of the northeastern part of the eastern goldfields province of western australia based on analysis of regional aeromagnetic data has resulted in a re evaluation of the structural data for that region five magnetic domains have been established in the granitic complexes which are marginal to the main greenstone belts at least two of these domains have a distinctive domal form and also have internal domeshaped regions the ballard and laverton domains have extensive areas of layered gneissic and migmatitic rocks which flank the internal domes boundary relationships at the laverton and ballard domains show that the domes are concordant sheets and the metamorphic conditions of the boundary rocks imply that the sheets were intruded at a middle crustal level strain conditions in the boundary zones indicate that emplacement of the gneiss domains to the crustal level of the surrounding lower grade greenstones was initially along relatively gently dipping shear zones which were active during uplift structural relationships around both the domal granitic complexes and the later granite batholiths however show that regional shortening deformation events were not caused directly by the emplacement of any of the granitic rocks the tectonic hypothesis presented for the eastern goldfields is similar to that proposed for the formation of cordilleran metamorphic core complexes the uplift event responsible for the crustal extension required to allow the emplacement of the gneiss may have been driven by the same thermal input responsible for the generation of the voluminous granites intrusive into both the gneiss complexes and the surrounding greenstone belts

an overview of the nature distribution and inferred tectonic setting of granitoids in the late archaean norseman wiluna belt abstract the highly mineralized late archaean norseman wiluna belt yilgarn block western australia has lithostratigraphic associations and a structural style and history that has recently been interpreted in terms of a subduction related tectonic setting it is important to investigate whether the geochemistry and petrology of the granitoids in the belt are compatible with such a model the granitoid suite within the belt can be subdivided into association 1 large composite batholiths of calc alkaline affinity spatially and temporally associated with calc alkaline volcanic centres association 2 plutons ranging from quartz diorite and tonalite to monzogranite and syenogranite spatially related to dike swarms of felsic to intermediate porphyries and calc alkaline lamprophyres and association 3 peralkaline to alkaline batholiths and stocks which are spatially and temporally associated with rhyolitic volcanic centres and major lineaments the calc alkaline associations 1 and 2 have characteristics comparable with suites of variable fractionated i type granitoids in phanerozoic continental margin are settings including 1 a wide range in sio 2 2 meta to peraluminous compositions 3 a progression from granodiorite to granite with plutons becoming more k 2 o rich and hornblende poor with time 4 lile enrichment and relative depletion of ta nb and ti in contrast to most phanerozoic granitoids the norseman wiluna belt granitoids have highly fractionated ree patterns and low contents of yb and y with respect to average post archaean equivalents ree data and trace element characteristics suggest derivation from a mafic source leaving hornblende and or garnet as residual phases peralkaline granitoids of association 3 exhibit enrichments on sio 2 na 2 o k 2 o zr y nb and ta with respect to the calc alkaline granitoids they post date associations 1 and 2 and are consistent with the concept that they represent a continuation of magmatism in a post orogenic environment thus the nature and distribution of the granitoids of the norseman wiluna belt are consistent with interpretations that the belt formed in a subduction related convergent margin setting

scale integrated architecture of a world class gold mineral system the archaean eastern yilgarn craton western australia abstract world class mineral systems such as those found in the archaean eastern yilgarn craton are the product of enormous energy and mass flux systems driven by lithospheric scale processes these processes can create big footprints or signatures in the lithosphere which can be observed at a range of scales and via a variety of methods including geophysics isotopes tectonostratigraphy and geochemistry we use these datasets to describe both the architecture structure of world class gold systems of the yilgarn craton and the signatures of their formation by applying an understanding of the most critical elements of the process and their signatures new areas especially undercover may be targeted more predictably than before knowledge of the major architectural elements of the yilgarn craton has increased greatly over the last decade through the collection of a wide range of geophysical geochemical and isotopic data these data range in scale from 1 lithospheric scale which provide information on the entire craton and their underlying volumes down to depths in excess of 350 km through 2 regional scale which provide information at the province scale and to depths of 30 40 km to 3 mine and camp scale which provide information on the top few kilometres of the crust the architecture structure in the upper mantle and lower crust can be inferred from broadband seismic tomography and analysis of long wavelength gravity data geophysical data such as magnetotellurics and deep crustal reflection seismic also provide evidence for the signatures of the flow of fluids through this architecture the pathways and they illustrate that the scale of the system is many orders of magnitude larger than the immediate deposit itself of particular importance is the role of deep crustal penetrating shear zones or faults which link the mantle with domes in the upper crust together these data provide first order insights into the physical and chemical properties of the yilgarn craton these insights provide geodynamic clues and constraints as to why the yilgarn is so well endowed in metals such as gold groves et al 1989 the intersection of favourable architectural features provides connections between the mantle and the upper crust in the kalgoorlie region possibly explaining why this area is so well endowed in comparison to others

extensional emplacement of a high grade granite gneiss complex into low grade greenstones eastern goldfields yilgarn craton western australia abstract a high grade granite gneiss complex was emplaced into low grade greenstones after an early episode of late archaean deformation d1 in the eastern goldfields of western australia the components of the granitic gneiss complex range from migmatitic granitic gneiss to foliated and massive granite the complex is surrounded by a marginal zone of high grade amphibolite facies greenstones the oldest phases of the complex are foliated and gneissic granite with igneous emplacement ages of c 2675 ma that postdate the bulk of greenstone volcanism c 2720 2675 ma the complex includes voluminous and largely undeformed monzogranite that is correlated with widespread granite plutonism at c 2660 ma fabrics in marginal high strain zones between the granite gneiss complex and greenstones and in faults separating high grade from low grade greenstones indicate that emplacement or uplift of the complex was partly accommodated by normal faulting final emplacement occurred during the c 2660 ma granite event and overlapped with regional east west shortening d2 d3 in the adjacent greenstones uplift of the granitic gneiss complex to higher crustal levels may have resulted from preferential injection of granite magma into gentle domes of the basal greenstone contacts these domes formed during earlier regional extension of the greenstones

conceptualizing delta forms and processes in arctic coastal environments climate warming in the arctic directly causes two opposite changes in arctic coastal systems increased melt water discharge through rivers induces extra influx of sediments and extended open water season increases wave impact which reworks and erodes the shores a shoreline change analysis along the southern coast of disko island in western greenland was conducted with aerial photographs and satellite images from 1964 1985 and 2012 the decadal morphologic evolution of this 85 km section showed that large parts of the coast had undergone very limited changes however two deltas were highly dynamic and popped up as hotspots the tuapaat delta and skansen delta showed large progradation rates 1 5 and 7 m yr and migration of the adjacent barriers and spits the dynamic behavior at the delta mouths was mainly caused by classic delta channel lobe switching at one delta tuapaat and by a breach of the fringing spit at the other delta skansen the longshore and cross shore transports are responsible for reworking the sediment with a result of migrating delta mouths and adjacent subaqueous mouth bars seaward progradation of the deltas is limited due to the steep nature of the bathymetry in disko bay finally a schematic conceptual overview of processes and associated morphological responses for deltas in arctic environments is presented including the climate drivers affecting delta evolution copyright 2016 john wiley sons ltd

subduction evolution and mantle dynamics at a continental margin central north island new zealand 1 central north island new zealand provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin whereas most subduction zones are innately two dimensional north island of new zealand displays a distinct three dimensional character in the back arc regions specifically we observe mariana type subduction in the back arc areas of central north island in the sense of back arc extension high heat flow prolific volcanism geothermal activity and active doming and exhumation of the solid surface evidence for emplacement of a significant percent of new lithosphere beneath the central north island comes from heat flux of 25 mw km of strike of volcanic zone and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust seismic attenuation qp 1 is high 240 and rhyolitic and andesitic volcanism are widespread almost complete removal of mantle lithosphere is inferred here in pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7 4 0 1 km s in contrast southwestern north island exhibits chilean type back arc activity in the sense of compressive tectonics reverse faulting low heat flow thickened lithosphere and strong coupling between the subducted and overriding plates this rapid switch from mariana type to chilean type subduction occurs despite the age of the subducted plate being constant under north island moreover stratigraphic evidence shows that processes that define the extensional back arc area the central volcanic region are advancing southward into the compressional system wanganui basin at about 10 mm yr we link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back arc regions thickening occurred during the miocene within the taranaki fault zone the process of thickening and convective removal is time and temperature dependent and has left an imprint in both the geological record and geophysical properties of central north island which we document and describe

broad synchroneity of three gold mineralization styles in the kalgoorlie gold field shrimp u pb and 40ar 39ar geochronological evidence there has been a long standing controversy regarding the timing and number of gold mineralization events at kalgoorlie uranium pb dating of zircons and hydrothermal monazite and xenotime as well as ar 40 ar 39 analysis of metasomatic fuchsite and white mica are used to date pre to synore dikes alteration and orebodies in order to resolve this issue the majority of gold mineralization at kalgoorlie including ductile brittle fimiston brittle ductile oroya and brittle mount charlotte style gold are different expressions of a complex mineralizing system that was active at broadly the same time at ca 2 64 ga gold mineralization was thus deposited in both ductile and brittle structures at approximately the same crustal level at broadly the same time limier similar pt conditions this giant ore system formed after ea 2 69 ga basic magmatism intrusion of the golden mile dolerite sill at 2680 9 ma and intrusion or calc alkaline feldspar quartz porphyry dikes at 2670 5 ma gold mineralization was broadly coeval with lamprophyre dike intrusion at 2642 6 ma and overlapped the waning stages of hornblende and albite bearing porphyry dike emplacement at 2650 6 ma and regional metamorphism subsequent brittle deformation in the kalgoorlie gold held way accompanied by hydrothermal activity that may have led to some late gold mineralization or remobilization in extensional quartz vein arrays in the golden mile between about 2 61 and 2 60 ca this late hydrothermal activity and associated brittle deformation marks the last event to significantly affect the rocks it kalgoorlie and may be related to uplift lift and final cooling of the terrane despite this late event the geometry of the kalgoorlie gold field and its contained lode systems has remained essentially the same since the time of gold mineralization

extension and gold mineralization in the archean kalgoorlie terrane yilgarn craton abstract this paper focuses on two extensional events affecting late archean crust of the kalgoorlie terrane in the eastern goldfields and which are associated with gold mineralization these events bracket the duration of the crustal shortening event known as the kalgoorlie orogen the early extension phase is preserved around the raeside batholith and gave rise to the earliest recognized structures d 1e this event is characterized by multi directional horizontal extension in contrast to unidirectional extension associated with core complexes extension uplifted the batholith in relation to the overlying greenstone sequence and produced recumbent folds gold including the large deposits at leonora was deposited in normal shear zones around the batholith we propose that extension triggered doming of gravitationally unstable granitic rocks buried under a greenschist sequence and amplified the growth of extensional nappes the late phase of extension is evident in a number of gold deposits in the kalgoorlie terrane this phase is characterized by a overprinting crustal shortening structures that suggests it is the latest structure in all localities b gently dipping foliation associated with recumbent folds which are dragged into moderately dipping normal shear zones c maximum stretching axis nw se or n s at high angles to the maximum shortening axis inferred from regional shortening phases of the kalgoorlie orogen and d hosting gold this phase records relaxation of the kalgoorlie orogen and the findings suggest that gold mineralization was not restricted to a single deformation phase but started before the kalgoorlie orogen and waned at the end of the orogeny

the world class wallaby gold deposit laverton western australia an orogenic style overprint on a magmatic hydrothermal magnetite calcite alteration pipe gold mineralisation at the wallaby gold deposit is hosted by a 1 200 m thick mafic conglomerate the conglomerate is intruded by an apparently comagmatic alkaline dyke suite displaying increasing fractionation through mafic monzonite monzonite syenite syenite porphyry to late stage carbonatite in the mine area a pipe shaped zone of actinolite magnetite epidote calcite amec alteration overprints the conglomerate gold mineralisation associated with dolomite albite quartz pyrite alteration is hosted in a series of sub horizontal structurally controlled zones that are largely confined within the magnetite rich pipe the deposit has a current ore reserve of 2 0 moz au and a total resource of 7 1 moz au

evolution of the archaean granite greenstone terranes of the eastern goldfields western australia shrimp upb zircon constraints abstract thirty five high precision shrimp u pb zircon dates with an average 95 confidence error of 6 ma have been obtained from the granite greenstone terranes in the southern part of the eastern goldfields of western australia these dates establish the timing of major deformation metamorphism and granite intrusion events and test inferred stratigraphic relationships within the greenstones these new data reveal that felsic volcanic rocks were erupted throughout the southern part of the eastern goldfields between c 2713 and c 2672 ma analytically indistinguishable dates of c 2705 ma were obtained for felsic volcanic rocks interbedded with komatiitic lavas at three sites dates on felsic volcanic rocks within tectonostratigraphic packages that include komatiites are also consistent with an inferred eruption age for these komatiites of c 2705 ma komatiitic lavas in the southern part of the eastern goldfields were probably emplaced during a single voluminous eruption that resulted in the flooding of a vast area of the late archaean landscape filling the topographic lows around older felsic volcanic vents the stratigraphic complexity within tectonostratigraphic domains is attributed to the existence of an undulating topography during the eruption of the mafic and ultramafic lavas and to the rapid and localized deposition of felsic volcanic rocks close to a number of isolated volcanic centres prior to and after the komatiite lava eruption event between c 2685 and c 2675 ma early pre d2 intrusive equivalents of the felsic volcanic rocks were emplaced as thick granite sheets into the base of the greenstone sequences regional east west compression between c 2675 and c 2657 ma reactivated early extensional structures and resulted in the stacking of the greenstones this was accompanied by further intrusion of granite within developing antiforms burial of greenstone slices by stacking and the effect of hydrothermal fluids emanating from both the granites and buried greenstones resulted in regional metamorphism to greenschist facies prior to c 2640 ma monzogranite and granodiorite emplaced near the western southern and eastern margins of the greenstones were deformed and metamorphosed to upper amphibolite facies and converted into gneisses during d2 and d3 compression events movement along large scale transcurrent d3 shear zones had ceased by c 2635 ma remnants of a c 2958 to c 2930 ma greenstone sequence preserved near norseman and ravensthorpe in the southeastern yilgarn craton and xenocryst zircons ranging in age from c 2910 2730 ma in the c 2713 2672 ma felsic volcanic rocks indicate that the exposed greenstone sequences were deposited on continental basement the eastern goldfields granite greenstone terranes were formed by the closure of a series of narrow back arc rift basins that developed along a continental margin and above an active subduction zone located to the east of the rift basins

assessing the importance of terrestrial organic carbon in the chukchi and beaufort seas abstract the western arctic ocean is a unique part of the world s oceans and is an area undergoing significant climate changes the effects and possible climate feedbacks of these changes are not yet fully understood decreased sea ice cover could lead to increased productivity in the water column or a reduction in total productivity through the loss of sea ice algal contributions climate change could also alter the patterns of terrestrial inputs from rivers and coastal erosion in order to better understand the balance of organic material inputs in the western arctic ocean this report presents carbon and nitrogen elemental and isotopic compositions from 19 surface sediment samples and 7 cores from 4 shelf to basin transects as evidence of the sources of organic matter buried in the sediments of the chukchi and alaskan beaufort seas the c n ratios for surface sediments were between 5 3 and 11 5 mean 9 0 1 3 the mean toc was 1 2 0 3 and mean tn was 0 16 0 02 the highest toc contents were observed in the barrow canyon transect likely reflecting heightened overlying productivity the 13 c of this preserved material varied from 22 1 to 16 7 mean 19 4 1 3 a trend to depletion in 13 c and higher c n in eastern sites was observed among the surface samples 15 n varied from 4 1 to 7 6 mean 5 7 1 1 an evaluation of the inputs of organic matter to the western arctic sediment was accomplished using 13 c and 15 n values with the novel technique of a bayesian analysis multi source mixing model this model was used to estimate proportional contributions of sea ice algae water column phytoplankton and terrestrial organic matter we conclude that water column productivity is the source of between 50 and 70 of the organic carbon buried in this portion of the western arctic the remaining 25 35 of carbon is mainly supplied by sea ice algal productivity with at most 15 of sedimentary carbon derived from terrestrial inputs

modeling erosion of ice rich permafrost bluffs along the alaskan beaufort sea coast the arctic climate is changing inducing accelerating retreat of ice rich permafrost coastal bluffs along alaska s beaufort sea coast erosion rates have increased roughly threefold from 6 8 to 19 m yr 1 since 1955 while the sea ice free season has increased roughly twofold from 45 to 100 days since 1979 we develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice free season sea level water temperature nearshore wavefield and permafrost temperature in controlling erosion rates in this setting the model captures the processes of erosion observed in short term monitoring experiments along the beaufort sea coast including evolution of melt notches topple of ice wedge bounded blocks and degradation of these blocks model results agree with time lapse imagery of bluff evolution and time series of ocean based instrumentation erosion is highly episodic with 40 of erosion is accomplished during less than 5 of the sea ice free season among the formulations of the submarine erosion rate we assessed we advocate those that employ both water temperature and nearshore wavefield as high water levels are a prerequisite for erosion any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion the certain increases in sea level and potential changes in storminess will both contribute to this effect as water temperature also influences erosion rates any further expansion of the sea ice free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates

model for the development of kyanite during partial convective overturn of archean granite greenstone terranes the pilbara craton australia restricted occurrences of early syn and late kinematic kyanite adjacent to large domal batholiths in the archean granite greenstone terrane of the east pilbara craton australia are considered to result from partial convective overturn of the crust the analogue models of dixon summers 1983 and thermo mechanical models of mareschal west 1980 involving gravitionational overturn of dense greenstone crust that initially overlay sialic basement successfully explain the geometry dimension kinematics and strain patterns of the batholiths and greenstone rims application of these models suggests that andalusite and sillimanite are the stable aluminosilicate polymorphs in domal crests and rims where prograde clockwise p t t paths with small pressure changes should be recorded both aluminosilicates are predicted to overprint kyanite which is observed locally around the east pilbara domes kyanite is the predicted aluminosilicate polymorph in the deeper parts of domal rims and within sinking greenstone keels reflecting rapid near isothermal burial the narrow zones of kyanite bearing schists adjacent to some batholiths in the pilbara craton are metamorphosed highly strained equivalents of altered felsic volcanic rocks in the low grade greenstone succession dragged to mid crustal depths 6 kbar during greenstone sinking the schists rebounded as an arcuate tectonic wedge along the southern mount edgar batholith rim during the later stages of doming and were juxtaposed against regional greenschist facies low strain greenstones thus kyanite was preserved if the walls had remained at depth it would have been overprinted by the higher temperature aluminosilicate polymorphs during thermal recovery kyanite growth in the pilbara craton is unlikely to have resulted from ballooning of plutons mantled gneiss doming metamorphic core complex formation or early crustal overthickening the typical subvertical foliations and lineations of the tectonic wedge suggest that subvertical fabrics extended to mid crustal depths c 20 km before rebound providing a three dimensional glimpse of archean dome and keel structures the general occurrence of large granitoid domes in archean granite greenstone terranes restriction of rare kyanite to the adjacent high strain batholith margins and its absence from the batholiths suggest that partial convective overturn of the crust may have been a common process at this early stage of earth history

architecture and geodynamic evolution of the st ives goldfield eastern yilgarn craton western australia abstract a new structural evolution consisting of both extensional and contractional events has been defined for the st ives goldfield in the south central kalgoorlie terrane of the eastern yilgarn craton in western australia these events shaped the development of the fault architecture which controlled the location of the regional anticlines the magmatic centres and the deposition of the archaean greenstone successions the fundamental grain of the st ives goldfield is north northwest trending this trend is marked by faults which developed during d1 extension which was oriented east northeast west southwest across these faults we map major stratigraphic changes in the thickness and composition of units especially of the previously undivided black flag group volcaniclastic rocks the centre of the st ives goldfield is dominated by the kambalda anticline this north northwest trending regional fold was likely established early during the d1 extensional history and was fully established during subsequent east northeast oriented d2 contraction the regional anticline is an important architectural element because 1 magmatism and gold mineralising fluids were focussed into this domed region and 2 deformation was partitioned across the limbs and crest of this structure the d3 event involved regional uplift and extension resulting in the formation of late basins merougil conglomerate locally and the emplacement of granitoids sourced from a metasomatised mantle wedge mafic type porphyries the most significant gold event in terms of endowment occurred during d4b sinistral strike slip shearing and associated thrusting e g tramways and republican thrusts these thrusts were previously interpreted as the first contractional structures to deform the area d1 but are here reinterpreted as relatively late d4b in this d4b event the north northwest trending faults underwent sinistral strike slip shearing and were linked across the kambalda anticline by accommodation structures represented by generally east to east northeast trending thrusts reactivation of d1 transfer structures may have influenced the location of these later accommodation structures late stage mineralisation during d5 was the result of dextral strike slip brittle shearing

detrital zircon provenance constraints on the evolution of the harts range metamorphic complex central australia links to the centralian superbasin until recently it has been widely accepted that protoliths to metasediments of the harts range metamorphic complex central australia were deposited prior to c 1 75 ga and form part of the palaeoproterozoic arunta inlier however new sensitive high resolution ion microprobe u pb analyses of detrital zircon together with recently published data suggest that they were deposited coeval with c 545 520 ma sediments from the adjacent little metamorphosed neoproterozoic to palaeozoic centralian superbasin protoliths of the harts range metamorphic complex were deposited in the irindina sub basin an early to mid cambrian rift located between the present day amadeus and georgina basin remnants of the centralian superbasin deposition occurred during a widespread and long lived interval of extension in parts of central australia associated with eruption of the voluminous kalkarinji continental flood basalts the harts range metamorphic complex was metamorphosed to upper amphibolite to granulite facies conditions within c 40 ma of deposition of its sedimentary protoliths

anomalous lithosphere beneath the proterozoic of western and central australia a record of continental collision and intraplate deformation a new surface wave seismic tomography model of australia is presented which provides a means of investigating the lithospheric structure beneath the proterozoic regions in the west north and centre of the continent with improved resolution and reliability the dominant feature of the model is a region of low seismic wavespeeds in the uppermost mantle at approximately 75 km depth beneath central australia the zone of slow wavespeeds is underlain by a region of fast wavespeeds more typical of continental lithosphere this layered velocity structure and strong positive wavespeed gradient makes the shallow anomaly hard to explain in terms of high mantle temperatures and typical steady state continental geotherms a possible thermal explanation requires the impact of the redistribution of high heat producing elements within the crust alternatively a mineral or minerals with low seismic velocities such as amphibole in the shallowest part of the lithosphere with a more conventional lithology in the deep continental root below could explain the seismic wavespeeds the anomaly is located directly beneath the zone where the australian cratons amalgamated in the proterozoic and where subsequently there have been periods of intraplate tectonic activity suggesting a correlation between the prolonged history of deformation and a highly unusual lithospheric structure in western australia the capricorn orogen and pilbara craton have a similar lithospheric thickness whereas a thicker lithosphere is observed beneath the yilgarn to the south in northern australia large regions appear to be underlain by fast wavespeeds similar to those observed beneath the yilgarn craton variations in the shear wavespeeds beneath the arunta also indicate that there is not always an obvious correlation between the overlying surface geology and seismic structures observed in the upper mantle

terrain controls on the occurrence of coastal retrogressive thaw slumps along the yukon coast canada retrogressive thaw slumps rtss are among the most active landforms in the arctic their number has increased significantly over the past decades while processes initiating discrete rtss are well identified the major terrain controls on the development of coastal rtss at a regional scale are not yet defined our research reveals the main geomorphic factors that determine the development of rtss along a 238 km segment of the yukon coast canada we 1 show the current extent of rtss 2 ascertain the factors controlling their activity and initiation and 3 explain the spatial differences in the density and areal coverage of rtss we mapped and classified 287 rtss using high resolution satellite images acquired in 2011 we highlighted the main terrain controls over their development using univariate regression trees model coastal geomorphology influenced both the activity and initiation of rtss active rtss and rtss initiated after 1972 occurred primarily on terrains with slope angles greater than 3 9 and 5 9 respectively the density and areal coverage of rtss were constrained by the volume and thickness of massive ice bodies differences in rates of coastal change along the coast did not affect the model we infer that rates of coastal change averaged over a 39 year period are unable to reflect the complex relationship between rtss and coastline dynamics we emphasize the need for large scale studies of rtss to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget

composition and fate of terrigenous organic matter along the arctic land ocean continuum in east siberia insights from biomarkers and carbon isotopes abstract climate warming is predicted to translocate terrigenous organic carbon terroc to the arctic ocean and affect the marine biogeochemistry at high latitudes the magnitude of this translocation is currently unknown so is the climate response the fate of the remobilized terroc across the arctic shelves represents an unconstrained component of this feedback the present study investigated the fate of permafrost carbon along the land ocean continuum by characterizing the terroc composition in three different terrestrial carbon pools from siberian permafrost surface organic rich horizon mineral soil active layer and ice complex deposit and marine sediments collected on the extensive east siberian arctic shelf esas high levels of lignin phenols and cutin acids were measured in all terrestrial samples analyzed indicating that these compounds can be used to trace the heterogeneous terrigenous material entering the arctic ocean in esas sediments comparison of these terrigenous biomarkers with other terroc proxies bulk 13c 14c and hmw lipid biomarkers highlighted contrasting across shelf trends these differences could indicate that terroc in the esas is made up of several pools that exhibit contrasting reactivity toward oxidation during the transport in this reactive spectrum lignin is the most reactive decreasing up to three orders of magnitude from the inner to the outer shelf while the decrease of hmw wax lipid biomarkers was considerably less pronounced alternatively degradation might be negligible while sediment sorting during the across shelf transport could be the major physical forcing that redistributes different terroc pools characterized by different matrix association despite the marked decrease shown by lignin the fingerprint of lignin phenols such as the acid aldehyde ratio of vanillyl and syringyl phenols showed a lack of any across shelf trends and exhibited an extremely wide range of values in all terrestrial samples by contrast the 3 5 dihydroxybenzoic vanillyl phenols ratio exhibited a clear across shelf trend suggesting either increasing degradation with distance from the coast or terroc sorting along the sediment dispersal system the ratio of syringyl vanillyl phenols indicated that gymnosperm tissues are more important than angiosperm tissues in surface sediments in particular off the lena river mouth consistent with the vegetation in its watershed conversely the fingerprint of p hydroxybenzenes suggests lack of substantial input of moss derived material finally autochthonous lipid and protein derived cuo reaction products displayed a strong along shelf gradient likely reflecting the inflow of nutrient rich pacific waters from the bering strait that stimulate primary productivity in the eastern esas in particular short chain fatty acids showed a clear frontal transition zone between pacific influenced and river influenced waters approximately along the 160 e longitude considering the labile nature of phytoplankton priming and co metabolism processes might stimulate degradation of terroc in the easternmost region of the siberian shelf this study demonstrated the need to consider multiple terroc proxies at isotopic molecular levels to differentiate the fate for different allocthonous components in arctic sediments and the need to assess how these terroc pools are distributed in different density size and settling fractions to better discriminate between the extent of hydrodynamic sorting versus degradation

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

character and regional implications of the sheared archaean granite greenstone contact near leonora western australia abstract the boundary between greenstone belt rocks and deformed domal bodies of granite and gneissic granite in the area west and northwest of leonora is marked by a wide zone of high strain within which the dominant fabric elements are parallel to the boundary the high strain zone is arcuate the granitic body is domal in form consistent sense of shear movement indicators show that the greenstones moved down relative to the granite rocks from a continuous core of 1 6 km drilled 4 km southeast of leonora exhibit mesoscale recumbent folding and ductile faulting the upper 900 m of core is characterised by recumbent flexural slip folds with half wavelengths up to 660 m separated by discrete shear zones below about 1200 m rock type and structural character change at this depth greenschistfacies rocks are juxtaposed against amphibolite facies rocks across a major ductile shear thermodynamic data give estimates of 370 c 2 1 kbar for greenschist and 610 c 5 6 kbar for amphibolite facies with high fluid pressures dominated by water in low grade rocks and co 2 in high grade ones several kilometres of section have therefore been lost across this zone the amphibolite hosts broad and narrow shear zones within which movement sense is consistently normal the structural and metamorphic data suggest that emplacement of the domal granitic and gneissic rocks was temporally linked with normal ductile shearing the regional structural setting and juxtaposition of high and low grade rocks across the shear zone with abrupt changes in temperature and fluid composition suggests that the domes were emplaced as uprising hot deep seated rock in a regional extensional tectonic environment comparable to the tectonic setting of metamorphic core complexes

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

coastal changes in the arctic the arctic s climate system is changing air temperatures major river discharges and open water season length have increased and storm intensities and tracks are changing thirteen quantitative studies of the rates of coastline position change throughout the arctic show that recently observed changes have not increased coastal erosion rates which currently range between 0 and 2 m yr when averaged for the arctic shelf seas current data is probably insufficient both spatially and temporally however to capture change at decadal to sub decadal time scales in this context we describe the current understanding of arctic coastal geomorphodynamics with an emphasis on erosional regimes of coasts with ice rich sedimentary deposits in the laptev east siberian and beaufort seas where local coastal erosion can reach 30 m yr we also examine coasts with lithified rocky substrates where geomorphodynamics are intensified by rapid glacial retreat coastlines of svalbard greenland and the canadian archipelago are less frequently studied than ice rich continental coasts of north america and siberia and studies often focus on coastal sections composed of unlithified material as air temperature and sea ice duration and extent change longer thaw and wave seasons will intensify coastal dynamics in the arctic

formation of earth s early archaean continental crust abstract subduction of oceanic crust at an unusually low angle has been proposed as a model for the growth of continental crust older than about 2 5 ga at modern zones of low angle or flat subduction magmatic additions to new crust come from partial melting of both the subducting oceanic crust slab and the thin wedge of mantle above the slab evidence for both a slab and wedge source is preserved in most late archaean 3 0 2 5 ga terrains but we find little evidence that a mantle wedge contributed to crustal growth prior to 3 1 ga this lack of evidence in part reflects a dearth of exposed crust aged between 3 0 and 3 3 ga but also suggests that subduction enriched mantle source regions did not develop before 3 3 ga and possibly not before 3 1 ga in contrast to most modern terrains and some late archaean terrains early archaean 3 3 ga continental crust evolved through direct melting of thick mafic crust we invoke a process of subduction that does not include the development of a mantle wedge and call this process archaean flat subduction to distinguish it from modern low angle subduction

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

the age of the kambalda greenstones resolved by ion microprobe implications for archaean dating methods abstract a chert horizon within the archaean basalt pile at kambalda western australia contains zircons from air fall tuffs erupted as the sediment was laid down ion microprobe analyses of these magmatic zircons constrain the long sought age of the kambalda lavas to 2692 4ma 2 and show that regional metamorphism and deformation of the greenstone pile occurred within 30 ma of deposition rare zircon xenocrysts are evidence of pre greenstone crust as old as 3450 ma exposed remnants of which are yet to be identified subsets of both the magmatic and xenocryst zircons show evidence of hitherto unsuspected low temperature u and or pb mobility in the proterozoic long after stabilisation of the craton the ion microprobe data unravel complexities of isotopic inheritance and alteration illustrating the hazards of using bulk or whole rock samples in archaean isotopic investigations identification of interflow cherts as a precisely dateable rock type opens the way to direct ion probe dating of mafic ultramafic piles and close numerical age control of the complex but ill exposed stratigraphic and structural relations in this richly mineralised greenstone belt

structural event framework for the eastern yilgarn craton western australia and its implications for orogenic gold abstract the nnw trending tectonic grain of the eastern yilgarn craton eyc was established as a result of predominantly ene wsw directed extension d1 and d3 and e ene w wsw d2 d4 to ne sw directed d5 contraction the result has been a succession of nnw striking temporally discrete fabric elements which can be difficult to interpret reliably at any single location despite this many past workers interpreted the nnw striking fabric as the result of only one regional contractional event and used it as a marker for correlating structural events across the region in order to unravel the complexity this paper presents a new sixfold d1 d6 deformation nomenclature based on 10 000 new mesoscale structural observations including their kinematic analysis and cross cutting relationships these mesoscale data were referenced with regional 3d map patterns stratigraphic magmatic metallogenic considerations and deep seismic reflection images this integrated geodynamic architectural approach is applicable to solving structural event histories in other polydeformed terrains gold mineralisation occurred during the first five events but was particularly concentrated from d3 onwards the d3 event marked the most profound change in the tectonic evolution of the eyc with changes in greenstones granites and tectonic mode lithospheric extension and core complexes with the first significant gold deposited within extensional shear zones that dissect the crust later contraction d4 was imposed at a high angle to the previously established anisotropic architecture the outcome was the creation of a new dynamic permeability framework which resulted in gold mineralisation during nnw striking sinistral strike slip faulting and associated thrusting a further stress switch d5 further modified the architecture resulting in n to nne striking dextral strike slip faulting and the final period of gold mineralisation before late stage extension d6

distribution of branched gdgts in surface sediments from the colville river alaska implications for the mbt cbt paleothermometer in arctic marine sediments significant climate fluctuations in the arctic over the recent past and additional predicted future temperature changes highlight the need for high resolution arctic paleoclimate records arctic coastal environments supplied with terrigenous sediment from arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia a potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts in this study we examine the source of brgdgts in the colville river alaska and the adjacent simpson lagoon and reconstruct temperatures from simpson lagoon sediments to evaluate the applicability of this proxy in arctic estuarine environments the colville catchment soils fluvial sediments and estuarine sediments contain statistically similar brgdgt distributions indicating that the brgdgts throughout the system are soil derived with little alteration from in situ brgdgt production in the river or coastal waters temperatures reconstructed from the mbt cbt indices for surface samples show good agreement with regional summer june through september temperatures suggesting a seasonal bias in arctic temperature reconstructions from the colville system in addition we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records these results support the application of this brgdgt based paleotemperature proxy for subdecadal scale summer temperature reconstructions in arctic estuaries containing organic material derived from sediment laden episodic rivers

sea ice loss enhances wave action at the arctic coast 1 erosion rates of permafrost coasts along the beaufort sea accelerated over the past 50 years synchronously with arctic wide declines in sea ice extent suggesting a causal relationship between the two a fetch limited wave model driven by sea ice position and local wind data from northern alaska indicates that the exposure of permafrost bluffs to seawater increased by a factor of 2 5 during 1979 2009 the duration of the open water season expanded from 45 days to 95 days open water expanded more rapidly toward the fall 0 92 day yr 1 when sea surface temperatures are cooler than into the mid summer 0 71 days yr 1 time lapse imagery demonstrates the relatively efficient erosive action of a single storm in august sea surface temperatures have already decreased significantly by fall reducing the potential impact of thermal erosion due to fall season storm waves

the genesis and tectonic control on archaean gold deposits of the western australian shield a metamorphic replacement model abstract gold deposits occur in greenstone belts world wide and contribute to anomalously high gold production from archaean terranes as in other cratons archaean gold mineralization of western australia represents a complex array of deposit styles despite this most deposits are clearly epigenetic and large deposits have a number of features in common including their strong structural controls distinctive wallrock alteration fe sulphide k mica albite ca mg fe carbonates consistent metal associations au ag as sb w b low base metals commonly fe rich host rocks great depth extension and lack of appreciable vertical zonation these shared characteristics combined with their ubiquitous occurrence indicate that archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic porphyry intrusions although these gold systems involved low salinity lowdensity reduced near neutral h 2 o co 2 fluids carrying gold as reduced sulphur complexes the origin of the fluids is equivocal most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic granitoid or felsic porphyry orggins but the lack of consistent spatial relationships between specific volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids the metamorphic replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile with high geothermal gradients inhibiting significant melting co 2 possibly formed by the decarbonation of early alteration related to mantle degassing along crustal scale synbasinal fault zones auriferous fluids were channelled along greenstone scale faults in part developed during reactivation of crustal scale faults in a strike slip regime gold deposition occurred largely under greenschist facies conditions about 300 400 c 1 2 kb in response to decreasing gold solubility with declining temperature however a major control on gold deposition was fluid wallrock interaction many large deposits formed by sulphidation of fe rich host rocks with synchronous deposition of fe sulphides and gold however the variable nature of gold depositing reactions including lowering of fo 2 and ph allowed a multitude of small and some large deposits to form wherever that fluid circulation occurred in consequence several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks there are few constraints on the source of components au s k co 2 added to gold deposits but even giant deposits such as the golden mile kalgoorlie could have formed from a realistic greenstone source volume ca 8 8 5 km convective circulation of fluids could have contributed to the generation of high fluid rock ratios on the regional scale the markedly heterogeneous distribution of large gold deposits gold productivity and host rocks to deposits can be accommodated by the metamorphic replacement model the most favourable conditions for development of auriferous hydrothermal systems operated in younger ca 2 7 0 1 ga rift phase greenstones where greatest extension and crustal thinning produced high geothermal gradients crustal scale synbasinal faults and rapid extrusion and burial of volcanics including abundant komatiites iron rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits the least favourable conditions existed in older ca 3 5 3 4 ga platformphase greenstones where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites commonly in very shallow water environments this allowed intense synvolcanic alteration of both gold source rocks and potential host rocks the generally smaller gold deposits formed mainly in ultramafic or greywacke hosts younger ca 3 0 ga platform phase greenstones appear intermediate in nature but unlike other greenstones have significant epigenetic gold deposits in originally oxide facies bif which were deposited on relatively deep water platforms similar controls appear to exist on a world scale with gold mineralization peaking at ca 2 7 0 1 ga in response to development of major rift zones in thickened relatively mature continental crust interestingly the giant witwatersrand goldfield formed at about the same time

spatio temporal variability of x band radar backscatter and coherence over the lena river delta siberia abstract satellite based monitoring strategies for permafrost remain under development and are not yet operational remote sensing allows indirect observation of permafrost a subsurface phenomenon by mapping surface features or measuring physical parameters that can be used for permafrost modeling we have explored high temporal resolution time series of terrasar x backscatter intensity and interferometric coherence for the period between august 2012 and september 2013 to assess their potential for detecting major seasonal changes to the land surface in a variety of tundra environments within the lena river delta siberia the terrasar x signal is believed to be strongly affected by the vegetation layer and its viability for the retrieval of soil moisture for example is therefore limited in our study individual events such as rain and snow showers that occurred at the time of terrasar x acquisition or a refrozen crust on the snowpack during the spring melt were detected based on backscatter intensity signatures the interferometric coherence showed marked variability the snow cover onset and snow melt periods were identified by significant reduction in coherence principal component analysis provided a good spatial overview of the essential information contained in backscatter and coherence time series and revealed latent relationships between both time series and the surface temperature the results of these investigations suggest that although x band sar has limitations with respect to monitoring seasonal land surface changes in permafrost areas high resolution time series of terrasar x backscatter and coherence can provide new insights into environmental conditions

temporal and spatial variability in coastline response to declining sea ice in northwest alaska abstract arctic sea ice is declining in extent leaving coastlines exposed to more storm wave events there is an urgent need to understand how these changes affect geomorphic processes along arctic coasts here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct storm wave dominated reaches of the chukchi sea coastline over the last 64 years one study area encompasses the west to southwest facing coarse clastic shoreline and ice rich bluffs of cape krusenstern cakr the other covers the north facing sandy shorelines on barrier islands ice rich bluffs and the cape espenberg spit in the bering land bridge national park bela both study areas lie within the zone of continuous permafrost which exists both on and offshore and outcrops as ice rich bluffs along the bela coast we mapped changes in coastal geomorphology over three observation periods 1950 1980 1980 2003 and 2003 2014 using aerial and satellite imagery we then compared these geomorphic changes to changes in sea ice coverage which declined 10 days per decade between 1979 and 2016 in the southern chukchi sea changes in coastal geomorphology in both bela and cakr exhibited high spatial variability over the study period between 2003 and 2014 shorelines of barrier islands in bela exhibited the highest mean rates of change 1 5 m yr 1 while coarse clastic barrier beaches in cakr showed only minimal change overall shorelines in both bela and cakr became more dynamic increasing erosion or increasing accumulation after ca 2003 with spatial variability in shoreline changes roughly doubling between the first period of observation 1950 1980 and the last 2003 2014 this increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice affected coastlines

crustal signature of late archaean tectonic episodes in the yilgarn craton western australia evidence from deep seismic sounding abstract deformation in the greenstone supracrustal rocks of the eastern goldfields province of the archaean yilgarn craton in western australia is delaminated from the underlying basement along a regional detachment surface presently at 3 7 km depth this might suggest that the history of crustal deformation cannot be inferred with any certainty from that of the greenstones however seismic images of the crust below the greenstones show structures that can be interpreted in terms of a series of tectonic events similar to those within the greenstones the upper crust below and to the west of the greenstones is largely unreflective with interpreted west dipping reverse faults the middle crust is reflective with reflector geometry implying thickening by west directed thrust stacking and the lower crust has a fabric indicative of ductile deformation these reflection fabrics imply crustal shortening probably during the late archaean regional d2 ene wsw shortening event they were subsequently overprinted and disrupted by structures consistent with regional nnw sse strike slip d3 faulting and probably younger more localised d4 faulting the seismic images of the crust therefore show that the crust suffered tectonic events in which both the order and direction of deformation are similar to those of the greenstones this is evidence that the whole crust deformed when the greenstones deformed however the scale and style of deformation vary with depth through the crust and include thrusting and probably folding in the upper crust thrust stacking in the middle crust and ductile deformation in the lower crust the length scale wavelength of structures in the middle and lower crust is greater than that in the greenstones

equilibrium responses of cliffed coasts to changes in the rate of sea level rise abstract basic formulae have long been used to predict the effects of sea level rise on coastal recession for instance the geometric bruun rule and its modifications has often been applied to sandy coasts both low lying and steep however the behavior of rocky coasts whether strongly or poorly lithified should be significantly different than that of sandy coasts given that rocky coast evolution depends upon the irreversible breakdown of rock whereas sandy and depositional systems are controlled by the transport and related transport gradients of mobile sediment here we investigate the basis of a modeled relationship which suggests with a number of caveats that the equilibrium soft rock cliff recession rate can be estimated by the square root of the relative change in sea level rise rate although this relationship was derived using the numerical model scape soft cliff and platform erosion which simulates a broad soft rock cliffed coastal system driven by stochastic environmental forces here we show that a simplified modeling approach also reproduces the relationship we then extend this approach to develop a general theoretical framework within which it is possible to consider the potential responses of the different types of cliffed coasts to changes in the rate of sea level rise although a wide variety of processes affect different coastal settings this framework demonstrates how the strength and the nature of feedbacks within cliffed system control their response to sea level rise this suggests that cliffed environments controlled by different processes can still respond in similar ways to changes in the rate of sea level rise most rocky coasts would be expected to respond as a damped or negative feedback system between the extremes of a no feedback system that is unresponsive to sea level rise rate and an instant response system characterized by a linear response similar to the bruun rule this framework suggests that a potential inverse feedback case could also exist in which increased rates of sea level rise reduce the rate of coastal recession in almost all cases it is apparent that cliffed coast response to sea level rise depends not only upon the total elevation change of sea level but on the rate of the sea level rise these theoretical investigations and the classifications presented provide a framework to understand the behavior of systems affected by a wide array of processes and provide expectations that can be tested using more complex models of cliffed coast evolution in a variety of environments whether sandy or rocky hard or soft

on kalgoorlie australia timmins porcupine canada and factors in intense gold mineralisation abstract the golden mile gold deposits of kalgoorlie eastern goldfields province yilgarn craton australia 46 moz au and the gold deposits in the timmins porcupine camp southern abitibi province superior craton canada 63 7 moz au are earth s two biggest archaean lode gold camps while similarities at the camp scale are dominant they differ in that the golden mile is a compact camp of one major deposit with two nearby subordinate deposits separated by less than 10 km along strike whereas timmins porcupine consists of a relatively large camp with 30 important mines distributed over 20 km strike length seismic data show a detachment fault at the base of the supracrustal rocks at kalgoorlie at between 5 and 9 km but none is identified in the timmins porcupine camp map scale patterns ages and lithologies are superficially similar the gabbros in kalgoorlie and conglomerates in timmins porcupine are distinctive rock types but served similar competence contrast functions late orogenic sediments are an important host at timmins porcupine for competence contrast reasons but are apparently absent in the golden mile area gold deposit formation in both camps is of the same age 2 67 ga with a long duration of mineralisation porphyries albitites and lamprophyres are characteristic features but played no major genetic role both camps have early elements of mineralisation that have an epithermal character in cu au w v 3 and f o 2 and both camps lie in belts locally characterised by the abundance of telluride minerals however none of these characteristics seem to be necessary or sufficient for intense gold mineralisation syn mineralisation transpressive deformation in both camps involved the imbrication of thrust slices followed by strike slip movement along a major crust scale fault with a dilatational curve in its trend in the centre of both camps the various deposits in each of the two camps were formed from immediately before to just after strike slip deformation and opening of late orogenic sedimentary basins both areas are characterised by an early episode of intense thrust faulting extensive intersecting fracture arrays likely developed as thrusting gave way to strike slip faulting these arrays may have enabled access to fertile source rock and also served as fluid conduits throughout deformation moreover both terranes are characterised by a relatively short pre mineralisation crustal history thin ned subcontinental lithospheric mantle and input of juvenile mantle derived material the pre mineralisation crustal history and evolution of the host terranes thus may have been the most important single factor in the formation of giant orogenic gold deposits at kalgoorlie and timmins porcupine

variability in rates of coastal change along the yukon coast 1951 to 2015 to better understand the reaction of arctic coasts to increasing environmental pressure coastal changes along a 210 km length of the yukon territory coast in north west canada were investigated shoreline positions were acquired from aerial and satellite images between 1951 and 2011 shoreline change rates were calculated for multiple time periods along the entire coast and at six key sites additionally differential global positioning system dgps measurements of shoreline positions from seven field sites were used to analyze coastal dynamics from 1991 to 2015 at higher spatial resolution the whole coast has a consistent spatially averaged mean rate of shoreline change of 0 7 0 2 m a with a general trend of decreasing erosion from west to east additional data from six key sites shows that the mean shoreline change rate decreased from 1 3 0 8 1950s 1970s to 0 5 0 6 m a 1970s 1990s this was followed by a significant increase in shoreline change to 1 3 0 3 m a in the 1990s to 2011 this increase is confirmed by dgps measurements that indicate increased erosion rates at local rates up to 8 9 m a since 2006 ground surveys and observations with remote sensing data indicate that the current rate of shoreline retreat along some parts of the yukon coast is higher than at any time before in the 64 year long observation record enhanced availability of material in turn might favor the buildup of gravel features which have been growing in extent throughout the last six decades

structural control of greenstone hosted gold mineralization by transcurrent shearing a new interpretation of the kalgoorlie mining district western australia abstract the kalgoorlie mining district encloses the golden mile and mt charlotte mining areas and has produced 1200 metric tons of gold it is classed as one of the largest archaean gold deposits in the world the district is located in the norseman wiluna greenstone belt of the yilgarn craton western australia this greenstone belt is characterized by nnw trending transcurrent shear zones some of which are traceable over more than 500 km strike length mineralization in the district is controlled by second third and fourth order structures located between principal shear zones of regional extent an early deformation phase of regional folding d1 associated with prograde regional metamorphism of low grade preceded two phases of wrenching the geometry of mineralized shear zones in both mining areas as well as field and microstructural studies allow us to distinguish an early phase of transpressional sinistral shearing d2 from a later phase of transcurrent dextral shearing d3 the earlier sinistral shear system in the golden mile area was in part reactivated but its gross original geometry was preserved these observations are consistent with clay model experiments carried out by the authors hydrothermal carbonate sericite alteration and gold mineralization commenced during the sinistral shear event and continued into the dextral event mineralization within individual shear zones forms tabular orebodies whereas pipe shaped ore shoots occur at the intersection of shear zones the ore shoots contain high grade telluride mineralization locally relative timing relationships show that mineralization postdates the peak of regional metamorphism hydrothermal activity in the district was preceded by the intrusion of calc alkaline porphyry dykes of granodioritic to tonalitic composition and accompanied by the intrusion of lamprophyre dykes

late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia part iii signatures of tectonic escape in an arc continent collision zone abstract siliciclastic supersequences in the eastern goldfields superterrane are remnants of basins that were linear zones of subsidence between intra terrane faults fluvial deposits record proximal to medial braid plains deep marine canyon and fan deposits were linked across intra terrane compartments only by mud rich deposits axial depositional systems dominate with only minor evidence for slope aprons although transverse and axial systems are preserved in some fluvial deposits basin development occurred during two stages separated by an inversion event with the kalgoorlie terrane recording change from a fluvial to a deep marine basin and the kurnalpi terrane change from distal to proximal deep marine facies tracts sparse palaeocurrents establish that uplift to the north controlled sediment dispersal lithofacies stacking is aggradational whereas abrupt upwards change in facies tracts is back stepping within depositional sequences and between depositional sequence sets but forward stepping between depositional sequences the stratigraphic architecture is atypical of synorogenic basins but consistent with a strike slip regime characterised by pulsed uplift subsidence steady state basin lengthening and subsidence punctuating catastrophic subsidence and lengthening and tectonic anchoring the basins are interpreted to have been similar to graben and half graben of the western anatolian extensional province of turkey with linear zones of subsidence developing adjacent to strike slip oblique slip or normal dip slip faults controls on stratigraphic patterns are considered to have been regional rather than at the scale of each basin the envisaged tectonic setting is similar to projected collision between the philippine archipelago west of the philippine fault and continental crust of the south china sea but the orogenic architecture is similar to that of accreted superterranes in the canadian cordillera interpreted north or northwest convergence between the burtville terrane to the east and the ancestral yilgarn continent to the northwest produced a south propagating orogen with the kalgoorlie gindalbie and kurnalpi terranes trapped between in a tectonic escape corridor tectonic escape to the south between bounding strike slip faults produced back stepping of facies tracts that simulated basin lengthening whereas forward stepping of facies tracts was the response to south propagating uplift

morphology of the canadian beaufort sea coast a study of the canadian beaufort sea coast alaskan yukon border to baillie island was conducted to provide a regional summary of a coastal morphology b coastal stability and c coastal processes a total of 2077 km of coastline was mapped using aerial photographs low altitude and oblique aerial video imagery and information from previous field studies the coast can be adequately characterized by six repetitive coastal types four of which are erosional landforms and comprise 60 of the coast ice rich cliffs ice poor cliffs low tundra cliffs and inundated tundra two repetitive coastal types are accretional landforms and comprise 40 of the coast barrier islands and spits and deltas the deltas in the study area are retreating rapidly and therefore over 80 of the coast is considered erosional and less than 20 accretional over 1000 measurements of coastal stability indicate wide scale coastal retreat most sections of the coast show mean coastal retreat rates in excess of 1 m yr 1 despite very low annual wave exposure levels near active areas of the mackenzie river delta mean retreat rates are in excess of 2 m yr 1 and a maximum retreat rate of 18 m yr 1 was documented near shallow bay the presence of significant quantities of ice in the coastal sediments both in the form of pore ice and massive ice beds appears to be the primary cause of the wide scale regional retreat of the coast although a relative sea level rise in the region may also be important

high geothermal gradient metamorphism during thermal subsidence the burial of a basement sequence enriched in heat producing elements during thermal subsidence following rifting produces two concomitant changes in the thermal structure of the crust firstly the burial of the enriched layer produces high geothermal gradients in the overlying sedimentary succession with the high gradients propagating down into but not through the enriched basement sequence secondly the lithospheric thickening that drives thermal subsidence reduces the heat flowing into the deeper crust from the mantle because the process of thermal subsidence promotes burial it naturally increases the depth extent of the high geothermal gradients in the upper crust potentially inducing significant temperature increases in the mid upper crust during burial the lowering of the thermal gradients in the deep crust accompanying burial severely limits the temperature changes affecting the moho potentially allowing moho cooling while the mid upper crust heats these effects can promote high geothermal gradient 40 c km metamorphism in the mid upper crust without inducing significant melting in the lower crust providing the basement heat production contributes 70 mw m 2 to the surface heat flow and that the horizontal length scale for the basement heat production anomaly is 50 km these conditions appear to be met in several australian intermediate to high temperature low pressure metamorphic terranes where the thermal causes of metamorphism have hitherto remained enigmatic one of these terrains the mt painter province in the northern flinders ranges south australia is used to illustrate some of the attributes of the model

a synmetamorphic lateral fluid flow model for gold mineralization in the archean southern kalgoorlie and norseman terranes western australia gold deposits are widely distributed in the archean southern kalgoorlie and norseman greenstone terranes eastern goldfields superterrane western australia which have collectively produced more than 1 850 metric tons t of gold gold deposits occur in a variety of host rocks and structural settings but all are associated with quartz veins and or shear zones that formed during the latest stages of regional compression available data indicate a similar h 2 o co 2 ch 4 ore fluid at each deposit alteration assemblages vary with metamorphic grade in a manner which indicates that late tectonic regional metamorphic gradients were still in place when gold was deposited from hydrothermal fluids these late tectonic thermal gradients were related to differential uplift of deep hot crust at the margin of the greenstone belt accompanied by intrusion of voluminous monzogranite magma at this time the western margin of the greenstone belt was a zone of high heat flow as were intrusive centers in the northern part of the southern kalgoorlie terrane these spatial and temporal relationships in combination with the apparent absence of a viable local source for the ore fluid at most deposits suggest that gold was deposited from a small number of large synmetamorphic hydrothermal systems published thermal models predict up temperature lateral fluid flow toward zones of high heat flow under these circumstances a model involving up temperature lateral flow of metamorphic fluids overcomes some of the problems associated with deeply sourced and conventional metamorphic models for the ore fluids and is consistent with most of the features of gold deposits in the southern kalgoorlie and norseman terranes potassium metasomatism and radiogenic isotope signatures associated with gold mineralization are ascribed to a metamorphic fluid that was modified by exchange with biotite bearing felsic rocks granitoids felsic volcanic and volcaniclastic rocks in the course of lateral flow toward zones of high heat flow

4 d evolution of rift systems insights from scaled physical models the four dimensional 4 d evolution of brittle fault systems in orthogonal oblique and offset rift systems has been simulated by scaled sandbox models using dry cohesionless fine grained quartz sand extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model the results of these analog model studies are compared with natural examples of rift fault systems rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction segmentation of the rift margin increases with increase in obliquity of the rift axis resulting in a consequent increase in displacement on intrarift fault systems offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone along strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones high relief extension parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults the second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low relief oblique slip zone or grabens these typically are found in highly oblique rift systems 45 degrees and above right steps in offset rift models

the archean lode gold deposits at wiluna western australia high level brittle style mineralization in a strike slip regime the wiluna lode hosted gold deposits comprise a group of individual archean lode hosted gold deposits located in the northern part of the norseman wiluna belt western australia collectively they are the fifth largest gold producer in the yilgarn block the deposits are hosted in a series of very low grade metamorphosed prehnite pumpellyite facies mafic and ultramafic lava flows with abundant primary igneous textures preserved lode hosted gold mineralization is controlled by the wiluna strike slip fault system which consists of north and northeast trending and west and east dipping sets of principal displacement faults and associated subsidiary structures the movement on all faults was dextral with minor oblique reverse or oblique normal motion and maximum apparent displacement of 1 350 m the lode deposits are centered on structural inhomogeneities in the principal displacement faults e g divergent bends and dilational jogs including horsetail splays and or subsidiary structures e g overstepping and intersecting faults the plunge of the ore shoots is generally moderately to steeply to the south and is controlled by the intersections between 1 lithologic layering and fault planes 2 two or more fault planes 3 a fault plane and an earlier formed barren or weakly mineralized quartz reef that is semiconcordant to the regional stratigraphy and 4 a fault plane and a felsic intrusion the shape and orientation of ore shoots becomes more complex downdip where they are controlled by additional features such as drag folds and link structures fault hosted ore breccias including implosion and net veined breccias and brecciated veins are significant loci of gold mineralization in all lode deposits they contain mainly quartz chalcedony carbonates fuchsite and arsenopyrite pyrite and or stibnite mineralization occurs also in shear veins and extensional veins and finely disseminated along foliation planes of the mineral fabric formed oblique to the principal displacement faults textures of implosion breccias at wiluna indicate a history of incremental extensional opening across dilational sites and multiple episodes of brecciation and hydrothermal recementation quartz textures such as vugs cavities comb textures and cockade textured quartz are ubiquitous indicating the preservation of open space due to low effective confining pressure geologic relations indicate that the mineralized strike slip fault system was generated late in the tectonic history of the greenstone belt and that high grade ore zones formed late in the strike slip deformation event the very low grade metamorphic facies and the brittle style of deformation in the host rocks combined with the style of mineralization indicate that the fault and mineralizing system formed in a shallow near surface crustal environment textural evidence combined with the tectonic setting of the lode deposits favors the suction pump mechanism as a fluid infiltration mechanism for the lode hosted gold deposits within the wiluna strike slip fault system