new constraints on the evolution of the mallina basin and their bearing on relationships between the contrasting eastern and western granite greenstone terranes of the archaean pilbara craton western australia abstract the northeast trending mallina basin in the central part of the archaean pilbara craton separates western and eastern granite greenstone terranes with significantly different structural histories and age distribution patterns the basin which is up to 70 km wide and has a strike length of more than 150 km is mainly composed of metamorphosed turbidites assigned to the de grey group in the north these rocks are in faulted contact with metamorphosed volcanosedimentary rocks of the whim creek group new shrimp u pb zircon dates show that the turbidite sequence and the whim creek group were deposited within the same period between ca 3010 and 2940 ma and that the basement to the mallina basin is as young as ca 3015 ma geochronological structural and stratigraphic data now mitigate against previous models which suggested that the whim creek group was significantly younger than the turbidite sequence and that the whim creek group evolved in a late ensialic pull apart basin the mallina basin reinterpreted to include at least part of the whim creek group is now believed to be an extensional basin containing an overlap sequence an ensialic setting is preferred in which the basement to the basin consisted of ca 3170 3020 ma granites and greenstones rifted by major northeast trending faults a continental block to the south and east of which the presently exposed east pilbara granite greenstone terrane is a remnant influenced sedimentation in most of the basin previous tectonostratigraphic models that correlated across and beneath the mallina basin and interpreted the entire granite greenstone terrane of the pilbara craton in terms of evolution during two cycles of arc accretion are not compatible with the new geochronological data and stratigraphic interpretations

palaeoearthquake surface rupture in a transition zone from strike slip to oblique normal slip and its implications to seismic hazard north island fault system new zealand

the dynamics of intraseasonal atmospheric angular momentum oscillations abstract the global and zonal atmospheric angular momentum aam budget is computed from seven years of national centers for environmental prediction data and a composite budget of intraseasonal 30 70 day variations during northern winter is constructed regressions on the global aam tendency are used to produce maps of outgoing longwave radiation 200 hpa wind surface stress and sea level pressure during the composite aam cycle the primary synoptic features and surface torques that contribute to the aam changes are described in the global budget the friction and mountain torques contribute about equally to the aam tendency the friction torque peaks in phase with subtropical surface easterly wind anomalies in both hemispheres the mountain torque peaks when anomalies in the midlatitude northern hemisphere and subtropical southern hemisphere are weak but of the same sign the picture is different for the zonal mean budget in which the meridional convergence of the northward relative angular moment

the age and origin of younger granitic plutons of the shaw batholith in the archaean pilbara block western australia the whole rock pb pb method has been used to date four of the younger mainly adamellite late tectonic plutonic phases within the ca 3 5 ga shaw batholith of the archaean east pilbara block three suites give ages within error of 2966 ma porphyritic granites at 2948 50 ma leuco adamellites at 2943 46 ma and garden creek adamellite at 3007 48 ma the post tectonic cooglegong adamellite gives an age of 2847 34 ma the sm nd model isotopic systematics of all four suites indicate derivation from crust ranging between ca 3200 and 3600 ma in age the sources for these four younger plutonic phases were heterogeneous and although exhibiting some isotopic characteristics of the older 3 5 3 3 ga calc alkali plutonic suites were more depleted in the lil elements rb u and th in addition the garden creek adamellite and the cooglegong adamellite lack the very fractionated and hree depleted ree patterns characteristic of both the older calc alkali plutonic rocks and the porphyritic granites and leuco adamellites the crust underlying the shaw batholith at ca 2950 ma must have been both markedly heterogeneous and variably depleted a conclusion consistent with the complex tectonic and plutonic evolution of this region

the atmospheric angular momentum cycle during the tropical madden julian oscillation abstract global scale wind and outgoing longwave radiation anomalies are documented during the atmospheric angular momentum aam cycle associated with the madden julian oscillation cross spectral and compositing techniques are applied to 150 and 850 mb national meteorological center wind data and outgoing longwave radiation olr data during ten northern winter and summer seasons coherent wind and olr signals are found in the tropics and in the winter hemisphere and are dominated by zonal wavenumbers 0 2 at the time of zero aam anomaly anomalous zonal winds are found over the western hemisphere tropics during northern winter while convection anomalies tend to be collocated with the seasonal mean australasian convection zonal mean olr anomalies are small as the aam anomaly increases the anomalous zonal winds move eastward and poleward while dipole convection anomalies become established over the oceanic warm pool and result in an east west shift of the australasian monsoon zonal mean olr ano

geochemical and petrogenetic features of mineralization in rare element granitic pegmatites in the light of current research abstract tremendous expansion of high technology applications of rare metals and specialty minerals requires periodic reassessment of their geological sources keeping in mind the long range technological potential of all hi tech materials available from a given type of deposit granitic pegmatites are a classic example of diversified sources li rb cs be ga sc y ree sn nb ta u th zr hf optical quartz and fluorite high purity feldpar petatite and refractory spodumene ceramic amblygonite e tc such rare element pegmatites can be subdivided into three principal families lct pegmatites with li rb cs be ga sn ta nb b p f nyf pegmatites with nb ta ti y ree zr th and u f pegmatites with a mixed geochemical signature the less evolved members of the lct family produce mainly only be nb ta and sn but exotic types with be ta nb f b p with li rb and cs and are also known so far no differences ini mineralization styles have been observed between the spodumene petalite and amblygonite subtypes of the complex type except the mineralogy of their substantial li contents however extensive divergence in k rb cs fractionation is observed violating the classic criteria for for example pollucite potential and economic ga concentration is recognized the lepidolite subtype is commonly enriched in y and h ree albitespodumene pegmatites have largely simple li sn nb ta be mineralization but a suprisingly broad range of alkali fractionation levels the not so common albite type seems to be typically enriched in sn nb ta ti the nyf family is much less abundant a general subdivision of these pegmatites is not yet available except for the recognition of sporadic lree enriched and much more widespread y hree enriched subtypes scandium is an element recognized recently as much more abundant than previously thought internal evolution of individual pegmatites is better understood today in terms of london s model of crystallization from highly hydrous but homogeneous melts experimental evidence does not support the jahns and burnham proposal of early separation of a fluid phase peraluminous fertile s granites generating lct pegmatites are derived by partial melting of upper middle crustal rocks undergoing their first anatexis and the pegmatites commonly show regional zoning metaluminous granites yeilding poorly zoned groups of nyf pegmatites are largely of the a type generated by second melting of short lived depleted lower crustal protoliths however a juvenile igneous or fluid component may be involved mixed nyf lct granite pegmatite suites may originate in several ways peraluminous lct sequences were traditionally regarded as orogenic in contrast to anorogenic nyf systems tectonic correlation with geochemistry is now considered secondary to the control by source lithologies it is the understanding of the association of pegmatite types with their geological setting and petrogenetic affiliation which assists in the search for selected hi tech materials

variations of atmospheric angular momentum associated with intraseasonal oscillations forced by zonally moving prescribed heating intraseasonal variations of atmospheric angular momentum aam are numerically studied with prescribed 40 day period external heating which moves eastward from 60 e to the dateline in the tropics intraseasonal oscillations are forced in a numerical model in accordance with the oscillations the variations of aam also show 40 day periods the phase relationship between the model intraseasonal oscillations and aam variations is similar to that observed further aam exhibits the largest variation in the equatorial region and a phase propagation from equatorial regions to the subtropics and from high latitudes to the subtropics as found in the real atmosphere after careful inspection of these features it was clarified that the source region for intraseasonal variations of aam is not the equatorial region but the subtropics also the equatorial region is an apparent or superficial source region since aam is transported from the subtropics in accordance with the propagation of rossby wave trains to the subtropics the phase propagation of aam from high latitudes to the subtropics can also be explained from the behavior of rossby wave trains in the midlatitudes radiating from the equatorial region thus rossby wave trains associated with intraseasonal oscillations play an important role in intraseasonal variations of aam

timing and tectonic significance of late archaean sinistral strike slip deformation in the central pilbara structural corridor pilbara craton western australia a north south striking zone of sinistral strike slip shear 20 100 km and associated folding and thrusting within the central part of the pilbara craton is described this zone referred to herein as the central pilbara structural corridor cpsc was formed during regional d3 deformation and overprints two earlier sets of structures associated with granitoid doming it is bound to the west by a continuous north south striking curviplanar fault at greenschist facies in the east it is bound by a series of ne sw striking fault segments located along sheared fold limbs and by a kilometre wide zone of amphibolite facies mylonite within the western margin of the shaw batholith faults vary from narrow high level brittle structures and retrograde breccia zones in the north to broader more ductile structures with sc mylonitic foliations in the south suggesting a southerly increase in exhumation a set of kilometre scale en echelon folds with ne sw striking upright axial planes and ne plunging axes characterize the interior of the cpsc and are wholly contained within the bounding faults thus indicating coeval development with faulting during sinistral wrenching 1 nw se strike slip deformation in the cpsc is interpreted to have resulted from northwesterly indentation of shaw batholith and contiguous rocks to the east westerly directed tectonic escape of the strelley granite laccolith and associated supracrustal rocks from in between shaw batholith and north pole dome was followed by ramping up the concave eastern margin of the yule batholith and eastward tilting during the transition from westerly to northerly displacement continued northward translation of the strelley granite at the leading edge of the system was terminated by constriction between the carlindi batholith and the north pole dome trailing greenstone successions were crumpled into a series of ne trending en echelon folds and related faults kinematic evidence and structural geometry indicate that sediments of the lalla rookh basin de grey group were deposited in advance of the north moving strelley granite within a basin bounded by faults of opposite displacement rather than in a pull apart basin as previously suggested the age of the d3 deformation is indicated by resetting of the ar ar and rb sr isotopic systems to ca 2950 ma in the western shaw region and by u pb ages of syn kinematic granitoid rocks

possible feedback path for low frequency atmospheric oscillations abstract equatorial low frequency oscillations with periods of 1 2 months are being intensively studied by many investigators a strong equatorial dipole pattern is observed in which atmospheric variables such as temperate wind and pressure are out of phase between the indian ocean indonesia region and the western pacific while it is generally thought that the oscillations make a complete circuit around the earth from their excitation region in the equatorial indian ocean western pacific the signal is more difficult to observe over the south america atlantic africa sector using analyses of four year of satellite derived microwave radiance data evidence is presented here for the possibility of a feedback route in the southern hemisphere the observed propagation path extends from the central equatorial pacific across lower south america and heads equatorward after passing south of africa the response route finally reenters the equatorial indian ocean with the correct phase to enhance the primary e

lode gold and epithermal deposits of the mallina basin north pilbara terrain western australia the mallina basin in the central west part of the north pilbara terrain is one of the more mineralized parts of the pilbara craton three styles of au mineralization are present in the region 1 lode au deposits associated with sericite carbonate pyrite alteration assemblages 2 lode au deposits associated with pyrophyllite bearing alteration assemblages and 3 lode sb au deposits gold resources have been identified at the withnell and camel deposits just to the north of the east trending mallina shear zone east trending mineralized zones at the withnell deposit are typical of turbidite hosted lode au deposits in that they are late tectonic syn to late local d3 and associated with extensive carbonate sericite alteration gold mineralization occurs in planar quartz carbonate veins and with pyrite and arsenopyrite in the host rocks to the veins fluid inclusion analyses indicate mainly low salinity carbonic inclusions with moderate homogenization temperatures the lode sb au deposits have a similar structural setting and fluid characteristics at the camel 2 deposit au is associated with syn to late d3 pyrophyllitic shear zones that have overprinted an earlier carbonate alteration assemblage structural relationships and limited pb isotope data suggest that the lode au mineralization in this district formed at about 2900 ma in addition to the lode au and sb au deposits north northwest trending quartz veins have textures typical of low sulfidation epithermal deposits the lithogeochemistry of samples collected from these veins indicates local enrichment of au as sb ag te and hg which is consistent with an epithermal origin based on geologic relationships and pb isotope data these deposits are interpreted to have formed in the mallina basin at ca 2750 ma if they are true epithermal deposits then they are among the oldest known their presence suggests that preservation not archean age is the key control on the temporal distribution of epithermal deposits

the spodumene deposit at weinebene koralpe austria the weinebene spodumene deposit is located in carinthia about 270 km southwest of vienna it is hosted by the medium to high grade metamorphic rocks of the koralpe the spodumene bearing pegmatites form unzoned dikelike bodies in eclogitic amphibolites and kyanite bearing micaschists with concordant foliations their lateorogenic emplacement is probably of variscan age a younger probably alpine metamorphic event affected the pegmatites it caused extensive recrystallization of the micaschist hosted pegmatites but had only a minor impact on the amphibolite hosted ones the spodumene bearing pegmatites have been traced over a length of 1 5 km along strike and to about 450 m down dip their average thickness is 2 m with a maximum of 5 5 m emplacement of the pegmatites caused an alteration halo of several dm in the hosting amphibolites characterized by biotitization and formation of holmquistite an aplitic spodumene free seam of about 10 cm symmetrically borders the pegmatites no contact phenomena are observed along the micaschist hosted dikes spodumene is the only lithium bearing mineral its average content is 22 vol equivalent to 1 68 wt li2o in the amphibolite hosted pegmatites and 15 vol equivalent to 1 13 wt li2o in the micaschist hosted dikes such a significant difference is also shown by rubidium 1 100 ppm vs 880 ppm and cesium 60 ppm vs 25 ppm beryllium and tin are the only other significant trace elements they show average contents of about 100 ppm and 120 ppm respectively with maxima of 1 690 ppm beryllium and 1 500 ppm tin no correlation is found between lithium tin and beryllium niobium and tantalum are very low a na k ratio of 1 2 emphasizes the predominance of albite over microcline there is no discernable correlation between spodumene and albite contents or between lithium and any other alkalies the average k rb ratio is 20 pointing to the high degree of fractionation spodumene contains 7 4 li2o and 0 45 feo there is no difference in the spodumene chemistry between the amphibolite hosted and the micaschist hosted pegmatites strong structural and textural evidence mineral zoning bulk composition corresponding to thermal minima in relevant experimental systems and trace element signature support an igneous derivation of the pegmatites however no granitic intrusion is exposed in the area and the pegmatites could have been displaced from their source by tectonic events

the latitude height structure of 40 50 day variations in atmospheric angular momentum abstract quasi periodic variations in the relative angular momentum of the atmosphere on time scales of around 40 50 days have been observed by langley et al 1981 a description of the two dimensional latitude height structure of the winds responsible for these changes is constructed here from five years of nmc twice daily global analyses using cross spectral and amplitude phase eigenvector techniques we find these variations are associated with wavelike motions in the tropical upper troposphere that propagate and downward in phase within the tropics a coherently connected midlatitude northern hemisphere component is also present whose phase is essentially independent of height we believe the tropical component to be the zonally averaged part of the motions described by madden and julian 1971 1972 the northern hemisphere midlatitude component may be a direct response to the tropical motions or both motions may be the common response to an as yet unidentified tropical forcing

genetic framework for the classification and distribution of archean rare metal pegmatites in the north pilbara craton western australia the pilbara pegmatite province in the archean north pilbara craton contains at least 120 pegmatite deposits in over 27 pegmatite groups and fields including the giant mount cassiterite tantalum orebody in the wodgina pegmatite district generally rare metal pegmatites in the province are hosted by mafic ultramafic volcanic dominated supracrustal sequences of predominantly greenschist facies adjacent to and rarely within domal multiphase granitoid gneiss complexes the most fractionated pegmatites are hosted by tongues or inliers of greenstone belts protruding into or within the larger granitoid complexes most of these are within two of the six tectonostratigraphic domains of the east pilbara granite greenstone terrane of the north pilbara craton they tend to be clustered along and within 5 km at surface of major faults and craton scale lineaments that coincide with or are parallel to domain boundaries all of the major tantalum deposits wodgina mount cassiterite tabba tabba strelley pilgangoora are along a north northeast trending corridor that is within one tectonostratigraphic domain most rare element pegmatites are within 5 km at surface of their apparent parent pluton and all are within 10 km where the pluton has been identified although granitic rocks of the north pilbara craton were emplaced over an 800 m y period 3600 2800 ma rare element class pegmatites can be tied to a number of post tectonic plutons of a younger granite suite that were emplaced into most of the granitoid complexes and adjacent greenstone belts at 2890 to 2830 ma subtle differences in the composition of these granites that have given rise to different petrogenetic pegmatite suites can be identified in processed radiometric data from airborne surveys these parental younger granites are enriched in lithophile and volatile elements and have a highly fractionated character that permitted formation of significant pegmatite mineralization they represent the culmination of the crustal evolution of the north pilbara craton and the onset of cratonization as part of a global appearance of rare metal pegmatite mineralization post 3 ga

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

tectonic settings of archaean 3325 2775 ma crustal supracrustal belts in the west pilbara block abstract the archaean pilbara block comprises six fault bounded tectonostratigraphic domains the west pilbara block contains from east to west domains 4 5 and 6 review of stratigraphic magmatic structural and geochronologic data and new field mapping indicates that the crustal and supracrustal rock records correlate to three megacycles megacycle ivu 3325 3135 ma is recorded by an intra arc basin and arc granitoids in domain 6 and a back arc basin in domains 4 and 5 the domains were an arc continent orogen from 3200 3155 ma during which the outboard are setting was accreted to the back arc continental margin although domain 6 is allochthonous with respect to domains 5 and 4 it was not exotic with respect to the tectonic settings of the pilbara continent megacycle vl 3135 2955 ma is recorded by in decreasing age i a back arc basin and arc granitoids in domain 5 ii a deep marine retroarc or remnant ocean basin in domain 4 and a plutonic belt in domain 5 iii a plutonic belt in domains 5 and 6 and possibly also in domain 4 and iv craton wide deformation belts coeval with the whim creek basin and granitoid plutons in domain 5 the whim creek basin was a half graben that developed at a releasing bend or overstep along the boundary fault to domains 4 and 5 and to the northeast domains 4 and 6 the basin was closed by sinistral transpression as the boundary fault between domains 4 and 6 propagated to the southwest from the releasing bend and thereby generating a restraining bend geometry fundamental strike slip faults which are interpreted to have been tectonic escape responses to a cause external to the preserved pilbara block juxtaposed domains craton wide the initial stage of megacycle vu 2955 2775 ma is recorded by the eroded remnants of a rift province preserved elements include the negri basin domain 5 only mafic ultramafic sub volcanic layered intrusions and granitic plutons and related high level sills two periods of granitoid intrusion are preserved base metal sulphide deposits hosted by the whim creek basin were probably sourced from extensional geofluids in the rift province a plume origin is likely for the komatiitic parent magmas to sub volcanic intrusions and to basalts of the negri basin plume magmatism is interpreted to have been coincident with but not the cause of lithospheric extension because plumerelated volcanism post dates the first period of plutonic intrusion by 25 million years extension was followed by orogenic deformation that converted domains 4 5 and 6 to a hinterland fold thrust belt deformation is interpreted to have been caused by collision orogeny during terrane accretion along the western pilbara margin collision orogeny was the last event of a long history of pacific type tectonics along the margins of the archaean pilbara continent

sequence of mineral assemblages in differentiated granitic pegmatites revised sequence is 1 plagioclase quartz muscovite 2 plagioclase quartz 3 quartz perthite plagioclase 4 perthite quartz 5 quartz plagioclase perthite spodumene or petalite amblygonite 6 quartz spodumene or petalite 7 quartz microcline or perthite 8 quartz and 9 lepidolite or lithian mica plagioclase quartz microcline modified journal abstract

contrasting geochemistry of two pegmatite fields in manitoba products of juvenile aphebian crust and polycyclic archean evolution abstract the geochemistry of the proterozoic wekusko lake pegmatite field in the flin flon snow lake greenstone belt of the churchill province is remarkably primitive compared with the kenoran cat lake winnipeg river pegmatite field in the superior province and its analogs elsewhere in archean cratons comparable pegmatite types at wekusko lake are slightly depleted in li considerably impoverished in rb cs be p and f and poor in sn nb and ta relative to those in the cat lake winnipeg river terrane eliminating differences in plutonic evolution level of erosion and to a degree in the effectiveness of volatile components the principal reason for the difference in the geochemical signature of the pegmatite fields is the nature of the crust and its evolution in the two regions the proterozoic greenstone belt resulted from a single cycle metamorphism and melting of juvenile volcanic sedimentary sequences derived from depleted mantle nd 5 with minimal if any contribution from pre existing crust consequently the source rocks of the granite pegmatite evolution were highly primitive in contrast the host terrane of the kenoran pegmatite field contains pre 2800 ma crustal components of several generations and a 2780 ma tonalitic basement the greenstone belt lithologies and associated batholithic granitoids are derived in part from a heterogeneous near chondritic to ree and lile enriched mantle nd 2 in part from the pre existing crust this polycyclic crustal evolution generated highly enriched protoliths from which the fertile granites and their pegmatite aureoles evolved the low level of geochemical evolution in the wekusko lake field is not necessarily characteristic of other proterozoic rare element pegmatites in the svecofennian terrane of sweden and finland developed in part over archean basement and with considerable archean components in its lithologies the fertile granites and their pegmatite aureoles reached the same fractionation levels as in the kenoran provinces

on the metamorphic history of an archaean granitoid greenstone terrane east pilbara western australia using the40ar 39ar age spectrum technique abstract age spectrum analyses of blue green hornblendes from amphibolites from the western shaw belt east pilbara western australia indicate an age of at least 3200 ma for early regional metamorphism ages on hornblende and muscovite from the narrow contact zone with the adjacent yule batholith probably date updoming of the granitoid gneiss terranes at 2950 ma hornblendes from within the shaw batholith and from a contact zone of a post tectonic granitoid yield ages of 2840 2900 ma indicating either prolonged high temperatures within the granitoid gneiss terranes or a separate thermal pulse associated with the intrusion of post tectonic granitoids the preservation of very old hornblendes in a narrow greenstone belt surrounded by massive granitoid gneiss domes indicates that remarkable contrasts in metamorphic geotherms existed over short distances during the late archaean suggesting that updoming occurred during a period of rapid tectonism

geochemistry and geodynamic setting of volcanic and plutonic rocks associated with early archaean volcanogenic massive sulphide mineralization pilbara craton abstract early archaean volcanic rocks and syn volcanic granites at strelley east pilbara craton western australia were formed during an extensional tectonic phase associated with an active convergent continental margin the volcanic sequence comprises a bimodal suite of fractionated sub alkalic tholeiitic basalts andesites and dacites siliceous laminites and volcanogenic massive sulphide vms deposits in the footwall and hangingwall calc alkaline dacites the footwall rocks are characterized by th lapm 1 variably fractionated lree and relatively high y and yb 33 and 3 ppm respectively negative normalized anomalies of nb p ti are consistent with derivation via slab dehydration fusing the mantle wedge the co magmatic and syn volcanic strelley granite is enriched in lile relative to hfse and has distinctively low al2o3 11 14 and la yb n 4 10 suggesting a relatively mature and cool subducted oceanic lithosphere as for the majority of phanerozoic arc granitoids and convergent margin magma compositions the chemical composition of the footwall basaltic to dacitic rocks and the sub volcanic strelley granite display signatures highly prospective for vms mineralization large ve eu anomalies low zr y ratios high level magmatic fractionation comparable with the noranda fiiia type suite the hangingwall dacites have more pronounced hree fractionation than footwall counterparts and lower y and yb the chemistry of the footwall volcanic rocks and granite reflect typical phanerozoic conditions of steep subduction hydrous metasomatism in the mantle wedge and fractionation similar characteristics are also evident in plutonic volcanic suites associated with vms deposits in the late archaean as at noranda canada early extension with nascent back arc development coupled with steep subduction is considered critical to the development of vms deposits

sequence stratigraphy of the archaean supracrustal belts of the pilbara block western australia abstract the stratigraphic succession of the 3580 2770 m y old granite greenstone terrain of the pilbara block is re assessed by the first and second order sequence stratigraphic techniques that are the standard for phanerozic terrains with the view to testing the conformity of stratigraphic cause and response a holistic tectonostratigraphic framework is presented that pairs the supracrustal and crustal rock records the resulting sequence scheme is tested against the cause of first order sequence cycles viz global sea level responses to supercontinent breakup and assembly three first order inter regional unconformities divide the stratigraphic succession of the supracrustal belts into four units of first order megasequence status in order of decreasing age these are named the warrawoona gorge creek roebourne and mount negri megasequences a total of 17 second order supersequences are also named although some may represent supersequence sets the megasequences and or their genetic crustal equivalents represent the preserved rock record of four megacycles of forearc arc and or back arc geotectonic evolution associated with the convergent margins of a pilbara continent individual supersequences are the rock record of separate second order basins or basin phases and reflect the different geotectonic components of each megasequence the four megacycles had respective longevities from oldest to youngest of 150 m y 230 m y 160 m y and 180 m y they are identical in their stratigraphic successions and predicted first order sea level cycles to phanerozoic first order tectono eustatic cycles and are interpreted as the same response to global tectonic change the warrawoona and gorge creek megacycles and the roebourne and mount negri megacycles are tectonogenetic pairs of the east pilbara and the west pilbara megacycle sets respectively the east pilbara megacycle set evolved over a period of 380 m y from 3490 ma to 3110 ma whereas the west pilbara megacycle set evolved over a period of 340 m y from 3110 ma to 2770 ma the two megacycle sets are identical in their longevity geotectonic components and predicted sea level cycles to convergent margin wilson and supercontinent cycles and are thereby interpreted individually as the oldest established records of the supercontinent cycle the implication of this interpretation is that a steady state global tectonic regime has been in operation from early in earth s history which has important consequences for theoretical modelling of the earth s early tectonic style and secular changes in its geochemical regime

fertile granites of precambrian rare element pegmatite fields is geochemistry controlled by tectonic setting or source lithologies abstract a total of twenty fertile granites and their rare element pegmatite aureoles was examined to correlate their tectonic position relative to the preceding orogenic event with their geochemical signature namely li rb cs be ga sn nb ta y ree sc ti zr be th u f nyf the range of t time difference between metamorphism and or deformation and granite intrusion is 20 to 465 ma for the examined cases there is some tendency toward syn to late orogenic origin of lct s as opposed to post to anorogenic timing of nyf s but the correlation is poor compared to the previously accepted stereotype similarly both metaluminous and peraluminous fertile granites are about equally spread among syn late and anorogenic environments lct systems are largely associated with peraluminous granites whereas all metaluminous to peralkaline plutons bear the nyf signature tectonic control on geochemistry of granite pegmatite suites is poor and secondary to the fundamental influence of the source lithologies yielding granitic melts the lct type suites are derived from undepleted upper crustal lithologies suffering their first anatectic event which mobilizes the most volatile components into low temperature low percentage melts supracrustal sequences as well as ortho and para lithologies of their basement serve as protoliths with variable degrees of involvement the nyf type suites whose plutons have the geochemical signature of a granites may be derived by melting of depleted lower crustal sources residual after preceding anatectic events or possibly by melting of juvenile lithologies with short crustal residence differentiation from mantle derived magmas is highly improbable volatile extraction of nyf elements from the mantle and their pre enrichment in protoliths or melts seems to be required the few mixed systems with variable expressions of a nyf lct signature are derived basically as nyf suites but contaminated by the lct elements from undepleted upper crust via several possible mechanisms