synorogenic hydrothermal origin for giant hamersley iron oxide ore bodies geologic mapping basin analysis and calculated fluid compositions indicate that giant orebodies of microplaty hematite and possibly martite goethite in the hamersley province of western australia were formed by heated fluids driven by early paleoproterozoic orogenesis detrital grains of microplaty hematite in the mcgrath trough a foreland basin in front of the northward advancing ophthalmian fold belt constrain the age of the earliest microplaty hematite ore formation to 200 c and locally up to 400 c were involved regional circulation of hydrothermal fluids including heated surface water through reduced banded iron formations occurred during or soon after the ophthalmian orogeny we speculate that martite goethite orebodies previously considered mesozoic cenozoic could also be related to heated paleoproterozoic meteoric fluids migrating northward away from the ophthalmian fold belt

roughness of fault surfaces over nine decades of length scales 1 we report on the topographic roughness measurements of five exhumed faults and thirteen surface earthquake ruptures over a large range of scales from 50 m to 50 km we used three scanner devices lidar laser profilometer white light interferometer spanning complementary scale ranges from 50 m to 10 m to measure the 3 d topography of the same objects i e five exhumed slip surfaces vuache sillingy bolu corona heights dixie valley magnola a consistent geometrical property i e self affinity emerges as the morphology of the slip surfaces shows at first order a linear behavior on a log log plot where axes are fault roughness and spatial length scale covering five decades of length scales the observed fault roughness is scale dependent with an anisotropic self affine behavior described by four parameters two power law exponents h constant among all the faults studied but slightly anisotropic h 0 58 0 07 in the slip direction and h 0 81 0 04 perpendicular to it and two pre factors showing variability over the faults studied for larger scales between 200 m and 50 km we have analyzed the 2 d roughness of the surface rupture of thirteen major continental earthquakes these ruptures show geometrical properties consistent with the slip perpendicular behavior of the smaller scale measurements our analysis suggests that the inherent non alignment between the exposed traces and the along or normal slip direction results in sampling the slip perpendicular geometry although a data gap exists between the scanned fault scarps and rupture traces the measurements are consistent within the error bars with a single geometrical description i e consistent dimensionality over nine decades of length scales

emplacement of a large igneous province as a possible cause of banded iron formation 2 45 billion years ago latest archaean and earliest palaeoproterozoic times from 2 6 to 2 2 billion years ago have generally been viewed as a largely quiescent period of earth history the geological record indicates the very slow deposition of pelagic and chemical sediments1 2 and bears only a limited record of magmatic and tectonic activity3 5 such quiescence is consistent with the contention that the earth s main banded iron formations bifs finely laminated chemical sedimentary rocks rich in iron oxide formed slowly as oxygen abundances in the oceans gradually increased thus reducing the capacity of sea water to retain dissolved iron6 10 here we show that a large igneous province comprising 30 000km3 of dolerite basalt and rhyolite accompanied deposition of a hamersley province bif 2 449 3 million years ago this observation indicates that hamersley bifs formed during a major tectono magmatic event and were deposited very much faster than previously thought at similar rates to or faster than modern pelagic sediments thus the largest palaeoproterozoic bifs rather than simply reflecting a gradual increase in the oxygen content of the oceans during a period of tectonic quiescence are more likely to have formed as a result of an increased supply of suboxic iron and silica rich sea water upwelling onto continental shelves during a pulse or pulses of increased submarine magmatic and hydrothermal activity

deformation induced silica redistribution in banded iron formation hamersley province australia abstract the formation of banded iron formations bif remains controversial despite their potential to provide key information on precambrian atmospheres and hydrospheres it is widely agreed that bif are chemical sedimentary rocks comprising alternating layers of iron oxides and chert formed from poorly known precursor phases many models address the chemical transformation of such precursor iron oxide phases into bif during compaction and diagenesis however the formation of chert and the influence of physical forces in this process have received less attention microstructural analysis of bif from the hamersley province western australia reveals that significant amounts of silica were redistributed by dissolution precipitation creep during both diagenesis and regional scale deformation this physicochemical process led to silica remobilisation and volume loss by stress induced dissolution of microcrystalline quartz in an aqueous fluid the dissolved solid phase was transported by diffusion and fluid flow along grain boundaries or within available porosity and then reprecipitated in low pressure zones leading to local volume increase these processes were further enhanced by rheological contrasts between different minerals resulting in significant variations of chert band thickness microstructural observations combined with quantitative microfabric analysis reveal domains of crystallographic preferred orientations cpo in quartz grains within chert layers the cpo fabrics record strain regimes e g pure and simple shear extension and shortening that modified quartz aggregates by dissolution precipitation creep providing new insights into the metamorphic and deformation history of bif we document microstructures that indicate that non coaxial deformation was active during diagenesis and subsequent deformation of the hamersley province bif further relatively undeformed chert layers may have been similarly affected by significant amounts of dissolution precipitation creep providing a possible explanation for the destruction of primary features we show that different generations of chert alternate on a micro scale suggesting that the role of deformation has been underestimated in many aspects of bif research the discovery of dissolution precipitation creep in low grade metamorphic bif provides a potential link between the physical and chemical processes that occur within these rocks after deposition in the hamersley province dissolution precipitation creep was active from the compaction or diagenesis stage and probably operated during all major extensional and compressional deformation events we also suggest that chert layers without cpo record the least overprint by diagenesis and as the most pristine form of bif should be targeted for future paleo environmental research

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

seismic stratigraphy of a buried volcanic arc northland new zealand and implications for neogene subduction abstract for over 6 million years in the early miocene the northland peninsula of new zealand s north island was the site of a volcanic arc comprising north westerly trending twin belts of marine and subaerial andesitic volcanoes approximately 50 volcanic edifices from major massifs to small cones have been newly identified on marine seismic profiles of the western belt which is largely buried the volcanoes were important point sources of sediment and the volcaniclastic deposits of each of the major and intermediate sized volcanoes form distinct seismic sequences the three main elements of the volcanic sequence are i a main body ii a sloping apron and iii a wide almost flat ring plain the downlap of the oldest discernible internal clinoform reflector relative to a known regional marker reflector underlying it indicates the approximate time of onset of activity whereas downlap of the top bounding reflector relative to those of other volcanic sequences provides a relative order of extinction sequence stratigraphic principles and super position determine relative stratigraphic hierarchy the volcanoes studied here were active only in the early miocene with few exceptions most were active by 22 ma and extinct by 16 ma with many extinct by 19 ma there was no pattern in their order of inception or extinction although a few became dominant burying or surrounding their neighbours at the south eastern end of the chain there is a rapid change over a short distance in both age and orientation from the northwest trending early miocene volcanism in the northland basin to north east trending middle and late miocene volcanism in the contiguous taranaki basin the northland volcanoes are interpreted to have been an arc facing the south westwards subducting south fiji basin whereas the taranaki volcanoes are interpreted to have been part of a separate pacific facing volcanic arc the lau colville ridge

petrographic and geochemical evidence for hydrothermal evolution of the north deposit mt tom price western australia high grade iron mineralisation 65 fe in the north deposit occurs as an e w trending synclinal sheet within banded iron formation bif of the early proterozoic dales gorge member and consists of martite microplaty hematite ore three hypogene alteration zones between unmineralised bif and high grade iron ore are observed 1 distal magnetite siderite iron silicate 2 intermediate hematite ankerite magnetite and 3 proximal martite microplaty hematite apatite alteration zones fluid inclusions trapped in ankerite within ankerite hematite veins in the hematite ankerite magnetite alteration zone revealed mostly h2o cacl2 pseudosecondary and secondary inclusions with salinities of 23 9 1 5 1 n 38 and 24 4 1 5 1 n 66 eq wt cacl2 respectively pseudosecondary inclusions homogenised at 253 59 9 c 1 n 34 and secondary inclusions at 117 10 0 c 1 n 66 the decrepitation of pseudosecondary inclusions above 350 c suggests that their trapping temperatures are likely to be higher i e 400 c hypogene siderite and ankerite from magnetite siderite iron silicate and hematite ankerite magnetite alteration zones have similar oxygen isotope compositions but increasingly enriched carbon isotopes from magnetite siderite iron silicate alteration 8 8 0 7 1 n 17 to hematite ankerite magnetite alteration zones 4 9 2 2 1 n 17 when compared to the dolomite in the wittenoom formation 0 9 0 7 1 n 15 that underlies the deposit a two stage hydrothermal supergene model is proposed for the formation of the north deposit early 1a hypogene alteration involved the upward movement of hydrothermal cacl2 rich brines 150 250 c likely from the carbonate rich wittenoom formation 13c signature of 0 9 0 7 1 n 15 within large scale folds of the dales gorge member fluid rock reactions transformed unmineralised bif to magnetite siderite iron silicate bif with subsequent desilicification of the chert bands stage 1b hypogene alteration is characterised by an increase in temperature possibly to 400 c depleted 13c signature of 4 9 2 2 1 n 17 and the formation of hematite ankerite magnetite alteration and finally the crystallisation of microplaty hematite late stage 1c hypogene alteration involved the interaction of low temperature 120 c basinal brines with the hematite ankerite magnetite hydrothermal assemblage leaving a porous martite microplaty hematite apatite mineral assemblage stage 2 supergene enrichment in the tertiary resulted in the removal of residual ankerite and apatite and the weathering of the shale bands to clay

similarities between mode iii crack growth patterns and strike slip faults why are strike slip faults not perfectly linear but made of successive segments are they reminiscences of the fracture of an initially sound crust by the bottom up propagation of a crack subjected

the role of deformation in the formation of banded iron formation hosted high grade iron ore deposits hamersley province australia abstract the hamersley province western australia hosts some of the world s largest iron ore deposits but despite decades of research their genesis is still extensively debated many iron ore deposits are hosted in complexly deformed archean to paleoproterozoic banded iron formations comprising thin chert and iron oxide bands interlayered with silicate rich shales and carbonates current iron ore genesis models have identified a strong structural control on ore formation linked to extensive hypogene and supergene fluid circulation along fault structures these fluid pathways facilitate the removal of vast amounts of gangue minerals leading to enrichment of the iron oxide residue to iron ore however the evolution of the associated structures has not yet been considered as a key element in ore genesis here we show through multiscale structural analyses that deformation not only forms suitable fluid channels but that folding and shearing also result in significant synkinematic removal of gangue minerals our multidisciplinary investigation of the structural evolution of the mount tom price deposit combines microtectonic field geology and 3d implicit modelling techniques to establish a link between deformation structures at various scales microscale shear bands and outcrop scale asymmetric parasitic folds share striking similarities in their evolution and their controlling mechanisms both features record substantial non coaxial deformation accompanied by volume changes due to stress induced silica remobilisation the closely spaced layering of rheologically different lithologies within hamersley province strata plays a crucial role in complex multilayer deformation which resulted in extensive strain partitioning our study suggests that deformation was of major significance in the upgrading of banded iron formation to iron ore and was active from the early stages of banded iron formation during diagenesis deformation structures also established a micro to deposit scale lateral and vertical fluid network which enabled infiltration by hypogene and supergene fluids during or after deformation these new insights have important implications for iron ore genesis models structural applications in the mine environment and for understanding complex multilayer deformation with volume loss

geologic inheritance and earthquake rupture processes the 1905 m 8 tsetserleg bulnay strike slip earthquake sequence mongolia in 1905 14 days apart two m 8 continental strike slip earthquakes the tsetserleg and bulnay earthquakes occurred on the bulnay fault system in mongolia together they ruptured four individual faults with a total length of 676 km using submetric optical satellite images pleiades with ground resolution of 0 5 m complemented by field observation we mapped in detail the entire surface rupture associated with this earthquake sequence surface rupture along the main bulnay fault is 388 km in length striking nearly e w the rupture is formed by a series of fault segments that are 29 km long on average separated by geometric discontinuities although there is a difference of about 2 m in the average slip between the western and eastern parts of the bulnay rupture along fault slip variations are overall limited resulting in a smooth slip distribution except for local slip deficit at segment boundaries we show that damage including short branches and secondary faulting associated with the rupture propagation occurred significantly more often along the western part of the bulnay rupture while the eastern part of the rupture appears more localized and thus possibly structurally simpler eventually the difference of slip between the western and eastern parts of the rupture is attributed to this difference of rupture localization associated at first order with a lateral change in the local geology damage associated to rupture branching appears to be located asymmetrically along the extensional side of the strike slip rupture and shows a strong dependence on structural geologic inheritance

tiny particles building huge ore deposits particle based crystallisation in banded iron formation hosted iron ore deposits hamersley province australia abstract the world s major source of iron ore is hosted in precambrian banded iron formations these chemical meta sedimentary rocks are composed of alternating laminae of iron oxide minerals and chert despite the economic significance of high grade iron ore deposits controversy persists after decades of research on how banded iron formations became upgraded to form iron ore the fundamental requirement for iron ore formation is the removal of vast amounts of chert coupled with an increased concentration of iron oxide minerals here we assess the fate of colloidal hematite inclusions encapsulated in chert after quartz dissolution and examine their role in the formation of hematite ore we have analysed hematite ores from the hamersley province australia using a combination of petrography high resolution electron microscopy and x ray diffraction these techniques reveal the presence of abundant nano and microscale hematite particles that we suggest form the building blocks of larger hematite crystals within the iron ore our textural observations indicate that hematite colloids that were previously encapsulated inside the microcrystalline quartz grains in chert layers are released during quartz dissolution and subsequently reassemble in a self similar fashion to from new microplaty hematite crystals via non classical crystallisation pathways progressive growth and fusion leads to the transformation of hematite microplates into hematite bands which resemble pre existing iron oxide laminae of banded iron formations in contrast to previous models we observe the direct transformation of banded iron formations to microplaty hematite and have not found evidence that significant amounts of hematite formed through metamorphism of goethite or that intermediate carbonate minerals were involved during the upgrading of banded iron formations to pure hematite ore given the strong evidence for hypogene fluids found in many deposits we have also assessed the role that such warm highly saline fluids may have played during the evolution of iron ore using insights from crystal chemistry we conclude that fluid infiltration impacts many aspects of iron ore formation by controlling hematite colloid liberation and aggregation and finally controlling the transformation of the colloids into macroscopic crystals of hematite via non classical crystallisation mechanisms our study underlines the significance of hypogene fluids in the upgrading of banded iron formation to iron ore however we suggest that their influence was mainly passive as hematite was not precipitated directly from these fluids

giant iron ore deposits of the hamersley province related to the breakup of paleoproterozoic australia new insights from in situ shrimp dating of baddeleyite from mafic intrusions banded iron formations of the ca 2770 2405 ma hamersley province of western australia were locally upgraded to high grade hematite ores during the early paleoproterozoic by a combination of hypogene and supergene processes after the initial rise of atmospheric oxygen ore genesis was associated with the stratigraphic break between the lower and upper wyloo groups of the ashburton province and has been variously linked to the ophthalmian orogeny late orogenic extensional collapse and anorogenic continental extension small spot in situ pb pb dating of baddeleyite by sensitive high resolution ion microprobe shrimp has resolved the ages of two key suites of mafic intrusions constraining for the first time the tectonic evolution of the ashburton province and the age and setting of iron ore formation mafic sills dated as ca 2208 ma were folded during the ophthalmian orogeny and then cut by the unconformity at the base of the lower wyloo group a mafic dike swarm that intrudes the lower wyloo group and has a close genetic relationship to iron ore is ca 2008 ma slightly younger than a new syneruptive 2031 6 ma zircon age for the lower wyloo group these new ages constrain the ophthalmian orogeny to the period between ca 2208 and 2031 ma before lower wyloo group extension sedimentation and flood basalt volcanism the ca 2008 ma dikes pre s ent a new maximum age for iron ore genesis and deposition of the upper wyloo group thereby linking ore genesis to a ca 2050 2000 ma period of continental extension similarly recorded by paleoproterozoic terrains worldwide well after the initial oxidation of the atmosphere by ca 2320 ma

relation between continental strike slip earthquake segmentation and thickness of the crust 1 high resolution maps of large continental strike slip earthquake surface ruptures show that they are formed of fault segments these segments are bounded by fault bends step overs or combinations of the two the lowest limit in size for such segments may not be relevant in the understanding of earthquake mechanics as it pertains to the granular properties of fault zones the maximum limit in segment length however is important as it is directly relates to the maximum extent of seismic rupture to measure the length of the segments a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from earthquake rupture maps next this approach is tested against a set of ten continental strike slip earthquake ruptures derived from similar high quality maps the test suggests that segments have a maximum length of 18 km independent of regional tectonic setting slip inversions for earthquakes based on seismological and or geodetic data most often are not unique and can show some variability even for one particular event some basic characteristics however such as total moment release or general source geometry seem to persist that are relevant to earthquake mechanics measurements of the maximum horizontal extent of individual slip patches derived from seismic source inversion for strike slip ruptures show that their strike dimension does not increase infinitely with magnitude but instead reaches a maximum value of 25 km these two independent lines of observations complemented by earlier data and analog experiments suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments and that it is independent of the ultimate size of individual earthquakes

structural evolution of the mount wall region in the hamersley province western australia and its control on hydrothermal alteration and formation of high grade iron deposits abstract the discovery of two relatively small but high grade iron ore deposits near mt wall an intensely faulted part of the southwestern hamersley province provides unique insights into the structural control on ore formation in this region the deposits have many geological features typical of the high grade microplaty hematite group which also contains the much larger mt tom price paraburdoo and mt whaleback deposits the deposits are structurally controlled along early normal faults and contain abundant microplaty hematite and martite and are largely confined to the dales gorge member of the brockman iron formation in addition to the microplaty hematite martite ore there are martite goethite ores and rare magnetite goethite or magnetite hematite ores below the modern weathering surface hydrothermally altered zones in wallrock bif from the lower dales gorge member contain magnetite hematite and carbonate talc bearing mineral assemblages a staged ore genesis model involving early extension and fluid circulation along normal faults hypogene silica leaching and carbonate alteration followed by deep meteoric oxidation with microplaty hematite formation and finally weathering can explain most features of the mt wall deposits the role of deformation was to provide pathways for mineralising fluids and initiate the seed points for the mineralised systems high grade iron in the wellthandalthaluna deposit is situated between the nw to nnw trending boolgeeda creek fault and a synthetic joining splay the northern fault both are high angle normal faults and formed during early extension in this part of the province faults are characterised by localised small scale deformation and brecciation deep carbonate alteration and oxidation recent weathering has penetrated deeply into the fault zones converting the carbonate rich assemblages into goethite mineralisation in the arochar deposit is situated in the overlap or relay zone between two segments of the mt wall fault zone a moderately to steeply southerly dipping normal fault system which at arochar is intruded by dolerite dykes at both locations the ore controlling faults are offset by later nw trending dextral and normal faults fault relay zones or fault splay zones were likely zones of increased permeability and fluid flow during fault development or reactivation and may also have been important in initiating mineralisation in larger deposits such as mt tom price and mt whaleback however structural controls on the largest iron ore deposits are often obscured due to the intensity and scale of ore development whereas they are better preserved in the smaller deposits recognition that carbonate bearing protores at mt wall survived for nearly two billion years until intense recent weathering converted them to martite goethite or magnetite goethite ores may imply that more of the giant hematite goethite deposits of the hamersley province had hydrothermal precursors and were not formed by supergene processes alone

genesis of high grade hematite orebodies of the hamersley province western australia a reply sir we are very thankful for the constructive comments provided by kneeshaw and kepert unfortunately the competitive ownership structure of the iron ore mining industry in the hamersley province limits our personal knowledge of the mount whaleback deposit to occasional mine visits and to the available literature published and unpublished we do however have access to the data on the smaller giles mini and lido deposits 50 and 10 km west of mount whaleback respectively and to extensive exploration mapping in the ophthalmia ranges to the north direct proof for rotation of the orebody as it is preserved at paraburdoo in the approximately 50 dip of the overlying proterozoic hematite conglomerates of the mount mcgrath formation is not preserved at mount whaleback however we believe that there is sufficient information available in the literature to think that a rotational model for a large part of the deposit is perfectly plausible first and above all as stated in taylor et al 2001 f2 folds are more upright with axial planes dipping about 50 s in the southern and western part of the deposit away from the whaleback fault e g as shown on section no 315120e fig 4 in powell et al 1999 interestingly the ore controlling faults are also more upright in this part of the deposit which suggests an intimate link between the dip of these fault planes and dip of the axial planes of f2 folds secondly

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

the fossil record and spatial structuring of environments and biodiversity in the cenozoic of new zealand there is increasing evidence to suggest that drivers of bias in the fossil record have also affected actual biodiversity history so that controls of artefact and true pattern are confounded here we examine the role of spatial structuring of the environment as one component of this common cause hypothesis our results are based on sampling standardized analyses of the postmiddle eocene record of shelf molluscs from new zealand we find that spatial structuring of the environment directly influenced the quality of the fossil record contrary to our expectations however we find no evidence to suggest that spatial structuring of the environment was a strong or direct driver of taxic rates net diversity or spatial structuring in mollusc faunas at the scale of analysis stage to stage variation in sampling standardized diversity over the past 40 ma exhibits two superficially independent dynamics a changes in net diversity were associated primarily with changes in origination rate and b an unknown common cause related extinction rate to the quality of the fossil record and indirectly to spatial structuring of the environment we suggest that tectonic drivers manifest as second order sequence stratigraphic cycles are likely to have been a key element of this common cause our perceptions of biodiversity history are influenced strongly by secular biases in the quality of the fossil record e g raup 1976 peters foote 2001 many authors have argued against a literal reading of the record and various techniques to minimize the impacts of sampling biases have been developed e g connolly miller 2001 foote 2003 alroy 2010 in addition however a number of studies have proposed that the relationship between sampling biases and diversity dynamics may be complex these studies have suggested that there are latent common cause factors such as plate tectonics and sea level change which have affected simultaneously the quality of the fossil record and true macroevolutionary history e g newell 1952 sepkoski 1976 smith 2001 peters foote 2002 foote 2003 peters 2005 2006a wall et al 2009 demonstrating potential common causes separating their effects from simple preservation and sampling biases and interpreting them mechanistically are challenging problems that must be solved if palaeobiologists are to resolve true patterns and processes of macroevolutionary change through geological time the aim of the present paper is to examine the role of spatial structuring of the environment and of biodiversity in driving both macroevolutionary dynamics and biases in the fossil record fig 1 specifically we are interested in the extent to which partitioning of marine environments may have influenced biodiversity and the preservation of that diversity in part the study is founded on the expectation that the geographical range and evolution extinction dynamics of organisms occupying a particular habitat will be related to the area and fragmentation of that habitat e g rosenzweig 1995 maurer nott 1998 at the same time we anticipate that the quality of the marine fossil record will be influenced by for example the areal extent and distribution of depositional v non depositional or erosional environments factors that are also likely to affect habitat fragmentation and diversity to test the role of spatial structuring in the common cause hypothesis we use the exemplary well studied and relatively complete fossil record of post middle eocene level bottom shelf molluscs from new zealand e g crampton et al 2003 2006a this record is approximately from mcgowan a j smith a b eds comparing the geological and fossil records implications for biodiversity studies geological society london special publications 358 105 122 doi 10 1144 sp358 8 0305 8719 11 15 00 the geological society of london 2011 40 complete at the species level for the neogene as estimated using two very different approaches cooper et al 2006 crampton et al 2006a in this paper therefore we derive an index for spatial heterogeneity of the environment and adapt established indices of spatial differentiation in the new zealand cenozoic mollusc fauna we then compare time series of these measures to time series of sampling probability a proxy for the quality of the fossil record and sampling standardized estimates of overall species richness origination rate and extinction rate all analyses and computations reported here were undertaken using r r development core team 2010 materials and methods

hydrothermal origin for the 2 billion year old mount tom price giant iron ore deposit hamersley province western australia giant iron ore deposits such as those in the hamersley province of northwestern australia may contain more than a billion tonnes of almost pure iron oxides and are the world s major source of iron it is generally accepted that these deposits result from supergene oxidation of host banded iron formation bif accompanied by leaching of silicate and carbonate minerals new textural evidence however shows that formation of iron ore at one of those deposits mount tom price involved initial high temperature crystallisation of magnetite siderite iron silicate assemblages this was followed by development of hematite and ferroan dolomite bearing assemblages with subsequent oxidation of magnetite leaching of carbonates and silicates and crystallisation of further hematite preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids initial hematite crystallisation occurred at about 250 c and high fluid pressures and continued as temperatures decreased although the largely hydrothermal origin for mineralisation at mount tom price is in conflict with previously proposed supergene models it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation

a pre 2 2 ga age for giant hematite ores of the hamersley province australia one current model for the origin of giant hematite ores of the hamersley province requires a two step process formation of martite and goethite by supergene enrichment followed by burial metamorphism to convert goethite to microplaty hematite our new structural stratigraphic and geoehronological data suggest that at least some microplaty hematite ores were present before metamorphism owing to burial under the lower wyloo group a shrimp u pb zircon age from volcaniclastic breccia within the lower wyloo group suggests that hematite detritus in that group was derived from hematite ores older than 2209 or 15 ma the action of pre 2 2 ga oxidizing fluids is implied although their origin supergene versus hypogene remains controversial

veins and hydrothermal fluid flow in the mt whaleback iron ore district eastern hamersley province western australia abstract with the advent of recent hydrothermal models for genesis of giant microplaty hematite ore deposits of the hamersley province we have undertaken regional scale analysis of veins and rocks surrounding the mt whaleback deposit with an aim to characterize the nature of fluid flow before during and after ore formation at least five groups of veins formed in the brockman iron formation in deformational events associated with the paleoproterozoic interaction between the yilgarn and pilbara cratons in a 600 km 2 area around the mt whaleback microplaty hematite orebody the five main veining events most likely correspond to the collisional d 2 and extensional collapse d 3 phases of the ca 2300 2200 ma ophthalmian orogeny with one or two later phases probably associated with the waning stages of the ca 1700 1650 ma capricorn orogeny d 4 and or later proterozoic events the abundance of veins associated with d 2 contraction and d 3 extensional fabrics and the composition up to 15 wt nacl equivalent and pressure corrected homogenisation temperatures of primary fluid inclusions 200 400 c indicate that the temperature salinity and likely volume of fluid reached a peak during the last stages of the ophthalmian orogeny and the first stages of post ophthalmian extension paragenesis of veins relative to the deformation history and localization of highest vein densities in the dales gorge member provides circumstantial evidence that the peak of hydrothermal activity in the district was synchronous with the main phase of microplaty hematite ore formation at mt whaleback we propose that the veins record part of the fluid flow system related to the genesis of this giant ore deposit

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

a new fluid flow model for the genesis of banded iron formation hosted martite goethite mineralization with special reference to the north and south flank deposits of the hamersley province western australia

oxygen isotope compositions of iron oxides from high grade bif hosted iron ore deposits of the central hamersley province western australia constraints on the evolution of hydrothermal fluids the hamersley province of northwest western australia is one of the world s premier iron ore regions with high grade martite microplaty hematite iron ore deposits mostly hosted within banded iron formation bif sequences of the brockman iron formations of the hamersley group these high grade iron ores contain between 60 and 68 wt percent fe and formed by the multistage interaction of hydrothermal fluids with the host bif formation the oxygen isotope compositions of magnetite and hematite from bif hydrothermal alteration assemblages and high grade iron ore were analyzed from the mount tom price paraburdoo and channar iron ore deposits the 18o values of magnetite and hematite from hydrothermal alteration assemblages and high grade iron ore range from 9 0 to 2 9 per mil a depletion of 5 to 15 per mil relative to the host bif the 18o values are spatially controlled by faults within the deposits a response to higher fluid flux and larger influence on the isotopic compositions by the hydrothermal fluids the oxygen isotope composition of hydrothermal fluids 18ofluid indicates that the decrease in the 18o content of iron oxides was due to the interaction of both basinal brines and meteoric fluids with the original bif late stage talc bearing ore at the mount tom price deposit formed in the presence of a pulse of 18o enriched basinal brine indicating that hydrothermal fluids may have repeatedly interacted with the bifs during the paleoproterozoic

structural control hydrothermal alteration zonation and fluid chemistry of the concealed high grade 4ee iron orebody at the paraburdoo 4e deposit hamersley province western australia high grade iron ore of the 4ee orebody of the 4e deposit 200 mt at 63 5 wt fe occurs as a southerly dipping sheet within banded iron formation bif of the paleoproterozoic dales gorge and joffre members of the brockman iron formation structural reconstruction of the 4e deposit shows that reactivation of the 18e fault and development of the nw striking steeply sw dipping 4e and 4ee normal faults resulted in preservation of the 4ee orebody below the 4e deposit and 400 m below the modern topographic surface three hypogene alteration zones between low grade bif and high grade iron ore are observed 1 distal magnetite quartz dolomite stilpnomelane hematite pyrite 2 intermediate magnetite dolomite hematitechlorite quartz stilpnomelane and 3 proximal hematite dolomite chlorite pyrite magnetite hydrothermal alteration is temporally and spatially constrained by nw trending dolerite dikes that intruded the 4e and 4ee faults prior to hypogene alteration six vein types v1 v6 are recognized at the 4e deposit the veins both cut and parallel the primary bif layers and were emplaced contemporaneously with the hydrothermal alteration zones that record the transformation of low grade bif to high grade iron ore our integrated structural hydrothermal alteration and fluid flow model proposes that during early stage 1a hypogene fluid flow in the 4e orebody occurred during a period of continental extension and enhanced heat flow within sedimentary basins to the south of the paraburdoo range heated basinal brines were focused by the nw striking steeply sw dipping 4e and 4ee normal faults and reacted with bif of the dales gorge and joffre members the warm to hot 160 255 c ca rich 26 6 31 9 equiv wt cacl2 basinal brine interacted with magnetite chert layers transforming them into magnetite quartz dolomite stilpnomelane hematite pyrite bif the iron rich brine up to 2 8 wt fe likely originated from evaporated seawater that had lost mg and na and gained li and ca through fluid rock reactions with volcaniclastic rocks and carbonate successions within the wittenoom formation the first incursion of deeply circulating low salinity 5 8 9 5 wt nacl equiv heated 106 201 c modified meteoric water is recorded in late stage 1a minerals this modified meteoric water had lost some of its na through wall rock interaction with plagioclase possibly by interaction with dolerite of the weeli wooli formation that directly overlies the joffre and dales gorge members stage 1b involved continuing reactions between the hydrothermal fluids and the magnetite quartz dolomite stilpnomelane hematite pyrite bif and produced both the intermediate magnetite dolomite hematite chlorite pyrite and the proximal hematite dolomite magnetite stilpnomelane alteration assemblages microplaty 10 80 m platy 100 250 m and anhedral hematite increasingly replace magnetite in the intermediate alteration zone forming the proximal alteration zones that consist of microplaty platy anhedral hematite and magnetite the intermediate and proximal alteration zones represent the mixing of a hot 250 400 c high salinity ca rich 30 40 wt cacl2 equiv sr rich basinal brine with low temperature and low salinity 5 wt nacl equiv modified meteoric water that was heated 100 200 c during its descent into the upper crust heterogeneous mixing of the two end member fluids resulted in the trapping of primary fluid inclusion assemblages containing a wide range of trapping temperatures up to 200 c and salinities up to 25 wt nacl equiv stage 1c of the hypogene hydrothermal fluid is characterized by low temperature 110 c low salinity 5 wt nacl meteoric water that interacted with the proximal hematite dolomite magnetite stilpnomelane altered bif leaving a porous hematite apatite high grade ore supergene alteration affected the orebody since the cretaceous and produced a hematite goethite alteration assemblage resulting in destruction of the hypogene alteration zones that are only preserved below the depth of modern weathering discovery of the concealed 4ee orebody of the 4e deposit demonstrates that structural geology plays a critical role in the exploration for high grade iron orebodies structural reconstruction should be considered a critical exploration activity in structurally complex terranes where concealed orebodies may exist

prolonged history of episodic fluid flow in giant hematite ore bodies evidence from in situ u pb geochronology of hydrothermal xenotime abstract absolute ages for hydrothermal mineralization and fluid flow are critical for understanding the geological processes that concentrate metals in the earth s crust yet many ore deposits remain undated because suitable mineral chronometers have not been found the origin of giant hematite ore deposits which are hosted in precambrian banded iron formations bifs remains contentious several models have been formulated based on different sources and timing for the mineralizing fluids supergene metamorphic syn orogenic late orogenic extensional collapse and syn extensional precise geochronology of the ore offers a means of discriminating between these models in this study two u pb chronometers xenotime and monazite have been identified in high grade hematite ore bodies from the mount tom price mine in the hamersley province northwestern australia both phosphate minerals occur as inclusions within the hematite ore and as coarser crystals intergrown with martite hematite pseudomorph after magnetite and microplaty hematite indicating that the xenotime and monazite precipitated during mineralization in situ u pb dating by ion microprobe indicates that both phosphate minerals grew during multiple discrete events our results suggest that ore genesis may have commenced as early as 2 15 ga with subsequent hydrothermal remobilization and or mineralization at 2 05 ga 1 84 ga 1 67 ga 1 59 ga 1 54 ga 1 48 ga and 0 85 ga the location of the ore bodies along ancient fault systems and the coincidence of at least some of the u pb phosphate dates with episodes of tectonothermal activity in the adjacent proterozoic capricorn orogen implies that fluids were channelled through major structures in the southern pilbara craton during discrete phases of tectonic compression and extension our results show that the hematite ore bodies formed at sites of repeated focussed hydrothermal fluid flow in contrast to the aforementioned models our results imply that iron ore formation was probably a long lived multi stage process spanning more than one billion years

experimental evidence for crustal control over seismic fault segmentation strike slip faults are described as continuous structures while they are actually formed of successive segments separated by geometrical complexities although this along strike segmentation is known to affect the overall dynamics of earthquakes the physical processes governing the scale of this segmentation remain unclear here we use analogue models to investigate the structural development of strike slip faults and the physical parameters controlling segmentation we show that length of fault segments is regular along strike and scales linearly with the thickness of the brittle material variations of the rheological properties only have minor effects on the scaling relationship ratios between the segment length and the brittle material thickness are similar for coseismic ruptures and sandbox experiments this supports a model where crustal seismogenic thickness controls fault geometry finally we show that the 2 geometrical complexity acquired during the strike slip fault formation withstands cumulative displacement thus inherited complexity impedes the formation of an ever straighter fault and might control the length of earthquakes ruptures

high resolution satellite imagery mapping of the surface rupture and slip distribution of the mw 7 8 14 november 2001 kokoxili earthquake kunlun fault northern tibet china the mw 7 8 kokoxili earthquake of 14 november 2001 which ruptured a 450 km long stretch of the sinistral kunlun strike slip fault at the northeastern edge of the tibet plateau china ranks as the largest strike slip event ever recorded instrumentally in asia newly available high resolution satellite hrs images pixel size 1 m acquired in the months following the earthquake proved a powerful tool to complement field investigations and to produce the most accurate map to date of the coseismic displacements along the central kusai hu segment of the rupture the coseismic rupture geometry south and west of buka daban feng near the earthquake epicenter was also investigated in detail along the kusai hu segment slip parti tioning is for the first time observed to occur simultaneously during a single event with two parallel strands 2 km apart localizing almost pure strike slip and normal faulting in all 83 new hrs coseismic offset measurements some of which calibrated by field work show large well constrained variations 100 of the slip function over distances of only25 km tension cracks opening ahead of the shear dislocation and later offset by the upward propagating strike slip rupture were observed dem onstrating that the rupture front propagated faster at depth than near the surface the triple junction between the central kusai hu segment the kunlun pass fault where the rupture ended and the xidatan dongdatan segment which could be the next segment to fail along the main kunlun fault acted as a strong barrier implying that direct triggering of earthquake rupture on the xidatan dongdatan segment by kokoxili type earthquakes may not be the rule