multiple foliation development during thrusting and synchronous formation of vertical shear zones abstract three orthogonal foliations developed during large scale n s thrusting in the central portion of the mount isa block australia two of these foliations which are well preserved in their original orientations in porphyroblasts of pelitic schists but considerably affected and commonly destroyed in the schist matrix due to the effects of subsequent deformation and metamorphism formed synchronously and have a common stretching lineation which is near horizontal and trends n s one foliation formed near horizontal and the other near vertical striking n s both developed during n s directed thrusting with the n s vertical foliation accommodating sinistral differential displacement between the thrust belt to the west and that to the east the third foliation which dips steeply to the north and strikes e w formed during n s shortening of the thrust belt and tends to overprint the other foliations formed in the same orogeny the n s vertical foliation is well preserved within a narrow belt of gneissic rocks called the wonga duchess belt that also locally contains the subsequently folded remains of the foliation that formed near horizontal this belt separates multiply thrust repeated beds to the west from large scale apparently less repetitive thrusts to the east the direction of thrusting appears to change across this belt from n to s on the west to s to n on the east the differential deformation to either side of the belt was taken up by sinistral shear along this belt numerous related but smaller scale vertical shear zones occur up to 3 km away to either side of this narrow zone the primary vertical foliation within the wonga duchess belt appears to have formed during transform like faulting by progressive inhomogeneous simple shear with no component of orthogonal shortening

a further study of the tropical western hemisphere warm pool abstract variability of the tropical western hemisphere warm pool whwp of water warmer than 28 5 c which extends seasonally over parts of the eastern north pacific the gulf of mexico the caribbean and the western tropical north atlantic tna was previously studied by wang and enfield using the da silva data from 1945 93 using additional datasets of the ncep ncar reanalysis field and the ncep sst from 1950 99 and the levitus climatological subsurface temperature the present paper confirms and extends the previous study of wang and enfield the whwp alternates with northern south america as the seasonal heating source for the walker and hadley circulations in the western hemisphere during the boreal winter a strong hadley cell emanates northward from the amazon heat source with subsidence over the subtropical north atlantic north of 20 n sustaining a strong north atlantic anticyclone and associated northeast ne trade winds over its southern limb in the tna this circulation including the ne

the 1800 1610 ma stratigraphic and magmatic history of the eastern succession mount isa inlier and correlations with adjacent paleoproterozoic terranes the chronostratigraphic and magmatic framework for the proterozoic mount isa inlier northwest queensland has been substantially revised to match insights provided by isotopic age constraints accumulated over recent years this material and existing chronometric constraints is used to construct a new time space plot for the inlier and to compare eastern succession volcanosedimentary accumulations with temporally equivalent units in the western fold belt the accumulation of volcanosedimentary sequences in the eastern succession occurred in four main periods namely 1890 1850 ma 1800 1750 ma 1710 1690 ma and 1680 1610 ma temporally equivalent units can be identified in the western fold belt periods of sedimentary accumulation were immediately preceded by bimodal igneous activity across the inlier the locus of bimodal volcanism migrates from west to east with time intracontinental rifting is the most likely tectonic setting for the sedimentary basins the majority of the soldiers cap group was deposited between ca 1675 and 1650 ma with the exception of units in the boomarra horst now known to belong to older sequences deposited ca 1775 1750 ma and the llewellyn creek formation at snake creek which may be as old as ca 1690 ma upper amphibolite facies rock units in the southwest e g the gandry dam gneiss are likely to be higher metamorphic grade temporal equivalents of the soldiers cap group five rock units previously assigned to the cover sequence 2 mary kathleen group namely the answer slate kuridala formation staveley formation marimo slate and agate downs siltstone are now known to have been deposited between ca 1675 and 1610 ma these units bar the kuridala formation have been removed from the cover sequence 2 mary kathleen group and given the informal name young australia group the kuridala formation has been included in the soldiers cap group the rock units within the young australia group are likely to be lateral facies equivalents of the younger units within the soldiers cap group rock units within the mount albert group although undated are considered likely to be temporal equivalents of the soldiers cap group and the young australia group the roxmere quartzite is included here in the young australia group that it tectonically overlays the ballara quartzite and mitakoodi quartzite represent a single regionally extensive sequence deposited at ca 1755 ma the double crossing metamorphics previously mapped as basement are likely to correlate with the argylla formation and mitakoodi quartzite most of the eastern succession to the west of the pilgrim fault is likely to have been a topographic high between ca 1780 and 1755 ma prior to the ballara quartzite unconformably overlying the ca 1780 ma argylla formation detrital zircons of argylla and wonga ages indicate that the mary kathleen belt is likely to have been a topographic high at least periodically during accumulation of the soldiers cap and young australia groups soldiers cap group units in the southeast contain numerous detrital zircons giving ages between ca 1730 and 1710 indicating a possible siliciclastic source to the east the host rocks to the pb zn ag deposits are restricted to cover sequence 3 units deposited between ca 1680 and 1590 ma and with the exception of century young from the southeast towards the northwest cu au deposits and prospects are hosted in units from all the major periods of volcanosedimentary accumulation however many of the most significant deposits are found within the younger sequences

tropical gradient influences on caribbean rainfall 1 interbasin and intrabasin gradients play an important role as a part of a regional system of caribbean climate drivers which include the atlantic warm pool awp and the caribbean low level jet cllj when the caribbean is conditioned to be wet between may and november near surface geopotentials in the caribbean are lower than in the nearby eastern tropical pacific and east tropical atlantic as a result there is vertical ascent in the caribbean through to the middle troposphere which connects to zonal circulations with both the eastern tropical pacific and the eastern tropical atlantic the caribbean sea is also warm and there is a moderate easterly flow regime indicating a weakening of the trade winds deviations from this state caused by changes in one or both sides of the pacific caribbean and caribbean atlantic circulations and diagnosed by changes in their geopotential gradients reasonably track the transition of the caribbean from wet to dry and vice versa on intraseasonal and interannual time scales the study also uses changes to the gradients to offer insight into why the caribbean region is projected to be drier during its traditional rainy season in the face of warmer surface temperatures under global warming the caribbean seemingly enters into a july mode which persists for the duration of the boreal summer the mode is characterized by higher lower geopotentials in the caribbean pacific and atlantic a stronger cllj and anomalous descent in the caribbean in spite of the warmer surface temperatures

influence of the warm pool and cold tongue el ninos on the following caribbean rainy season rainfall caribbean rainfall and associated regional scale ocean atmosphere anomalies are analyzed during and after warm pool wp and cold tongue ct el nino en events i e from the usual peak of en events in boreal winter to next summer from 1950 to 2011 during and after a ct event a north south dipolar pattern with positive negative rainfall anomalies over the northern southern caribbean during the boreal winter tends to reverse in spring and then to vanish in summer on the contrary during and after a wp event weak rainfall anomalies during the boreal winter intensify themselves from spring with anomalous wet conditions over most of the caribbean basin observed during summer except over the eastern coast of nicaragua and costa rica the caribbean rainfall anomalies associated with wp and ct events are shaped by competition between at least four different but interrelated mechanisms 1 the near equatorial large scale subsidence anomaly over the equatorial atlantic linked to the zonal adjustment of the walker circulation 2 the extra tropical wave like train combining positive phase of the pacific north american mode and negative phase of the north atlantic oscillation 3 the wind evaporation sea surface temperature sst positive feedback coupling warmer than normal sst with weaker than normal low level easterlies over the tropical north atlantic and 4 the air sea coupling between the speed of low level easterlies including the caribbean low level jet and the sst anomaly ssta gradient between the caribbean basin and the eastern equatorial pacific it seems that caribbean rainfall anomalies are shaped mostly by mechanisms 1 3 during ct events from the boreal winter to spring these mechanisms seem less efficient during wp events when the atmospheric response seems driven mostly by mechanism 4 coupling positive west east ssta gradient with weaker than normal low level easterlies and secondary by mechanism 3 from the boreal spring to summer

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

radiogenic and stable isotope constraints on the genesis of the eloise cu au deposit cloncurry district northwest queensland new radiogenic 40ar 39ar and stable oxygen hydrogen and sulfur isotope analyses of metamorphic and metasomatic minerals constrain the age metasomatic evolution and genesis of the eloise cu au deposit 3 1 mt 5 5 cu 1 4 g t au and 16 g t ag biotite from a pre to syn d2 stage vein has an 40ar 39ar age of 1555 4 ma which is interpreted to coincide with a regional metamorphic event synchronous with d2 six later stages of alteration and mineralization are recognized all of which postdate peak metamorphism and d2 stages i to iii are volumetrically the most significant and comprise early albitization stage i quartz hornblende biotite veins and alteration stage ii and cu au mineralization stage iii stages iv v and vi are localized vein events and postdate the main cu au mineralization stage ii vein and alteration hornblendes have 40ar 39ar ages of 1530 3 ma biotite from the same stage has an 40ar 39ar age of 1521 3 ma muscovite from a postore shear zone has an 40ar 39ar age of 1514 3 ma these results provide a maximum ca 1530 ma and minimum ca 1514 ma age for the mineralizing event however the intimate relationship between stage ii mafic silicate veins and alteration and the stage iii cu au event combined with fluid inclusion results which indicate that a cooling evolving high salinity fluid was responsible for both stages suggests that the older age is likely to be closer to the age of mineralization the stage ii biotite age of ca 1521 ma is interpreted to record thermal resetting during postore ductile deformation the results suggest that micas in the cloncurry district are more susceptible to later thermal resetting than amphiboles which may have significant implications for deposits which have only been dated by micas quartz from stages ii iii and iv have 18oquartz values ranging between 10 1 and 11 9 per mil stage ii biotite has a lower 18o composition 5 6 than biotite from a pre d2vein 6 9 but both have identical d compositions 84 stage ii hornblende has lower 18o 6 8 and 7 4 and d 88 and 90 values than does stage iii actinolite 8 0 and 84 respectively the 34s values for chalcopyrite pyrrhotite and pyrite fall in a narrow range between 0 0 and 2 3 per mil a distinct trend can be recognized with 34s values becoming progressively greater from south to north thus reflecting the zoned alteration system magnetite pyrite rich in the south through to pyrrhotite rich in the north the change in mineralogy and sulfur isotope values may be due to cooling and sulfidation processes which resulted in changes in oxygen and sulfur fugacities the oxygen hydrogen and sulfur isotope data combined with high temperature and high salinity fluid inclusion data indicate a predominantly magmatic origin for the ore forming fluids the deposit is interpreted to have formed from magmatic hydrothermal fluids which were tapped by deep seated crustal structures

aeromagnetic patterns of half graben and basin inversion implications for sediment hosted massive sulfide pb zn ag exploration the inverted extensional basins of the palaeoproterozoic north australian craton are amongst the most metallogenically endowed on earth for sediment hosted massive sulphide shms pb zn ag deposits faults that evolved during the evolution of these basins are an important exploration vector as they have behaved as conduits for mineralizing fluids controlled facies architecture and impacted on hydrothermal convection cells we attempt to map out ancient normal faults using integrated structural and aeromagnetic analysis to identify faults that are either buried beneath younger cover or have been inverted during later orogenic events this technique can be used for targeting potential conduits for mineralising fluids during shms pb zn ag exploration as well as a tool to map the architecture of extensional basins we have constructed simplified cross sections of half graben and inverted half graben and have forward modelled their magnetic response the aeromagnetic signature of a pre inverted half graben shows that the tilt block is characterised by a shallow magnetic gradient related to the shallowing of the magnetic marker beneath the half graben normal offset of the marker unit across a normal fault is characterised by a steeper magnetic gradient as the depth to the marker horizon increases simplified cross sections of isolated growth anticlines and the hanging wall buttressing show that the general shape of the magnetic profiles are maintained until the half graben has been completely inverted and the magnetic marker horizon displays reverse offset along the reactivated normal fault

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

beryllium 10 transport to antarctica results from seasonally resolved observations and modeling 1 cosmogenic 10be measured in polar ice cores has important application in the reconstruction of past solar activity however the processes controlling its atmospheric transport and deposition to the ice sheets are not fully understood here we use the seasonal changes in 10be concentrations in a 10 year monthly resolved ice core record from the law dome site east antarctica in conjunction with echam5 ham general circulation model gcm simulations of 10be and 7be deposition as tools to examine this problem maximum 10be concentrations are observed in the ice core during the austral late summer to early autumn summer autumn while minimum concentrations are observed during the austral winter the gcm simulations corroborated by earlier observations of 10be 7be ratios in antarctica from the georg von neumayer air sampling station suggest that the 10be concentration maximum is linked to direct input of stratospheric 10be from the antarctic stratosphere to the lower levels of the antarctic troposphere during the austral summer autumn this result contrasts with the modeled transport of 10be to greenland where the seasonal maximum in stratospheric input is seen in the late winter to spring synchronous with the timing of the seasonal maximum in midlatitude stratosphere to troposphere exchange our results suggest that a different combination of processes is responsible for the transport of 10be to the antarctic and greenland ice sheets

a cosmic trip 25 years of cosmogenic nuclides in geology terrestrial cosmogenic nuclides produced by secondary cosmic ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere are widely used to date surface exposure of rocks and sediments to estimate erosion and weathering rates and to date sediment deposition or burial their use has transformed geomorphology and quaternary geology for the first time allowing landforms to be dated and denudation rates to be measured over soil forming time scales the application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry ams in 1977 and increased dramatically with the measurement of in situ produced nuclides in mineral grains near earth s surface in the 1980s the past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool this review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today and by identifying key advances in that period that moved the field forward we emphasize the most commonly used in situ produced nuclides measured by ams for geological applications but we also discuss other nuclides where their applications overlap our review covers ams instrumentation cosmogenic nuclide production rates the methods of surface exposure dating measurement of erosion and weathering and burial dating and meteoric 10 be in memoriam devendra lal 1929 2012 whose vision inspired the field

impact of the cerro hudson and pinatubo volcanic eruptions on the antarctic air and snow chemistry atmospheric records of sulfate and msa in aerosols were obtained by year round samplings in the boundary layer at two coastal antarctic sites neumayer 1983 1995 and dumont d urville 1991 1997 at dumont d urville and neumayer the non sea salt sulfate nssso42 level observed from october 1991 to october 1993 exceeded by 44 and 48 ng m 3 respectively the mean level 150 ng m 3 observed during nonvolcanic years the neumayer and dumont d urville records first exhibit spring october to december 1991 nssso42 concentrations exceeding mean spring concentrations by some 100 to 150 ng m 3 caused by a significant poleward transport of the cerro hudson volcanic aerosol in the lower stratosphere beneath the polar vortex and possibly in the middle upper troposphere limited to 10 ng m 3 during winter 1992 the nssso42 perturbation reached 78 ng m 3 in fall 1993 at neumayer the latter enhancement corresponds to the input of the pinatubo volcanic aerosol advected through stratosphere troposphere air mass exchanges an enhancement of nssso42 concentrations is also recorded in snow layers deposited between 1991 and 1993 at various sites located over the high antarctic plateau on the basis of these firn data the relative impact of the three latest volcanic eruptions of global concern namely mount agung 1963 el chichon 1982 and pinatubo together with cerro hudson 1991 was evaluated in terms of sulfate input at high southern latitudes the fallout of sulfate in central antarctic snow following the cerro hudson pinatubo eruptions was slightly lower than fallout after the mount agung eruption sulfate fallout after el chichon was 2 to 3 times lower than that from either mount agung or pinatubo the enhancement of sulfate levels detected in central antarctic snow deposits during the 1991 1993 time period allows us to estimate a mean atmospheric sulfate perturbation of around 60 ng m 3 in the boundary layer of these regions i e at least 35 higher than that seen at coastal sites this observation suggests that coastal antarctic regions are less sensitive than the high plateau in detecting volcanic sulfate fallouts following eruptions of global concern atmospheric near surface year round sampling achieved at coastal antarctic sites reveals no significant enhancement of the nitrate level over 1992 and 1993 suggesting that volcanic aerosols have had a limited effect on the transfer of nitric acid from the lower antarctic stratosphere to the boundary layer in these regions

three dimensional structure along the inverted palaeoproterozoic fiery creek fault system mount isa terrane australia abstract the nw dipping fiery creek fault system located in the northern mount isa terrane comprises numerous sub parallel faults that record multiple episodes of palaeo to mesoproterozoic movement hanging wall wedge shaped stratal geometries and marked stratal thickness variation across the fault system indicate that the earliest movement occurred during episodic intracontinental extension mount isa rift event ca 1710 1655 ma reactivation of the fault system during regional shortening and basin inversion associated with the mesoproterozoic isan orogeny ca 1590 1500 ma resulted in complex three dimensional hanging wall geometries and highly variable strain in the hanging wall strata along the fault system this has resulted in the development of discrete hanging wall deformation compartments that are characterised by different structural styles high strain compartments are characterised by relatively intense folding and the development of break back thrusts whereas low strain compartments are only weakly folded variations in hanging wall strain are attributed to selective reactivation of normal fault segments controlled by the pre inversion fault dip and lithological contrasts across the faults variation of the pre inversion fault dip is interpreted to have been caused by episodic tilt block rotation during crustal extension moderately dipping faults active early in the mount isa rift event show the greatest degree of reactivation whereas younger and steeper normal faults have behaved as buttresses during inversion with strain focussed in zones of upright folding in the hanging wall

the antarctic ice sheet its history and response to sea level and climatic changes over the past 100 million years abstract the development surface form flow and erosive activity of the antarctic ice sheet over the past 100 million years is related to geological evidence that indicates long term trends of global climate the glaciological description of the evolution of the ice sheet covers its interactions with the atmosphere and with the ocean discussion focuses on changes of the equilibrium line altitude ela with time of the accumulation rate with global temperature and basal melting of ice shelves by ocean waters the tendency of global climate to change rapidly or to drift slowly between two near equilibrium states involves two types of changes the former that has been widely recognized is reversible a second type involving ice sheets or ice shelves appears to be almost irreversible since they remain in their changed state unless a much larger reversal of factors driving climate occurs we refer to any rapid but reversible changes as climatic jumps and to the latter as climate ice switches variability of climate in response to changing radiation with the earth s orbital parameters and other causes is included in our model extensive glaciation of east antarctica commenced after 40 m y b p with wide fluctuations until shortly after 20 m y b p a climate ice switch then prevented any major deglaciation a further climate ice switch associated with the ela falling below sea level occurred soon after 10 m y b p this led to rapid formation of ice shelves and the marine ice sheet of west antarctica which advanced as grounded ice to the edge of the continental shelf after 5 m y b p the grounded ice started to retreat extensive ice shelves remained and most glacial debris was then deposited beneath the inner regions of ice shelves response to northern hemisphere glaciation since 2 4 m y b p during glacial periods involved extension of the grounded ice area a large decrease of mass input and decreased melting of outer parts of large ice shelves while the melting rate beneath inner regions was probably similar to the present marine core evidence suggests that retreat caused by global cooling has been dominant since 5 m y b p and that changes in extent due to northern hemisphere glaciation since 2 4 m y b p have had different effects on the major and on smaller northerly ice shelves

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

the role of ductility contrast and basement architecture in the structural evolution of the crystal creek block mount isa inlier nw queensland australia abstract the leichhardt river fault trough of the mount isa inlier comprises fault blocks which exhibit different local deformational histories and structural orientations many structural patterns in the stratigraphically highest cover sequences do not occur in adjacent fault blocks that expose older and mechanically stronger rocks within the mount isa group sediments of the crystal creek block for example tight e trending upright folds appear to be at odds with the surrounding north south regional trends in this paper it is proposed that an inherited extensional fault geometry played a significant role in controlling the structural patterns developed during later shortening through the integration of detailed surface mapping and forward magnetic modelling an inverted half graben was identified beneath the crystal creek block exposing the underlying origin of local structural complexities structural inversion and buttressing against pre existing faults simultaneously removed extensional displacement across pre rift rocks and induced folds and faults in overlying sag phase sediments this led to the development of two structural levels characterized by different deformational styles and apparently distinct deformational histories

interhemispheric influence of the atlantic warm pool on the southeastern pacific abstract the atlantic warm pool awp is a large body of warm water comprising the gulf of mexico caribbean sea and western tropical north atlantic the awp can vary on seasonal interannual and multidecadal time scales the maximum awp size is in the boreal late summer and early fall with the largest extent in the year being about 3 times the smallest one the awp alternates with the amazon basin in south america as the seasonal heating source for circulations of the hadley and walker type in the western hemisphere during the boreal summer fall a strong hadley type circulation is established with ascending motion over the awp and subsidence over the southeastern tropical pacific this is accompanied by equatorward flow in the lower troposphere over the southeastern tropical pacific as dynamically required by the sverdrup vorticity balance it is shown by analyses of observational data and ncar community atmospheric model simulations that an anomalously large small awp during the boreal summer f

tectonic inversion and basement buttressing an example from the central appalachian blue ridge province abstract the structural geometry of the central appalachian blue ridge province is primarily the result of paleozoic contractional deformation however the tye river fault zone in the western blue ridge of central virginia preserves an extensional map pattern these ene wsw striking faults place neoproterozoic to early cambrian volcanic and sedimentary rocks over grenvillian granitic basement detailed mapping cross section restoration and balancing reveals partially inverted faults original half grabens and significantly thicker cover units on hanging walls the orientation and geometry of the tye river fault zone as well as the thickness changes in the cover rocks are inconsistent with extensional reactivation of paleozoic reverse faults during mesozoic rifting the extrusion and deposition of cover rocks was contemporaneous with normal displacement on the tye river fault zone and the formation of rift basins recording 5 crustal extension faults were reactivated as paleozoic contractional structures but an extensional map pattern is generally still preserved regional shortening of 10 20 was accomplished primarily by folding of the cover rocks rather than by reactivation of older faults the basement formed a rigid buttress that controlled the geometry of folding in the cover sequence

a shortened intraplate rift system in the proterozoic mount isa terrane nw queensland australia the leichhardt river fault trough of the mount isa terrane developed a complex extensional architecture between approximately 1800 and 1600 ma forming the underlying template upon which compressional structures were superimposed during the 1590 to 1500 ma isan orogeny basin fill material accumulated during at least five multiphase periods of rifting and associated postrift subsidence forming a stacked succession of unconformity bounded sequences initial e w extension was associated with a massive magmatic event half graben greater than 50 km in width and of alternating asymmetry localized the extrusion of up to 4 km of continental tholeiites thereafter a period of n s extension resulted in southward tapering north tilted half graben in which synrift basaltic and siliciclastic strata accumulated n s extension was followed by regional postrift subsidence and the deposition of a laterally continuous quartzite carbonate package a multiphase period of e w to nw se extension ensued during which time two unconformity bounded sequences accumulated the stratal architectures of these sequences are strongly asymmetric in cross section exhibiting a pronounced rotational thickening toward the east consistent with their deposition in the hanging walls of east dipping tilt blocks between 15 and 40 km in width finally a period of n s extension resulted in the development of e w trending f1 drag synclines in the highest level cover rocks the association of angular unconformities and block bounding faults e w trending synclines and e w striking faults and the unique internal fold geometries of fault blocks suggest that many fault bounded blocks originated as coherent structural entities during rifting and continued to act as such during subsequent shortening

basin inversion by distributed deformation the southern margin of the bristol channel basin england several models of basin inversion described in the literature are tested in a study of triassic and early jurassic strata exposed along the southern margin of the bristol channel basin in somerset england that has been exhumed by 95 of them are still in net extension despite widespread kinematic evidence for reverse reactivation when coupled with the general absence of thin skinned thrusts and the widespread occurrence of regional contractional folds it appears that none of three main inversion models the fault reactivation model the thin skinned model and the buttress model are by themselves applicable we erect a new model of basin inversion the distributed deformation model which consists of three stages of basin inversion stage one involved early partial reactivation of large displacement steep normal faults stage two was dominated by folding wherein fault blocks underwent oblique non coaxial shortening by map scale folding accompanied by formation of outer arc normal faults minor cleavage and neoformed thrusts stage three involved reverse reactivation of outer arc normal faults and activation of oblique and strike slip faults that partitioned deformation into compartments

geochemistry of post 1540 ma granites in the cloncurry district northwest queensland proterozoic fe oxide cu au co mineralization in the cloncuriy district is spatially and temporally related to intrusion of voluminous postpeak metamorphic granites that form most of the williams and naraku batholiths detailed mapping and geochemical study of these granites in the southern part of the district have identified two groups of intrusions that are referred to here as the cloncurry supersuite and eureka supersuite the cloncurry supersuite is composed mainly of monzogranite and syenogranite which consist of quartz plagioclase alkali feldspar hornblende biotite with accessory magnetite titanite apatite and zircon the timing of intrusion of the wiley igneous complex is interpreted to be pre or syn d 3 based on overprinting relationships while hornblende geobarometry suggests an emplacement depth of approximately 14 km the granites are subalkaline high k metaluminous rocks and range from 59 to 74 wt percent sio 2 increasing sio 2 is accompanied by increasing k 2 o rb and th and decreasing mgo fe 2 o 3 feo tio 2 cao p 2 o 5 sr eu zr cu zn ni v and sc this is consistent with fractionation of observed phases including plagioclase amphibole biotite magnetite titanite and apatite the eureka supersuite ranges from diorite to syenogranite in composition more mafic varieties contain pyroxene and hornblende while more felsic varieties contain biotite as the only ferromagnesian silicate sodiccalcic alteration events are closely linked in space and time to intrusion of eureka supersuite magmas the timing of intrusion is interpreted to be pre and post d 3 based on overprinting relationships between different plutons and mylonitic fabrics hornblende geobarometry suggests an emplacement depth of approximately 10 km for the mount angelay igneous complex eureka supersuite granites in the mount angelay igneous complex range from 51 to 76 wt percent sio 2 the granites are alkaline and k 2 o rich leading to their classification as a shoshonite series with increasing sio 2 content tio 2 al 2 o 3 fe 2 o 3 t mno mgo cao p 2 o 5 sr eu cu zn ni v and sc decrease indicating fractionation of observed minerals including apatite magnetite pyroxene hornblende plagioclase and biotite some samples are characterized by very high abundances of k 2 o p 2 o 5 sr ba and light rare earth elements lree compared to other eureka supersuite samples this may reflect their derivation from a source that was variably enriched in incompatible elements compared with many other shoshonitic rocks high k eureka supersuite samples are strongly depleted in sr and to a lesser extent eu and enriched in y and heavy rare earth elements hree this suggests that garnet was not a stable phase in the source region that the source contained plagioclase as a stable phase and or the granites evolved by extensive plagioclase fractionation partial melting in the lower crust to generate post 1540 ma granites was most likely caused by intrusion of basic magma into the crust eureka supersuite magmas were probably derived from partial melting of variably incompatible element enriched gabbroic rocks while cloncurry supersuite magmas were most likely derived from partial melting of more felsic material of dioritic to tonalitic composition

nd isotope and petrogenetic constraints for the origin of the mount angelay igneous complex implications for the origin of intrusions in the cloncurry district ne australia abstract the mesoproterozoic mount angelay igneous complex contained intrusions that were emplaced into amphibolite facies metasedimentary rocks during two periods of 1550 and post 1540 ma magmatism sm nd isotopic analysis together with mineralogical and chemical considerations suggest that the intrusions were produced from a paleoproterozoic crustal source with a t 2 model age 2200 ma on geochemical and petrological grounds the 1550 ma trondhjemitic intrusions are interpreted to have been produced by melting of amphibolite under garnet stable conditions 8 10 kbar the late syn to post peak metamorphic timing of these intrusions suggested that they were associated with the tectono thermal event that produced regional peak metamorphic mineral assemblages the post 1540 ma intrusions are k rich and consist of two groups of synchronously emplaced intrusions 1 a high k monzodiorite and monzogranite suite that range between 51 and 77 wt sio 2 and 2 a high k na enriched hornblende monzonite the chemistry and mineralogy of these intrusions suggested that they were derived via plagioclase stable and garnet unstable melting 2 o p 2 o 5 cr v and zn compared with slightly younger high k monzonite which is interpreted to have formed via one of two mechanisms 1 melting of a low k amphibole and plagioclase rich source or 2 melting of residual material that produces a potassic and incompatible element rich melt these magmas likely contained mantle derived material particularly the k rich intrusions of mafic composition the heat required for the production of post 1540 ma intrusions appears to have been generated by the intrusion of high t mantle derived mafic material into the crust 25 30 km 8 10 kbar this model is consistent with the synchronous emplacement of mafic and felsic magma and the lack of a consanguineous regional metamorphic association and suggests high t high degree partial melting in localised pockets within fertile source regions in the crust an increase in sm nd model source age and decrease in end with increasing sio 2 in the k rich intrusions suggests the incorporation of juvenile material in the more mafic rocks the origin of this component is unknown but it may represent either the incorporation of mantle derived material during melting or the partial melting of crust with a younger mafic component on a district scale the 30 million year period over which the k rich post 1540 ma intrusions were emplaced suggested that mantle derived material continued to be injected into the crust a mantle component to these rocks and the global distribution of proterozoic intrusions with similar geochemical affinities strongly suggests a world wide period of mantle induced crustal melting at that time the dominant paleoproterozoic isotopic composition of most of these intrusions suggests melting of similarly composed and matured source rocks

using the sunspot cycle to date ice cores for many ice cores the snow accumulation rate is too low to preserve annual stratigraphy precluding direct measurement of annual layer thickness for selected holocene sections of the taylor dome core east antarctica we instead use high resolution 10be measurements to establish a nominal 11 year thickness taking advantage of the solar cycle in cosmogenic isotope production we compare measured thicknesses with the layer thickness profile predicted by a finite element ice flow model the results are in good agreement supporting the assumption that the length of the solar cycle has remained essentially constant throughout the holocene for ice cores where annual layers are not preserved the 10be 11 year layer method can be used as an independent check on flow model estimates of layer thickness and to estimate past accumulation rates it should be possible to accurately date ice cores by counting 11 year layers detected with continuous high resolution 10be measurements

210 pb dating of the miaoergou ice core from the eastern tien shan china in 2005 two ice cores with lengths of 58 7 and 57 6 m respectively to bedrock were recovered from the miaoergou flat topped glacier 43 degrees 03 19 n 94 degrees 19 21 e 4512 m a s l eastern tien shan pb 210 dating of one of the ice cores 57 6 m was performed and an age of ad 1851 6 at a depth of 35 2 m w e was determined for the period ad 1851 2005 a mean annual net accumulation of 229 7 mm w e a 1 was calculated at the nearby oasis city of hami similar to 80 km from the miaoergou flat topped glacier the annual precipitation rate is 38 mm w e a 1 hence glacial meltwater is a major water supply for local residents the surface activity concentration of pb 210 ex was found to be similar to 400 mbq kg 1 which is higher than observed at other continental sites such as belukha russia and tsambagarav mongolia which have surface activity concentrations of 280 mbq kg 1 the pb 210 dating agrees well with the chronological sequence deduced from the annual layer counting resulting from the seasonalities of delta o 18 and trace metals for the period ad 1953 2005 and beta activity horizons resulting from atmospheric nuclear testing during the period ad 1962 63 we conclude that pb 210 analysis is a suitable method for obtaining a continuous dating of the miaoergou ice core for similar to 160 years which can also be applied to other ice cores recovered from the mountains of western china

geodynamic evolution of the proterozoic mount isa terrain the proterozoic mount isa terrain records the effects of four periods of intraplate tectonism the c 1870 ma barramundi orogeny was characterized by a massive felsic magmatic event and global correlations suggest a physical link between australia and laurentia at this time thereafter the terrain underwent an extensional history spanning 200 ma involving repeated episoded of rifting post rift subsidence and associated depositional and magmatic phases this protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25km above attenuated continental crust rifting was interrupted prior to the formation of ocean crust by the compressional isan orogeny 1590 1500 ma the isan orogeny was synchronous with low pressure high temperature metamorphism and widespread metasomatism in the waning stages of shortening the mount isa terrain evolved into a wrench system characterized by an extensive network of strike slip faults the current level of exposure in this terrain provides spectacular examples of superimposed rifts basin inversion and wrench geometries developed at middle to upper crustal levels

a framework of overprinting orogens based on interpretation of the mount isa deep seismic transect a deep seismic reflection transect and coincident refraction study reveal the crustal structure developed during mesoproterozoic orogenesis preserved in the mount isa inlier of northwest queensland australia geologic interpretation of the reflection data indicates a two stage evolution for east west shortening the first stage involved west directed folding and thrusting above a decollement in the eastern part of the terrane this decollement system was the forehand of an orogenic system rooted east of the present day inlier the second stage is characterized by a network of basement cutting reverse and strike slip faults that dissected the decollement this overprinting system was linked to crustal thickening within the mount isa terrane the refraction profile indicates the crust beneath the inlier is currently approximately 55 km thick rocks with transitional velocities 7 km s in the lower 15 km are interpreted as mafic underplate formed during the pre orogenic rift history of the inlier the refraction profile also reveals two west dipping high velocity layers within the crust evaluating the origin of these layers in light of the kinematics of crustal thickening suggests they are portions of the underplated material thrust to midcrustal levels during the second stage of shortening the overprinting orogenic scenario has implications for the geodynamic evolution of the inlier that should have a direct bearing on mineralizing systems localized by reverse faults developed during the second stage of shortening this basement cutting stage established a linked fault network able to tap deeper crustal circulation during the intrusion of late to postorogenic granitoids

microstructural evidence for n s shortening in the mount isa inlier nw queensland australia the preservation of early w e trending foliations in porphyroblasts revealed by independent 3d measurement techniques 3d microstructural analyses of porphyroblast inclusion trails using both the asymmetry switch method for determining foliation intersection axes preserved in porphyroblasts fias and the recently developed fitpitch method reveal w e and n s trending fia sets in the white blow formation of the mount isa inlier each method reveals two subsets of fias centered on each of these major trends these were distinguished based on the relative timing trend and orientation of inclusion trail patterns thirty six samples were analyzed using both techniques and produced very similar results pitches of the inclusion trails preserved within the porphyroblasts in vertically oriented thin sections and trends in horizontal sections yield distinct near orthogonal modal orientations from all the analyzed samples this indicates that the porphyroblasts host successive fabrics as crenulation foliations and did not rotate with respect to geographical axes w e and n s trending fias have been obtained from both garnet and staurolite porphyroblasts hosting differentiated crenulation cleavages garnet and staurolite growth during bulk north south shortening recorded the development of multiple foliations and an associated succession of metamorphic events at middle amphibolite facies conditions that predates the metamorphic history generally recognized in this terrain this period of bulk shortening and associated metamorphism formed during a period of orogenesis called o1 w e shortening formed n s striking foliations that preserve a period of orogenesis o2 and another succession of metamorphism involving more phases of porphyroblast growth preserving n s trending fias overprinting of successive fia trends wsw ene wnw ese nnw sse and ssw nne suggests a relative clockwise rotation of the bulk shortening direction through time as it switches from n s to w e overall with a major tectonic break or decompression between o1 and o2 the porphyroblast inclusion trail patterns preserving w e trending fias provide a window into the lengthy period of earlier deformation and metamorphism that is no longer preserved within the matrix foliations

contrasting styles of proterozoic crustal evolution a hot plate tectonic model for australian terranes proterozoic terranes in australia record complex tectonic histories in the interval 1900 1400 ma that have previously been interpreted by means of simple intracratonic or plate tectonic models however these models do not fully account for 1 repeated tectonic reactivation both orogenesis and rifting 2 mainly high temperature low pressure metamorphism 3 rifting and sag creating thick sedimentary basins 4 the nature and timing of voluminous felsic magmatism 5 relatively large aspect ratio orogenic belts and 6 a general paucity of diagnostic plate boundary features a key to understanding these histories is the observation that australian proterozoic terranes are characterized by an extraordinary but heterogeneous enrichment of the heat producing elements this enrichment must contribute to long term lithospheric weakening and thus we advocate a hybrid lithospheric evolution model with two tectonic switches plate boundary derived stresses and heat producing element related lithospheric weakening the australian proterozoic crustal growth record is therefore a function of the magnitude of these stresses the way in which the heat producing elements are distributed and how both of these change with time

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

proterozoic low pressure high temperature metamorphism and an anticlockwise p t t path for the hazeldene area mount isa inlier queensland australia in the hazeldene area situated in the mount isa inlier queensland the metamorphic grade changes from chlorite zone through biotite and cordierite zones to sillimanite k feldspar zone microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation s2 was replaced by biotite andalusite and sillimanite at the metamorphic peak late in s2 and in turn by kyanite chlorite adjacent to localized small post d2 shear zones although the anticlockwise p t t path is well defined the precise p t conditions are uncertain because of problems with experimental and thermodynamic data the best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600 c at 4 kbar the metamorphism has been dated at 1544 ma and was synchronous with a major crustal shortening event because proposed extensional events occurred more than 60 ma earlier their contribution to the peak metamorphic thermal perturbation would have been insignificant the syn metamorphic mica creek pegmatites the abundance of high heat producing elements in the nearby pre d2 sybella granite and advective heat by fluids which caused considerable metasomatism in the hazeldene area may have each contributed to the thermal budget however the metamorphic thermal gradient may be 80 c km 1 or higher strongly suggesting a local magmatic control as none are known in the area such syn metamorphic plutons would have to lie beneath the exposed high grade rocks

the synchronism of crustal thickening and high t low p metamorphism in the mount isa inlier australia 1 an example the central soldiers cap belt abstract in the soldiers cap group of the central eastern part of the early to middle proterozoic mount isa inlier tracing of mesoscopic structures has led to the recognition of an early nw closing fold nappe with an e w trending coaxially shortened frontal zone d1 folded around a n s trending upright syncline d2 an andalusite sillimanite prograde metamorphic event indicating a paleo geothermal gradient of approximately 50 c km occurred during early d2 times the coexistence of such moderately high paleo geothermal gradients and crustal thickening is common in the early to middle proterozoic mobile belts of northern australia crust mantle delamination has been suggested by etheridge et al 1987 to explain this coexistence here the thermal implications of this model and the additional thermal effects of waning crustal extension magmatic events and of the radioactive selfheating of the thickened crust are qualitatively discussed

geometry of a middle proterozoic extensional decollement in northeastern australia abstract an 80 km long belt of gneissic and mylonitic rocks is exposed in the core of a major anticlinorium in the middle proterozoic mt isa inlier of northeastern australia these rocks in the mary kathleen fold belt represent an early originally horizontal mid crustal shear zone which is interpreted as an extensional decollement between a lower ductile sheet and an upper more brittle plate the decollement was subhorizontal over a distance of at least 80 km and its depth was perhaps as shallow as 7 km shearing was accompanied by the syn tectonic intrusion of a bimodal complex of granitic and basic rocks over a period of 70 90 m y moderate to extreme ductile shearing was pervasive throughout the 1 1 5 km thickness of the lower plate that is now exposed massive dilation accompanied shearing and approximately 70 of the volume of the shear zone is occupied by igneous intrusive rocks which have been variably deformed to gneissic granite mylonite and amphibolite strain softening driven by this high thermal input is responsible for the pervasive ductile response at such shallow depths peak metamorphic conditions at the decollement were approximately 625 c to 675 c at 2 kbar intense ductile shearing in the upper plate is restricted to the lower few hundred metres above this zone brittle processes dominate although evidence is presented that the sheet as a whole has undergone a component of ductile shearing probably heterogeneously distributed large sheet like granite and dolerite bodies were introduced into dilation sites associated with synthetic faults in this plate but unlike their synchronous counterparts in the lower plate about 1 km below these are internally undeformed the middle proterozoic history of the area involves a cycle of extension and shortening with the shortening axis perpendicular to the earlier extension axis we speculate that the driving mechanism for both extension and shortening is mantle convection with switches in stress related to mantle upwelling

the synchronism of crustal thickening and low pressure facies metamorphism in the mount isa inlier australia 2 fast convective thinning of mantle lithosphere during crustal thickening the mount isa inlier is like some other northern australian early to middle proterozoic fold belts characterized by an anti clockwise p t t path i e regional prograde low p facies metamorphic assemblages grew during crustal thickening p t and were overprinted by a phase of essentially isobaric cooling p 0 t in this study two possible models for the synchronism of regional low p facies metamorphism and crustal thickening are quantitatively evaluated using a one dimensional finite difference technique 1 extreme elevation of isotherms immediately before the thickening event due to e g lithospheric extension magmatic activity or crust mantle delamination and 2 crustal thickening accompanied by convective thinning of the mantle lithosphere only the latter results in prograde low p facies metamorphism during crustal thickening it is the preferred model for the mount isa inlier

a mid holocene paleoprecipitation record from belize abstract understanding past climate may contribute to a better understanding of future climate change allowing for adaptations to changing water resources high latitude paleoclimate reconstructions reveal a warmer northern hemisphere during the mid holocene yet paleoclimate records from tropical central america are lacking especially seasonally resolved reconstructions needed to resolve seasonal shifts here we reconstruct mid holocene precipitation using high resolution sub annual to biannual stable isotope ratios oxygen and carbon extracted from a speleothem recovered from belize to investigate the frequency and magnitude of precipitation variability we found a slight increase in precipitation during the mid holocene in belize with less variability compared to the late holocene this increase in precipitation may be a result of the expansion of the north atlantic subtropical high nash which strengthens the caribbean lower level jet enhancing westward advection of atmospheric moisture to belize the decrease in precipitation variability could be derived from a northward movement of the intertropical convergence zone itcz placing belize within the bounds of the itcz for a longer period each year time series analysis reveals periodicities of 200 250 years which correspond to the suess solar cycle the additional periods of 100 and 50 years also have origins in solar irradiance the north atlantic oscillation nao and the atlantic multidecadal variability amv also known as the atlantic multidecadal oscillation amo long recognized as important drivers of precipitation variability in the region are present but only at the 90 significance level we posit that the reduced influence of the nao and amv could be caused by the northerly migration of the itcz during the mid holocene

beryllium isotope geochemistry in tropical river basins abstract the distributions of beryllium 9 and beryllium 10 in rivers within the orinoco and amazon basins have been examined to extend our understanding of their geochemical cycles and to develop their use both in geochronometry and in studying erosional processes beryllium 9 the stable isotope is weathered from mineral lattices before entering the riverine dissolved or exchangeable phase the cosmogenic radioisotope 10be t 1 2 1 5 myr is produced primarily in the atmosphere and is brought into riverine systems via rainfall in dissolved or exchangeable form it may be used to examine the processes which affect beryllium partitioning between the dissolved and particulate phases ancillary data such as major ion distributions provide a basis for selecting regions in which riverine chemistry is dominated by a single geochemical process allowing examination of its effects on be distributions in isolation analyses of 9be in dissolved and suspended material from rivers with a wide range of chemical compositions indicate that its geochemistry is primarily controlled by two major factors 1 1 its abundance in the rocks of the watershed and 2 2 the extent of its adsorption onto particle surfaces the relative importance of these parameters in individual rivers is determined by the extent of interaction with flood plain sediments and the riverine ph this understanding of 9be geochemistry forms a basis for examination of the geochemical cycling of 10be in rivers which are dominated by interaction with sediments the riverine concentration of dissolved 10be is far lower than that in the incoming rainwater indicating that a substantial proportion of it is retained within the soils of the basin or is adsorbed onto riverine particles however in acidic rivers in which the stable dissolved be concentration is determined by the be level in the rocks of the drainage basin dissolved 10be has essentially the same concentration as in precipitation these observations imply that the soil column in such regions must be saturated with respect to 10be and that the ratio of the inventory to the flux does not represent an age as may be the case in temperate latitudes but rather a residence time

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

accommodation of compressional inversion in north western south island new zealand old faults versus new in the nw south island new zealand high angle faults inherited from episodes of late cretaceousepaleocene and eocene extension have since the early miocene undergone compressional inversion in association with right lateral shearing and transpression on the alpine fault active reverse faulting and large historical earthquakes occur along nes to nneessw trending faults which at the surface dip 45e75 to both the east and west the faults truncate subparallel folds that deform the tertiary sequence overlying a composite paleozoicemesozoic crystalline basement however the deep geometry of these faults their penetration into the middle to lower crust and their relationship to the alpine fault are poorly understood the tectonic architecture of this compressional inversion province is analysed by reconstructing structural contours at the base of the oligocene carbonate sequence in the north west of the south island deformation of the oligocene carbonate sequence structural analyses in the field and subsurface data indicate a mixed style of inversion with 1 reactivation of some high angle normal faults and 2 thrusting on new moderate dipping cross cutting faults that detach slivers of basement and cause flexural folding in the sedimentary cover these faults may remain blind or concealed beneath cover sequences but are likely to control seismic rupturing in the basement at depths of w10e15 km 2006 elsevier ltd all rights reserved

synchronous climate changes in antarctica and the north atlantic central greenland ice cores provide evidence of abrupt changes in climate over the past 100 000 years many of these changes have also been identified in sedimentary and geochemical signatures in deep sea sediment cores from the north atlantic confirming the link between millennial scale climate variability and ocean thermohaline circulation it is shown here that two of the most prominent north atlantic events the rapid warming that marks the end of the last glacial period and the bolling allerod younger dryas oscillation are also recorded in an ice core from taylor dome in the western ross sea sector of antarctica this result contrasts with evidence from ice cores in other regions of antarctica which show an asynchronous response between the northern and southern hemispheres

a comparison of deep antarctic ice cores and their implications for climate between 65 000 and 15 000 years ago abstract three ice cores drilled in the central part of the antarctic continent extend back to the last glacial period one from west antarctica byrd and two from east antarctica vostok and dome c this period is also partly covered by a few cores from the coastal areas in these cores climatic information is mostly derived from the isotopic profiles d or 18 o from which surface temperature and more indirectly precipitation rate can be estimated the main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period from ca 65 000 15 000 yr b p the time scales have been examined in detail and a new 40 000 yr chronology for the dome c core adopted special emphasis is placed on the link between the concentration of 10 be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers elevation changes of the ice sheet derived from gas content and isotopic data bear directly on interpretations of past temperature and precipitation rate changes

the cloncurry lineament geophysical and geological evidence for a deep crustal structure in the eastern succession of the mount isa inlier the cloncurry lineament is a major feature evident from wavelet processed magnetic and gravity potential field data over the mount isa inlier eastern succession it is laterally continuous over 200 km of strike length and is inferred from the gravity data to extend to at least 30 km depth it delineates the contact between two major paleoproterozoic sedimentary sequences and is spatially associated with a number of mineral deposits including cannington ag pb zn ernest henry cu au and many smaller cu au deposits mapping and magnetic forward modelling along several profiles perpendicular to the cloncurry lineament suggests that it corresponds to the eastern margin of a 5 10 km wide deformation zone within the calc silicate dominated doherty formation the western boundary of this deformation zone is a distinct narrow fault zone the cloncurry fault the deformation zone consists of multiple generations of shearing and faulting accompanied by metasomatic alteration large variations in the magnetic response within the deformation zone can be modelled as sub vertical brecciation zones breccia types range from highly magnetic actinolite albite magnetite breccias through to late stage non magnetic quartz k feldspar hematite breccias the long lived history of multiple reactivation strike continuity width and vertical extent of the deformation zone suggest that it is a major crustal structure the structure may have originated during basin formation and later acted as a fluid pathway for alteration and base metal mineralization

application of geometric models to inverted listric fault systems in sandbox experiments paper 2 insights for possible along strike migration of material during 3d hanging wall deformation abstract fault geometry is a primary control on hanging wall deformation in this study a series of positive inversion analogue experiments was conducted using rigid fault surfaces of true 3d geometry with consistent listric geometry along the transport direction the deformed geometry of the top horizon of the syn extension sequence on vertical serial sections was examined with a conventional 2d geometric restoration technique to calculate the inclined antithetic shear angle that best approximates the actual fault shape and to estimate the amount of apparent horizontal shortening during contraction the apparent shear inclination and the estimated apparent shortening show a systematic change along strike corresponding to the plan geometry of the master detachment surface at the hanging wall above embayments in the fault geometry the uplift is highest the apparent shear inclination is gentlest and the apparent horizontal shortening is greatest in contrast the apparent shear inclination is steepest and the estimated shortening is smallest above salients in the master detachment geometry where the uplift is lowest these changes suggest that the hanging wall displacement had an along strike component during deformation the hanging wall material moves from the regions above salients to those above embayments in the detachment surface during contraction average of the estimated apparent shortening was smaller than the actual amount of the experiments probably due to tectonic compaction this study shows that the geometry of the master detachment in plan view has the primary control on the lateral variation of the hanging wall deformation the data presented in this paper help understand 3d geometric relations between the hanging wall deformation and the underlying detachment surfaces

crustal scale structures in the proterozoic mount isa inlier of north australia their seismic response and influence on mineralisation abstract the proterozoic mount isa inlier in northern australia is prospective for base metals and gold it contains a western fold belt including the leichhardt river fault trough and an eastern fold belt separated by older basement rocks of the kalkadoon leichhardt belt sediments and volcanics in both fold belts were deposited in rifts which were subsequently shortened by up to 50 mineralisation appears to be partitioned large tonnage lead and zinc deposits are more prevalent in the leichhardt river fault trough and most gold and copper occurrences are in the eastern fold belt cross sections of the inlier derived from coincident seismic reflection and refraction profiling are dominated by the youngest tectonic events the refraction data imply a west dipping lens of high velocity intermediate to mafic rock in the middle to upper crust in the east of the inlier it is collinear with another lens in the lower crust in the west of the inlier the lenses form a belt of high velocity rock cutting the crust from top to bottom and from east to west the reflection data reveal different styles of compression related structures in the east and west of the inlier thin skinned tectonics dominate in the eastern fold belt the sediments and volcanics are thrust to the west along a number of shallowly east dipping upper crustal detachments the detachments in turn are cut by steeply east dipping reverse faults which link into the zone of high velocity rocks defined by the refraction data in contrast faults in the western fold belt are steep and penetrate to mid crustal levels and probably also link into the belt of high velocity material deeper in the crust the partitioning into different tectonic styles occurs across the kalkadoon leichhardt belt which appears to have acted as a buttress during the crustal shortening published mineralisation models attribute the lead zinc mineralisation to circulating fluids at shallow crustal levels within the leichhardt river fault trough high reflectivity of faults with a close spatial association with mineralisation is attributed to alteration along the fault caused by migrating fluids copper gold mineralisation in the eastern fold belt is scattered but known major deposits lie along trend from a thrust fault shown in the seismic data to be highly reflective this fault links via the upper crustal detachments and the high velocity lenses into the middle to lower crust and is seen as a likely control on fluid migration pathways from lower crustal levels into the supracrustal eastern fold belt the partitioning of the tectonic styles seen in the seismic data and the mode of linking of faults into the middle to lower crust are seen as primary factors in the partitioning of mineralisation in the region

age constraints on the tectonothermal evolution of the selwyn zone eastern fold belt mount isa inlier the selwyn zone is characterized by multiple ductile deformation and metamorphic events there is general consensus that early in the isan orogeny there were both extensional and thrust events that produced bedding parallel foliation sbp we propose that these were followed by the d1 event that resulted in a regional steep east west foliation and that the snake creek anticline and the dominant s2a regional foliation formed as upright north south structures local overturning of d2 structures was due to subsequent localized deformation d2b that resulted in structures with flat lying axial planes d3 and d4 produced steep upright folds and crenulations with north northwest and northeast trending axial surfaces metamorphism largely controlled by the emplacement of mafic rocks is dominantly low pressure but the p t t path is complex early growth of cordierite m1 followed by andalusite was succeeded by a clockwise medium pressure loop of ca 500 600 mpa in the northern snake creek anticline as indicated by early d2a kyanite growth the metamorphic peak during d2 was around 580 c and 400 mpa at the sillimanite isograd and reached a maximum of around 670 c and 400 500 mpa in the migmatitic sillimanite k feldspar zone at the cannington and osborne mines previous age determinations for the metamorphic peak of 1580 1600 ma are confirmed with new electron microprobe dating of monazite whereas an age grouping of 1600 1630 ma may represent the d1 m2 event additional ages in the range 1640 1680 ma are recorded in albitites from the soldiers cap group and it is suggested that they formed by infiltration of hydrothermal fluids during extension and the emplacement of mafic sills this is supported by shrimp dating of zircon from a trondhjemite lens in a largely mafic sill complex in the snake creek anticline that provided an age of 1686 8 ma also indicating that at least part of the soldiers cap group is older than previously indicated a zircon shrimp age of 1527 4 ma was obtained for a sample of albitized saxby granite this age also represents the d4 m6 event and is the timing of the extensive brecciation and albitization of calc silicate rocks of the corella formation in the selwyn zone

the intra cratonic evolution of the central eastern mount isa inlier northwest queensland australia the central eastern part of the mount isa inlier can be subdivided into three major tectono stratigraphic domains from west to east i the mitakoodi anticlinorium a tight northeast plunging composite anticline which is developed within subaerial to shallow marine continental rift facies lithologies ii the marimo staveley block in which tight to isoclinal folds are developed within a marine shelf iii the central part of the soldiers cap group belt which is dominated by a series of metaturbidites and which hosts a fold nappe refolded about n s to ne sw trending axes the transition from subaerial sediments in the west through marine shelf sediments to turbidites in the east has been one of the main arguments used by advocates for a proterozoic continental margin at this locality here however it is argued that folding and differential uplift along late fault and shear zones led to the juxtaposition of different stratigraphic levels and to the apparent deepening of palaeobasins from subaerial in the west to deep water in the east the age of the soldiers cap group is poorly constrained but it is likely to be older than that of rocks cropping out in the marimo staveley block the marimo staveley block lithologies overlie those of the mitakoodi anticlinorium so here time transgression rather than eastward deepening may be deduced thus a palinspastic reconstruction based on an eastwards progressive deepening is not justified this adds to other evidence that refutes the continental margin model previously proposed for the eastern margin of the mount isa inlier instead the lithostratigraphic sequences reflect several stages of intra continental rifting all without formation of oceanic crust the pervasive post depositional deformational event is associated with regional low p facies metamorphism which indicates a further ensialic history

past precipitation rates derived from ice core measurements methods and data analysis ice cores in which annual layers can be identified or particular horizons dated provide a record of past precipitation rates if measured layer thicknesses can be corrected for thinning by flow since deposition total strain is usually calculated from steady state flow models because of lack of information about the ice cap s history an assumption of uniform vertical strain rate is valid at best in the upper half of the ice column complex models are needed to take account of uneven bedrock and variations in precipitation rate upstream of the borehole drilling at an ice divide avoids these complications new data analyses suggest that precipitation at camp century has fluctuated by only plus or minus 10 for the past 8500 years whereas at devon island on the opposite side of baffin bay precipitation has been uniform only for the past 1300 years with significantly higher values before that estimation of pre holocene precipitation rates is especially difficult because that ice may have an effective viscosity different from holocene ice three published estimates of pre holocene precipitation at camp century are unreliable the authors did not allow for thinning and their time scales differ appreciably data from three antarctic stations show some inconsistencies measuring concentrations of 10be in ice cores may be an alternative method of determining past precipitation rates

structure of the isan orogeny under cover to the east of the mount isa inlier revealed by multiscale edge analysis and forward and inverse modelling of aeromagnetic data aeromagnetic data reveals the presence of three north south orientated tens of kilometre scale elliptical structures under cover to the east of the mount isa inlier in queensland australia the holy joe creek boot creek and nora creek structures are typically defined by three narrow continuous magnetic ridges highly magnetically susceptible amphibolite bodies similar to those exposed in the inlier are probably the source of most of these magnetic anomalies multiscale edge analysis 2d forward modelling and 3d inverse modelling methods have been used to resolve the geometry and near surface dip of the structures these techniques indicate that the structures dip moderately to steeply around their edges the holy joe creek structure exhibits sub vertical to steeply west dipping sides and a moderate plunge around the northern closure the boot creek and nora creek structures are more complex magnetically but their eastern edges also have sub vertical to steep westerly dips diapirism and domes in an egg box style type 1 fold interference pattern are considered as possible origins for the elliptical structures however disparity between the shape of the structures and possible diapiric bodies and the lack of complementary basin structures to the domes makes these two explanations unlikely a more plausible alternative is that the structures are the result of deformation in a single phase producing folds with a variable hinge line plunge these results indicate that east west shortening during the d2 event of the isan orogeny was the major deformation in the buried rocks of the study area suggesting a shared structural history with the mount isa inlier to the west

atlantic warm pool acting as a link between atlantic multidecadal oscillation and atlantic tropical cyclone activity 1 multidecadal variability of atlantic tropical cyclone activity is observed to relate to the atlantic multidecadal oscillation amo a mode manifesting primarily in sea surface temperature sst in the high latitudes of the north atlantic in the low latitudes of the north atlantic a large body of warm water called the atlantic warm pool awp comprises the gulf of mexico the caribbean sea and the western tropical north atlantic awp variability occurs on both interannual and multidecadal timescales as well as with a secular variation the awp multidecadal variability coincides with the signal of the amo that is the warm cool phases of the amo are characterized by repeated large small awps since the climate response to the north atlantic sst anomalies is primarily forced at the low latitudes and the awp is in the path of or a birthplace for atlantic tropical cyclones the influence of the amo on atlantic tropical cyclone activity may operate through the mechanism of the awp induced atmospheric changes the awp induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability more specifically an anomalously large small awp reduces enhances the vertical wind shear in the hurricane main development region and increases decreases the moist static instability of the troposphere both of which favor disfavor atlantic tropical cyclone activity this is the most plausible way in which the amo relationship with atlantic tropical cyclones can be understood

evolution of the starra and selwyn high strain zones eastern fold belt mount isa inlier implications for au cu mineralization the starra magnetite ironstone hosted au cu deposit in the eastern fold belt mt isa inlier is localized by the development of the starra high strain zone the associated eastern barren hematite rich ironstones occur in the adjacent selwyn high strain zone integrated macro meso and microstructural analysis of rocks from both of these high strain zones and the surrounding country rocks reveals that they have undergone the same sequence of successive shallow and steeply oriented deformation events all of these rocks preserve evidence for four main ductile deformation events d 1 to d 4 d 1 d 2 and d 4 equate with regional d 1 d 2 and d 3 respectively as observed by workers in the mount isa region followed by two weaker events d 5 d 6 which exhibit both ductile and brittle character d 1 produced a shallowly dipping layer parallel foliation d 2 is the most pervasive event and produced upright tight to isoclinal f 2 folds with an intense steeply southeast dipping axial plane foliation s 2 trending northeast southwest d 3 rotated initially upright f 2 folds onto their western limb by top to the west shear and formed crenulations with shallowly dipping east west striking axial planes the fourth deformation event d 4 produced a steeply east dipping foliation s 4 which is similar in orientation to s 2 consequently differentiation of s 2 from s 4 is difficult except where s 2 was rotated by d 3 s 4 when observed is generally developed as a broad crenulation cleavage microstructural analysis of 115 spatially oriented thin sections from the vicinity of the starra orebodies demonstrates that the dominant fabric is a strongly differentiated composite s sub 2 4 foliation rather than simply s 2 as had been thought previously the starra and selwyn high strain zones resulted from a significant increase in strain during d 4 and preserve a predominant shear sense of west side up the western mineralized and eastern unmineralized ironstones resulted from intense iron metasomatism and were emplaced as en echelon north northeast striking lenses late syn post d 4 the rocks between the high strain zones young consistently eastward hence duplication of the ironstones by folding is precluded au cu mineralization within the starra orebodies was emplaced during and after iron metasomatism late syn to post d 4

volcanic and solar activity and atmospheric circulation influences on cosmogenic 10be fallout at vostok and concordia antarctica over the last 60years abstract the cosmogenic nuclide beryllium 10 10be recovered from ice cores is often used to study solar activity on long timescales however the 10be signal is also influenced by factors other than the sun to identify and quantify various contributions to the 10be signal two antarctic snow records from the vostok and concordia sites spanning the last 60 years were studied at a sub annual resolution three factors that contribute to the 10be signal were identified first a significant period of approximately 11 yr that can be associated with the modulation of 10be production by solar activity was detected in both records the solar imprint constitutes 20 35 of the variance within the total signal the 11 yr 10be snow component was attenuated by a factor of 0 5 and was delayed by 1 4 yr compared to the 10be production expected within the polar atmosphere the result could be interpreted as the composite response of a stratospheric 10be reservoir with an 11 yr modulation that was attenuated and delayed with respect to 10be polar production and to a tropospheric 10be reservoir with an 11 yr modulation that was not attenuated or delayed then peaks in 10be concentrations that were 66 and 35 higher than the average concentration were observed during the stratospheric volcanic eruptions of agung in 1963 and pinatubo in 1991 respectively in light of these new results published 10be ice core records could be reinterpreted because spikes in 10be concentration appear at the time of several stratospheric events the data indicate that stratospheric volcanic eruptions can impact 10be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds psc also an interannual variability of 4 yr was determined in both 10be records corresponding to 26 of the variance within the signal at vostok as with species of marine origin sodium this 4 yr variability is interpreted as a tropospheric modulation the 4 yr variability could be associated with atmospheric circulation associated with the coupled southern ocean ocean atmosphere system the results presented here from sites within the high antarctic plateau open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

structure of the alice anticline papua new guinea serial balanced cross sections and their restoration abstract the structure of the western part of the papuan fold belt is characterised by both thin skinned thrusting and basement involved structures basement involvement is attributed to inversion of earlier formed extensional faults the alice anticline is a frontal structure of the papuan fold belt and formed due to inversion of a tertiary extensional fault system complex forelimb geometry of the alice anticline changes markedly along strike and suggests varying amounts of shortening in this part of the structure balanced cross sections quantify differential shortening along the anticline whereas palinspastic restoration shows that the differential shortening is compatible between cross sections three dimensional restoration of the alice anticline makes use of a series of balanced cross sections and is based on a line length method paradoxically the restoration reveals non plane strain in the balanced cross sections upon which it relies however the restoration also reveals and quantifies a component of rotation about vertical axes which would not be detected by application of conventional methods of structural analysis rotations about vertical axes are attributed to pinning of progressive foreland propagating deformation the distribution of rotations about vertical axes suggest that zones of pinning are coincident with relay zones in the early extensional fault geometry two relay zones associated with the original geometry acted as obstructions to deformation and have effectively pinned contractional structures during their formation causing the rotations about vertical axes such rotations are not manifested in changing fold axis orientations and have only been derived from a consideration of material balance during deformation

interannual and intra annual variability of rainfall in haiti 1905 2005 the interannual variability of annual and monthly rainfall in haiti is examined from a database of 78 rain gauges in 1905 2005 the spatial coherence of annual rainfall is rather low which is partly due to haiti s rugged landscape complex shoreline and surrounding warm waters mean sea surface temperatures 27 c from may to december the interannual variation of monthly rainfall is mostly shaped by the intensity of the low level winds across the caribbean sea leading to a drier or wetter than average rainy season associated with easterly or westerly anomalies increasing or decreasing winds the varying speed of low level easterlies across the caribbean basin may reflect at least four different processes during the year 1 an anomalous trough ridge over the western edge of the azores high from december to february peaking in january 2 a zonal pressure gradient between eastern pacific and the tropical northern atlantic from may june to september with a peak in august i e lower than average rainfall in haiti is associated with positive sea level pressure anomalies over the tropical north atlantic and negative sea level pressure anomalies over the eastern pacific 3 a local ocean atmosphere coupling between the speed of the caribbean low level jet and the meridional sea surface temperature sst gradient across the caribbean basin i e colder than average sst in the southern caribbean sea is associated with increased easterlies and below average rainfall in haiti this coupling is triggered when the warmest caribbean waters move northward toward the gulf of mexico 4 in october november a drier or wetter than usual rainy season is related to an almost closed anticyclonic or cyclonic anomaly located ene of haiti on the sw edge of the azores high this suggests a main control of the interannual variations of rainfall by intensity track and or recurrence of tropical depressions traveling northeast of haiti during this period the teleconnection of haitian rainfall with synchronous atlantic and eastern pacific sst is at a minimum

atmospheric 10be in an antarctic soil implications for climate change 1 concentrations of 10be 9be and salt in a soil profile from the lower wright valley reveal two distinct climatic regimes in the upper horizon of the soil profile a thin gravel lag overlies the hart ash 3 9 0 3 ma and this sits on the surface of a well developed paleosol which makes up the lower horizon of the profile the surface lag has a smaller inventory of 10be than predicted from the fallout rate at nearby taylor dome below the gravel the hart ash is virtually devoid of 10be and the calculated erosion rate for the gravel ash horizon is 2 8 m ma 1 the paleosol which has been sealed by the overlying ash has a relatively high inventory of 10be and this gives it a significantly lower erosion rate 0 5 m ma 1 than the gravel ash horizon beryllium 10 migrates into a soil profile either by solution transport or by fine particle translocation the lack of 10be in the hart ash indicates that neither of these processes have been active at this site for the past 3 9 ma however enrichment of 10be in the paleosol indicates they were active prior to deposition of the ash the most likely reason these processes were active is that there was more water which could translocate fine particles with attached 10be thus the gravel ash horizon developed in climatic conditions similar to the present while the paleosol developed in wetter and possibly warmer conditions during the early pliocene and possibly before that time

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

the dependence of caribbean rainfall on the interaction of the tropical atlantic and pacific oceans abstract seasonally stratified analyses of rainfall anomalies over the intra americas sea and surrounding land areas and of onset and end dates of the central american rainy season show that the variability of the tropical atlantic sea surface temperature anomaly ssta is more strongly associated with rainfall over the caribbean and central america than is tropical eastern pacific ssta seasonal differences include the importance of antisymmetric configurations of tropical atlantic ssta in the dry season but not in the rainy season both oceans are related to rainfall but the strength of the rainfall response appears to depend on how ssta in the tropical atlantic and eastern pacific combine the strongest response occurs when the tropical atlantic is in the configuration of a meridional dipole antisymmetric across the itcz and the eastern tropical pacific is of opposite sign to the tropical north atlantic when the tropical north atlantic and tropical pacific are of the same sign the rainfall respons

application of geometric models to inverted listric fault systems in sandbox experiments paper 1 2d hanging wall deformation and section restoration abstract fault geometry is a primary control on hanging wall deformation in order to examine their geometrical relationships a positive inversion analogue experiment was conducted using a rigid fault surface of listric geometry the hanging wall deformation observed on a representative vertical section was examined with conventional 2d geometric models and was restored to its pre inversion phase with two techniques these results suggest that the deformation can be best approximated by inclined simple shearing iss the iss model can determine the inclination of the apparent shear plane and the amount of apparent horizontal shortening which is equivalent to that calculated with the conventional depth to detachment method this estimated apparent shortening was generally smaller than the actual amount of the experiments probably due to tectonic compaction

basin inversion and fault reactivation in laboratory experiments abstract a series of analogue models have been performed to get insights into the relationships between the reactivation of pre existing normal faults and the orientation of a successive compressive stress field the models were deformed in two phases 1 a first extension phase h 3 generating a graben and 2 a successive compressive phase with the orientation of the shortening direction h 1 trending between 0 and 90 obliquity angle to the faults bounding the graben the deepening of this graben was accompanied by syn tectonic sedimentation that included a basal ductile layer simulating salt in nature overlain by a brittle sand pack the experimental results suggest that the development of compressive structures is strongly controlled by the pre existing normal faults and by the obliquity angle the experiments have invariably shown that the extensional faults were reactivated during shortening whatever the value of the angle whereas strike slip reactivation of major normal faults is favoured by low obliquity angles mostly dip slip reactivation of pre existing structures is instead promoted for high obliquity angles the analysis of model results highlights the important role played by a ductile layer at the base of the basin fill and the obliquity angle in controlling both strain partitioning and brittle ductile decoupling

proterozoic extensional deformation in the mount isa inlier queensland australia the earliest of four distinct phases of deformation recognized in the central part of the proterozoic mount isa inlier involved brittle extensional faulting at shallow crustal levels extensional faulting produced stacks of imbricate fault slices listric normal faults and characteristic tourmalinerich breccias structures belonging to this phase occur over a large part of the inlier and indicate an important phase of basin forming crustal or lithospheric extension at 1750 1730 ma late intense ductile deformation and tight folding of the imbricate systems destroyed part of these older structures and obscures their existence in many parts of the inlier

the crustal scale architecture of the eastern succession mount isa the influence of inversion the three dimensional crustal architecture of the eastern part of the mount isa inlier is investigated from serial cross sections constructed using geological map data revised chronostratigraphy gravity magnetics worms multiscale wavelet edges of potential field data and seismic data the top part of the crust consists of rift and platform type metasediments that were deposited in three cover sequences from 1850 to 1610 ma these rocks constitute the mount isa eastern succession and they were intruded by mafic felsic plutons dykes and sills of various ages before and during the isan orogeny ca 1 6 1 5 ga the eastern succession overlies a felsic metamorphic basement which in turn sits on a tonalitic gabbroic lower crust the depositional basin architecture for the eastern succession was controlled by major n s trending structures that penetrated the lower crust and accommodated e w extension these structures also underlie major upper crustal structures such as the mitakoodi culmination and snake creek anticline that were formed by contraction in the isan orogeny positive inversion may therefore have been a key process in the evolution of the eastern part of the inlier and governs its architecture at the crustal scale inversion involved reactivation of basement penetrating structures which localised contractional structures in the cover sequences above as well as influencing pluton emplacement the felsic metamorphic basement may have been penetratively deformed during inversion the spatial association between the basin controlling and contractional structures suggests that either early extensional displacements were completely reversed by later contraction or that much of the eastern succession has remained essentially parauthochthonous relative to the basement

the midsummer drought over mexico and central america abstract the annual cycle of precipitation over the southern part of mexico and central america exhibits a bimodal distribution with maxima during june and september october and a relative minimum during july and august known as the midsummer drought msd the msd is not associated with the meridional migration of the intertropical convergence zone itcz and its double crossing over central america but rather with fluctuations in the intensity and location of the eastern pacific itcz during the transition from intense to weak weak to intense convective activity the trade winds over the caribbean strengthen weaken such acceleration in the trade winds is part of the dynamic response of the low level atmosphere to the magnitude of the convective forcing in the itcz the intensification of the trade winds during july and august and the orographic forcing of the mountains over most of central america result in maximum precipitation along the caribbean coast and minimum precipitation along the pacific

environmental patterns associated with active and inactive caribbean hurricane seasons this study of hurricanes passing through the caribbean in the 1950 2005 period reveals that seasons with more intense hurricanes occur with the onset of pacific la nina events and when atlantic ssts west of africa are above normal composites of ncep reanalysis fields with regard to caribbean hurricanes reveal de velopment of an anomalous equatorial atlantic zonal overturning circulation upper easterly lower westerly that shifts toward the caribbean coincident with a westward spread of the cold tongue in the east pacific ocean atmosphere coupling is promoted through interaction of the southern hadley cell and the atlantic itcz a heat budget analysis suggests that evaporation governs ssts in the major development region mdr and near venezuela but the signal is weak prior to may using the knowledge gained statistical algorithms are developed to predict caribbean hurricanes at seasonal lead times these make use of equa torial pacific sst subtropical atlantic sst and the zonal walker cell over the atlantic

evidence for early extensional tectonics in the proterozoic mount isa inlier australia in the proterozoic mount isa inlier queensland australia structures belonging to an early brittle deformation event are overprinted and strongly disturbed by a phase of ductile east west shortening many of these early structures have been attributed to thrusting but data from the southern part of the inlier provide new evidence for extensional faulting analysis of the internal geometry of imbricates can provide a tool for the reconstruction of these strongly reworked precambrian fault belts

a sediment based reconstruction of caribbean effective precipitation during the little ice age from freshwater pond barbuda contemporary climate dynamics of the circum caribbean region are characterised by significant precipitation variability on interannual and interdecadal timescales controlled primarily by el nino southern oscillation enso and the atlantic multidecadal oscillation amo however our understanding of pre industrial climate variability in the region is hampered by the sparse geographic distribution of palaeoclimate archives here we present a high resolution reconstruction of effective precipitation for barbuda since the mid 16th century based on biostratigraphic and stable isotope analyses of fossil ostracods and gastropods recovered from lake sediment cores from freshwater pond the only freshwater lake on the island we interpret episodic fluctuations in shell accumulation in the sediment record to represent changes in the balance between precipitation and evaporation during the little ice age lia 1400 1850 ce and industrial 1850 present periods comparisons between indices of reconstructed enso and amo variability the abundance of the freshwater gastropod pyrgophorus parvulus and the 18o records from ostracod calcite suggest that the relative influence of enso and amo on long term rainfall patterns in barbuda has changed over the last 400 years our findings are in agreement with other high resolution palaeoclimate studies that suggest that long term changes in effective precipitation during the lia were much more variable temporally and spatially than previously suggested