2 61 ga potassic granites and crustal reworking in the western dharwar craton southern india tectonic geochronologic and geochemical constraints abstract we present combined field structural data and spot image analysis petrographic data u pb zircon ages nd isotopes and whole rock geochemical data for the late archaean granite plutons from arsikere banavara ab suite and chitradurga jampalnaikankote hosdurga cjh suite in the western dharwar craton wdc ab plutons are syn kinematic with respect to the development of dome and basin patterns resulting from partial crustal diapiric overturn d1 whilst cjh suite plutons show deformation patterns resulting from the superimposition of large scale regional strike slip shearing d2 onto d1 syn emplacement fabrics sims u pb zircon ages of 2614 10 ma for the chitradurga pluton cjh and of 2617 3 ma for the arsikere pluton ab define the minimum age of the d1 strain pattern the cjh and ab suites are mainly high k granites whose origin is to be sought in partial melting of an old 3 0 ga depleted lower crust of intermediate composition the cjh and ab suites correspond mainly to the ca1 and ca2 types of archaean calc alkaline granites and some facies to the transitional ttg their heterogeneous chemical compositions indicate involvement of various sources and also significantly different depths of partial melting to produce these granites these results allow documenting regional partial reworking of the wdc 2615 ma ago requiring an ht event to have taken place before 2 61 ga and thus different from the 2 55 to 2 51 ga granulite facies metamorphic episode associated to regional scale strike slip shearing d2 that affected the entire craton partial reworking of the older lower crust at 2 61 ga and associated deformation would result from heat advection and or crustal thickening that may relate to voluminous mafic greenstone volcanism and moderate shortening at that time

coral ages and island subsidence hilo drill hole a 25 8 m thick sedimentary section containing coral fragments occurs directly below a surface lava flow the 1340 year old panaewa lava flow at the hilo drill hole ten coral samples from this section dated by accelerator mass spectrometry ams radiocarbon and five by thermal infrared multispectral scanner tims 230th u methods show good agreement the calcareous unit is 9790 years old at the bottom and 1690 years old at the top and was deposited in a shallow lagoon behind an actively growing reef this sedimentary unit is underlain by a 34 m thick lava flow which in turn overlies a thin volcaniclastic silt with coral fragments that yield a single 14c date of 10 340 years the age depth relations of the dated samples can be compared with proposed eustatic sea level curves after allowance for island subsidence is taken island subsidence averages 2 2 mm yr for the last 47 years based on measurements from a tide gage near the drill hole or 2 5 2 6 mm yr for the last 500 000 years based on the ages and depths of a series of drowned coral reefs offshore from west hawaii the age depth measurements of coral fragments are more consistent with eustatic sea levels as determined by coral dating at barbados and albrolhos islands than those based on oxygen isotopic data from deep sea cores the panaewa lava flow entered a lagoon underlain by coral debris and covered the drill site with 30 9 m of lava of which 11 m was above sea level this surface has now subsided to 4 2 m above sea level but it demonstrates how a modern lava flow entering hilo bay would not only change the coastline but could extensively modify the offshore shelf

displacement accumulation from earthquakes on isolated normal faults abstract displacement profiles for isolated normal faults are most often triangular rather than semi elliptical as predicted for linear elastic materials simple modelling indicates that triangular displacement profiles can arise from gutenberg richter earthquakes randomly distributed on fault surfaces of constant dimensions near triangular profiles are generated after a small number of earthquake cycles and for earthquake magnitude ranges as small as 0 5 the results are only weakly dependent on the shape of earthquake slip profiles and reproduce the geometry of displacement profiles on the non propagating active cape egmont fault in new zealand by contrast growth models in which fault displacement and length increase in proportion result in unrealistic displacement profiles for realistic slip profiles irrespective of whether earthquake populations are characteristic or gutenberg richter

archaean gold mineralization synchronous with late cratonization of the western dharwar craton india 2 52 ga u pb ages of hydrothermal monazite and xenotime in gold deposits new zircon u pb ages for a felsic volcanic rock 2 588 10 ma and an intrusive granite 2 555 6 ma in the gadag greenstone belt in the western dharwar craton southern india are similar to dates for equivalent rocks in the eastern dharwar craton and indicates docking of the two cratons prior to this time the zircons in the intrusive granite are strongly overprinted and coexisting titanites yielded two different age populations the dominant group gives an age of 2 566 7 ma interpreted as the emplacement age whereas the minor group gives an age of 2 516 10 ma reflecting a hydrothermal overprint in situ u pb dating of monazite and xenotime in gold reefs of the gadag 2 522 6 ma and ajjanahalli 2 520 9 ma gold deposits reveal a previously undated episode of gold mineralization at 2 52 ga substantially younger than the 2 55 ga hutti deposit in the eastern dharwar craton the new dates confirm that both the younger greenstone belts and lode gold mineralization in the dharwar craton are about 100 120 my younger than in other well dated archaean cratons although gold mineralization across the craton postdates most of the magmatic activity and metamorphism at upper crustal levels widespread thermal reworking of the lower middle crust involving partial melting metamorphism and lower crustal granitoid intrusion occurred concurrently with gold mineralization it is likely that the large scale hydrothermal fluid flow that produced widespread gold deposition was also part of this tectono thermal event during the final stages of cratonization of the dharwar craton in southern india

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

overpressure compartments in the central paleo uplift sichuan basin southwest china the sichuan basin is a prime gas producing basin in china besides the giant neoproterozoic weiyuan gas field discovered in the central paleo uplift an extra giant gas reservoir in the cambrian in this area has been confirmed in recent years although the lower paleozoic in the southwest weiyuan area is normally pressured it is overpressured in the central area moxi gaoshiti area combined with the seal distribution five pressure systems including three overpressure systems can be divided based on drill stem test mud weight and sonic transit time data overpressures appear at depth interval of 1500 to 4900 m 4921 to 16 076 ft approximately benefiting from the good sealing capacity of the gypsum in the upper and middle triassic high overpressure pressure coefficient r 2 0 has been preserved in the lower triassic and the upper triassic and cambrian are moderately overpressured 1 3 r 1 7 mechanisms for various overpressure systems are different abnormally high sonic transit time in the permian indicates disequilibrium compaction overpressure the analyses of sonic transit time effective stress suggest that disequilibrium compaction is the primary mechanism for the overpressure in the upper triassic xujiahe formation but the cambrian overpressure system is predominantly associated with fluid expansion which mainly resulted from gas generation furthermore we consider that the late thermal cracking of oil to gas is a key factor for gas and overpressure preservation in old strata the high overpressure in the lower triassic marine carbonate rocks was caused by oil cracking and gypsum dehydration mechanisms combining the origin analysis with the burial and hydrocarbon generation histories we constructed the cambrian pore pressure evolution model which is characterized by roughly normal pressure before 200 ma overpressuring from 200 to 90 ma and overpressure releasing since 90 ma

the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data abstract a new inverse technique is presented here to separate stresses from heterogeneous fault slip data without a priori information on the stresses or on the classification of faults according to the stresses four parameters are determined by the inversion one for the shape of the stress ellipsoid and three for the direction of the stress axes accordingly the inversion is equivalent to the projection of the fault slip data to a point in four dimensional parameter space the data are divided into k element subsets to which the inverse technique is applied where k 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation significant solutions are identified as clusters in parameter space the technique is demonstrated first by simulated fault slip data as an example field data obtained from miocene fore arc sediments in western japan were processed by the method

evolution of fabric in chitradurga granite south india a study based on microstructure anisotropy of magnetic susceptibility ams and vorticity analysis abstract in this paper the fabric in massive granite 2 6 ga from the chitradurga region western dharwar craton south india is analyzed using microstructure anisotropy of magnetic susceptibility ams study and kinematic vorticity analysis the microstructural investigation on the granite shows a progressive textural overprint from magmatic through high t to low t solid state deformation textures the mean magnetic foliation in the rocks of the region is dominantly nw se striking which have developed during regional d1 d2 deformation on account of ne sw shortening the plunge of the magnetic lineation varies from nw to vertical to se and interpreted to be a consequence of regional d3 deformation on account of nw se to e w shortening the vorticity analysis from magnetic fabric in the region reveals that the nw se oriented fabric formed under pure shear condition during d1 d2 regional deformation however some parts of the region particularly close to the adjacent chitradurga shear zone show that the magnetic fabrics are oblique to the foliation as well as shear zone orientation and inferred to be controlled by simple shearing during d3 regional deformation the shape preferred orientation spo analysis from oriented thin sections suggest that the shape of the recrystallized quartz grains define the magnetic fabric in chitradurga granite and the degree of the spo reduces away from the chitradurga shear zone it is interpreted that the change in magnetic fabrics in some parts of the granite in the region are dominantly controlled by the late stage sinistral shearing which occurred during the development of chitradurga shear zone

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

origin of ultramafic xenoliths containing exsolved pyroxenes from hualalai volcano hawaii hualalai volcano hawaii is best known for the abundant and varied xenoliths included in the historic 1800 kaupulehu alkalic basalt flow xenoliths which range in composition from dunite to anorthosite are concentrated at 915 m elevation in the flow rare cumulate ultramafic xenoliths which include websterite olivine websterite wehrlite and clinopyroxenite display complex pyroxene exsolution textures that indicate slow cooling websterite olivine websterite and one wehrlite are spinel bearing orthopyroxene olivine cumulates with intercumulus clinopyroxene plagioclase two wehrlite samples and clinopyroxenite are spinel bearing olivine cumulates with intercumulus clinopyroxene orthopyroxene plagioclase two pyroxene geothermometry calculations based on reconstructed pyroxene compositions indicate that crystallization temperatures range from 1225 to 1350 c migration or unmixing of clinopyroxene and orthopyroxene stopped between 1045 and 1090 c comparisons of the abundance of k2o in plagioclase and the abundances of tio2 and fe2o3in spinel of xenoliths and mid ocean ridge basalt and a single 87sr 86sr determination indicate that these hualalai xenoliths are unrelated to mid ocean ridge basalt similarity between the crystallization sequence of these xenoliths and the experimental crystallization sequence of a hawaiian olivine tholeiite suggest that the parental magma of the xenoliths is hualalai tholeiitic basalt xenoliths probably crystallized between about 4 5 and 9 kb the 155 230 c of cooling which took place over about 120 ka the age of the youngest hualalai tholeiitic basalt yield maximum cooling rates of 1 3 10 3 1 91 10 3 c yr hualalai ultramafic xenoliths with exsolved pyroxenes crystallized from hualalai tholeiitic basalt and accumulated in a magma reservoir located between 13 and 28 km below sealevel we suspect that this reservoir occurs just below the base of the oceanic crust at about 19 km below sealevel

improvements in procedure and paleointensity selection criteria picrit 03 for thellier and thellier determinations application to hawaiian basaltic long cores abstract in this paper we first describe the paleointensity furnaces and the procedures specifically designed to minimize oxidation of the samples during thellier and thellier paleointensity experiments routinely used at gif we also propose some improvements to the set of criteria commonly used to select the results of the thellier experiments in order to further increase the reliability of paleointensity determination finally to be included in databases the new set of paleointensity criteria picrit 03 paleointensity criteria in 2003 is discussed and the results obtained from two long hawaiian basaltic cores the scientific observation hole 4 soh 4 and the hawaiian scientific drilling project 1 hsdp1 are used to illustrate its effectiveness some of the results are re evaluated and a new composite record of absolute paleointensity and inclination spanning 420 kyr is presented the inclination values obtained from the two cores combined support the hypothesis of persistent shallow inclinations at hawaii in intensity the upper 100 kyr are covered by the data from soh 4 with 309 reliable determinations out of 766 examined obtained from 143 units which belong to the kilauea volcano at the top of this core the 341 reliable data covering the 100 420 kyr interval are from 149 units of core hsdp1 belonging to the mauna kea volcano the interval 320 to 420 kyr is particularly detailed because of high extrusion rate of the volcano the use of more stringent criteria decreases the number of determinations considered as reliable in previous publications but it improves their accuracy and robustness

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

kinematic and dynamic fault slip analyses implications from the surface rupture of the 1999 chi chi taiwan earthquake the 1999 chi chi earthquake created a 100 km long surface rupture on the chelungpu thrust fault in taiwan due to convergence between the phillipine sea and eurasian plates fault slip measurements were made by several researchers from the entire length of the rupture directly following the earthquake and can thus be attributed to a single tectonic event conventional fault slip analyses are applied to these data and the results are compared with independent seismological and kinematic observations unlike many fault slip analyses complications due to multiple deformations can be categorically excluded and the results can be evaluated from the seismological and plate movement data kinematic analyses of fault slip data that are weighted by displacement show sub horizontal nw se shortening that is parallel to the plate convergence vector a single fault plane solution satisfies almost all the data right dihedra and trihedra solutions also satisfy almost all the surface rupture measurements and give 1 in a nw se orientation that is similar to the results of stress inversion and to inversion from earthquakes in the chi chi earthquake sequence despite criticisms of fault slip analysis methods these results show that fault slip analyses from data collected along major faults which have not witnessed multiple deformation events can be valid homogeneous strain and stress states exist in the sense that kinematic and dynamic solutions can be found that fit essentially all the data and these solutions have tectonic significance

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

morphology and evolution of drowned carbonate terraces during the last two interglacial cycles off hilo ne hawaii abstract the eastern side of hawaii island is a rapidly subsiding margin dominated by drowned carbonate platforms we present detailed bathymetric and backscatter data remotely operated vehicle and submersible observations sedimentological and 14c accelerator mass spectrometry and u th age data from seven submerged terraces h7 h2a d h1a b in water depths between 1100 and 25 m off hilo north eastern hawaii the main carbonate deposits on these terraces are coral deposits rhodolith beds coralline algal mounds crusts pavements and tabular sheets we identified five previously described sedimentary shallow to deep water facies and one new facies type that are consistent with reef drowning on a rapidly subsiding margin we used palaeobathymetric data derived from the sedimentary facies age versus depth relationships and published sea level curves to estimate a uniform long term subsidence rate of 2 80 0 36 m ky for the eastern side of hawaii over the last 150 ky terrace h7 developed about 380 ka based on data from the western side of the island active coral growth on terrace h2d occurred during the marine isotope stage mis 6 to 5 transition and the terrace drowned during the peak of mis 5e when sea level rose faster than reefs could grow favoured by the gentle platform gradient reefs established progressively landwards with a backstepping pattern during mis 5e to form the terraces h2c and h2b 122 ka final turn off of shallow water carbonate production on terraces h2b d coincided with the relative sea level rise of the interstadial mis 5a bathymetry and submersible data suggest that carbonate sediments on terraces h2a and h1b were deposited over an antecedent topography of local lava deltas emplaced during rising sea levels at ca 85 and 65 ka while terrace h1a established on lava delta substrates of the mauna loa volcano ca 11 ka we conclude that the initiation growth and drowning of coral reef terraces off hilo differ in some ways from the pattern observed in the submerged terraces in the western side of hawaii and that the platform evolution off hilo is more strongly influenced by emplacement of offshore lava flows

tectonic significance of fault slip data abstract the statistical analysis of populations of minor faults is commonly used by structural geologists working in areas of brittle rock it is based on measurements of fault attitude direction and sense of slip at individual sampling localities results are classically interpreted as indicators of stress or strain rate fields assuming a homogeneous stress or strain rate tensor respectively however fault patterns are expected to vary with time because of displacements rigid rotations and internal strains which generally occur along boundaries of fault bounded blocks as deformation proceeds thus in the general situation where early faults accumulate displacements and rigid rotations and where new faults develop during progressive deformation fault slip data can be rather complex and variable in space and reflect neither local stress or strain rate tensors nor finite strains and finite rotations in a simple way we use two examples of faulted regions to illustrate the spatial variability of fault slip data this can be due to local complications at the edges of fault blocks or to complex kinematic conditions at regional boundaries such complications may make it difficult to deduce a consistent and simple pattern of either stresses or strain rates instead our results suggest that information contained in fault slip data can be pertinent to finite deformation in particular the principal axes that we have deduced from the analysis of fault slip data are consistent with the finite displacements at block boundaries that we have calculated by numerical restoration

quaternary glacial interglacial climate cycles in hawaii abstract the upper kilometer of the hawaiian scientific drilling program core consists of lavas that were emplaced subaerially burying paleosols these paleosols were preserved with minimal alteration and are used to construct a 330 kyr quaternary climate record within the temporal resolution of this record there appears to be a 100 kyr climate oscillation between cool dry and warm wet conditions indicating that tropical regions such as hawaii have responded to the same global climate forcings as have higher latitude areas during at least the past three glacial interglacial cycles it is also suggested that hawaiian climate may have become progressively warmer and wetter over the same period

piggyback tectonics long term growth of kilauea on the south flank of mauna loa abstract compositional and age data from offshore pillow lavas and volcaniclastic sediments along with on land geologic seismic and deformation data provide broad perspectives on the early growth of kilauea volcano and the long term geometric evolution of its rift zones sulfur rich glass rinds on pillow lavas and volcaniclastic sediments derived from them document early underwater growth of a large compositionally diverse alkalic edifice the alkalic rocks yield 40ar 39ar ages as old as about 275 ka transitional composition lavas which mark beginning of the shield stage while most or all the edifice remained below sea level probably first erupted after about 150 ka and tholeiitic lavas of present day type are probably younger than 100 ka breccia clasts from papau seamount and along the lower southwest corner of the hilina bench are derived from subaerial mauna loa requiring that mauna loa s flank underlies western parts of kilauea at shallow depth the volume of the kilauea edifice is therefore smaller 10 000 km3 than previous estimates 15 40 000 km3 lava thickness accumulation rates appear to have remained nearly constant during edifice growth as effusion rates increased from 25 106 m3 yr at end of the alkalic stage to the present day tholeiite rate of 100 106 m3 yr seismic and gravity data show that the deep plumbing system for kilauea s magma supply extends nearly vertically through the oceanic crust at least to mantle depths of 30 35 km directly below its present day caldera proximity of kilauea s caldera to the surface boundary with mauna loa and the presence of mauna loa rocks at shallow depth beneath the south flank are difficult to reconcile with a submarine origin for early kilauea alkalic lavas unless geometric relations between the two volcanoes have changed substantially during growth of the kilauea shield seismic and ground deformation data suggest seaward spreading of the entire south flank of hawaii island independently of the boundary between kilauea and mauna loa along a landward dipping detachment fault system near the basal contact of the composite volcanic edifices with underlying oceanic crust current steady state horizontal displacements increase seaward at rates of 1 5 cm yr on the lower flank of mauna loa and reaching 5 8 cm yr at the kilauea coastline infrequent 100 yr large earthquakes generate similar geometries but 102 larger displacements per event present day kilauea is the more dynamic edifice but prior to inception of kilauea and during its early growth mauna loa is inferred to have undergone intense volcano spreading involving the kaoiki honuapo fault system considered a geometric analog of the hilina system on kilauea cumulative deformation of mauna loa s south flank during growth of kilauea since 200 300 ka is estimated to have involved 10 km of seaward spreading displacing the rift zones of k lauea while its deep plumbing system and summit magma reservoir remained nearly fixed in space kilauea s rift zones rather than migrating southward with time solely due to dike emplacement preferentially on the mobile seaward side alternatively are interpreted to have been transported passively southward piggyback style during shield stage growth of kilauea as a blister on the still mobile south flank of mauna loa such an evolution of kilauea accounts for the arcuate geometry of the present day rift zones proximity of the summit magma supply to the exposed flank of mauna loa initial submarine growth of the ancestral edifice and present day location of mauna loa rocks at shallow depth beneath the south flank of kilauea

origin of xenoliths in the trachyte at puu waawaa hualalai volcano hawaii rare dunite and 2 pyroxene gabbro xenoliths occur in banded trachyte at puu waawaa on hualalai volcano hawaii mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir subsequently the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite compositions by decreasing their mg numbers in addition olivine lost cao and plagioclase lost mgo and fe2o3 during subsolidus reequilibration the xenoliths also reacted with the host trachyte to form secondary mica amphibole and orthopyroxene and to further modify the compositions of some olivine clinopyroxene and spinel grains the reaction products indicate that the host trachyte melt was hydrous clinopyroxene in one dunite sample and olivine in most dunite samples have undergone partial melting apparently in response to addition of water to the xenolith these xenoliths do not contain co2 fluid inclusions so common in xenoliths from other localities on hualalai which suggests that co2 was introduced from alkalic basalt magma between the time co2 inclusion free xenoliths erupted at 106 6 ka and the time co2 inclusion rich xenoliths erupted within the last 15 ka

hydrogeology of the hawaii scientific drilling project borehole kp 1 2 groundwater geochemistry and regional flow patterns a series of downhole and surface water samples were taken from the i km deep kp 1 borehole located on the eastern flank of the island of hawaii early samples from depths of more than 700 m showed salinities nearly equivalent to seawater but having anomalous cation concentrations that are attributed to ion exchange between formation fluids and residual drilling mud clays later deep samples found only minor variations from seawater cation chemistry that are consistent with low temperature weathering of basalts delta 18 o values are equivalent to seawater values and are consistent with this interpretation carbon 14 activities of dissolved inorganic carbonate indicate a water age ranging from 5890 to 7170 years b p and fluid transport rates of 1 8 to 2 2 m yr fluid samples from perforations at 310 m in the borehole demonstrate that a freshwater aquifer is present at the mauna kea mauna loa interface borehole resistivity logs indicate that it is similar to 200 m thick although it ha s not yet been possible to obtain samples of the freshwater zone without contamination from the deep saline fluids the chloride concentrations of the low salinity zone are estimated using a mixing enthalpy calculation to be less than 100 mg l light stable isotope data indicatemore that the fresh water at 320 m is derived from recharge entering the island at an average elevation of 2000 m inferred c 14 activities of the dissolved bicarbonate in the freshwater zone indicate an average calibrated age of 2200 years b p and an average fluid velocity of at least 14 m yr a regional water flow model is proposed that suggests that the fresh water found at the 320 m depth is derived from rainfall recharge from the middle elevations of mauna kea volcano this rainfall is channeled beneath the mauna loa lavas by the thick soil layer separating the two volcanoes a second shallow fresh to brackish water zone derived from mauna loa recharge is also inferred to exist below the carbonate formation that underlies the shallow basal lens the results of our preliminary study of the groundwater system below the kp 1 drill site demonstrate that intervolcano and interflow aquicludes can have a substantial impact on water circulation and discharge from young island volcanoes less

preliminary determinations of geomagnetic field intensity for the last 400 kyr from the hawaii scientific drilling project core big island hawaii preliminary paleointensity determinations using the thelliers method have been carried out on 141 samples of core hsdp hawaii scientific drilling project drilled into the mauna loa and mauna kea volcanoes and spanning the last 400 kyr rock magnetic investigations identify pseudo single domain magnetite as the main carrier of the natural remanent magnetization nrm all along the core in the mauna kea sequence 75 of the specimens yielded exploitable results with linear nrm trm thermoremanent magnetization plots and positive partial trm ptrm checks generally up to the highest temperatures 550 c a lower percentage of successful experiments 50 was observed for the mauna loa samples and the nrm trm diagrams are linear over a shorter temperature interval than for the mauna kea samples these preliminary results based on only one sample per flow document a marked geomagnetic field intensity low at about 40 kyr probably related to the laschamp event they also suggest that the geomagnetic field at hawaii might be characterized by large sharp intensity fluctuations spaced by a few thousand years the average value of the field intensity suggested by these results for the last 400 000 years is slightly higher than the present field at hawaii

origin and depositional environment of clastic deposits in the hilo drill hole hawaii volcaniclastic units cored at depths of about 87 164 178 226 and 246 m below sea level and carbonate units located between depths of 27 and 53 m below sea level in the hilo drill core were found to be deposited at or near sea level four of these units are hydroclastic deposits formed when subaerially erupted mauna loa lava flows entered the ocean and fragmented to produce quenched glassy fragments during hydrovolcanic explosions ash units 24 and 26 at 178 m depth accumulated at sea level in a freshwater bog they contain pyroxenes crystallized from tholeiitic magma that we infer erupted explosively at the summit of kilauea volcano two carbon rich layers from these ashes have a weighted average radiocarbon age of 38 6 0 9 ka the ashes probably correlate with the oldest and thickest part of the pahala ash ash unit 44 at the transition from mauna kea to mauna loa lava flows was probably nearly 3 2 m thick and is inferred to be equivalent to the lower thick part of the composite homelani ash mapped in hilo and on the flanks of mauna kea the age of this part of homelani ash is between 128 33 and 200 10 ka it may have erupted subglacially during the pohakuloa glacial maxima on mauna kea beach sand units 12 and 22 were derived from nearby mauna loa and mauna kea lava flows the middle of beach sand unit 38 was derived mainly from lava erupted near the distal end of the subaerial east rift zone of kilauea volcano these sands were transported about 33 km northwest to hilo bay by prevailing longshore currents combined age depth and sea level markers in the core allow us to determine that lava flow recurrence intervals averaged one flow every 4 kyr during the past 86 kyr and one flow every 16 kyr between 86 and 200 ka at the drill site and that major explosive eruptions that deposit thick ash in hilo have occurred only twice in the last 400 kyr these recurrence intervals support the moderate lava flow hazard zonation zone 3 for coastal hilo previously determined from surficial mapping

paleostress field reconstruction in the western dharwar craton south india evidence from brittle faults and associated structures of younger granites abstract we present new fault slip data to decipher the tectonic stress regime in younger granites 2 61 ga of western dharwar craton wdc south india the study is based on paleostress reconstruction of the terrain using fault slip data from the small scale oblique slip normal faults of chitradurga granite paleostress analysis using right dihedron and rotational optimization methods reveal that these faults have developed under nne ssw directed extension similar results are also obtained when left lateral and right lateral oblique slip normal faults are treated as separate entities it is envisaged that all faults in chitradurga granite have developed under a single tectonic event and are considered to be extensional shear fractures we interpret that the oblique slip normal faults in granite oriented along nnw sse to n s p shear nw se r shear ne sw r shear and wnw ese t are defined as the respective shear components of the regional riedel shear system it developed due to sinistral movement along the chitradurga shear zone csz during late d3 deformation at shallow crustal level the fault planes act as primary or secondary shear planes depending on their proximity to the csz and kinematically fit well with regional far field compression the present study addresses the formation of oblique slip normal faults in the chitradurga granite and its implication in reconstructing the paleostress field in the precambrian south indian shield

geomagnetic field inclinations for the past 400 kyr from the 1 km core of the hawaii scientific drilling project a volcanic record of geomagnetic field inclination for the past 400 kyr at hilo hawaii has been obtained from the 941 5 m of core recovered by the hawaii scientific drilling project the analysis of 195 lava flows reveals six instances of near zero inclination and two instances of fully negative inclination reverse polarity within an otherwise normal polarity core in particular flow unit 23 178 m depth records a horizontal inclination and may be associated with the laschamp event flow units 40 and 42 260 m depth record negative inclinations and are close in age to the blake event and flow unit 55 320 m depth records a negative inclination with a relative declination change of 75 with respect to the overlying flow and is probably the jamaica biwa i pringle falls event the five instances of shallow inclination found below 400 m depth appear to have resulted from long term secular variation as they are part of inclination swings between 0 and 60 with a periodicity of 10 50 kyr in contrast the inclination shifts at 178 m and 320 m depths significantly deviate from long term trends suggesting the existence of at least two independent processes producing time variations of the geomagnetic field the secular variation has a mean of 30 9 95 2 27 which is significantly shallower than the expected dipole mean of 36 the dispersion 12 5 agrees with global paleosecular variation data for 0 5 ma and secular variation models

fault development and interaction in distributed strike slip shear zones an experimental approach analogue model experiments using both brittle and viscous materials were performed to investigate the development and interaction of strike slip faults in zones of distributed shear deformation at low strain bulk dextral shear deformation of an initial rectangular model is dominantly accommodated by left stepping en echelon strike slip faults riedel shears r that form in response to the regional bulk stress field push up zones form in the area of interaction between adjacent left stepping riedel shears in cross sections faults bounding push up zones have an arcuate shape or merge at depth adjacent left stepping r shears merge by sideways propagation or link by short synthetic shears that strike subparallel to the bulk shear direction coalescence of en echelon r shears results in major through going faults zones master faults several parallel master faults develop due to the distributed nature of deformation spacing between master faults is related to the thickness of the brittle layers overlying the basal viscous layer master faults control to a large extent the subsequent fault pattern with increasing strain relatively short antithetic and synthetic faults develop mostly between old but still active master faults the orientation and evolution of the new faults indicate local modifications of the stress field in experiments lacking lateral borders closely spaced parallel antithetic faults cross faults define blocks that undergo clockwise rotation about a vertical axis with continuing deformation fault development and fault interaction at different stages of shear strain in our models show similarities with natural examples that have undergone distributed shear

palaeostress analysis of normal faults in granite implications for interpreting riedel shearing related to regional deformation in this study field data from mesoscopic scale brittle structures faults are used to decipher palaeostress and relate it to regional scale kinematics fault slip data from oblique slip normal faults in granite mulgund west dharwar craton southern india are analysed in three steps 1 determination of palaeostress direction using fault slip data 2 kinematic interpretation of fault data 3 fitting the kinematic model to the regional far field stress palaeostress analysis of two sets of faults left lateral and right lateral oblique slip normal faults reveals that both formed under the same compression direction ene wsw it is shown that inferring the faults to be r p r and x shears of a riedel shear system explains their kinematic evolution within the granite the riedel shears developed as a result of sinistral movement along the 305 oriented contact between the granite and the surrounding gneisses riedel shear kinematics is interpreted as being a consequence of deformation partitioning which was favoured by the rheological contrast between the above lithologies during the late stage of a third phase of deformation under 315 135 directed s hmax far field stress

the 40ar 39ar and k ar dating of lavas from the hilo 1 km core hole hawaii scientific drilling project mauna kea lava flows cored in the hilo hole range in age from 200 ka to about 400 ka based on 40ar 39ar incremental heating and k ar analyses of 16 groundmass samples and one coexisting plagioclase the lavas all subaerially deposited include a lower section consisting only of tholeiitic basalts and an upper section of interbedded alkalic transitional tholeiitic and tholeiitic basalts the lower section has yielded predominantly complex discordant 40ar 39ar age spectra that result from mobility of 40ar and perhaps k the presence of excess 40ar and redistribution of 39ar by recoil comparison of k ar ages with 40ar 39ar integrated ages indicates that some of these samples have also lost 39ar nevertheless two plateau ages of 391 40 and 400 26 ka from deep in the hole combined with data from the upper section show that the tholeiitic section accumulated at an average rate of about 7 to 8 m kyr and has a mean recurrence interval of 0 5 kyr flow unit samples from the upper section yield relatively precise 40ar 39ar plateau and isotope correlation ages of 326 23 241 5 232 4 and 199 9 ka for depths of 415 7 m to 299 2 m within their uncertainty these ages define a linear relationship with depth with an average accumulation rate of 0 9 m kyr and an average recurrence interval of 4 8 kyr flow unit the top of the mauna kea sequence at 280 m must be older than the plateau age of 132 32 ka obtained for the basal mauna loa flow in the corehole the upward decrease in lava accumulation rate is a consequence of the decreasing magma supply available to mauna kea as it rode the pacific plate away from its magma source the hawaiian mantle plume the age depth relation in the core hole may be used to test and refine models that relate the growth of mauna kea to the thermal and compositional structure of the mantle plume

argon geochronology of kilauea s early submarine history submarine alkalic and transitional basalts collected by submersible along kilauea volcano s south flank represent early eruptive products from earth s most active volcano strongly alkalic basalt fragments sampled from volcaniclastic deposits below the mid slope hilina bench yield 40 ar 39 ar ages from 212 38 to 280 20 ka these ages are similar to high precision 234 9 and 239 10 ka phlogopite ages from nephelinite clasts in the same deposits above the mid slope bench two intact alkalic to transitional pillow lava sequences protrude through the younger sediment apron samples collected from a weakly alkalic basalt section yield 138 30 to 166 26 ka ages and others from a transitional basalt section yield 138 115 and 228 114 ka ages the ages are incompatible with previous unspiked k ar studies from samples in deep drill holes along the east rift of kilauea the submarine birth of kilauea volcano is estimated at 300 ka if the weakly alkalic sequence we dated is representative of the volcano as a whole the transition from alkalic to tholeiitic basalt compositions is dated at 150 ka

pseudotachylyte bearing strike slip duplex structures in the fort foster brittle zone s maine abstract detailed 1 60 scale mapping of the fort foster brittle zone in the mylonitic rye formation of southernmost maine has revealed the intricate internal duplex structure of a system of probable paleozoic age dextral strike slip faults that have produced abundant pseudotachylyte and minor breccia the internal configuration of this brittle zone consists of a mosaic of individual pseudotachylyte generation zones as slab duplex structures individual duplex zones are up to 100 m in length and 1 m or less in width and are defined by pairs of layer parallel slip surfaces along which frictional melts were produced these slab duplex structures are interpreted as zones of displacement transfer between long overlapping layer parallel en echelon strike slip fault surfaces contractional duplexes develop layer parallel compressional structures that tend to shorten and thicken the fault bounded slabs by the formation of lateral ramps and conjugate faults kinks and asymmetric folds extensional duplexes develop layer parallel stretching and thinning by the formation of oblique dextral shears high angle conjugate pairs and localized fault breccias the production of pseudotachylyte by friction melting along layer parallel fault surfaces in these exposures is attributed to rapid slip during paleoseismic events the rupture structures developed during these events may be characteristic of fault structure and mechanics at near focal depths in a strike slip seismogenic zone

mauna loa lava accumulation rates at the hilo drill site formation of lava deltas during a period of declining overall volcanic growth accumulation rates for lava flows erupted from mauna loa as sampled in the uppermost 280 m of the hilo drill hole vary widely for short time intervals several thousand years but overall are broadly similar to those documented elsewhere on this volcano since 100 ka thickness variations and accumulation rates for mauna loa lavas at the hilo drill site have been strongly affected by local paleotopography including funneling and ponding between mauna kea and kilauea in addition gentle submerged slopes of mauna kea in hilo bay have permitted large shoreline displacements by mauna loa flows ages of eruptive intervals have been determined from published isotopic data and from eustatic sea level curves modified to include the isostatic subsidence of the island of hawaii at 2 2 2 6 mm yr prior to 10 ka rates of mauna loa lava accumulation at the drill site varied from 0 6 to 4 3 mm yr for dateable intervals with an overall rate of 1 8 mm yr major eruptive pulses at about 1 3 and 10 ka each probably representing a single long lived eruption based on lack of weathering between flow units increase the overall accumulation rate to 2 4 mm yr the higher rate since 10 ka reflects construction of thick near shoreline lava deltas as postglacial sea levels rose rapidly large lava deltas form only along coastal segments where initially subaerial slopes have been submerged by the combined effects of eustatic sea level rise isostatic subsidence or spreading of volcano flanks overall accumulation of 239 m of lava at the drill site since 100 120 ka closely balances submergence of the hilo area suggesting that processes of coastal lava deposition have been modulated by rise in sea level the hilo accumulation rate is slightly higher than average rates of 1 2 mm yr determined elsewhere along the mauna loa coast based on rates of shoreline coverage and dated sea cliff and fault scarp exposures low rates of coastal lava accumulation since 100 ka near or below the rate of island wide isostatic subsidence indicate that mauna loa is no longer growing vigorously or even maintaining its size above sea level

geomagnetic field intensity at hawaii for the last 420 kyr from the hawaii scientific drilling project core big island hawaii four hundred twenty five new paleointensity thellier thellier determinations out of 545 analyzed samples have been obtained from core hsdp which penetrates about 1000 meters 208 flows of the mauna loa and mauna kea volcanic series encompassing the last 420 kyr rock magnetic investigations identify pseudo single domain magnetite as the main magnetic mineral inclinations are shallower than expected from a geocentric dipole field but are consistent with data from other geographical regions at the same latitude the inclination record reveals three episodes of negative inclination whose interpolated age correlates well with that of known geomagnetic events the paleointensity record from the mauna loa sequence is not very detailed and does not allow precise comparison with other data in the 0 50 kyr interval the record from the mauna kea sequence on the contrary is very detailed and documents relatively short lived episodes of low and high field strength from 15 to 60 t the average virtual dipole moment 8 7 3 0 10 22 a m 2 is not significantly different from the value reported by kono and tanaka 1995 for the last 2 5 myr a comparison with other data from hawaii and other geographical regions is described in detail there are no drastic changes in paleointensity with the inclination anomaly in agreement with previous results from hawaii but in contrast with most published results which however consider data from polarity transition spectral analysis of a particularly detailed portion of the record between 420 and 326 kyr documents significant periodicities at 36 8 5 and 4 ka in the inclination record but not in the intensity record suggesting that changes in time of the inclination are to a certain extent independent from those of the intensity

facies distributions and structure of a dharwar volcanosedimentary basin evidence for late archaean transpression in southern india the bababudan nallur basin c 60 km 125 km is part of a series of late archaean basins accommodating volcanic and sedimentary rocks of the dharwar supergroup within the low grade terrain of the province of karnataka initial development of the bababudan nallur basin was characterized by rapid subsidence with eruption of mainly basaltic lavas breaks in eruption were marked in some instances by thin but persistent deposits of shallow marine quartz sands and muds subsidence in the south continued with accumulation of banded ferruginous cherts and muds whilst uplift of the volcanic pile took place in the north this uplift promoted erosion of the volcanic cover and its basement gneisses and granodiorites with deposition of alluvial and shallow marine fans and debris flows adjacent to the uplifted blocks the fans passed laterally into intertidal and offshore quartz sands greywackes and muds with interbedded dolomitic limestones accumulation of rhyolites banded ferruginous cherts and greywackes took place further north the structure of the basin is dominated by mainly upright folds and faults with the trend of the folds broadly parallel to the boundaries of exposed blocks of basement the basement deformed cataclastically on myriad fractures in contrast with the ductile behaviour of the cover many cover basement contacts are faults with mylonites although unconformities are preserved especially in the south the facies distributions and structure of bababudan nallur and other dharwar belts have characteristics in common with mixed mode basins developed as a consequence of strike or oblique slip on long lived fault zones these relations suggest that transcurrent plate interactions comparable with those of the phanerozoic were significant in the late archaean evolution of southern india

displacement gradients on fault surfaces abstract the maximum displacements and the dimensions of single faults are systematically related and the variation in displacement from a maximum at the centre of a fault to zero at an elliptical tip line loop is described by a simple theoretically derived expression these relationships are used to examine the theoretical ranges and distributions of rates of change of displacement on fault surfaces the dimensions and maximum displacement of a fault can be estimated from a limited number of displacement gradient measurements estimates are further constrained by a knowledge of the effective shear modulus of the rocks containing a fault an understanding of displacement gradients can be applied to problems commonly encountered in mining operations and in the interpretation and use of seismic reflection data in addition to field problems a comparison of theoretical displacement gradients with measured displacement gradients from british coalfield faults shows that i fault surface ellipticities are between 1 5 and 2 5 and ii gross displacement gradients expressed as the ratio of maximum displacement long axis radius of the fault ellipse range from 0 02 to 0 002 the measured displacement gradients indicate that the shear moduli of the faulted rocks range from 3 to 11 gpa which is within the known range for coal measure rocks displacement gradients along an array of fault segments are similar to those of single faults for analysis of displacement gradients it is necessary to sum the discontinuous and continuous components of displacement in extreme cases all the displacement may be accommodated by continuous deformation

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

african stress pattern from formal inversion of focal mechanism data abstract the kinematic models and the associated orientation of extensional stress of the east african rift system have been subjected to much debate since a long time in the past decades the proposed models relied on the interpretation of the overall rift geometry geological fault slip data and the few focal mechanisms available these models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space in the recent years there has been a significant increase in the number of focal mechanisms available for the entire rift system and it is now possible to estimate the present day stress field in relative detail based on seismotectonic data alone we compile 347 focal mechanism data from the global harvard cmt catalogue and various other sources and grouped 332 of them in 24 distinct regions boxes on the basis of their geographical proximity kinematic homogeneity and tectonic setting for each box and for the same data set reduced stress tensors have been obtained by formal stress inversion using both the tensor program delvaux sperner 2003 and the slick method michael 1984 1987 both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes which stem for the robustness of the approach the obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces including plate boundary forces and 2nd and 3rd order effects as gravitational potential of topography intra lithospheric processes and the influence of structural heterogeneities of the rift structures the evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns

the dharwar craton southern india interpreted as the result of late archaean oblique convergence abstract the dharwar craton comprises two distinct parts separated by a steep n s sinistral shear zone in the western part a pre 2900 ma complex of orthogneisses granodiorites and narrow tracts of supracrustal rocks sargur group forms the basement to volcanic and sedimentary basins of the dharwar supergroup ca 2800 2550 ma late archaean deformation is characterised by ne sw crustal shortening and steep n s sinistral shear zones the eastern part is underlain by parallel steep n s or nw se linear belts of calc alkaline anatectic and juvenile granites and granodiorites dharwar batholith ca 2750 2510 ma with intervening volcanic and sedimentary schist belts ca 2800 2550 ma the plutonic belts are 15 25 km wide up to 150 km long and bounded by steep nw se high strain zones up to 2 km wide with sinistral shear sense except one which is dextral magmatic state fabrics and structures in the plutonic rocks are parallel to solid state sinistral shear fabrics in the high strain zones but diffuse magmatic banding is commonly oblique to these zones and coincides with the plane of instantaneous shortening in sinistral shear magmatic state structures swarms of vertical nw se dykes of granite and the vertical wedge shape of the linear belts are consistent with emplacement of the batholith during sinistral shear when magma pressure exceeded regional horizontal compressive stress upright folds and schistosity steep reverse faults and effects of regional ht lp metamorphism show that deformation was partitioned into ne sw shortening in the schist belts during emplacement of the plutonic belts in the sinistral shear regime the western part of the craton is interpreted as the foreland to an accretionary arc represented by the batholith and schist belts intra arc basins in the east ne sw shortening and sinistral transcurrent displacements in the foreland and arc are consistent with arc normal and arc parallel displacements during oblique convergence analogous to mesozoic cenozoic convergent settings

use of the block punch test to predict the compressive and tensile strengths of rocks this study aimed to explore the applicability of the block punch test in estimating uniaxial compressive and brazilian tensile strengths of granite schist and sandstone from india it was experimentally shown that when predicting uniaxial compressive strength of rocks the block punch test is as useful as the point load test efficacy of the existing empirical equations for predicting uniaxial compressive strength by the block punch index was also evaluated prediction of brazilian tensile strength by block punch index appears to be more precise than by the point load strength performances of the existing strength anisotropy transformation factors in the literature in order to normalize the block punch index in the direction perpendicular to foliations were assessed based on the results of the tests performed on the schistose rocks

fabric analysis in rocks of the gadag region southern india implications for time relationship between regional deformation and gold mineralization abstract in this paper the fabric in archaean age massive metabasalts and granite from the gadag region western dharwar craton southern india are identified using the anisotropy of magnetic susceptibility ams the magnetic foliation in the rocks is dominantly nw se striking this is inferred to have developed during regional d1 d2 deformation known to have affected the region which was on account of ne sw shortening the plunge of the magnetic lineation varies from nw to se this doubly plunging orientation is inferred to be a consequence of superimposition of nw se shortening d3 deformation over the earlier structure that is known to have resulted in dome basin geometry in the surrounding metapelitic rocks of the region thus it is concluded that the massive rocks preserve evidence of superposed deformation that affected the region which can be deciphered from the orientation of magnetic fabric data the gadag region comprises lode gold deposit 2500 ma in age and field investigations show that the quartz veins are dilational with dominantly nw se strike orientation the veins are inferred to have formed by dilation under nw se shortening during d3 it is envisaged that the nw se oriented fabric that formed in the metabasalt during d1 d2 channelized fluid flow thus leading to vein emplacement during d3 it is concluded that gold deposition in the veins took place during d3 which is related to the final stages of cratonization of the dharwar craton at 2500 ma

geodynamic significance of the trm segment in the east african rift w tanzania active tectonics and paleostress in the ufipa plateau and rukwa basin abstract the tanganyika rukwa malawi trm rift segment in western tanzania is a key sector for understanding the opening dynamics of the east african rift system ears in an oblique opening model it is considered as a dextral transfer fault zone that accommodates the general opening of the ears in an nw se direction in an orthogonal opening model it accommodates pure dip slip normal faulting with extension orthogonal to the rift segments and a general e w extension for the entire ears the central part of the trm rift segment is well exposed in the ufipa plateau and rukwa basin within the paleoproterozoic ubende belt it is also one of the most seismically active regions of the ears we investigated the active tectonic architecture and paleostress evolution of the ufipa plateau and adjacent rukwa basin and in order to define their geodynamic role in the development of the ears and highlight their pre rift brittle tectonic history the active fault architecture fault kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the trm segment two pre rift brittle events are evidenced an older brittle thrusting is related to the interaction between the bangweulu block and the tanzanian craton during the late pan african early paleozoic it was followed by a transpressional inversion during the early mesozoic this inversion stage is the best expressed in the field and caused dextral strike slip faulting along the fault systems that now control the major rift structures it has been erroneously interpreted as related to the late cenozoic ears which instead is characterized by pure normal faulting our third and last stress stage

coastal lava flows from mauna loa and hualalai volcanoes kona hawaii a major carbonate reef which drowned 13 ka is now submerged 150 m below sea level on the west coast of the island of hawaii a 25 km span of this reef was investigated using the submersiblemakali i the reef occurs on the flanks of two active volcanoes mauna loa and hualalai and the lavas from both volcanoes both underlie and overlie the submerged reef most of the basaltic lava flows that crossed the reef did so when the water was much shallower and when they had to flow a shorter distance from shoreline to reef face lava flows on top of the reef have protected it from erosion and solution and now occur at seaward projecting salients on the reef face these relations suggest that the reef has retreated shoreward as much as 50 m since it formed a 7 km wide shadow zone occurs where no hualalai lava flows cross the reef south of kailua these lava flows were probably diverted around a large summit cone complex a similar shadow zone on the flank of mauna loa volcano in the kealakekua bay region is downslope from the present mauna loa caldera which ponds mauna loa lava and prevents it from reaching the coastline south of the mauna loa shadow zone the 150 m reef has been totally covered and obscured by mauna loa lava the boundary between hualalai and mauna loa lava on land occurs over a 6 km wide zone whereas flows crossing the 150 m reef show a sharper boundary offshore from the north side of the subaerial transition zone this indicates that since the formation of the reef hualalai lava has migrated south mantling mauna loa lava more recently mauna loa lava is again encroaching north on hualalai lava

plate margin paleostress variations and intracontinental deformations in the evolution of the cuddapah basin through proterozoic abstract the sedimentary basins are often influenced by adjoining mobile belts as is the case of the proterozoic cuddapah basin in southern india lying in proximity of the eastern ghats granulite belt egb and the southern granulite terrain sgt two major faults gani kalva and kona faults in the western part of the cuddapah basin have been examined in this work to comment on the changes in paleostress conditions affecting the basin evolution punctuated by several stages of extensional and compressional regimes in the time interval 1 9 0 5 ga the tensor solutions were obtained for the mesoscale faults and fault striae using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 combining the paleostress field reconstruction and other structural stratigraphic attributes we propose a possible scenario of punctuated evolution of the cuddapah basin and its inversion the stress regimes are tentatively correlated with multiple stages of basin opening and deformation of basin in fill representing the pre grenvillian through the pan african orogeny the paleostress conditions derived from various stratigraphic horizons provide an opportunity to comment on the changes in tectonic stresses including several stages of extensional and compressive regimes in the cuddapah basin the tensor solutions were obtained for the mesoscale faults and fault striae in the neighborhood of above two fault lines using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 the most prominent stress states recorded around the two fault lines can be classified into those affecting 1 the paleoproterozoic lower cuddapah successions 2 the younger kurnool group and 3 both the groups integrating the stress states of the fault slip analysis obtained from different unconformity bounded rock groups of lower cuddapah and other geologic data we suggest extensional to transtensive pure strike slip regime to be active during the first phase of basin opening and c 1 89 ga mafic igneous activity late compressional to transpressive pure strike slip regimes are well recorded from the younger kurnool group representing late neoproterozoic deformations the tensor solutions from different unconformity bound stratigraphic horizons constrain different states of deformation we relate the extensional to transtensive pure strike slip regimes from lower cuddapah successions to the ongoing basin opening events and the associated palaeoproterozoic igneous activities the late neoproterozoic to early paleozoic compressional to transpressive strike slip regime present the possible effects of compressional activities happening around the cratonic margin the present analysis lends further support to the idea that estimation of paleostress states from fault slip data even in regions of relatively weak deformation in continental interior are important while assessing influence of plate margin stresses on the continental interior

hawaiian xenolith populations magma supply rates and development of magma chambers hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types magma supply rates and xenolith populations magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage these magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained during the earliest and latest stages no magma storage zone exists and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava during the tholeiitic second stage magma storage reservoirs develop and persist both at the base of the ocean crust and 3 7 km below the caldera only xenoliths of shallow origin are carried to the surface by differentiated lava during the alkalic third stage magma in the shallow subcaldera reservoir solidifies and crustal xenoliths including oceanic crustal rocks are carried to the surface in lava that fractionates in an intermediate depth reservoir worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs

the dharwar craton and the assembly of peninsular india peninsular india can be separated into five discrete crustal areas the bhandara singhbhum and aravalli bundelkhand cratons the eastern ghats and a block in southern india containing the dharwar craton and adjoining granulite terrain these areas are separated by four major joins eastern ghats front godavari rift mahanadi rift sukinda thrust and narmada son lineament and associated thrusts all joins except the godavari rift are former orogenic belts where thrusts juxtapose rocks of different metamorphic grade these thrusts and the absence of clear correlation of suites among different cratons suggest that the indian shield formed by accretion of separate continental fragments epicontinental late archean early pro terozoic sediments throughout india however may indicate that the joins are intracontinental formed within a coherent block the term dravidian shield is used for the southernmost of the five crustal blocks including all of india south of the deccan basalts and godavari rift

stratigraphic constraints on the timing and emplacement of the alika 2 giant hawaiian submarine landslide abstract previous work has found evidence for giant tsunami waves that impacted the coasts of lanai molokai and other southern hawaiian islands tentatively dated at 100 and 200 ka by u series methods on uplifted coral clasts seafloor imaging and related work off hawaii island has suggested the alika phase 2 debris avalanche as the source of the 100 ka giant wave deposits although its precise age has been elusive more recently a basaltic sand bed in odp site 842 300 km west of hawaii estimated at 100 20 ka has been suggested to correlate with this or another large hawaiian landslide our approach to the timing and linkage of giant submarine landslides and paleo tsunami deposits is a detailed stratigraphic survey of pelagic deposits proximal to the landslide feature beginning with a suite of seven piston gravity and box cores collected in the vicinity of the alika 2 slide we used u series dating techniques including excess 230 th and 210 pb profiling high resolution paleomagnetic stratigraphy including continuous u channel analysis 18 o stratigraphy visual and x ray sediment lithology and the petrology and geochemistry of the included turbidites and ash layers minimum ages for the alika phase 2a slide from detailed investigation of two of the cores are 112 15 ka and 125 24 ka 2 based on excess 230 th dating a less precise age for the alika phase 1 and or south kona slide is 242 80 ka 2 consistent with previous geological estimates oxygen isotope analyses of entrained planktonic foraminifera better constrain the alika phase 2a maximum age at 127 5 ka which corresponds to the beginning of the stage 5e interglacial period it is proposed that triggering of these giant landslides may be related to climate change when wetter periods increase the possibility of groundwater intrusion and consequent phreatomagmatic eruptions of shallow magma chambers our study indicates the contemporaneity of the alika giant submarine landslides and distal deposits from enormous turbidity currents as well as coral clasts reported to be tsunami deposits on lanai and molokai through direct dating and compositional analysis of the landslide deposits

3 d mohr circle construction using vein orientation data from gadag southern india implications to recognize fluid pressure fluctuation abstract in this paper orientations of quartz veins from the archaean age lode gold bearing region of gadag southern india are used to determine the relative stress and fluid pressure p f conditions by constructing 3 d mohr circle anisotropy of magnetic susceptibility ams analysis of the host massive metabasalt reveals that the magnetic foliation is nw se striking which is related to early ne sw compression d1 d2 deformation that affected the region the quartz veins have a wide range of orientations with nw se striking veins steep northeasterly dips being the most prominent vein emplacement is inferred to have taken place under nw se compression that is known to have caused late deformation d3 in the region it is argued that the nw se fabric defined the pre existing anisotropy and channelized fluid flow during d3 the permeability was initially low which resulted in high p f 2 3 d mohr circle analysis indicates that the driving pressure ratio r was 0 94 a condition that favoured fracturing and reactivation of fabric elements foliations and fractures having a wide range of orientations this led to an increase in permeability and fluid flowed burped into the fractures resulting vein emplacement and sealing of fractures led to a reduction of p f 2 it is argued that at this low p f nw se oriented structures continued to remain susceptible to reactivation and vein emplacement while fractures of all other orientations were inactive and remained sealed as a consequence the study area has a cluster of nw se oriented veins r is calculated to be 0 07 from 3 d mohr circle analysis at low p f when fractures with nw se orientation only were susceptible to dilation however it is envisaged that any emplacement of veins in these fractures would have sealed them thus reducing the permeability and initiating the next cycle of rise in p f 2 thus it is concluded that the quartz veins in the gadag region are a consequence of an interplay between conditions that fluctuated from p f 2 to p f 2

neoarchean greenstone volcanism and continental growth dharwar craton southern india constraints from sims u pb zircon geochronology and nd isotopes abstract we present sims u pb zircon ages and nd isotope data for the felsic volcanic rocks from seven neoarchean greenstone belts of the eastern dharwar craton edc and from the chitradurga greenstone belt in the western dharwar craton wdc zircon ages show bimodal age distribution of felsic volcanism the ca 2 70 2 65 ga felsic volcanic event is contemporaneous with 2 7 ga mafic greenstone volcanism and emplacement of juvenile tonalitic to granodioritic crust while 2 58 2 54 ga felsic volcanics are coeval and spatially and probably genetically in some cases linked to the major episode calc alkaline magmatic accretion in the edc the chitradurga and veligallu greenstone belts host felsic volcanics of the first generation the latter showing inheritance at ca 2 95 ga four of the five greenstone belts hosting the second generation of felsic volcanics chitradurga kolar kadiri hutti show crustal inheritance at ca 2 6 2 7 2 9 3 0 3 1 and 3 3 ga ndt indicate derivation of the felsic volcanics from juvenile sources or short lived crustal sources with minor influence of older crust the new and existing data are consistent with two stage growth of the dharwar craton in the neoarchean first stage accretion led to the growth of a 2 7 2 6 ga juvenile crustal province of mafic volcanics and felsic plutons along the eastern margin of the wdc second stage accretion 2 58 2 52 ga led to the emplacement of ttg and calc alkaline plutons and felsic volcanics throughout the eastern dharwar craton an active margin context could apply for the two stage accretion scenario considering a west dipping subducting slab beneath the craton in the framework of long lived ultra hot accretionary orogen but the great width of influence of magmatic accretion and or reworking particularly during the second stage would suggest large scale mantle flow reorganization that would have generated large plume s

40ar 39ar geochronology of submarine mauna loa volcano hawaii 1 new geochronologic constraints refine the growth history of mauna loa volcano and enhance interpretations of the petrologic geochemical and isotopic evolution of hawaiian magmatism we report results of 40ar 39ar incremental heating experiments on low k tholeiitic lavas from the 1 6 km high kahuku landslide scarp cutting mauna loa s submarine southwest rift zone and from lavas in a deeper section of the rift obtaining precise40ar 39ar ages from young tholeiitic lavas containing only 0 2 0 3 wt k2o is challenging due to their extremely low radiogenic 40ar contents analyses of groundmass from 45 lavas yield 14 new age determinations 31 success rate with plateau and isochron ages that agree with stratigraphic constraints lavas collected from a 1250 m thick section in the landslide scarp headwall were all erupted around 470 10 ka implying an extraordinary period of accumulation of 25 mm yr possibly correlating with the peak of the shield building stage this rate is three times higher than the estimated vertical lava accumulation rate for shield building at mauna kea 8 6 3 1 mm yr based on results from the hawaii scientific drilling project between 470 and 273 ka the lava accumulation rate along the southwest rift zone decreased dramatically to 1 mm yr we propose that the marked reduction in lava accumulation rate does not mark the onset of post shield volcanism as previously suggested but rather indicates the upward migration of the magma system as mauna loa evolved from a submarine stage of growth to one that is predominantly subaerial thereby cutting off supply to the distal rift zone prior to 250 ka lavas with loihi like isotopic signatures were erupted along with lavas having typical mauna loa values implying greater heterogeneity in the plume source earlier in mauna loa s growth in addition to refining accumulation rates and the isotopic evolution of the lavas erupted along the southwest rift zone our new40ar 39ar results constrain the eruption of the ninole basalts from 227 to 108 ka and provide maximum estimates on the timing of the ka lae and south kona landslides

the petrology of some picrites from mauna loa and kilauea volcanoes hawaii the mineralogy and chemistry of picrites from mauna loa and kilauea have been investigated to evaluate for hawaiian tholeiitic picrites the contrasting genetic models which have been proposed for these mg rich volcanics namely products of direct crystallization of high mg melts 20 25 mgo or the result of accumulation of olivine phenocrysts into less mg rich melts genetic interpretations rely heavily on mg fe partitioning relations between olivines and their picrite hosts although the 100 mg mg fe2 ratios m of picrites are wide ranging m 73 6 82 9 for fe2o3 feo 0 15 with mgo as high as 27 8 the average 100 mg mg fe ratios mg of the cores of olivine phenocrysts megacrysts show only restricted compositional variation mg 87 2 89 0 successive olivine generations are progressively more fe rich olivine liquid mg fe partitioning data and the mn and ni abundances in olivine phenocrysts collectively indicate that they were precipitated by mg rich basaltic melts with 12 14 mgo spinel compositions range from liquidus magnesiochromites occurring mainly as inclusions in olivine phenocrysts to groundmass titanomagnetites which crystallized at nearsolidus temperatures the cr2o3 contents and m values of liquidus magnesiochromites suggest that their parent melts were neither mg rich picritic mgo 20 nor relatively mg poor basaltic types