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Sample records for kaapvaal craton seismic

  1. Diamond genesis, seismic structure, and evolution of the Kaapvaal-Zimbabwe craton.

    Science.gov (United States)

    Shirey, Steven B; Harris, Jeffrey W; Richardson, Stephen H; Fouch, Matthew J; James, David E; Cartigny, Pierre; Deines, Peter; Viljoen, Fanus

    2002-09-06

    The lithospheric mantle beneath the Kaapvaal-Zimbabwe craton of southern Africa shows variations in seismic P-wave velocity at depths within the diamond stability field that correlate with differences in the composition of diamonds and their syngenetic inclusions. Middle Archean mantle depletion events initiated craton keel formation and early harzburgitic diamond formation. Late Archean accretionary events involving an oceanic lithosphere component stabilized the craton and contributed a younger Archean generation of eclogitic diamonds. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the Archean diamond suite.

  2. Compositional trends among Kaapvaal Craton garnet peridotite xenoliths and their effects on seismic velocity and density

    DEFF Research Database (Denmark)

    Schutt, Derek; Lesher, Charles

    2010-01-01

    garnet and clinopyroxene enrichment. Using the parameterization of Schutt and Lesher (2006) we show that at cratonic mantle temperatures and pressures, orthopyroxene enrichment results in little change in bulk density (ρbulk) and shear-wave velocity (VS), but decreases compressional wave velocities (VP...... and clinopyroxene enrichment possibly as a consequence of melt infiltration. More than half of the mineral mode variance among Kaapvaal Craton xenoliths can be accounted for by opx enrichment. Melt depletion effects can account for as much as 30% of the variance, while less than 20% of the variance is associated......) and VP/VS. In contrast, melt depletion has little effect on VP, but leads to an increase in VS and a decrease in ρbulk and VP/VS. Garnet (gt) and clinopyroxene (cpx) enrichment cause an increase in ρbulk, VP, VS, and VP/VS. The isolation of the major contributions to xenolith compositional variations...

  3. Metasomatic control of water contents in the Kaapvaal cratonic mantle

    Science.gov (United States)

    Peslier, A. H.; Woodland, A. B.; Bell, D. R.; Lazarov, M.; Lapen, T. J.

    2012-11-01

    Water and trace element contents were measured by FTIR and laser ablation-ICPMS on minerals from peridotite xenoliths in kimberlites of the Kaapvaal craton from Finsch, Kimberley, Jagersfontein (South Africa), Letseng-La-Terae, and Liqhobong (Lesotho) mines. The peridotites record a wide range of pressure, temperature, oxygen fugacity, and metasomatic events. Correlations between water content or OH vibration bands with major, minor and trace elements in pyroxene and garnet precludes disturbance during xenolith entrainment by the host kimberlite magma and indicate preservation of mantle water contents. Clinopyroxene water contents (150-400 ppm H2O, by weight) correlate with those of orthopyroxene (40-250 ppm). Olivines (Peslier et al., 2008, 2010) and garnets have 0-86 and 0-20 ppm H2O, respectively. Relations in individual xenolith suites between the amount of water and that of incompatible elements Ti, Na, Fe3+ and rare earths in minerals suggests that metasomatism by oxidizing melts controls the water content of olivine, pyroxene and garnet. At pressures ⩽5.5 GPa, hydrous, alkaline, siliceous fluids or melts metasomatized Liqhobong and Kimberley peridotites, producing high water contents in their olivine, pyroxenes and garnet. At higher pressures, the percolation of ultramafic melts reacting with peridotite resulted in co-variation of Ca, Ti and water at the edge of garnets at Jagersfontein, and the overall crystallization of garnet with lower water contents than those in the original peridotites. The upward migration of these ultramafic melts through the lithospheric mantle also increased the water content of olivines with decreasing pressure at Finsch Mine. H2O/Ce ratios of melts in equilibrium with Kaapvaal peridotites range from 100 to 20,000 and the larger values may indicate metasomatism in subduction zone settings. Metasomatic events in Kaapvaal peridotites are thought to have occurred from the Archean to the Mesozoic. However, circumstantial evidence

  4. Paleomagnetism of the early Paleoproterozoic, volcanic Hekpoort Formation (Transvaal Supergroup) of the Kaapvaal craton, South Africa

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    Humbert, F.; Sonnette, L.; de Kock, M. O.; Robion, P.; Horng, C. S.; Cousture, A.; Wabo, H.

    2017-02-01

    The Kaapvaal craton (South Africa) was the host of several major magmatic events during the Paleoproterozoic, including the volcanic Hekpoort and Ongeluk formations. Their possible comagmatic origin is the subject of a long debate. We performed a paleomagnetic study of the Hekpoort Formation to get a primary pole can be compared with the available paleopole of the Ongeluk Formation, but also to contribute to the apparent pole wander path of the Kaapvaal craton. Characterization of magnetic mineralogy by 3-axis thermal demagnetization of IRM and magnetic susceptibility vs temperature points out magnetite as the main remanence carrier in most samples.

  5. Palaeointensity determinations on rocks from Palaeoproterozoic dykes from the Kaapvaal Craton (South Africa)

    Science.gov (United States)

    Shcherbakova, V. V.; Shcherbakov, V. P.; Zhidkov, G. V.; Lubnina, N. V.

    2014-06-01

    Palaeointensity study of the Proterozoic-Archean volcanic rocks from the Kaapvaal Craton South Africa) are reported. Palaeomagnetic study of this collection was performed earlier by Olsson et al. Electron microscope observations, thermomagnetic and hysteresis measurements indicate the presence of single-domain and pseudo-single-domain (SD-PSD) magnetite grains as the main magnetic mineral. The samples demonstrated a very good stability to heating, the electron micrograph observations revealed magnetite-ilmenite exsolution structure. Palaeointensity determinations were obtained by Coe-modified Thellier procedure. A total 58 samples from 14 sites were studied but only seven samples from one site NL28 of the Early Proterozoic age of 1.9 Ga passed palaeointensity selection criteria. Reliable palaeointensity determinations were obtained by both Thellier and Wilson methods on 18 cubes (subsamples) from site NL28 yielding rather low mean virtual dipole moment (VDM) = (2.82 ± 0.12) ×1022 Am2 which is in agreement with the suggestion of existence of the `Proterozoic dipole low period'.

  6. Palaeointensity and palaeodirection determinations of Paleoproterozoic dykes in the Kaapvaal Craton (South Africa)

    Science.gov (United States)

    Shcherbakova, V. V.; Lubnina, N. V.; Shcherbakov, V. P.; Zhidkov, G. V.

    2012-04-01

    A combined palaeodirectional and palaeointensity study of a representative collection from the Bushveld Igneous Complex from 27 dolerite dykes from the 2.9, 2.7, and 1.8 Ga age swarms radiating SE, E and NE, respectively [Olsson et al., 2010] was carried out. Conventional progressive thermal or AF demagnetization was applied to all specimens. The palaeomagnetic directions have been calculated after thermal demagnetization. The ChRMs were isolated over the temperature interval 440-590 C and their intensities amount to 95% of total NRMs. Paleopole calculate from the primary high-temperature component, separated in the 2.9 Ga SE-dykes, is close to the paleopoles, obtained by Wingate (1998) and Strik et al. (2007) for 2.78 Ga volcanics. The paleopole calculated for the 2.7 Ga age E-trending dykes of the eastern region does not correspond to any of the previously obtained Archean-Paleoproterozoic paleopoles for the Kaapvaal Craton. The paleopole calculated for some NE-trending dykes of the Black Ridge swarm in the NE region is close to the 1.87 Ga pole of the Kaapvaal Craton obtained by Hanson et al. (2004). Palaeointensity determinations were carried out on rocks from ten dykes of different ages using Thellier-Coe method with the "check-points" procedure on specimens of 1 cm in edge length cut from either drilled cores or hand samples. Rock magnetic measurements were made on sister specimens. Curie temperatures and the thermal stability of magnetic minerals were estimated from thermomagnetic heating-cooling cycles to incrementally higher temperatures Ti with a Curie balance in an external magnetic field H = 0.45 T. To assess the magnetic hardness and mineralogy of samples, measurements of magnetic susceptibility and hysteresis loop parameters were performed. The domain structure (DS) was estimated also from the thermomagnetic criterion by evaluating the tails of pTRMs. Wilson's method of palaeointensity determination based on comparison of thermodemagnetization curves

  7. Seismic Structure of Southern African Cratons

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Artemieva, Irina; Levander, Alan

    2014-01-01

    Cratons are extremely stable continental crustal areas above thick depleted lithosphere. These regions have remained largely unchanged for more than 2.5 Ga. This study presents a new seismic model of the seismic structure of the crust and lithospheric mantle constrained by seismic receiver...... functions and finite-frequency tomography based on data from the South Africa Seismic Experiment (SASE). Combining the two methods provides high vertical and lateral resolution. The main results obtained are (1) the presence of a highly heterogeneous crustal structure, in terms of thickness, composition (as...

  8. Seismic imaging of Southern African cratons

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad

    Cratonic regions are the oldest stable parts of continents that hold most of Earth’s mineral resources. There are several open questions regarding their formation and evolution. In this PhD study, passive source seismic methods have been used to investigate the crustal and lithosphere structures...

  9. Petrochemical evolution of the White Mfolozi Granite pluton: Evidence for a late Palaeoarchaean A-type granite from the SE Kaapvaal Craton, South Africa

    Science.gov (United States)

    Misra, Saumitra; Reinhardt, Jürgen; Wilson, Allan H.

    2017-08-01

    One of the major limitations in understanding the geochemical evolution of the Kaapvaal Craton, South Africa, is the scarcity of whole rock trace element data of the granitoid and other rocks compared to the vastness of this cratonic block. Here we present new XRF major oxide and ICP-MS trace element analyses of the White Mfolozi Granitoid (WMG) pluton, SE Kaapvaal Craton, which suggest that the 3.25 Ga (U-Pb zircon age) old WMG pluton is a peraluminous A-type granite and could be equivalent to the intrusive potassic granite phase of the Anhalt Granitoid suite, occurring to the North of the WMG pluton. The pluton was generated by batch partial melting of a pre-existing TTG source in two major phases under relatively anhydrous conditions, and the heat of partial melting could have been provided by a voluminous mantle-derived mafic magma, which intruded into mid-crustal levels (c. 17 km), perhaps during a period of crustal extension. The estimated pressure and temperature of generation of the WMG parent magma with average molar [or/(or + ab)] 0.48 could be 500 MPa and close to 1000 °C, respectively, when compared with the results of experimental petrology. Interstitial occurrence of relatively iron-rich biotite [Mg/(Mg + Fe) 0.41-0.45] suggests that the final temperature of crystallization of the pluton was close to 800 °C. An important magmatic event following the main phase of partial melting was limited mixing between the intrusive mafic magma and co-existing newly generated granitic melt. This magma mixing resulted in distinct variations in SiO2 and a low initial Sr isotopic ratio (0.7013) of the WMG pluton. Although both the models of partial melting of quartzo-feldspathic sources and fractional crystallization of basaltic magmas with or without crustal assimilation have been proposed for the origin of A-type granites, the model of magmatic evolution of the WMG pluton presented here can also be an alternative model for the generation of A-type granites. In

  10. EVOLUTION OF SOUTHERN AFRICAN CRATONS BASED ON SEISMIC IMAGING

    DEFF Research Database (Denmark)

    Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina

    2014-01-01

    present a new seismic model for the structure of the crust and lithospheric mantle of the Kalahari Craton, constrained by seismic receiver functions and finite-frequency tomography based on the seismological data from the South Africa Seismic Experiment (SASE). The combination of these two methods...

  11. The extent of the Cratonic keel underneath the Southern African region: A 3D image using Finite-Frequency Tomograph

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Bezada, Max; Thybo, Hans;

    2010-01-01

    We have re-examined the P body wave data from the South Africa Seismic Experiment (Carlson et al, EOS 77, 1996) across the Kaapvaal and Zimbabwe cratons and the Bushveld complex. Using finite-frequency kernels, we inverted the P-wave delay times to obtain 3-D images of compressional velocity...... between the Archean and modified regions such as the Bushveld complex, and the mobile belts surrounding the cratons. The high velocity (+1.0%) cratonic roots extend to 220-250 km depth beneath the Kaapvaal and Zimbabwe cratons. Lower P-velocities are found under the Bushveld complex and the mobile belts...

  12. Effects of low-pressure igneous processes and subduction on Fe3+/ΣFe and redox state of mantle eclogites from Lace (Kaapvaal craton)

    Science.gov (United States)

    Aulbach, S.; Woodland, A. B.; Vasilyev, P.; Galvez, M. E.; Viljoen, K. S.

    2017-09-01

    Reconstructing the redox state of the mantle is critical in discussing the evolution of atmospheric composition through time. Kimberlite-borne mantle eclogite xenoliths, commonly interpreted as representing former oceanic crust, may record the chemical and physical state of Archaean and Proterozoic convecting mantle sources that generated their magmatic protoliths. However, their message is generally obscured by a range of primary (igneous differentiation) and secondary processes (seawater alteration, metamorphism, metasomatism). Here, we report the Fe3+/ΣFe ratio and δ18 O in garnet from in a suite of well-characterised mantle eclogite and pyroxenite xenoliths hosted in the Lace kimberlite (Kaapvaal craton), which originated as ca. 3 Ga-old ocean floor. Fe3+/ΣFe in garnet (0.01 to 0.063, median 0.02; n = 16) shows a negative correlation with jadeite content in clinopyroxene, suggesting increased partitioning of Fe3+ into clinopyroxene in the presence of monovalent cations with which it can form coupled substitutions. Jadeite-corrected Fe3+/ΣFe in garnet shows a broad negative trend with Eu*, consistent with incompatible behaviour of Fe3+ during olivine-plagioclase accumulation in the protoliths. This trend is partially obscured by increasing Fe3+ partitioning into garnet along a conductive cratonic geotherm. In contrast, NMORB-normalised Nd/Yb - a proxy of partial melt loss from subducting oceanic crust (1) - shows no obvious correlation with Fe3+/ΣFe, nor does garnet δ18OVSMOW (5.14 to 6.21‰) point to significant seawater alteration. Median bulk-rock Fe3+/ΣFe is roughly estimated at 0.025. This observation agrees with V/Sc systematics, which collectively point to a reduced Archaean convecting mantle source to the igneous protoliths of these eclogites compared to the modern MORB source. Oxygen fugacites (fO2) relative to the fayalite-magnetite-quartz buffer (FMQ) range from Δlog ⁡ fO2 = FMQ-1.3 to FMQ-4.6. At those reducing conditions, the solubility

  13. Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

    Science.gov (United States)

    Petrescu, Laura; Darbyshire, Fiona; Bastow, Ian; Totten, Eoghan; Gilligan, Amy

    2017-05-01

    The thick, seismically fast lithospheric keels underlying continental cores (cratons) are thought to have formed in the Precambrian and resisted subsequent tectonic destruction. A consensus is emerging from a variety of disciplines that keels are vertically stratified, but the processes that led to their development remain uncertain. Eastern Canada is a natural laboratory to study Precambrian lithospheric formation and evolution. It comprises the largest Archean craton in the world, the Superior Craton, surrounded by multiple Proterozoic orogenic belts. To investigate its lithospheric structure, we construct a frequency-dependent anisotropic seismic model of the region using Rayleigh waves from teleseismic earthquakes recorded at broadband seismic stations across eastern Canada. The joint interpretation of phase velocity heterogeneity and azimuthal anisotropy patterns reveals a seismically fast and anisotropically complex Superior Craton. The upper lithosphere records fossilized Archean tectonic deformation: anisotropic patterns align with the orientation of the main tectonic boundaries at periods ≤110 s. This implies that cratonic blocks were strong enough to sustain plate-scale deformation during collision at 2.5 Ga. Cratonic lithosphere with fossil anisotropy partially extends beneath adjacent Proterozoic belts. At periods sensitive to the lower lithosphere, we detect fast, more homogenous, and weakly anisotropic material, documenting postassembly lithospheric growth, possibly in a slow or stagnant convection regime. A heterogeneous, anisotropic transitional zone may also be present at the base of the keel. The detection of multiple lithospheric fabrics at different periods with distinct tectonic origins supports growing evidence that cratonization processes may be episodic and are not exclusively an Archean phenomenon.

  14. Evolution of the South African mantle — A case study of garnet peridotites from the Finsch diamond mine (Kaapvaal craton); part 1: Inter-mineral trace element and isotopic equilibrium

    Science.gov (United States)

    Lazarov, Marina; Brey, Gerhard P.; Weyer, Stefan

    2012-12-01

    A thorough assessment of inter-mineral equilibrium is essential for the understanding of trace element partitioning and also for the interpretation of isotopic data. Here we investigated high temperature (~ 1200 °C and 6 GPa) garnet peridotite xenoliths from the Kaapvaal craton (Finsch mine, South Africa), with exceptionally well equilibrated mineral major element compositions, for their trace element and isotopic inter-mineral equilibrium. Trace element compositions for all major mineral phases, i.e. olivine, orthopyroxene (opx), clinopyroxene (cpx) and garnet, were analysed by laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Garnet, cpx and opx of selected samples were analysed for their Sm-Nd and Lu-Hf isotope compositions by multi collector ICP-MS. Most important mineral characteristics include: a) olivines from most samples are enriched in high-field-strength elements relative to other incompatible trace elements. Their lithium content correlates negatively with Mg#, indicating a depletion signature; b) all other minerals are depleted in heavy and middle rare earth elements (H- and M-REE) and enriched in light REE and large ion lithophile elements. This implies a complex history of depletion and metasomatic overprint for the Finsch cratonic mantle; c) orthopyroxene has similarly shaped trace element patterns as cpx, with one to two orders of magnitude lower abundances; and d) both, garnet and cpx, display variable, mostly positive ɛHf coupled with moderate variations in ɛNd. Trace element partitioning between garnet/cpx, cpx/opx and garnet/opx, displays only a weak pressure and temperature dependency. However, equilibrium partitioning of most trace elements between garnet and cpx shows a strong compositional dependency, i.e. on the Cr- (and Ca-) content of the garnets. Garnet-cpx partition coefficients follow a second grade polynomial correlation with Cr2O3 of garnet, whereby high chromium garnets (Cr2O3 > 6 wt.%) have generally higher

  15. Seismic structure of the mantle ; from subduction zone to craton

    NARCIS (Netherlands)

    Kennett, B.L.N.; Hilst, R.D. van der

    1998-01-01

    Seismological techniques have provided much of the currently available information on the internal structure of the Earth, and in particular on the mantle. Early studies revealed the need for an increase in seismic velocity with depth in the Earth, and by 1915 Gutenberg was able to make a good estim

  16. Seismic structure of a late-Archean microcontinent in the middle of the Western Australian Craton

    Science.gov (United States)

    Yuan, Huaiyu; Johnson, Simon; Dentith, Mike; Murdie, Ruth; Gessner, Klaus; Korhonen, Fawna; Bodin, Thomas

    2017-04-01

    The Capricorn Orogen recorded the Paleoproterozoic amalgamation of the Archean Pilbara and Yilgarn cratons to form the Western Australian Craton. Regional surveys involving geological mapping, geochemistry, and geophysics reveal a prolonged tectonic history in craton assembly and subsequent intracratonic reworking, which have significantly re-shaped the orogenic crust. A high-density earthquake seismology deployment targeted the Glenburgh Terrane, an exotic late-Archean to Paleoproterozoic crustal block previously inferred from distinct structural and isotopic characters in the core region of the terrane. Prominent Moho and intracrustal discontinuities are present, replicating the overall trend and depth range found in the previous high-resolution deep crustal reflection image. Significant lateral variations in the seismic signal are found across the terrane boundary, showing a relatively thin crust (40km) crust with elevated Vp/Vs ratios (>1.76) in the margin. The small Vp/Vs ratios ( 1.70) are mapped terrane-wide, indicating a felsic bulk crustal composition. Considering the available constraints from isotopic age, magnetotelluric models and absolute shear wave velocities from ambient noise tomography, the Glenburgh Terrane is interpreted as a microcontinent made in the Archean, which however may have been altered during the WAC assembly and cratonization, as well as subsequent intracratonic reworking/magmatic differentiation processes. Our results illustrate that multi-disciplinary datasets bring complementary resolution and therefore may put tighter constraints on the tectonic processes that have affected the crust.

  17. Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions

    DEFF Research Database (Denmark)

    Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina

    2015-01-01

    Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....

  18. Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions

    DEFF Research Database (Denmark)

    Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina

    2015-01-01

    Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....

  19. Integrated Seismic Arrays for Imaging the North China Craton: the ¡°Destruction of the North China Craton¡± Project

    Science.gov (United States)

    Chen, Y. J.; Chen, L.; Zheng, T.; Zhou, S.

    2007-12-01

    It has been known, mostly according to the petrological and geochemical studies particularly the xenolith's data, that the North China craton (NCC), which is part of the Archaean Sino-Korean craton, had been reactivated since Mesozoic, and experienced widespread extension and volcanism through much of the Cenozoic. Currently the NCC is characterized by a thin lithosphere (as thin as 80 km according to published studies) and strong internal deformation, where over half of the eastern China's earthquakes occurred while the two major plate boundaries about China are thousands kilometers away. Although it is seismically quite active this region encompasses the China's capital and several mega cities which together hosts a large population and are very important to China's growing economy. Supported by the Chinese earth science community, the Chinese NSF recently started a major research program, the ¡°Destruction of the North China craton¡± (DNCC). About 150 million RMB (~ 20 million US dollars) will be allocated for this 5-year multi-disciplinary research program which is open for competition for all the earth scientists in China. Here we report one major seismic observation project of ¡°Integrated Seismic Arrays of DNCC¡± just funded during the first phase funding of DNCC. This observation-driven project integrates two groups at the Institute of Geology and Geophysics, Chinese Academy of Sciences and Peking University, and both institutions have their own broadband seismometers and have recently conducted pilot portable seismic array studies in North China. Up to seven linear broadband seismic arrays, each consists of 60-100 stations, are planned within the NCC. The principle objectives are to quantify the range and degree of the craton destruction in spatial domain with major focus on the east-west variation from the previously proposed intact craton in the west to the rejuvenated region in the east and the transition zone in the middle. With the expected

  20. Physico-chemical constraints on cratonic lithosphere discontinuities

    Science.gov (United States)

    Aulbach, Sonja; Rondenay, Stéphane; Huismans, Ritske

    2014-05-01

    The origins of the mid-lithospheric discontinuity (MLD) and lithosphere-asthenosphere boundary (LAB) have received much attention over the recent years. Peculiarities of cratonic lithosphere construction - compositional and rheological stratification due to thickening in collisional settings or by plume subcretion, multiple metasomatic overprints due to longevity - offer a variety of possibilities for the generation of discontinuities. Interconnected small degrees of conductive partial melt (carbonate-rich melts, such as carbonatites and kimberlites, or highly alkaline melts) at the cratonic LAB, which produce seismic discontinuities, may be generated in the presence of volatiles. These depress the peridotite solidus sufficiently to intersect the mantle adiabat at depths near the cratonic LAB at ~160-220 km, i.e. above the depth of metal saturation where carbonatite becomes unstable. The absence of agreement between the different seismic and magnetotelluric estimates for the depth of the LAB beneath Kaapvaal may be due to impingement of a plume, leading to a pervasively, but heterogeneously metasomatised ('asthenospherised') hot and deep root. Such a root and hot sublithosphere may yield conflicting seismic-thermal-geochemical depths for the LAB. The question arises whether the chemical boundary layer should be defined as above or below the asthenospherised part of the SCLM, which has preserved isotopic, compositional (non-primitive olivine forsterite content) and physical evidence (e.g. from teleseismic tomography and receiver functions) for a cratonic heritage and which therefore is still distinguishable from the asthenospheric mantle. If cratonic lithosphere overlies anomalously hot mantle for extended periods of time, the LAB may be significantly thinned, aided by penetration of relatively high-degree Fe-rich partial melts, as has occurred beneath the Tanzanian craton. Xenoliths from the deep Slave craton show little evidence for 'asthenospherisation'. Its root

  1. Extremely depleted lithospheric mantle and diamonds beneath the southern Zimbabwe Craton

    Science.gov (United States)

    Smith, Chris B.; Pearson, D. Graham; Bulanova, Galina P.; Beard, Andrew D.; Carlson, Richard W.; Wittig, Nadine; Sims, Keith; Chimuka, Lovemore; Muchemwa, Ellah

    2009-11-01

    Inclusion-bearing diamonds, mantle xenoliths, and kimberlite concentrates from the Cambrian-aged Murowa and Sese kimberlites have been studied to characterise the nature of the lithospheric mantle beneath the southern Zimbabwe Craton. The diamonds are mostly octahedral, moderately rich in nitrogen with moderate to high aggregation, and contain mainly dunite-harzburgite mineral inclusions. Similarly, dunite xenoliths predominate over harzburgite and lherzolite and carry olivines with Mg/Mg + Fe (Mg#) values of 0.92-0.95, spanning the average signatures for Kaapvaal Craton peridotites. Eclogitic xenoliths are extremely rare, in contrast to the Kaapvaal mantle lithosphere. The Zimbabwe mantle assemblage has been only slightly affected by later silicic metasomatism and re-fertilisation with re-introduction of pyroxenes in contrast to the Kaapvaal and many cratonic lithospheric blocks elsewhere where strong metasomatism and re-fertilisation is widespread. Pyroxene, garnet and spinel thermobarometry suggests an ambient 40 mW m - 2 geotherm, with the lithosphere extending down to 210 km at the time of kimberlite eruption. Whole rock peridotite Re-Os isotope analyses yield T RD model ages of 2.7 to 2.9 Ga, providing minimum estimates of the time of melt depletion, are slightly younger in age than the basement greenstone formation. These model ages coincide with the mean T RD age of > 200 analyses of Kaapvaal Craton peridotites, whereas the average Re-Os model age for the Zimbabwe peridotites is 3.2 Ga. The Os data and low Yb n/Lu n ratios suggest a model whereby thick lithospheric mantle was stabilised during the early stages of crustal development by shallow peridotite melting required for formation of residues with sufficiently high Cr/Al to stabilise chromite which then transforms to low Ca, high Cr garnet. Sulphide inclusions in diamond produce minimum T RD model ages of 3.4 Ga indicating that parts of the lithosphere were present at the earliest stages of crust

  2. THE STRUCTURE OF THE LITHOSPHERIC MANTLE OF THE SIBERAIN CRATON AND SEISMODYNAMICS OF DEFORMATION WAVES IN THE BAIKAL SEISMIC ZONE

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    A. A. Stepashko

    2015-09-01

    Full Text Available  The evolution and specific features of seismogynamics of the Baikal zones are reviewed in the context of interactions between deep deformation waves and the regional structure of the lithospheric mantle. The study is based on a model of the mantle structure with reference to chemical compositions of mantle peridotites from ophiolotic series located in the south-western framing of the Siberian craton (Fig. 1. The chemical zonation of the lithospheric mantle at the regional scale is determined from results of analyses of the heterogeneity of compositions of peridotites (Fig. 2, Table 1 and variations of contents of whole rock major components, such as iron, magnesium and silica (Fig. 3. According to spatial variations of the compositions of peridotites, the mantle has the concentric zonal structure, and the content of SiO2 is regularly decreasing, while concentrations of FeO∑ and MgO are increasing towards the centre of such structure (Fig. 4. This structure belongs to the mantle of the Siberian craton, which deep edge extends beyond the surface contour of the craton and underlies the north-western segment of the Central Asian orogenic belt.Results of the studies of peridotites of the Baikal region are consistent with modern concepts [Snyder, 2002; O’Reilly, Griffin, 2006; Chen et al., 2009] that suggest that large mantle lenses underlie the Archaean cratons (Fig. 5. The lenses are distinguished by high-density ultrabasic rocks and compose high-velocity roots of cratons which have remained isolated from technic processes. Edges of the mantle lenses may extend a few hundred kilometers beyond the limits of the cratons and underlie orogenic belts that frame the cratons, and this takes place in the south-western segment of the Siberian craton.The revealed structure of the lithospheric mantle is consistent with independent results of seismic and magmatectonical studies of the region. The Angara geoblock is located above the central part of the

  3. Stacked uppermost mantle layers within the Slave craton of NW Canada as defined by anisotropic seismic discontinuities

    Science.gov (United States)

    Snyder, David B.

    2008-08-01

    A 20-station seismic array in NW Canada recorded 336 teleseismic events with distribution in back azimuth and epicentral distance sufficient to characterize uppermost mantle discontinuities between depths typical of the Mohorovicic and Lehman discontinuities. Following wavefield decomposition, groups of seismograms were source-normalized through simultaneous deconvolution to estimate the near-receiver impulse response and thus detect major discontinuities beneath each seismic station. Stations within the Lac de Gras kimberlite field display an unusually strong negative impulse on the radial component within the NW quadrant and two moderate impulses on the transverse component. Forward modeling of these impulses suggests a mantle layer dipping at 22° to the southeast with a mildly anisotropic (2%) upper discontinuity at 120-135 km depth and another mildly anisotropic (2%) discontinuity at about 170 km depth. Superimposed on these layers is another, stronger anisotropic (4%) layer between 110 and 180 km depths that dips to the west. Stations outside of the Lac de Gras field, but within the southeastern Slave craton, display more numerous, but weaker, impulses. The most prominent of these occurs at about 150 km depth on the transverse component and has opposite polarity to that observed farther north. The prominent negative impulse observed on the radial component is interpreted to arise from structural-preferred orientation in the form of a stockwork of wehrlite dykes beneath the Lac de Gras field. Interpretation of the other layers in the context of known surface geology as well as xenolith petrology and garnet geochemistry of diamondiferous kimberlites favors previous suggestions that they represent 4000-2900 Ma depleted harzburgite and eclogite layers underthrust from the northwest at 2600 or 1880 Ma. The layer beneath the SE Slave craton has a similar, but distinct, tectonic history of NW-verging underthrusting associated with the 2635-2615 Ma Defeat Suite of

  4. The elusive lithosphere-asthenosphere boundary (LAB) beneath cratons

    Science.gov (United States)

    Eaton, David W.; Darbyshire, Fiona; Evans, Rob L.; Grütter, Herman; Jones, Alan G.; Yuan, Xiaohui

    2009-04-01

    The lithosphere-asthenosphere boundary (LAB) is a first-order structural discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Although it is the most extensive type of plate boundary on the planet, its definitive detection, especially beneath cratons, is proving elusive. Different proxies are used to demarcate the LAB, depending on the nature of the measurement. Here we compare interpretations of the LAB beneath three well studied Archean regions: the Kaapvaal craton, the Slave craton and the Fennoscandian Shield. For each location, xenolith and xenocryst thermobarometry define a mantle stratigraphy, as well as a steady-state conductive geotherm that constrains the minimum pressure (depth) of the base of the thermal boundary layer (TBL) to 45-65 kbar (170-245 km). High-temperature xenoliths from northern Lesotho record Fe-, Ca- and Ti-enrichment, grain-size reduction and globally unique supra-adiabatic temperatures at 53-61 kbar (200-230 km depth), all interpreted to result from efficient advection of asthenosphere-derived melts and heat into the TBL. Using a recently compiled suite of olivine creep parameters together with published geotherms, we show that beneath cratons the probable deformation mechanism near the LAB is dislocation creep, consistent with widely observed seismic and electrical anisotropy fabrics. If the LAB is dry, it is probably diffuse (> 50 km thick) and high levels of shear stress (> 2 MPa or > 20 bar) are required to accommodate plate motion. If the LAB is wet, lower shear stress is required to accommodate plate motion and the boundary may be relatively sharp (≤ 20 km thick). The seismic LAB beneath cratons is typically regarded as the base of a high-velocity mantle lid, although some workers infer its location based on a distinct change in seismic anisotropy. Surface-wave inversion studies provide depth-constrained velocity models, but are relatively insensitive to the sharpness of the LAB

  5. Seismic velocity model of the crust and upper mantle along profile PANCAKE across the Carpathians between the Pannonian Basin and the East European Craton

    DEFF Research Database (Denmark)

    Starostenko, V.; Janik, T.; Kolomiyets, K.

    2013-01-01

    Results are presented of a seismic wide-angle reflection/refraction survey along a profile between the Pannonian Basin (PB) and the East European Craton (EEC) called PANCAKE. The P- and S-wave velocity model derived can be divided into three sectors: the PB; the Carpathians, including the Transca......Results are presented of a seismic wide-angle reflection/refraction survey along a profile between the Pannonian Basin (PB) and the East European Craton (EEC) called PANCAKE. The P- and S-wave velocity model derived can be divided into three sectors: the PB; the Carpathians, including...

  6. Crustal and uppermost mantle structure of the eastern margin of the Yilgarn Craton (Australia) from passive seismic data

    Science.gov (United States)

    Sippl, Christian; Tkalčić, Hrvoje; Kennett, Brian; Spaggiari, Catherine; Gessner, Klaus

    2016-04-01

    The Yilgarn Craton in Western Australia is one of the largest units of Archean lithosphere on earth. Along its southern and southeastern margin, it is bounded by the Albany-Fraser Orogen (AFO), a Paleo- to Mesoproterozoic extensioal-accretionary orogen. In this contribution, we investigate the crustal and upper mantle structure of the AFO and adjacent regions using passive seismic data collected during the recent ALFREX experiment. Since the entire region has not been significantly reactivated since the Mesoproterozoic, the old signature of craton edge modification should have been well preserved until today. From November 2013 until January 2016, we operated a temporary passive seismic network consisting of 70 stations in the eastern Albany-Fraser Orogen. The array had an average station spacing of about 40 km and was designed to fill the gap between recently acquired active seismic profiles. We present results from the analysis of P receiver functions and ambient noise tomography using the ALFREX data. Receiver functions were used to derive a Moho depth map via H-K stacking, for direct imaging (common conversion point stacking) as well as joint inversion with surface wave dispersion data to derive 1D S-velocity profiles beneath the stations. The obtained receiver functions show a marked change of character from west to east across the array. Whereas they feature clear and sharp Moho phases for stations on the Yilgarn Craton, significantly more crustal complexity and fainter Moho phases are seen throughout the AFO. Crustal thickness increases from 36-39 km for the Yilgarn Craton to values between 42 and 48 km across the AFO, decreasing to around 40 km in the east. Ambient noise cross-correlations were used to derive maps of phase and group velocities of Rayleigh waves at periods between 1 and 30 seconds. A three-dimensional model of S wavespeeds throughout the area was then computed by pixelwise inversion of dispersion curves. Obtained S wavespeeds are generally

  7. Research on lithospheric density distributions beneath North China Craton and its destruction mechanism by gravity and seismic observations

    Science.gov (United States)

    Wang, X.; Fang, J.; Hsu, H.

    2011-12-01

    North China Craton (NCC) has been a research hotspot for geoscientists all over the world. Partial North China Craton (NCC) has lost its lithospheric keel since Mesozoic. Researchers have reached a consensus on destruction of NCC' lithosphere, however, the destruction mechanism and dynamic processes still remain controversy. In this study, a three-dimensional density distribution of lithosphere beneath NCC is determined using gravity datum combined with P-wave travel times by sequential inversion method. After the analyses and discussions on our density results referred to other geophysical and geochemical researches and then gave our viewpoint about destruction mechanisms of NCC lithosphere from the standpoint of density distribution. A linear velocity-density relationship is used to achieve mutual transformations and constraints between density and velocity. As we know, the gravity anomalies measured on the ground surface are the integrated reflection of the interface undulations and underground density inhomogeneous. In order to invert the lithospheric density structures, we firstly separated the gravity effects of lithospheric density inhomogeneous by removing the effects of other contributions to the gravity field from the observed integrated gravity filed before density inversion. The method of Zhao et al.,(1994) is used for seismic tomography, while Algebraic Reconstruction Technique (ART) is applied in density inversion, which highly improved the calculation velocity compared to common least squares method. The inversion results indicate that, the lithospheric density beneath NCC is extremely inhomogeneous and its distributions are coherent with surface regional tectonics; Low density anomalies exist in lower crust beneath rift basins around Ordos block. High poisson' ratios are found in these regions (about 3.0), which may indicate partial melting occurred. Receive function studies prevailed thinned ( 8.2km/s) is also found in this region. The prominent

  8. The evolution of the southern margin of the East European Craton based on seismic and potential field data

    Science.gov (United States)

    Kostyuchenko, S. L.; Morozov, A. F.; Stephenson, R. A.; Solodilov, L. N.; Vedrentsev, A. G.; Popolitov, K. E.; Aleshina, A. F.; Vishnevskaya, V. S.; Yegorova, T. P.

    2004-03-01

    This paper presents an integrated geophysical study of the southern margin of the East European Craton (EEC) in the Karpinksy Swell-North Caucasus area. It presents new interpretations of deep refraction and wide-angle reflection "deep seismic sounding" (DSS) data as well as conventional seismic and CDP profiling and new analyses of potential field data, including three-dimensional gravity and magnetic modelling. An integrated model of the physical properties and structure of the Earth's crust and, partially, upper mantle displays distinct features that are related to tectonic history of the study area. The Voronezh Massif (VM), the Ukrainian Shield and Rostov Dome (RD) of the EEC as well as the Donbas Foldbelt (DF), Karpinsky Swell (KS), Scythian Plate (SP) and Precaspian Basin (PCB) constitute the geodynamic ensemble that developed on the southern margin of the continent Baltica. There proposed evolutionary model comprises a stage of rifting during the middle to late Devonian, post-rift extension and subsidence during Carboniferous-early Permian times (synchronous with and related to the southward displacement of the Rostov Dome and extension in a palaeo-Scythian back-arc basin), and subsequent Mesozoic and younger evolution. A pre-Ordovician, possibly Riphean (?), mafic magmatic complex is inferred on a near vertical reflection seismic cross-section through the western portion of the Astrakhan Dome in the southwest part of the Precaspian Basin. This complex combined with evidence of a subducting slab in the upper mantle imply the presence of pre-Ordovician (Riphean?) island arc, with synchronous extension in a Precaspian back-arc basin is suggested. A middle Palaeozoic back-arc basin ensemble in what is now the western Karpinsky Swell was more than 100 km to the south from its present location. The Stavropol High migrated northwards, dislocating and moving fragments of this back-arc basin sometime thereafter. Linear positive magnetic anomalies reflect the

  9. Water and Metasomatism in the Slave Cratonic Lithosphere (Canada): An FTIR Study

    Science.gov (United States)

    Kilgore, McKensie; Peslier, Anne H.; Brandon, Alan D.; Schaffer, Lillian Aurora; Pearson, D. Graham; O'Reilly, Suzanne Yvette; Kopylova, Maya G.; Griffin, William L.

    2017-01-01

    Water in the mantle influences melting, viscosity, seismic velocity, and electrical conductivity. The role played by water in the long-term stabilization of cratonic roots is currently being debated. This study focuses on water contents of mantle minerals (olivine, pyroxene and garnet) from xenoliths found in kimberlites of the Archean Slave craton. 19 mantle xenoliths from central Lac de Gras, and 10 from northern Jericho were analyzed by FTIR for water, and their equilibration depths span the several compositional layers identified beneath the region. At both locations, the shallow peridotites have lower water contents in their olivines (11-30 ppm H2O) than those from the deeper layers (28-300 ppm H2O). The driest olivines, however, are not at the base of the cratonic lithosphere (>6 GPa) as in the Kaapvaal craton. Instead, the deepest olivines are hydrous (31-72 ppm H2O at Lac de Gras and 275 ppm H2O at Jericho). Correlations of water in clinopyroxene and garnet with their other trace element contents are consistent with water being added by metasomatism by melts resembling kimberlite precursors in the mantle approx.0.35 Ga ago beneath Lac de Gras. The northern Jericho xenoliths are derived from a region of the Slave craton that is even more chemically stratified, and was affected at depth by the 1.27 Ga Mackenzie igneous events. Metasomatism at Jericho may be responsible for the particularly high olivine water contents (up to 300 ppm H2O) compared to those at Lac de Gras, which will be investigated by acquiring trace-element data on these xenoliths. These data indicate that several episodes of metasomatic rehydration occurred in the deep part of the Slave craton mantle lithosphere, with the process being more intense in the northern part beneath Jericho, likely related to a translithospheric suture serving as a channel to introduce fluids and/or melts in the northern region. Consequently, rehydration of the lithosphere does not necessarily cause cratonic root

  10. Crust structure of the Northern Margin of North China Craton and adjacent region from Sinoprobe-02 North China seismic WAR/R experiment

    Science.gov (United States)

    Li, W.; Gao, R.; Keller, G. R.; Li, Q.; Cox, C. M.; Hou, H.; Guan, Y.

    2011-12-01

    The Central Asian Orogen Belt (CAOB) or Altaids, situated between the Siberian craton(SC) to the north and north China craton (NCC) with tarim to the south, is one of the world's largest accretionary orogens formed by subduction and accretion of juvenile material from the Neoproterozoic through the Paleozoic. The NCC is the oldest craton in China, which suffered Yanshan intercontinental orogenic process and lithosphere thinning in Mesozoic. In the past 20 years, remarkable studies about this region have been carried out and different tectonic models were proposed, however, some crucial geologic problems remain controversial. In order to obtain better knowledge of deep structure and properties of crust on the northern margin of north China craton, a 450 km long WAR/R section was completed jointly by Institute of Geology, CAGS and University of Oklahoma. Our 450 km long NW-SE WAR/R line extends from west end of the Yanshan orogen, across the Bainaimiao arc, Ondor sum subduction accretion complex to the Solonker suture zone. The recording of seismic waves from 8 explorations was conducted in 4 deployments of 300 reftek-125A records and single-channel 4.5Hz geophones with station spacing of 1km. The shooting procedure was employ 500 or 1500kg explosives in 4-5 or 15-23 boreholes at 40-45m depth. The sampling rate was 100 HZ, and recording time window was 1200s. The P wave field on the sections got high quality data for most part of the profile, but have low signal-to-noise for the south end, where closed to Beijing with a lot of ambient noise from traffic, industry and human activity. Arrivals from of refracted and reflected waves from sediments and basement (Pg), intracrust (Pcp, Plp) and Moho (Pmp) were typically observed, but Pn phase through the upper most mantle was only observed for 2 shots. Identification and correlation of seismic phases was done manually on computer screen Zplot software. Each trace has been bandpass filtered (1-20Hz) and normalized with AGC

  11. Water in the Cratonic Mantle Lithosphere

    Science.gov (United States)

    Peslier, A. H.

    2016-01-01

    The fact that Archean and Proterozoic cratons are underlain by the thickest (>200 km) lithosphere on Earth has always puzzled scientists because the dynamic convection of the surrounding asthenosphere would be expected to delaminate and erode these mantle lithospheric "keels" over time. Although density and temperature of the cratonic lithosphere certainly play a role in its strength and longevity, the role of water has only been recently addressed with data on actual mantle samples. Water in mantle lithologies (primarily peridotites and pyroxenites) is mainly stored in nominally anhydrous minerals (olivine, pyroxene, garnet) where it is incorporated as hydrogen bonded to structural oxygen in lattice defects. The property of hydrolytic weakening of olivine [4] has generated the hypothesis that olivine, the main mineral of the upper mantle, may be dehydrated in cratonic mantle lithospheres, contributing to its strength. This presentation will review the distribution of water concentrations in four cratonic lithospheres. The distribution of water contents in olivine from peridotite xenoliths found in kimberlites is different in each craton (Figure 1). The range of water contents of olivine, pyroxene and garnet at each xenolith location appears linked to local metasomatic events, some of which occurred later then the Archean and Proterozoic when these peridotites initially formed via melting. Although the low olivine water contents ( 6 GPa at the base of the Kaapvaal cratonic lithosphere may contribute to its strength, and prevent its delamination, the wide range of those from Siberian xenoliths is not compatible with providing a high enough viscosity contrast with the asthenophere. The water content in olivine inclusions from Siberian diamonds, on the other hand, have systematically low water contents (water contents. The olivine inclusions, however, may have been protected from metasomatism by their host diamond and record the overall low olivine water content of

  12. Crustal high-velocity anomaly at the East European Craton margin in SE Poland (TESZ) modelled by 3-D seismic tomography of refracted and reflected arrivals

    Science.gov (United States)

    Środa, Piotr; Dec, Monika

    2016-04-01

    The area of Trans-European Suture Zone in SE Poland represents a contact of major tectonic units of different consolidation age - from the Precambrian East European Craton, through Palaeozoic West European Platform to Cenozoic Carpathian orogen. The region was built by several phases of crustal accretion, which resulted in a complex collage of tectonic blocks. In 2000, this region was studied by several seismic wide-angle profiles of CELEBRATION 2000 experiment, providing a dense coverage of seismic data in SE Poland and allowing for detailed investigations of the crustal structure and properties in this area. Beneath the marginal part of the EEC, the 2-D modelling of in-line data form several CELEBRATION profiles revealed a prominent high P-wave velocity anomaly in the upper crust, with Vp of 6.7-7.1 km/s, starting at 10-16 km depth (e.g., Środa et al., 2006). Anomalously high velocities are observed in the area located approximately beneath Lublin trough, to the NE of Teisseyre-Tornquist Zone. Based on 3-D tomography of first arrivals of in- and off-line CELEBRATION 2000 recordings (Malinowski et al., 2008), elevated velocities are also reported in the same area and seem to continue to the SW, off the craton margin. Gravimetric modelling also revealed anomalously high density in the same region at similar depths. High seismic velocities and densities are interpreted as indicative for a pronounced mafic intrusion, possibly related to extensional processes at the EEC margin. Previous 3-D models of the high-velocity intrusion were based on first arrivals (crustal refractions) only. In this study, also off-line reflections (not modelled up to now) are used, in order to enlarge the data set and to better constrain the geometry and properties of the velocity anomaly. A code for 3-D joint tomographic inversion of refracted and reflected arrivals, with model parametrization allowing for velocity discontinuities was used (Rawlinson, 2007). With this approach, besides the

  13. Deep vs. shallow expressions of continental cratons: Can cratonic roots be destroyed by subduction?

    Science.gov (United States)

    Perry-Houts, J.; Calo, M.; Eddy, C. L.; Guerri, M.; Holt, A.; Hopper, E.; Tesoniero, A.; Romanowicz, B. A.; Becker, T. W.; Wagner, L. S.

    2013-12-01

    Cratons are parts of continents that have remained tectonically quiescent over billion-year timescales. Although cratonic lithosphere has the stabilizing properties of chemical buoyancy and high viscosity, it can still be destroyed. The best known example of a missing cratonic root is beneath the eastern North China Craton (NCC). Despite strong evidence for the past existence of a craton in northern China, high heat flow, Mesozoic basin formation, extensive seismicity, and the lack of a fast seismic root imply that the deep cratonic lithosphere is missing. The mechanism for the lithospheric root loss is a source of much debate. Many mechanisms have been proposed, among them: shearing of the lithospheric root by asthenospheric flow induced by the Indo-Eurasian collision; ponding of the Pacific slab in the transition zone acting as a source of fluids that enable hydrous weakening; and thermal erosion due to the corner-flow upwelling of hot, deep material. It is generally agreed that the influence of subduction is key, both from the temporal coincidence of subduction with increased tectonomagmatic activity on the craton and from the spatial correlation of lithospheric loss adjacent to the Pacific trench. We investigate how cratons extend to depth through comparison between seismic signatures of the cratonic lithosphere in the upper mantle and surficial evidence of cratonic boundaries. We examine global and regional tomography, as well as receiver-function constraints on lithospheric thickness in the NCC. We define craton boundaries at the surface through analyses on crust and lithospheric mantle ages and kimberlite locations. We aim to identify regions where the fast cratonic root has been lost or altered beneath Archean and Proterozoic crust and in particular place constraints on the extent of the remaining cratonic root beneath North China. Given the common emphasis on the role of subduction as a driving force for the root loss beneath the eastern NCC, we focus on

  14. Nature of the mantle roots beneath the North American craton: mantle xenolith evidence from Somerset Island kimberlites

    Science.gov (United States)

    Schmidberger, S. S.; Francis, D.

    1999-09-01

    The recently discovered Nikos kimberlite on Somerset Island, in the Canadian Arctic, hosts an unusually well preserved suite of mantle xenoliths dominated by garnet-peridotite (lherzolite, harzburgite, dunite) showing coarse and porphyroclastic textures, with minor garnet-pyroxenite. The whole rock and mineral data for 54 Nikos xenoliths indicate a highly refractory underlying mantle with high olivine forsterite contents (ave. Fo=92.3) and moderate to high olivine abundances (ave. 80 wt.%). These characteristics are similar to those reported for peridotites from the Archean Kaapvaal and Siberian cratons (ave. olivine Fo=92.5), but are clearly distinct from the trend defined by oceanic peridotites and mantle xenoliths in alkaline basalts and kimberlites from post-Archean continental terranes (ave. olivine Fo=91.0). The Nikos xenoliths yield pressures and temperatures of last equilibration between 20 and 55 kb and 650 and 1300°C, and a number of the peridotite nodules appear to have equilibrated in the diamond stability field. The pressure and temperature data define a conductive paleogeotherm corresponding to a surface heat flow of 44 mW/m 2. Paleogeotherms based on xenolith data from the central Slave province of the Canadian craton require a lower surface heat flow (˜40 mW/m 2) indicating a cooler geothermal regime than that beneath the Canadian Arctic. A large number of kimberlite-hosted peridotites from the Kaapvaal craton in South Africa and parts of the Siberian craton are characterized by high orthopyroxene contents (ave. Kaapvaal 32 wt.%, Siberia 20 wt.%). The calculated modal mineral assemblages for the Nikos peridotites show moderate to low contents of orthopyroxene (ave. 12 wt.%), indicating that the orthopyroxene-rich mineralogy characteristic of the Kaapvaal and Siberian cratons is not a feature of the cratonic upper mantle beneath Somerset Island.

  15. Density structure of the cratonic mantle in Southern Africa. 2. Correlations with kimberlite distribution, seismic velocities, and Moho sharpness

    DEFF Research Database (Denmark)

    Artemieva, Irina; Vinnik, Lev

    2016-01-01

    across) lowdensity (down to 3.34 g/cm3) and high-density (up to 3.41 g/cm3) anomalies. High (3.40–3.42 g/cm3) mantle densities beneath the Eastern Cape Fold belt require the presence of a significant amount of eclogite in the mantle, such as associated with subducted oceanic slabs. We find a strong...... the composition and rheology of the lithospheric mantle to make it unfavorable for consequent kimberlite eruptions. (5) Density anomalies in the lithospheric mantle show inverse correlation with seismic Vp, Vs velocities at 100–150 km depth. However, this correlation is weaker than reported in experimental...

  16. Structure of the lithosphere below the southern margin of the East European Craton (Ukraine and Russia) from gravity and seismic data

    Science.gov (United States)

    Yegorova, T. P.; Stephenson, R. A.; Kostyuchenko, S. L.; Baranova, E. P.; Starostenko, V. I.; Popolitov, K. E.

    2004-03-01

    The present study was undertaken with the objective of deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the East European Craton (EEC). The study area includes the inverted southernmost part of the intracratonic Dnieper-Donets Basin (DDB)-Donbas Foldbelt (DF), its southeastern prolongation along the margin of the EEC-the sedimentary succession of the Karpinsky Swell (KS), the southwestern part of the Peri-Caspian Basin (PCB), and the Scythian Plate (SP). These structures are adjacent to a zone, along which the crust was reworked and/or accreted to the EEC since the late Palaeozoic. In the Bouguer gravity field, the southern margin of the EEC is marked by an arc of gravity highs, correlating with uplifted Palaeozoic rocks covered by thin Mesozoic and younger sediments. A three-dimensional (3D) gravity analysis has been carried out to investigate further the crustal structure of this area. The sedimentary succession has been modelled as two heterogeneous layers—Mesozoic-Cenozoic and Palaeozoic—in the analysis. The base of the sedimentary succession (top of the crystalline Precambrian basement) lies at a depth up to 22 km in the PCB and DF-KS areas. The residual gravity field, obtained by subtracting the gravitational effect of the sedimentary succession from the observed gravity field, reveals a distinct elongate zone of positive anomalies along the axis of the DF-KS with amplitudes of 100-140 mGal and an anomaly of 180 mGal in the PCB. These anomalies are interpreted to reflect a heterogeneous lithosphere structure below the supracrustal, sedimentary layers: i.e., Moho topography and/or the existence of high-density material in the crystalline crust and uppermost mantle. Previously published data support the existence of a high-density body in the crystalline crust along the DDB axis, including the DF, caused by an intrusion of mafic and

  17. Lithosphere structure of the Donbas Fodbelt and Karpinsky Swell region (the southern margin of the East-European Craton), Ukraine and Russia, from seismic and gravity data

    Science.gov (United States)

    Yegorova, T.; Baranova, E.; Starostenko, V.

    2003-04-01

    LITHOSPHERE STRUCTURE OF THE DONBAS FOLDBELT AND KARPINSKI SWELL REGION (THE SOUTHERN MARGIN OF THE EAST-EUROPEAN CRATON), UKRAINE AND RUSSIA, FROM SEISMIC AND GRAVITY DATA T.Yegorova (1), E.Baranova (1), V.Starostenko (1) (1) Institute of Geophysics, National Academy of Sciences of Ukraine egorova@igph.kiev.ua Along the southern margin of the East-European platform (EEC) super deep Late Devonian rift basins Dnieper-Donets Basin (DDB) and Peri-Caspian Basin (PCB) are located. The structures are adjacent to a zone along which crust was reworked and/or accreted to the EEC during Late Palaeozoic-Triassic times. The objective of the present study is deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the EEC. The study area includes the inverted southernmost part of the intracratonic DDB Donbas Foldbelt (DF), its south-eastern prolongation along the margin of the EEC the sedimentary succession of the Karpinsky Swell (KS), the south-western part of the Peri-Caspian Basin (PCB) and the Scythian Plate. According to the structure of the sedimentary basin, the DF and the KS form a single linear structure, represented by the uplift of Palaeozoic rocks, with the exposure of Carboniferous coal-bearing rocks in the DF, and by deep trough (down to the depth of 20 km and more) on the top of the crystalline Precambrian basement. The 3D gravity back-stripping analysis, implemented to test the sediment structure, reveals a distinct elongate zone of positive sediment corrected anomalies along the axis of the DF-KS and strong positive anomaly in the PCB. This is caused by heterogeneous lithosphere structure below the basin: Moho topography and/or the existence of a high density material in the crystalline crust and uppermost mantle. Our previous investigations have supported the existence of high-density body in the crystalline crust along the DDB axis. The

  18. Support for a Uniformitarian Model of Continental Mantle Lithosphere Formation from the "Near-Cratonic" Composition of Proterozoic Southern African Mantle Lithosphere

    Science.gov (United States)

    Janney, P. E.

    2014-12-01

    The transition at the end of the Archean between the generation of cratonic and mobile belt continental lithosphere is regarded as a first-order change in the mode of generation of continental lithosphere. It is widely debated whether this transition represented a fundamental change in the process by which the lithospheric mantle was generated (i.e., as melting residues of deep-seated mantle upwellings to residues of relatively shallow mantle melting at subduction zones), or whether it primarily reflected a more gradual change in the conditions (i.e., temperatures, depths and degrees of melting) of lithosphere generation in a suprasubduction zone setting. The marked contrast, in many cases, between the major element compositions of peridotite xenoliths from Archean cratons and those from adjacent post-Archean mobile belts has accentuated the significance of this transition. Peridotite xenoliths from the post-Archean mobile belt terranes surrounding the Kaapvaal craton in southern Africa are clearly Proterozoic in age from Re-Os isotope constraints, but they are unusual in that they share several key similarities in composition and mineralogy with Archean Kaapvaal peridotites (e.g., low bulk-rock Al2O3, relatively low modal olivine and high modal orthopyroxene). Although they lack the low FeO and high olivine Mg# values of the most extreme Kaapvaal samples, they show a very large degree of overlap (extending to olivine Mg# values of greater than 93 for example). These similarities support a common mode of origin for cratonic and post-cratonic lithosphere in southern Africa (although varying somewhat in the degrees and depths of melt extraction) and a similar history of post-formation modification. A comparison of the conditions of melt extraction for cratonic and post-cratonic lithosphere inferred from compatible and mildly incompatible trace elements will be presented.

  19. The Role of Water in the Stability of Cratonic Keels

    Science.gov (United States)

    Peslier, Anne H.; Woodland, Alan B.; Bell, David R.; Lazarov, Marina

    2011-01-01

    Cratons are typically underlain by large, deep, and old lithospheric keels (to greater than 200 km depth, greater than 2.5 Ga old) projecting into the asthenosphere (e.g., Jordan, 1978; Richardson et al., 1984). This has mystified Earth scientists as the dynamic and relatively hot asthenosphere should have eroded away these keels over time (e.g., Sleep, 2003; O'Neill et al., 2008; Karato, 2010). Three key factors have been invoked to explain cratonic root survival: 1) Low density makes the cratonic mantle buoyant (e.g., Poudjom Djomani et al., 2001). 2) Low temperatures (e.g., Pollack, 1986; Boyd, 1987), and 3) low water contents (e.g., Pollack, 1986), would make cratonic roots mechanically strong. Here we address the mechanism of the longevity of continental mantle lithosphere by focusing on the water parameter. Although nominally anhydrous , olivine, pyroxene and garnet can accommodate trace amounts of water in the form of H bonded to structural O in mineral defects (e.g., Bell and Rossman, 1992). Olivine softens by orders of magnitude if water (1-1000 ppm H2O) is added to its structure (e.g., Mackwell et al., 1985). Our recent work has placed constraints on the distribution of water measured in peridotite minerals in the cratonic root beneath the Kaapvaal in southern Africa (Peslier et al., 2010). At P greater than 5 GPa, the water contents of pyroxene remain relatively constant while those of olivine systematically decrease from 50 to less than 10 ppm H2O at 6.4 GPa. We hypothesized that at P greater than 6.4 GPa, i.e. at the bottom of the cratonic lithosphere, olivines are essentially dry (greater than 10 ppm H2O). As olivine likely controls the rheology of the mantle, we calculated that the dry olivines could be responsible for a contrast in viscosity between cratonic lithosphere and surrounding asthenosphere large enough to explain the resistance of cratonic root to asthenospheric delamination.

  20. High Water Contents in the Siberian Cratonic Mantle: An FTIR Study of Udachnaya Peridotite Xenoliths

    Science.gov (United States)

    Doucet, Luc S.; Peslier, Anne H.; Ionov, Dimitri A.; Brandon, Alan D.; Golovin, Alexander V.; Ashchepkov, Igor V.

    2013-01-01

    Water is believed to be a key factor controlling the long-term stability of cratonic lithosphere, but mechanisms responsible for the water content distribution in the mantle remain poorly constrained. Water contents were obtained by FTIR in olivine, pyroxene and garnet for 20 well-characterized peridotite xenoliths from the Udachnaya kimberlite (central Siberian craton) and equilibrated at 2-7 GPa. Water contents in minerals do not appear to be related to interaction with the host kimberlite. Diffusion modeling indicates that the core of olivines preserved their original water contents. The Udachnaya peridotites show a broad range of water contents in olivine (6.5 +/- 1.1 to 323 +- 65 ppm H2O (2 sigma)), and garnet (0 - 23 +/- 6 ppm H2O). The water contents of olivine and garnet are positively correlated with modal clinopyroxene, garnet and FeO in olivine. Water-rich garnets are also rich in middle rare earth elements. This is interpreted as the result of interaction between residual peridotites and water rich-melts, consistent with modal and cryptic metasomatism evidenced in the Siberian cratonic mantle. The most water-rich Udachnaya minerals contain 2 to 3 times more water than those from the Kaapvaal craton, the only craton with an intact mantle root for which water data is available. The highest water contents in olivine and orthopyroxene in this study (>= 300 ppm) are found at the bottom of the lithosphere (> 6.5 GPa). This is in contrast with the Kaapvaal craton where the olivines of peridotites equilibrated at > 6.4 GPa have 6 GPa is lower or similar (8.4× 10(exp 16) to 8.0× 10(exp 18) Pa./s) to that of the asthenosphere (<= 3.7x10(exp 18) Pa./s ). Such lithologies would not be able to resist delamination by the convecting asthenosphere. However, seismology studies as well as the high equilibration pressures of our samples indicate that the Udachnaya cratonic lithosphere is 220-250 km thick. Consequently, the water-rich peridotites are likely not

  1. Crustal-scale pop-up structure in cratonic lithosphere: DOBRE deep seismic reflection study of the Donbas fold belt, Ukraine

    Science.gov (United States)

    Maystrenko, Yuriy; Stovba, Sergiy; Stephenson, Randell; Bayer, Ulf; Menyoli, Elive; Gajewski, Dirk; Huebscher, Christian; Rabbel, Wolfgang; Saintot, Aline; Starostenko, Vitaly; Thybo, Hans; Tolkunov, Anatoliy

    2003-08-01

    The DOBRE project investigated the interplay of geologic and geodynamic processes that controlled the evolution of the Donbas fold belt, Ukraine, as an example of an inverted intracratonic rift basin. A deep seismic reflection profile provides an excellent image of the structure of the Donbas fold belt, which is the uplifted and compressionally deformed part of the late Paleozoic Pripyat-Dniepr-Donets basin. Both the effects of rifting and those of later structural inversion are recognized in the seismic and geologic data. The interpretation of the reflection data shows that the inversion of the Donbas fold belt occurred at the crustal scale as a mega pop-up, which involved a major detachment fault through the entire crust and an associated back thrust. The DOBREflection image provides a simple concept of intracratonic basin inversion, the crustal pop-up being uplifted and internally deformed. The association of such a structure with inverted intracratonic basins such as the Donbas fold belt implies brittle deformation of relatively cold crust.

  2. Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

    Science.gov (United States)

    Aulbach, Sonja; Massuyeau, Malcolm; Gaillard, Fabrice

    2017-01-01

    Geophysically detectible mid-lithospheric discontinuities (MLD) and lithosphere-asthenosphere boundaries (LAB) beneath cratons have received much attention over recent years, but a consensus on their origin has not yet emerged. Cratonic lithosphere composition and origin is peculiar due to its ultra-depletion during plume or accretionary tectonics, cool present-day geothermal gradients, compositional and rheological stratification and multiple metasomatic overprints. Bearing this in mind, we integrate current knowledge on the physical properties, chemical composition, mineralogy and fabric of cratonic mantle with experimental and thermodynamic constraints on the formation and migration of melts, both below and within cratonic lithosphere, in order to find petrologically viable explanations for cratonic mantle discontinuities. LABs characterised by strong seismic velocity gradients and increased conductivity require the presence of melts, which can form beneath intact cratonic roots reaching to 200-250 km depth only in exceptionally warm and/or volatile-rich mantle, thus explaining the paucity of seismical LAB observations beneath cratons. When present, pervasive interaction of these - typically carbonated - melts with the deep lithosphere leads to densification and thermochemical erosion, which generates topography at the LAB and results in intermittent seismic LAB signals or conflicting seismic, petrologic and thermal LAB depths. In rare cases (e.g. Tanzanian craton), the tops of live melt percolation fronts may appear as MLDs and, after complete lithosphere rejuvenation, may be sites of future, shallower LABs (e.g. North China craton). Since intact cratons are presently tectonomagmatically quiescent, and since MLDs produce both positive and negative velocity gradients, in some cases with anisotropy, most MLDs may be best explained by accumulations (metasomes) of seismically slow minerals (pyroxenes, phlogopite, amphibole, carbonates) deposited during past

  3. Structure and extent of the southern African cratons: Integrated images from receiver functions and teleseimic tomography

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Levander, Alan; Bezada, Max

    2011-01-01

    components we find that most of the strong anisotropy is confined to the lower crust. Using finite-frequency kernels, we inverted the P- and S- wave delay times to obtain 3-D images of com- pressional and shear velocity perturbations in the mantle by use of three frequency bands: 1, 0.5 and 0.25 Hz for P......4◦ checkerboards show moderately good recovery. To isolate the depth extent of anomalies in the model we ran two suites of squeezing tests: 1) For maximum depth of the model being 1000, 700 and 410 km. 2) For the 1000 km deep model, we increased the damping parameter in the deeper layers....... The Receiver Functions show a thin crust with a flat and sharp Moho discontinuity throughout the entire Kaapvaal and Zimbabwe cratons. These results are consistent with expectations for Archean areas. The lowest Vp/Vs value sites are found around the locations of diamondiferous kimberlite pipes at flat Moho...

  4. Charts of episodes and chronometric duration have implications for provinces such as the Kaapvaal

    Directory of Open Access Journals (Sweden)

    H. de la R. Winter

    1997-07-01

    Full Text Available An accurate basin analysis and knowledge of its evolutionary development being a prerequisite framework for metallogenic model­ling, a procedure was developed for the Kaapvaal Province to maximise quantitative observational data and constrain assumptions and interpretations. Employing an episodes chart to display various events interactively and its conversion to a geochronometric chart as the geological model, the method was applied to existing stratigraphic studies.

  5. Olivine water contents in the continental lithosphere and the longevity of cratons.

    Science.gov (United States)

    Peslier, Anne H; Woodland, Alan B; Bell, David R; Lazarov, Marina

    2010-09-02

    Cratons, the ancient cores of continents, contain the oldest crust and mantle on the Earth (>2 Gyr old). They extend laterally for hundreds of kilometres, and are underlain to depths of 180-250 km by mantle roots that are chemically and physically distinct from the surrounding mantle. Forming the thickest lithosphere on our planet, they act as rigid keels isolated from the flowing asthenosphere; however, it has remained an open question how these large portions of the mantle can stay isolated for so long from mantle convection. Key physical properties thought to contribute to this longevity include chemical buoyancy due to high degrees of melt-depletion and the stiffness imparted by the low temperatures of a conductive thermal gradient. Geodynamic calculations, however, suggest that these characteristics are not sufficient to prevent the lithospheric mantle from being entrained during mantle convection over billions of years. Differences in water content are a potential source of additional viscosity contrast between cratonic roots and ambient mantle owing to the well-established hydrolytic weakening effect in olivine, the most abundant mineral of the upper mantle. However, the water contents of cratonic mantle roots have to date been poorly constrained. Here we show that olivine in peridotite xenoliths from the lithosphere-asthenosphere boundary region of the Kaapvaal craton mantle root are water-poor and provide sufficient viscosity contrast with underlying asthenosphere to satisfy the stability criteria required by geodynamic calculations. Our results provide a solution to a puzzling mystery of plate tectonics, namely why the oldest continents, in contrast to short-lived oceanic plates, have resisted recycling into the interior of our tectonically dynamic planet.

  6. The structure of the Amazonian craton: Available geophysical evidence

    Science.gov (United States)

    Rosa, João Willy Corrêa; Rosa, José Wilson Corrêa; Fuck, Reinhardt A.

    2016-10-01

    The Amazonian craton, which covers a large area of South America, and is thought to have been stable since the end of the Mesoproterozoic, has recently benefited from a series of regional geophysical surveys. The Amazonian craton comprises the northern Guyana shield and the southern Central Brazil shield. It has become the main subject of seismological studies aiming to determine crustal thickness. Moho thickness maps that cover a large part of the South American continent summarize these studies. Receiver function studies, aided by surface wave dispersion tomography, were also useful tools applied in the region over the past decade. These have been improved by the addition of temporary and permanent regional seismological arrays and stations. An interesting NNW-SSE Moho depth anomaly, pointing to crustal thickening of up to 60 km in the central Guyana shield and a 50 km thick anomaly of the southern Central Brazil shield were recently identified. Areas with crustal thickening correspond to Paleoproterozoic magmatic arcs. The upper mantle seismic anisotropy in part of the region has been determined from SKS splitting studies. The currently available seismic anisotropy information shows that the orientation of the determined anisotropic axis is related to the frozen in anisotropy hypothesis for the Amazonian craton. The orientation of the anisotropic axis shows no relation to the current South American plate motion in the Amazonian craton. Most recently, detailed information for the two shields has benefited from a series of high-resolution, regional aerogeophysical surveys, made available by CPRM, the Brazilian Geological Survey. In addition to the mentioned contribution from seismology for imaging deeper crustal structures, regional gravity surveys have been expanded, adding to previous Bouguer anomaly maps, and deep drilling information from early exploration efforts have been compiled for the Amazon basin, which covers the Amazonian craton separating the Guyana

  7. The 3-dimensional construction of the Rae craton, central Canada

    Science.gov (United States)

    Snyder, David B.; Craven, James A.; Pilkington, Mark; Hillier, Michael J.

    2015-10-01

    Reconstruction of the 3-dimensional tectonic assembly of early continents, first as Archean cratons and then Proterozoic shields, remains poorly understood. In this paper, all readily available geophysical and geochemical data are assembled in a 3-D model with the most accurate bedrock geology in order to understand better the geometry of major structures within the Rae craton of central Canada. Analysis of geophysical observations of gravity and seismic wave speed variations revealed several lithospheric-scale discontinuities in physical properties. Where these discontinuities project upward to correlate with mapped upper crustal geological structures, the discontinuities can be interpreted as shear zones. Radiometric dating of xenoliths provides estimates of rock types and ages at depth beneath sparse kimberlite occurrences. These ages can also be correlated to surface rocks. The 3.6-2.6 Ga Rae craton comprises at least three smaller continental terranes, which "cratonized" during a granitic bloom. Cratonization probably represents final differentiation of early crust into a relatively homogeneous, uniformly thin (35-42 km), tonalite-trondhjemite-granodiorite crust with pyroxenite layers near the Moho. The peak thermotectonic event at 1.86-1.7 Ga was associated with the Hudsonian orogeny that assembled several cratons and lesser continental blocks into the Canadian Shield using a number of southeast-dipping megathrusts. This orogeny metasomatized, mineralized, and recrystallized mantle and lower crustal rocks, apparently making them more conductive by introducing or concentrating sulfides or graphite. Little evidence exists of thin slabs similar to modern oceanic lithosphere in this Precambrian construction history whereas underthrusting and wedging of continental lithosphere is inferred from multiple dipping discontinuities.

  8. The story of a craton from heart to margins: illuminating cratonic lithosphere with Rayleigh wave phase velocities in Eastern Canada

    Science.gov (United States)

    Petrescu, L.; Darbyshire, F. A.; Gilligan, A.; Bastow, I. D.; Totten, E. J.

    2015-12-01

    Cratons are Precambrian continental nuclei that are geologically distinct from modern continental regions and are typically underlain by seismically fast lithospheric roots (keels) to at least 200 km depth. Both plate and non-plate tectonic origin theories such as stacking of subducted slabs or multiple mantle plume underplating have been proposed to explain keel growth.Eastern Canada is an ideal continental region to investigate cratonization processes and the onset of plate tectonics. It comprises part of the largest Archean craton in the world, the Superior Province, flanked by a ~1.1 Ga Himalayan-scale orogenic belt, the Grenville Province, and the 500-300 Ma old Appalachian orogenic province, following the same general SW-NE axial trend. The region is also cross-cut by the Great Meteor Hotspot track, providing an excellent opportunity to study the interaction of hotspot tectonism with progressively younger lithospheric domains.We investigate the lithospheric structure of Precambrian Eastern Canada using teleseismic earthquake data recorded at permanent and temporary networks. We measure interstation dispersion curves of Rayleigh wave phase velocities between ~15 and 220 s, and compare the results to standard continental and cratonic reference models. We combine the dispersion curves via a tomographic inversion which solves for isotropic phase velocity heterogeneity and azimuthal anisotropy across the region at a range of periods. The phase velocity maps indicate variations in lithospheric properties from the heart of the Superior craton to the SE Canadian coast.The new regional-scale models will help to understand the processes that generated, stabilized and reworked the cratonic roots through their billion-year tectonic history. We investigate how surface tectonic boundaries relate to deeper lithospheric structural changes, and consider the effects of the multiple Wilson cycles that affected Laurentia.

  9. 3-D Structure of the Slave and Rae Cratons Provides Clues to Their Construction

    Science.gov (United States)

    Snyder, D. B.

    2013-12-01

    Deep geologic structures within cratons that make up continental cores were long neglected. Recently acquired geophysical data from large observational arrays and geochemical data resulting from exploration for diamond has now made possible co-registration of large-scale (400-km depth), truly 3-dimensional data sets. P-waves, surface waves and magnetotelluric observations provide 3-D wavespeed and conductivity models. Multi-azimuthal receiver functions map seismic discontinuity surfaces in 3-D. Xenolith suites erupted in kimberlites provide rock samples at key lithospheric depths, albeit at sparsely distributed locations. These multi-disciplinary models are becoming available for several key cratons worldwide; here the deep structure of the Slave and Rae cratons of the Canadian Shield is described. Lithospheric layers with tapered, wedge-shaped margins are common. Slave craton layers are sub-horizontal and indicate construction of the craton core at 2.7 Ga by underthrusting and flat stacking of lithosphere. The central Rae craton has predominantly dipping discontinuities that indicate construction at 1.9 Ga by thrusting similar to that observed in crustal ';thick-skinned' fold-and-thrust belts. 3-D mapping of conductivity and metasomatism, the latter via mineral recrystallization and resetting of isotopic ages, overprints primary structures in both cratons. Distribution of more conductivitve mantle suggests that assumed causative pervasive metasomatism occurs at 100-200 km depths with ';chimneys' reaching to shallower depths, typically in locations where kimberlites or mineralization has occurred.

  10. Density structure of the cratonic mantle in southern Africa

    DEFF Research Database (Denmark)

    Artemieva, Irina; Vinnik, Lev P.

    2016-01-01

    . An unusually high topography may be caused by a low density (high depletion) of the cratonic lithospheric mantle and/or by the dynamic support of the mantle with origin below the depth of isostatic compensation (assumed here to be at the lithosphere base). We use free-board constraints to examine the relative...... contributions of the both factors to surface topography in the cratons of southern Africa. Our analysis takes advantage of the SASE seismic experiment which provided high resolution regional models of the crustal thickness.We calculate the model of density structure of the lithospheric mantle in southern Africa...... and show that it has an overall agreement with xenolith-based data for lithospheric terranes of different ages. Density of lithospheric mantle has significant short-wavelength variations in all tectonic blocks of southern Africa and has typical SPT values of ca. 3.37-3.41g/cm3 in the Cape Fold and Namaqua...

  11. Aeromagnetic interpretation in the south-central Zimbabwe Craton: (reappraisal of) crustal structure and tectonic implications

    Science.gov (United States)

    Ranganai, Rubeni T.; Whaler, Kathryn A.; Ebinger, Cynthia J.

    2016-11-01

    Regional aeromagnetic data from the south-central Zimbabwe Craton have been digitally processed and enhanced for geological and structural mapping and tectonic interpretation integrated with gravity data, to constrain previous interpretations based on tentative geologic maps and provide new information to link these structural features to known tectonic events. The derived maps show excellent correlation between magnetic anomalies and the known geology, and extend lithological and structural mapping to the shallow/near subsurface. In particular, they reveal the presence of discrete crustal domains and several previously unrecognised dykes, faults, and ultramafic intrusions, as well as extensions to others. Five regional structural directions (ENE, NNE, NNW, NW, and WNW) are identified and associated with trends of geological units and cross-cutting structures. The magnetic lineament patterns cut across the >2.7 Ga greenstone belts, which are shown by gravity data to be restricted to the uppermost 10 km of the crust. Therefore, the greenstone belts were an integral part of the lithosphere before much of the upper crustal (brittle) deformation occurred. Significantly, the observed magnetic trends have representatives craton-wide, implying that our interpretation and inferences can be applied to the rest of the craton with confidence. Geological-tectonic correlation suggests that the interpreted regional trends are mainly 2.5 Ga (Great Dyke age) and younger, and relate to tectonic events including the reactivation of the Limpopo Belt at 2.0 Ga and the major regional igneous/dyking events at 1.8-2.0 Ga (Mashonaland), 1.1 Ga (Umkondo), and 180 Ma (Karoo). Thus, their origin is here inferred to be inter- and intra-cratonic collisions and block movements involving the Zimbabwe and Kaapvaal Cratons and the Limpopo Belt, and later lithospheric heating and extension associated with the break-up of Gondwana. The movements produced structures, or reactivated older fractures

  12. Crustal and upper mantle structure of the Slave craton from P- and S- Receiver Functions

    Science.gov (United States)

    Barantseva, Olga; Vinnik, Lev; Artemieva, Irina

    2017-04-01

    Teleseismic events recorded by POLARIS array in NW Canada (Slave craton) and Yellowknife station were used to calculate a sufficient number of receiver functions for P (PRF) and S (SRF) waves. Velocity (Vp and Vs) and Vp/Vs profiles from the Earth's surface down to 300 km are obtained through the simultaneous inversion of PRF and SRF with teleseismic travel time residuals for the crust and upper mantle. We observe highly heterogeneous structure of the cratonic upper mantle. The Lehman discontinuity (the bottom of the low velocity zone) is found in the western Slave craton, whereas it is not observed in the eastern part of the Slave craton. At stations located in the southern part of the craton, we observe an increase of S-wave velocities (as compared to IASP91 values) at the depths 45-150 km which is typical for depleted cratonic mantle. Low Vp/Vs ratio, obtained for the uppermost mantle (1.65-1.70) can be explained by a high fraction of Opx. A comparison of our results with available xenoliths data shows a good agreement between seismic velocity change at a depth of ca. 160 km and a decrease in mantle depletion at about the same depth.

  13. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction

    Science.gov (United States)

    Pilet, Sebastien; Guex, Jean; Muntener, Othmar; Bartolini, Annachiara; Spangenberg, Jorge; Schoene, Blair; Schaltegger, Urs

    2016-04-01

    studies of the composition of the Kaapvaal craton have shown that sulfide minerals are enclosed in the basal part of the cratonic lithosphere. The formation of these sulfide minerals are linked to multiple refertilization/metasomatic events, which affected the base of the subcontinental lithospheric mantle from the Archean to the Proterozoic. We suggest that the transitions from an initial cool period to greenhouse conditions recorded by T-J and Pl-To sedimentary sections result of changing gas species emitted during the progressive thermal erosion of cratonic lithosphere by plume activity or thermal internal heating of the lithosphere. Our petrological model for LIP magmatism argues that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere causing global cooling and eustatic regression, which was followed by warming/transgression associated with the progressive increase of CO2 in the atmosphere associated to LIPs emission and metamorphic reactions in sedimentary basins. We suggest that the nature of the underlying lithosphere during large LIP eruption potentially exerts an important control on the consequences at the Earth's surface. This model offers an explanation for why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere.

  14. Metasomatism and the Weakening of Cratons: A Mechanism to Rift Cratons

    Science.gov (United States)

    Wenker, Stefanie; Beaumont, Christopher

    2016-04-01

    The preservation of cratons is a demonstration of their strength and resistance to deformation. However, several cratons are rifting now (e.g. Tanzania and North China Craton) or have rifted in the past (e.g. North Atlantic Craton). To explain this paradox, we suggest that widespread metasomatism of the originally cold depleted dehydrated craton mantle lithosphere root can act as a potential weakening mechanism. This process, particularly melt metasomatism, increases root density through a melt-peridotite reaction, and reduces root viscosity by increasing the temperature and rehydrating the cratonic mantle lithosphere. Using 2D numerical models, we model silicate-melt metasomatism and rehydration of cold cratonic mantle lithosphere that is positioned beside standard Phanerozoic lithosphere. The models are designed to investigate when a craton is sufficiently weakened to undergo rifting and is no longer protected by the initially weaker adjacent standard Phanerozoic lithosphere. Melt is added to specified layers in the cratonic mantle lithosphere at a uniform volumetric rate determined by the duration of metasomatism (3 Myr, 10 Myr or 30 Myr), until a total of ~30% by volume of melt has been added. During melt addition heat and mass are properly conserved and the density and volume increase by the respective amounts required by the reaction with the peridotite. No extensional boundary conditions are applied to the models during the metasomatism process. As expected, significant refertilization leads to removal and thinning of progressively more gravitationally unstable cratonic mantle lithosphere. We show that the duration of metasomatism dictates the final temperature in the cratonic upper mantle lithosphere. Consequently, when extensional boundary conditions are applied in our rifting tests in most cases the Phanerozoic lithosphere rifts. The craton rifts only in the models with the hottest cratonic upper mantle lithosphere. Our results indicate rifting of cratons

  15. Electrical conductivity of continental lithospheric mantle from integrated geophysical and petrological modeling: Application to the Kaapvaal Craton and Rehoboth Terrane, southern Africa

    OpenAIRE

    Fullea, J.; Muller, M.R.; Jones, A. G.

    2011-01-01

    The electrical conductivity of mantle minerals is highly sensitive to parameters that characterize the structure and state of the lithosphere and sublithospheric mantle, and mapping its lateral and vertical variations gives insights into formation and deformation processes. We review state-of-the-art conductivity models based on laboratory studies for the most relevant upper mantle minerals and define a bulk conductivity model for the upper mantle that accounts for temperature, pressure, and ...

  16. Speculations on the formation of cratons and cratonic basins

    Science.gov (United States)

    McKenzie, Dan; Priestley, Keith

    2016-02-01

    Surface wave tomography using Rayleigh waves has shown that Tibet and the surrounding mountain ranges that are now being shortened are underlain by thick lithosphere, of similar thickness to that beneath cratons. Both their elevation and lithospheric thickness can result from pure shear shortening of normal thickness continental lithosphere by about a factor of two. The resulting thermal evolution of the crust and lithosphere is dominated by radioactive decay in the crust. It raises the temperature of the lower part of the crust and of the upper part of the lithosphere to above their solidus temperatures, generating granites and small volumes of mafic alkaline rocks from beneath the Moho, as well as generating high temperature metamorphic assemblages in the crust. Thermal models of this process show that it can match the P, T estimates determined from metamorphic xenoliths from Tibet and the Pamirs, and can also match the compositions of the alkaline rocks. The seismological properties of the upper part of the lithosphere beneath northern Tibet suggest that it has already been heated by the blanketing effect and radioactivity of the thick crust on top. If the crustal thickness is reduced by erosion alone to its normal value at low elevations, without any tectonic extension, over a time scale that is short compared to the thermal time constant of thick lithosphere, of ∼250 Ma, thermal subsidence will produce a basin underlain by thick lithosphere. Though this simple model accounts for the relevant observations, there is not yet sufficient information available to be able to model in detail the resulting thermal evolution of the sediments deposited in such cratonic basins.

  17. Magnetotelluric characterization of the northern margin of the Yilgarn Craton (Western Australia)

    Science.gov (United States)

    Piña-Varas, Perla; Dentith, Michael

    2017-04-01

    The northern margin of the Yilgarn Craton (Western Australia) was deformed during the convergence and collision with the Pilbara Craton and the intervening Glenburgh Terrain that created the Capricorn Orogen. The Yilgarn Craton is one of the most intensively mineralised areas of continental crust with world class deposits of gold and nickel. However, the region to its north has surprisingly few deposits. Cratonic margins are considered to be key indicators of prospectivity at a regional scale. The northern limit of the Yilgarn Craton within the Capricorn Orogen is not well resolved at date because of overlying Proterozoic sedimentary basins. We present here some of the results of an extensive magnetotelluric (MT) study that is being performed in the area. This study is a component of large multi-disciplinary geoscience project on the 'Distal Footprints of Giant Ore Systems' in the Capricorn Orogen. The MT dataset consists of a total of 240 broadband magnetotelluric stations (BBMT) and 84 long period stations (LMT). Analysis of the dataset reveals a clear 3-D geoelectrical behaviour and extreme complexity for most of the sites, including an extremely high number of sites with phases out-of-quadrant at long periods. 3-D inverse modelling of the MT data shows high resistivity Archean units and low resistivity Paleoproterozoic basins, including very low resistivity structures at depth. These strong resistivity contrasts allow us to successfully map northern margin of the Yilgarn Craton beneath basin cover, as well as identifying major lateral conductivity changes in the deep crust suggestive of different tectonic blocks. Upper crustal conductive zones can be correlated with faults on seismic reflection data. Our results suggest MT surveys are a useful tool for regional-scale exploration in the study area and in area of thick cover in general.

  18. Complex evolution of the lower crust beneath the southeastern North China Craton: The Junan xenoliths and xenocrysts: Comment

    Science.gov (United States)

    Yuan, Ya-Juan; Xia, Bin

    2015-10-01

    The Junan granulite xenoliths and xenocrysts have a distinct overlap in U-Pb ages and Lu-Hf isotopic compositions with the Precambrian basement of the Yangtze craton. We thus believe that the Junan granulite cannot be derived from the North China lower crust. Moreover, broad deep seismic and magnetotelluric probing across the Sulu UHP terrane indicates the former is well coupled with the lower crust of the Yangtze craton. Therefore, we suggest that the Junan granulites are most likely to have been derived from the Yangtze Precambrian basement and their zircon U-Pb-Lu-Hf isotope systematics are more likely to indicate the complex evolution of the Precambrian lower crust along the northern margin of the Yangtze craton.

  19. P and S Wave Finite-frequency Imaging of the Cordillera-craton Boundary Zone in Western Canada

    Science.gov (United States)

    Gu, Y. J.; Chen, Y.; Hung, S. H.

    2016-12-01

    The Western Canada Sedimentary Basin (WCSB) marks a boundary zone and a strong seismic lateral velocity gradient in the upper mantle between the Precambrian North American craton and the Phanerozoic Cordillera. While much of the tectonic imprints are buried below thick sediments, seismic data coverage in this region has been greatly improved to unravel the underlying structure, owing to a growing number of regional broadband arrays. In this study we conduct a high-resolution survey of the mantle P- and S-wave velocities in the WCSB using a multi-scale parameterization and the finite-frequency theory. Our models suggest respective increases of 4% and 6% of Vp and Vs velocities across the Cordilleran Deformation Front (CDF) toward the craton interior. This sharp gradient resides to the west of the CDF, which may imply the over-thrusting of the crustal terranes of the Cordillera onto the craton edge. Significant along-strike variation in the lithospheric basal geometry and dip could reflect secular tectonic modifications such as episodic shortening/extension and convective erosion. The results of our finite-frequency tomography indicate vertically continuous high velocities at least down to 200 km beneath the crustal domains of the Precambrian Buffalo Head Terrane (BHT), Hearne craton and Medicine Hat Block (MHB). The lithosphere beneath the southern Hearne province could extend down to 280 km, nearly 70 km deeper than those of its neighboring cratons of similar ages. The velocity anomalies and their intricate variations/reversals within the mantle lithosphere may be evidence for a multi-stage formation of western Laurentia during Precambrian plate convergence. On the other hand, destruction processes since formation, e.g., convective removal and thermomagmatic erosion, may also have played key roles in shaping the mantle lithosphere beneath the western margin of the North American craton.

  20. Density heterogeneity of the cratonic lithosphere

    DEFF Research Database (Denmark)

    Cherepanova, Yulia; Artemieva, Irina

    2015-01-01

    Using free-board modeling, we examine a vertically-averaged mantle density beneath the Archean-Proterozoic Siberian craton in the layer from the Moho down to base of the chemical boundary layer (CBL). Two models are tested: in Model 1 the base of the CBL coincides with the LAB, whereas in Model 2...... the base of the CBL is at a 180 km depth. The uncertainty of density model is density structure of the Siberian lithospheric mantle with a strong...... correlation between mantle density variations and the tectonic setting. Three types of cratonic mantle are recognized from mantle density anomalies. 'Pristine' cratonic regions not sampled by kimberlites have the strongest depletion with density deficit of 1.8-3.0% (and SPT density of 3.29-3.33 t/m3...

  1. Cratonic lithospheric mantle: Is anything subducted?

    Institute of Scientific and Technical Information of China (English)

    William L. Griffin; Suzanne Y. O'ReiUy

    2007-01-01

    @@ If the subcontinental lithospheric mantle (SCLM) formed through the repeated underthrusting of oceanic slabs, peridotitic SCLM should resemble oceanic peridotites, and mafic rocks (eclogites, s.l.) should be distributed throughout the SCLM. However, cratonic peridotites (both exposed massifs and xenoliths) differ markedly from oceanic and ophiolitic peridotites in their Fe-Cr-Al relationships and abundances of trace elements (Li and B) diagnostic of subduction. "Typical"cratonic peridotites have experienced extensive metaso matism; modelling of their refractory protoliths indicates high-degree melting at high P, perhaps a uniquely Archean process.

  2. Mid-lithosphere discontinuities beneath the western and central North China Craton

    Science.gov (United States)

    Sun, Weijia; Kennett, B. L. N.

    2017-02-01

    By analyzing P reflectivity extracted from stacked autocorrelograms for teleseismic events on a dense seismic profile, we obtain a detailed image of the mid-lithosphere discontinuity (MLD) beneath western and central North China Craton (NCC). This seismic daylight imaging exploits a broad high-frequency band (0.5-4 Hz) to reveal the fine-scale component of multi-scale lithospheric heterogeneity. The depth of the MLD beneath the western and central parts of the NCC ranges 80-120 km, with a good match to the transition to negative S velocity gradient with depth from Rayleigh wave tomography. The MLD inferred from seismic daylight imaging also has good correspondence with the transition from conductive to convective regimes estimated from heat flow data indicating likely thermal control within the seismological lithosphere.

  3. Cyclic Cratonic Carbonates and Phanerozoic Calcite Seas.

    Science.gov (United States)

    Wilkinson, Bruce H.

    1982-01-01

    Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary calcite sediment components in past Paleozoic seas, outlining problems, focusing on models explaining existing data, and identifying background. Future sedimentary geologists will need to address these and related areas…

  4. Petroleum Exploration of Craton Basins in China

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Craton basins are a significant petroliferous provenance. Having undergone multiple openclose tectonic cycles and strong reworking of the late Cenozoic tectonic movement, the craton basins in China are highly broken. This has resulted in multi-source and multiphase hydrocarbon generation and later hydrocarbon accumulation so that a complicated spatial assemblage of primary, paraprimary and secondary oil-gas pools has been formed. The primary factors controlling hydrocarbon accumulation include hydrocarbon-generating depressions, paleouplifts, paleoslopes, unconformity surfaces, paleo-karst, faults and fissure systems as well as the later conservation conditions. In consequence, the strategy of exploration for China's craton basins is to identify the effective source rocks, pay attention to the different effects of paleohighs and late reworking, enhance studies of the secondary storage space, attach importance to the exploration of lithologic oil-gas reservoirs and natural gas pools, and approach consciously from the secondary oil pools to the targets near the source rocks. At the same time, a complete system of technologies and techniques must be built up.

  5. How craton margins are preserved: Insights from geodynamic models

    Science.gov (United States)

    Currie, Claire A.; van Wijk, Jolante

    2016-10-01

    Lateral variations in lithosphere thickness are observed in many continental regions, especially at the boundary between the ancient cratonic core and the adjacent more juvenile lithosphere. In some places, such as the North America craton margin in western Canada and the Sorgenfrei-Tornquist Zone in northern Europe, the transition in lithosphere thickness has a steep gradient (>45°) and it appears to be a long-lived feature (at least 50 Ma). We use thermal-mechanical numerical models to address the dynamics of lithospheric thickness changes on timescales of 100 Ma. Models start with the juxtaposition of 60 km thick lithosphere ("mobile belt") and 160 km thick lithosphere ("craton"). In the reference model, all mantle materials have a damp olivine rheology and a density comparable to primitive mantle. With this configuration, edge-driven mantle convection occurs at the craton boundary, resulting in a lateral smoothing of the thickness transition. The density and rheology of the craton mantle lithosphere are then varied to approximate changes in composition and water content. For all densities, a steep transition is maintained only if the craton strength is 5-50 times stronger than the reference damp olivine. If dry olivine is an upper limit on strength, only cratonic mantle with moderate compositional buoyancy (20-40 kg/m3 less dense than primitive mantle) remains stable. At higher densities, the thick lithosphere is eroded through downwellings, and the craton margin migrates inboard. Conversely, a compositionally buoyant craton destabilises through lateral spreading below the mobile belt.

  6. On the Origin of High Shear Wave Velocities in the Deep Roots of Cratons

    Science.gov (United States)

    Zeng, L.; Duncan, M. S.; Garber, J. M.; Hernandez, J. A.; Maurya, S.; Zhang, H.; Faul, U.; McCammon, C. A.; Montagner, J. P.; Moresi, L. N.; Romanowicz, B. A.; Rudnick, R. L.; Stixrude, L. P.

    2016-12-01

    Some seismic models derived from tomographic studies indicate very high shear wave velocities around 150 km depth, which cannot be explained by standard cratonic peridotite compositions derived from kimberlites, even under the assumption of very cold geotherms (i.e. 28mW/m3 surface heat flux). We present the results of a multi-disciplinary study conducted at the CIDER Summer 2016 program in Santa Barbara (CA), in which we have reviewed various geophysical and petrological constraints on the nature of cratonic roots (seismic velocities, electrical conductivity, gravity, lithologies) and explored a range of possible solutions. We find that matching the high shear wave velocities requires a large proportion of eclogite that is not matched by observed eclogite proportions in kimberlite samples. The high shear velocity of diamond makes it a viable candidate to account for such high velocities, in a proportion that is compatible with the global carbon budget. Our most recent results will be presented as well as suggestions for possible mechanisms for diamond formation and emplacement.

  7. Petrogenesis of Early Cretaceous basaltic lavas from the North China Craton: Implications for cratonic destruction

    Science.gov (United States)

    Qian, Sheng-Ping; Ren, Zhong-Yuan; Richard, Wysoczanski; Zhang, Le; Zhang, Yin-Hui; Hong, Lu-Bing; Ding, Xiang-Li; Wu, Ya-Dong

    2017-03-01

    The North China Craton (NCC) is believed to be the best example of cratonic destruction. However, the processes leading to cratonic destruction remain unclear, largely due to a lack of knowledge of the nature of the Mesozoic NCC lithospheric mantle. Here we report new petrological and geochemical data for Early Cretaceous NCC basalts, which provide insights into the nature of the underlying lithospheric mantle. The Early Cretaceous basalts (all tholeiites) show a limited variation in geochemical composition. In contrast, olivine-hosted melt inclusions from these basalts display a wide range in compositional variation and include both alkalic and tholeiitic basaltic compositions. This result provides the direct evidence of the contribution of silica-undersaturated alkali basaltic melts in the petrogenesis of the Early Cretaceous NCC basalts. In addition, the compositions of olivine phenocrysts and reconstructed primary melts indicate that the Early Cretaceous basalts are derived from a mixed peridotite and refertilized peridotite source. The Pb isotopic compositions of melt inclusions in high fugacity of oxygen (fo) olivines combined with trace element characteristics of these basalts reveal that heterogeneous lithospheric mantle sources for Early Cretaceous basalts were metasomatized by carbonate-bearing eclogite-derived melts. The Pb isotopic variations of the melt inclusions and clinopyroxene and plagioclase phenocrysts demonstrate that the mantle-derived magmas were variably contaminated by lower continental crust. We propose that multiple subduction events during the Phanerozoic, combined with mantle-plume activity, likely play a vital role in the generation of the Early Cretaceous voluminous magmatism and cratonic destruction.

  8. Moho Depth Variations in the Northeastern North China Craton Revealed by Receiver Function Imaging

    Science.gov (United States)

    Zhang, P.; Chen, L.; Yao, H.; Fang, L.

    2016-12-01

    The North China Craton (NCC), one of the oldest cratons in the world, has attracted wide attention in Earth Science for decades because of the unusual Mesozoic destruction of its cratonic lithosphere. Understanding the deep processes and mechanism of this craton destruction demands detailed knowledge about the deep structure of the region. In this study, we used two-year teleseismic receiver function data from the North China Seismic Array consisting of 200 broadband stations deployed in the northeastern NCC to image the Moho undulation of the region. A 2-D wave equation-based poststack depth migration method was employed to construct the structural images along 19 profiles, and a pseudo 3D crustal velocity model of the region based on previous ambient noise tomography and receiver function study was adopted in the migration. We considered both the Ps and PpPs phases, but in some cases we also conducted PpSs+PsPs migration using different back azimuth ranges of the data, and calculated the travel times of all the considered phases to constrain the Moho depths. By combining the structure images along the 19 profiles, we got a high-resolution Moho depth map beneath the northeastern NCC. Our results broadly consist with the results of previous active source studies [http://www.craton.cn/data], and show a good correlation of the Moho depths with geological and tectonic features. Generally, the Moho depths are distinctly different on the opposite sides of the North-South Gravity Lineament. The Moho in the west are deeper than 40 km and shows a rapid uplift from 40 km to 30 km beneath the Taihang Mountain Range in the middle. To the east in the Bohai Bay Basin, the Moho further shallows to 30-26 km depth and undulates by 3 km, coinciding well with the depressions and uplifts inside the basin. The Moho depth beneath the Yin-Yan Mountains in the north gradually decreases from 42 km in the west to 25 km in the east, varying much smoother than that to the south.

  9. Seismic basement in Poland

    Science.gov (United States)

    Grad, Marek; Polkowski, Marcin

    2016-06-01

    The area of contact between Precambrian and Phanerozoic Europe in Poland has complicated structure of sedimentary cover and basement. The thinnest sedimentary cover in the Mazury-Belarus anteclize is only 0.3-1 km thick, increases to 7-8 km along the East European Craton margin, and 9-12 km in the Trans-European Suture Zone (TESZ). The Variscan domain is characterized by a 1- to 2-km-thick sedimentary cover, while the Carpathians are characterized by very thick sediments, up to c. 20 km. The map of the basement depth is created by combining data from geological boreholes with a set of regional seismic refraction profiles. These maps do not provide data about the basement depth in the central part of the TESZ and in the Carpathians. Therefore, the data set is supplemented by 32 models from deep seismic sounding profiles and a map of a high-resistivity (low-conductivity) layer from magnetotelluric soundings, identified as a basement. All of these data provide knowledge about the basement depth and of P-wave seismic velocities of the crystalline and consolidated type of basement for the whole area of Poland. Finally, the differentiation of the basement depth and velocity is discussed with respect to geophysical fields and the tectonic division of the area.

  10. Reprocessing Coincident Refraction and Reflection Data to Constrain the Moho Depth in the Slave Craton, Northwest Territories, Canada.

    Science.gov (United States)

    Aristimuno, J.

    2005-12-01

    The Slave geological province, a relatively small area in the Canadian Northwest Territories incluiding the oldest rocks on Earth, is one of five cratons that form the Archean continental core of North America. Its tectonic evolution differs from the classical "life-raft model" proposed for most Archean terranes. In the Slave Craton, radiometric dating has revealed an east-west disparity between the various bedrock units exposed. The underlying lithospheric mantle, on the other hand, exhibits a NW-SE zonation, comprising three regions with distinctive geochemical and geophysical characteristics. This complex superposition suggests that crust-mantle coupling and stabilization occurred late in the orogenic development of the craton. Previous reflection and refraction studies in the Slave Craton have shown coincident reflection and refraction Moho depths at 33-35 km, which remain relatively constant beneath the Archean Slave Province and the Proterozoic domains located to the west. This is contrary to average values of crustal thickness from global compilations that would suggest a thicker Proterozoic crust of approximately 45 km. This observation implies that the Moho probably acted as a zone of detachment (mechanical boundary) during the Proterozoic Hottah-Slave collision. The Slave Craton has been extensively surveyed using seismic methods as part of the SNORCLE transect of the Canadian Lithoprobe project. The available data for this study are from a 600 km long seismic refraction/deep wide-angle reflection 2D profile acquired in 1997. In this paper, we present results from reprocessing both refraction and reflection seismic data. First, the refraction data is inverted and the resulting synthetic shot gathers are compared to observed data to validate the refraction velocity model. Then, the new velocity model is used as input to migrate the wide-angle reflection data. In addition, the depth to the Moho derived from inverted data will be compared to the interpreted

  11. Traces of the crustal units and the upper mantle structure in the southwestern part of the East European Craton

    Directory of Open Access Journals (Sweden)

    I. Janutyte

    2014-04-01

    Full Text Available The presented study is a part of the passive seismic experiment PASSEQ 2006–2008 which took place around the Trans-European Suture Zone (TESZ from May 2006 to June 2008. The dataset of 4195 manually picked arrivals of teleseismic P waves of 101 earthquakes (EQs recorded in the PASSEQ seismic stations deployed to the east of the TESZ was inverted using the non-linear teleseismic tomography algorithm TELINV. Two 3-D crustal models were used to estimate the crustal travel time (TT corrections. As a result, we obtained a model of P wave velocity variations in the upper mantle beneath the TESZ and the EEC. In the study area beneath the craton we observed 5 to 6.5% higher and beneath the TESZ about 4% lower seismic velocities compared to the IASP91 velocity model. We found the seismic lithosphere-asthenosphere boundary (LAB beneath the TESZ at a depth of about 180 km, while we observed no seismic LAB beneath the EEC. The inversion results obtained with the real and the synthetic datasets indicated a ramp shape of the LAB in the northern TESZ where we observed values of seismic velocities close to those of the craton down to about 150 km. The lithosphere thickness in the EEC increases going from the TESZ to the NE from about 180 km beneath Poland to 300 km or more beneath Lithuania. Moreover, in western Lithuania we possibly found an upper mantle dome. In our results the crustal units are not well resolved. There are no clear indications of the features in the upper mantle which could be related with the crustal units in the study area. On the other hand, at a depth of 120–150 km we possibly found a trace of a boundary of proposed palaeosubduction zone between the East Lithuanian Domain (EL and the West Lithuanian Granulite Domain (WLG. Also, in our results we may have identified two anorogenic granitoid plutons.

  12. Proterozoic granitoids of the Amazonian craton

    Science.gov (United States)

    dalĺAgnol, R.; Costi, H. T.; Lamarão, C. N.; Teixeira, N. P.; Bettencourt, J. S.; Fraga, L. M.

    2003-04-01

    Proterozoic granitoids are widespread in all provinces of the Amazonian craton. In the Maroni-Itacaiunas Province, granitoids associated with the Trans-Amazonian event include: subduction related, 2.16 to 2.14 Ga, calc-alkaline tonalites and trondhjemites; 2.10 to 2.08 Ga, syncolisional potassic granites; 2.05 Ga, charnockites. In the Tapajós Province, ˜2.01 Ga, tonalites are followed by ˜2.0 Ga volcanic sequences and ˜1.98 to 1.96 Ga calc-alkaline granitoids. A reappraisal of magmatic activity occurred at ˜1.88 Ga when calc-alkaline granitoids, as well as subalkaline, A-type granites, associated with felsic volcanic sequences were formed. A similar picture is observed in the northern Roraima region, where post-collisional 2.0 to 1.96 Ga calc-alkaline granitoids and associated volcanic sequences are followed by 1.92 Ga A-type granites. The remarkable 1.88 Ga magmatic event has a continental scale and is related to an extensional tectonism. It affected also the Archean Carajás Province, where, at this time, within-plate, shallow-level, A-type granites were emplaced. Coeval intermediate to felsic volcanic sequences are widespread in the Central Amazonian Province. In the Pitinga region, these sequences are intruded by ˜1.82 Ga, tin-mineralized granites. In the Central Guiana Belt and in the northwestern domains of the Guiana shield ˜1.55 Ga rapakivi complexes, locally with associated anorthosites and mangerites, are common. In the Rio Negro Province, 1.8 to 1.60 calc-alkaline (?) granitoids and gneisses are dominant. They are followed by 1.55 to 1.52 Ga, oxidized, titanite-bearing A-type granites and S-type, two-mica granites. The evolution of the southwestern part of the Amazonian craton is characterized by the occurrence of successive tectonic events extending from ˜1.75 Ga to ˜1.0 Ga. The oldest granitoids are dominantly calc-alkaline tonalites, trondhjemites and granodiorites. However, the Rondonia region is marked by the occurrence of 1.6 to 1.0 Ga old

  13. Geological evolution of the Antongil Craton, NE Madagascar

    Science.gov (United States)

    Schofield, D.I.; Thomas, Ronald J.; Goodenough, K.M.; De Waele, B.; Pitfield, P.E.J.; Key, R.M.; Bauer, W.; Walsh, G.J.; Lidke, D.J.; Ralison, A.V.; Rabarimanana, M.; Rafahatelo, J.-M.; Randriamananjara, T.

    2010-01-01

    The Antongil Craton, along with the Masora and Antananarivo cratons, make up the fundamental Archaean building blocks of the island of Madagascar. They were juxtaposed during the late-Neoproterozoic to early Palaeozoic assembly of Gondwana. In this paper we give a synthesis of the geology of the Antongil Craton and present previously published and new geochemical and U-Pb zircon analyses to provide an event history for its evolution.The oldest rocks in the Antongil Craton form a nucleus of tonalitic gneiss, characteristic of Palaeo-Mesoarchaean cratons globally, including phases dated between 3320 ?? 14. Ma to 3231 ?? 6. Ma and 3187 ?? 2. Ma to 3154 ?? 5. Ma. A series of mafic dykes was intruded into the Mesoarchaean tonalites and a sedimentary succession was deposited on the craton prior to pervasive deformation and migmatisation of the region. The age of deposition of the metasediments has been constrained from a volcanic horizon to around 3178 ?? 2. Ma and subject to migmatisation at around 2597 ?? 49. Ma. A subsequent magmatic episode generated voluminous, weakly foliated granitic rocks, that also included additions from both reworked older crustal material and younger source components. An earlier granodiorite-dominated assemblage, dated between 2570 ?? 18. Ma and 2542 ?? 5. Ma, is largely exposed in xenoliths and more continuously in the northern part of the craton, while a later monzogranite-dominated phase, dated between 2531 ?? 13. Ma and 2513 ?? 0.4. Ma is more widely developed. Together these record the stabilisation of the craton, attested to by the intrusion of a younger dyke swarm, the age of which is constrained by a sample of metagabbro dated at 2147 ?? 6. Ma, providing the first evidence for Palaeoproterozoic rocks from the Antongil Craton.The youngest events recorded in the isotopic record of the Antongil Craton are reflected in metamorphism, neocrystallisation and Pb-loss at 792 ?? 130. Ma to 763 ?? 13. Ma and 553 ?? 68. Ma. These events are

  14. Construction and destruction of some North American cratons

    Science.gov (United States)

    Snyder, D. B.; Humphreys, G.

    2015-12-01

    Construction histories of Archean cratons remain poorly understood; their destruction is even less clear because of, by definition, its rarity. By assembling geophysical and geochemical data in 3-D lithosphere models, a clearer understanding of the geometry of major structures within the Rae, Slave and Wyoming cratons of central North America is now possible. Little evidence exists of subducted slabs similar to modern oceanic lithosphere in these construction histories whereas underthrusting and wedging of proto-continental lithosphere is inferred from multiple dipping discontinuities. Archean continental building blocks may resemble the modern lithosphere of Ontong-Java-Hikurangi oceanic plateau. Radiometric dating of xenoliths provides estimates of rock types and ages at depth beneath sparse kimberlite occurrences. These ages can be correlated to surface rocks. The 3.6-2.6 Ga Rae, Slave and Wyoming cratons comprise smaller continental terranes that 'cratonized' during a granitic bloom at 2.61-2.55 ga. Cratonization probably represents the final differentiation of early crust into a relatively homogeneous, uniformly thin (35-42 km), tonalite-trondhjemite-granodiorite crust with pyroxenite layers near the Moho atop depleted lithospheric mantle. Peak thermo-tectonic events at 1.86-1.7 Ga broadly metasomatized, mineralized and recrystallized mantle and lower crustal rocks, apparently making mantle peridotite more 'fertile' and conductive by introducing or concentrating sulfides or graphite throughout the lithosphere at 80-120 km depths. This metasomatism may have also weakened the lithosphere or made it more susceptible to tectonic or chemical erosion. The arrival of the subducted Shatsky Rise conjugate at the Wyoming craton at 65-75 Ma appears to have eroded and displaced the thus weakened base of the craton below 140-160 km. This replaced old refertilized continental mantle with new depleted oceanic mantle. Is this the same craton?

  15. Neotectonic activity and parity in movements of Udaipur block of the Arvalli Craton and Indian Plate

    Indian Academy of Sciences (India)

    Harsh Bhu; Ritesh Purohit; Joga Ram; Pankaj Sharma; S R Jakhar

    2014-03-01

    We report site motion of a permanent GPS site at Udaipur (udai), Rajasthan on the Udaipur block of Aravalli Craton. The GPS measurements of 2007–2011 suggest that the site moves at a rate of about 49 mm/year towards northeast. As the site motion is consistent with the predicted plate motion using the estimated euler pole of rotation for the Indian Plate, it implies that there is insignificant internal deformation/strain in the region. Such a deformation is consistent with very low seismic activity in the region. The epicenters of the infrequent low magnitude earthquakes are located on the Precambrian lineaments on the west of Udaipur Block, and on the NW–SE striking younger lineament in the south of the block.

  16. Causes of intraplate seismicity in central Brazil from travel time seismic tomography

    Science.gov (United States)

    Rocha, Marcelo Peres; Azevedo, Paulo Araújo de; Marotta, Giuliano Sant'Anna; Schimmel, Martin; Fuck, Reinhardt

    2016-06-01

    New results of travel time seismic tomography in central Brazil provide evidence that the relatively high seismicity in this region is related to the thinner lithosphere at the limit between the Amazonian and São Francisco paleocontinents. The transition between these paleocontinents is marked by low velocity anomalies, spatially well correlated with the high seismicity region, which are interpreted as related to the lithospheric thinning and consequent rise of the asthenosphere, which have increased the temperature in this region. The low-velocity anomalies suggest a weakness region, favorable to the build-up of stress. The effective elastic thickness and the strain/stress regime for the study area are in agreement with tomographic results. A high-velocity trend is observed beneath the Parnaíba Basin, where low seismicity is observed, indicating the presence of a cratonic core. Our results support the idea that the intraplate seismicity in central Brazil is related to the thin lithosphere underlying parts of the Tocantins Province between the neighboring large cratonic blocks.

  17. Crustal seismicity and the earthquake catalog maximum moment magnitudes (Mcmax) in stable continental regions (SCRs): correlation with the seismic velocity of the lithosphere

    Science.gov (United States)

    Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun

    2012-01-01

    A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (δVS) relative to the Preliminary Reference Earth Model (PREM). We compare δVS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by δVS≥3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with δVS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.

  18. Southern Appalachian Regional Seismic Network

    Energy Technology Data Exchange (ETDEWEB)

    Chiu, S.C.C.; Johnston, A.C.; Chiu, J.M. [Memphis State Univ., TN (United States). Center for Earthquake Research and Information

    1994-08-01

    The seismic activity in the southern Appalachian area was monitored by the Southern Appalachian Regional Seismic Network (SARSN) since late 1979 by the Center for Earthquake Research and Information (CERI) at Memphis State University. This network provides good spatial coverage for earthquake locations especially in east Tennessee. The level of activity concentrates more heavily in the Valley and Ridge province of eastern Tennessee, as opposed to the Blue Ridge or Inner Piedmont. The large majority of these events lie between New York - Alabama lineament and the Clingman/Ocoee lineament, magnetic anomalies produced by deep-seated basement structures. Therefore SARSN, even with its wide station spacing, has been able to define the essential first-order seismological characteristics of the Southern Appalachian seismic zone. The focal depths of the southeastern U.S. earthquakes concentrate between 8 and 16 km, occurring principally beneath the Appalachian overthrust. In cross-sectional views, the average seismicity is shallower to the east beneath the Blue Ridge and Piedmont provinces and deeper to the west beneath the Valley and Ridge and the North American craton. Results of recent focal mechanism studies by using the CERI digital earthquake catalog between October, 1986 and December, 1991, indicate that the basement of the Valley and Ridge province is under a horizontal, NE-SW compressive stress. Right-lateral strike-slip faulting on nearly north-south fault planes is preferred because it agrees with the trend of the regional magnetic anomaly pattern.

  19. An infrared investigation of inclusion-bearing diamonds from the Venetia kimberlite, Northern Province, South Africa : implications for diamonds from craton-margin settings

    Science.gov (United States)

    Viljoen, (Fanus)

    2002-08-01

    The Venetia kimberlites in the Northern Province of South Africa sampled diamonds from the lithosphere underlying the Central Zone of the Limpopo Belt. Given the general correlation of diamond-bearing kimberlites with old stable cratons, this tectonic setting is somewhat anomalous and, therefore, it is desirable to characterise the diamonds in terms of their infrared characteristics. A suite of diamonds of known paragenesis from the Venetia mine spans a large range of nitrogen concentrations from less than the detection limit to 1,355 ppm. Diamond nitrogen contents are, on average, higher in the eclogitic diamond population relative to the websteritic and peridotitic diamonds. Nitrogen aggregation states are variable, ranging from almost pure type IaA diamond (poorly aggregated nitrogen) to pure type IaB diamond (highly aggregated nitrogen). On a nitrogen aggregation diagram two distinct groups can be identified based on nitrogen content and nitrogen aggregation state. These are a minor population of diamonds with nitrogen contents generally higher than 500 ppm and nitrogen aggregation states of less than 40% IaB, and another, dominant population that is characterised by higher and more variable nitrogen aggregation. The unusually aggregated nature of the majority of the diamonds analysed is unique to Venetia relative to other intrusives on the Kaapvaal-Kalahari craton, but is similar to aggregation states observed for diamonds from other craton margin or adjacent mobile belt settings such as the Argyle lamproite and the George Creek kimberlite. This could be a consequence of diamond mantle residence at mantle temperatures higher than the norm for other kimberlites from the interior of cratons. Deformation of the mantle, associated with dynamic processes such as orogenesis or subduction, might also be responsible for accelerating the rate of nitrogen aggregation in these diamonds. Low numbers of diamonds with degradation of platelets at the Venetia kimberlite

  20. The formation and the geochemical and thermal evolution of the lithospheric mantle beneath the Kaapvaal craton recorded by subcalcic garnets from harzburgites and by pristine eclogites and garnet-pyroxenites

    OpenAIRE

    Shu, Qiao

    2013-01-01

    The mantle xenoliths collected by kimberlites indicate that the subcratonic mantle underneath the Archean crust is mostly a residue of high degrees of partial melting which was subsequently reenriched. The majority of the xenoliths show cryptic metasomatism and only few modal metasomatism. Much effort has been put into deciphering different kinds of enrichment processes within the mantle. Here, we take the approach to look into the inventory of subcalcic garnets which stem from cpx-free ha...

  1. A trace element and Pb isotopic investigation into the provenance and deposition of stromatolitic carbonates, ironstones and associated shales of the ∼3.0 Ga Pongola Supergroup, Kaapvaal Craton

    Science.gov (United States)

    Bolhar, Robert; Hofmann, Axel; Siahi, Mehrnaz; Feng, Yue-xing; Delvigne, Camille

    2015-06-01

    Major and trace element, and Pb isotopic data for chemical and clastic sedimentary rocks of the Mesoarchaean Pongola Supergroup are employed to infer aspects of the provenance and depositional environment, including ambient seawater composition. Stromatolitic carbonates of the Nsuze Group were formed in a tidal-flat setting, whereas ironstones of the Mozaan Group were deposited in an outer-shelf setting during marine transgression. Geochemical criteria, employed to test for crustal contamination and diagenetic/metamorphic overprinting, demonstrate that carbonates and ironstones preserved their primary chemical signature. In comparison to other documented Precambrian stromatolites, shale-normalised REE+Y patterns for Nsuze carbonates show pronounced enrichment in middle REE, but lack strong elemental anomalies (La, Gd, Y) that are diagnostic for derivation from open marine waters. In contrast, normalised REE+Y for ironstones exhibit distinct positive La, Gd and Y anomalies. Both rock types are devoid of normalised Ce anomalies and show only minor enrichment in Eu, suggesting deposition in anoxic environments (with respect to the Ce3+/Ce4+ redox couple) accompanied by minor high-temperature hydrothermal input. Trace element geochemical data are most consistent with deposition of Nsuze carbonates in a shallow-water epicontinental basin with restricted but variable exchange to the open-ocean and dominant fluvial input, whereas ironstone precipitated in a deeper-water, epicontinental sea. Estuarine fractionation and organic complexation due to microbial activity is possibly indicated by MREE enrichment of the carbonates, also consistent with a restricted environment. Shales belonging to the Mozaan Group are characterised by high concentrations of Al and K relative to Ca, Na and Sr, indicative of pronounced in-situ weathering, coupled with K-metasomatism. The provenance is mixed, comprising (ultra)mafic and granitic source rocks. Pb isotope regression for Nsuze carbonates documents a widespread, tectono-thermal or fluid percolation event at around 2.4 Ga. Two-stage modelling of Pb isotope data, in association with published Sr and Nd isotope data, requires a source for Nzuse carbonates that was derived from evolved continental crust with an elevated U/Pb ratio (μ-value) and an approximate crustal residence time of ∼100-600 Ma.

  2. The Acasta Gneiss - a Hadean cratonic nucleus

    Science.gov (United States)

    Sprung, P.; Scherer, E. E.; Maltese, A.; Bast, R.; Bleeker, W.; Mezger, K.

    2016-12-01

    The known terrestrial rock record lacks undisputed, chemically intact Hadean crust. Direct evidence from this eon has been restricted to zircon grains within younger rocks [1]. The Acasta Gneiss Complex (AGC; NT, CA) has yielded zircon with Hadean domains [e.g., 2,3], but the time at which AGC rocks became closed chemical systems is unclear [4,5]. Determining this `time of last disturbance' (tld) would provide a minimum protolith age, and is crucial for using radiogenic isotope compositions of bulk rocks to trace crust-mantle evolution. Recent studies mostly focused on the `low-strain' eastern AGC [e.g., 6, 7], which records an evolving, early-mid Archean cratonic nucleus [7]. We also studied the `high-strain' banded gneiss in the western AGC, which hosts >4 Ga zircon domains [2,3], too. Our focusing lay on adjoining, lithologically distinct bands [8] of two distinct chemical groups: A) Mafic, chondrite-normalized LaN/YbN ≦20, slightly HFSE- depleted, and B) TTG-like, LaN/YbN up to 145, markedly HFSE-depleted. Six adjacent bands yield a well-defined 4 Ga Sm-Nd isochron with a ɛNd4Ga of +2 and ɛHf4Ga values from +1 to +6. Within-band Sm-Nd and Lu-Hf systematics imply younger mineral re-equilibration [9]. We interpret the 4 Ga Sm-Nd isochron to date the physical juxtaposition of bands in the gneiss unit and to define tld among bands for elements less mobile and diffusive than Sm and Nd. Contrasting Sm-Nd results from the same unit [10] likely are due to sampling at too fine a scale. Digestion of metamict pre-tld zircon likely caused the scatter in Lu-Hf. Both decay systems hint at the existence of a possibly local, strongly depleted Hadean mantle domain. The TTG-like bands are 0.4 Gyr older than similar rocks in the `low-strain' eastern AGC [7]. The AGC was thus an evolved cratonic nucleus already at 4 Ga, possibly with a depleted lithospheric keel. [1] Cavosie et al. (2004) Prec. Res. 135, 251-279 [2] Bowring & Williams (1999) CMP 134, 3-16 [3] Iizuka et al

  3. Crustal uplift of the Precambrian cratons due to metamorphism in crustal rocks under infiltration of mantle fluids

    Science.gov (United States)

    Artyushkov, Eugene; Chekhovich, Peter; Korikovsky, Sergey; Massonne, Hans-Joachim

    2017-04-01

    Precambrian cratons cover about 70% of the total area of the continents. During the last several million years cratonic areas underwent rapid uplift, from 100-200 m in East Europe to 1000-1500 m Southern Africa. Shortening of the Precambrian crust terminated half a billion years ago or earlier and this popular mechanism cannot be applied to its recent uplift. Large thickness of cratonic mantle lithosphere, 100-200 km in most regions, together with its low density precludes delamination of this layer and magmatic underplating as possible causes of recent uplift. It cannot be precluded that in some cratonic regions recent uplift occurred due to delamination of the lower part of mantle lithosphere with the density increased by metasomatism. Even a small uplift of ≥ 100-200 m would require delamination of a thick layer of mantle lithosphere. As a result a temperature drop of > 200 C would arise at the base of the lithosphere producing a shear wave velocities drop of > 2%. According to the seismic tomography data such a drop in VS is observed only in some regions with the Precambrian lithosphere, e.g., in Northeastern Africa. Spatial distribution of the Precambrian cratons is quite different from that predicted by the main models of dynamic topography in the mantle. Moreover, many uplifted blocks are bounded by steep slopes hundreds of meters to one kilometer high and only tens of kilometers wide. Such slopes could not have been formed by bending of thick cratonic lithosphere under the forces acting from below. Their recent formation indicates rock expansion within the crust at shallow depth comparable with the slope width. Rocks formed at the pressure P ˜ 0.5-1.0 GPa are widespread on the Precambrian cratons. This indicates that during their lifetime a layer of rocks ˜ 15-30 km thick has been removed from the crustal surface by denudation. As a result rocks which were initially located in the lower crust emerged to the middle or upper crust. Due to metamorphic

  4. Lithospheric thermal structure of the North China Craton and its geodynamic implications

    Science.gov (United States)

    Liu, Qiongying; Zhang, Linyou; Zhang, Chao; He, Lijuan

    2016-12-01

    We conduct 2-D numerical modeling of the lithospheric thermal structure of the North China Craton (NCC) on basis of twenty-four crustal velocity structure profiles. About five hundred heat flow data constitute the principal constraints for our modeling. The modeling results demonstrate marked lateral variations in thermal regime of the crust-lithosphere system in the NCC. The average mantle heat flow decreases from 38 ± 5 mW m-2 under the Bohai Bay Basin in the eastern NCC to 27 ± 4 mW m-2 under the Ordos Basin in the western NCC, characterized by a 'cold crust but hot mantle' structure and a 'hot crust but cold mantle' structure, respectively. Thermal lithospheric thickness varies from ∼65 km beneath the Tan-Lu Fault zone to ∼160 km beneath the western and northern Ordos Basin, with similar trend to the seismic lithosphere. However, the disparities in thickness between the thermal and seismic lithosphere are within 20 km beneath the Bohai Bay Basin, but 30-90 km beneath the Shanxi-Weihe Graben and 50-120 km beneath the Ordos Basin. This may imply a westward thickening trend of the rheological boundary layer, which might be attributed to the reducing of asthenosphere viscosity due to hydrous fluid released by dehydration of the subducting Pacific Plate under the eastern NCC. Combined with other pieces of evidence, we suggest that vigorous mantle processes may occur beneath the eastern NCC, whereas the western NCC is relatively stable.

  5. Lithological and age structure of the lower crust beneath the northern edge of the North China Craton: Xenolith evidence

    Science.gov (United States)

    Wei, Ying; Zheng, Jianping; Su, Yuping; Ma, Qiang; Griffin, William L.

    2015-02-01

    Deep-seated xenoliths in volcanic rocks offer direct glimpses into the nature and evolution of the lower continental crust. In this contribution, new data on the U-Pb ages and Hf isotopes of zircons in six felsic granulite xenoliths and one pyroxenite xenolith from the Hannuoba Cenozoic basalts, combined with published data from mafic to felsic xenoliths, are used to constrain the lithological and age structure of the lower crust beneath the northern edge of the North China Craton. Two newly-reported felsic granulites contain Precambrian zircons with positive (+ 7.5-+ 10.6) and negative εHf values (- 10.1 to - 3.7) corresponding to upper intercept ages of 2449 ± 62 Ma and 1880 ± 54 Ma, respectively, indicating crustal accretion in the late Archean and reworking in Paleoproterozoic time. Zircons in another four felsic xenoliths give Phanerozoic ages from 142 Ma to 73 Ma and zircons from one pyroxenite xenolith give a concordant age of 158 Ma. The zircon εHf values of these four felsic xenoliths range between - 23.3 and - 19.1, reflecting re-melting of the pre-existing lower crust. Integration of geothermobarometric, and geochronological data on the Hannuoba xenoliths with seismic refraction studies shows that the lower crust beneath the northern edge of the North China Craton is temporally and compositionally zoned: the upper lower crust (24-33 km) consists dominantly of Archean (~ 2.5 Ga with minor 2.7 Ga) felsic granulites with subordinate felsic granulites that reworked at 140-120 Ma; both Precambrian and late Mesozoic mafic granulites are important constituents of the middle lower crust (33-38 km); major late Mesozoic (140-120 Ma) and less Cenozoic (45-47 Ma) granulites and pyroxenites are presented in the lowermost crust (38-42 km). The zoned architecture of the lower crust beneath Hannuoba suggests a complex evolution beneath the northern margin of the craton, including late Neoarchean (~ 2.5 Ga) accretion and subsequent episodic accretion and/or reworking

  6. Multi-stage crustal growth and cratonization of the North China Craton

    Directory of Open Access Journals (Sweden)

    Mingguo Zhai

    2014-07-01

    The ∼2.5 Ga metamorphic-magmatic event is stronger than in most other cratons in the world. How to understand the geological significance of the 2.5 Ga event? The following points are emphasized: (1 nearly all old rocks >2.5 Ga underwent metamorphism at ∼2.52–2.5 Ga; (2 Archean basement rocks in the NCC experienced strong partial melting and migmatization; (3 granitoid rocks derived from partial melting include potassium granites, TTG granites and monzonites. These granitoids rocks intruded both the Archean greenstone belts and micro-blocks; (4 ∼2.5 Ga mafic dikes (amphibolites, granitic dikes (veins and syenitic-ultramafic dykes are also developed. Therefore, we suggest an assembly model that all micro-blocks in the NCC were welded together by late Archean greenstone belts at the end of the late Neoarchean. We also propose that the various micro-blocks were surrounded by small ocean basins, and the old continental crust and the oceanic crust were hotter than today. Subduction and collision were on much smaller scales as compared to the Phanerozoic plate tectonic regime, although the tectonic style and mechanisms were more or less similar. The formation of crustal melt granites is one of the processes of cratonization, inducing generation of stable upper and lower crustal layers. This process also generated an upper crust of more felsic composition and a lower crust of more mafic composition, due to molten residual materials and some underplated gabbros.

  7. Geochemistry of khondalites from the central portion of North China craton (NCC): implications for the continental cratonization in the Neoarchean

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Within the high-grade metamorphic basement, the central portion of North China Craton (NCC), a group of Neoarchean khondalites (KS) is identified. They are characterized by large ion lithophile elements (LILE) enrichment, lower abundances of Zr, Hf and Sr. Their rare earth element (REE) distribution has significant LREE enrichment and negative Eu anomalies. The protoliths of KS are interpreted as feldspathic quartzite, shale or pelite and carbonite, deposited in a shallow sea upon cratonic shelf distant from the land. KS's source region might be dominated by granitic rocks, with a minor amount of TTG, underwent comparatively severe chemical weathering. Considering relevent tectonic constraints, we suggest that khondalites from central portion of NCC, an important metamophosed sedimentary cover, are the most significant exogenetic marker of Neoarchean continental cratonization for NCC.

  8. An integrated petrological, geochemical and Re-Os isotope study of peridotite xenoliths from the Argyle lamproite, Western Australia and implications for cratonic diamond occurrences

    Science.gov (United States)

    Luguet, A.; Jaques, A. L.; Pearson, D. G.; Smith, C. B.; Bulanova, G. P.; Roffey, S. L.; Rayner, M. J.; Lorand, J.-P.

    2009-11-01

    An integrated study of the petrology and Re-Os geochemistry of a suite of peridotite xenoliths, some carrying abundant diamonds, from the richly diamondiferous Argyle AK1 lamproite pipe provides definitive evidence for a depleted lithospheric root of Neoarchean age (T RD eruption ˜ 2.2-3.1 Ga) beneath the Proterozoic Halls Creek Orogen at the margin of the Kimberley Craton, Western Australia. The microdiamonds from the peridotitic xenoliths are similar in their properties to the minor population of small, commercial sized, peridotitic diamonds from Argyle, both formed in the Archean from isotopically mantle-like carbon. The major element bulk chemistry and mineral chemistry of the Argyle peridotites are slightly less depleted than Archean cratonic peridotites as a whole but similar to those reported from Neoarchean-Paleoproterozoic cratonic provinces. The Argyle peridotite xenoliths were derived from within the diamond stability field (1050-1300 °C and 4.9-5.9 GPa) near the base of the lithosphere (typically 160-200 km depth) with a geothermal gradient of 41.5 mW/m 2. This thick diamondiferous lithosphere, estimated at up to 225 km thick from present day seismic S-wave tomography, appears to have persisted since the time of eruption of the Argyle lamproite (˜ 1180 Ma). The existence of late Archean age lithosphere beneath the Argyle diamond pipe, in a region where no crustal rocks of Archean age are known, suggests a decoupling of the crust and mantle in the region of the Halls Creek Orogen, perhaps as a consequence of Paleoproterozoic (˜ 1.85 Ga) reworking and/or subduction at the margin of the Kimberley Craton. The confirmation of an Archean lithospheric root beneath the Argyle pipe at the margin of the Kimberley Craton seemingly conforms with "Clifford's Rule", regarding the restriction of economic diamond deposits to those underlain by Archean cratons. However, Argyle owes its rich diamond grades not to its Neoarchean mantle roots but to the presence of

  9. Seismic Receiver Functions and the Lithosphere-Asthenosphere Boundary

    Science.gov (United States)

    Kind, R.; Yuan, X.; Kumar, P.

    2012-12-01

    The lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists, since it is relatively poorly observed by seismic means. There is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves. Seismic techniques which use shorter period P-to-S or S-to-P converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution. The principle of this technique (the so-called receiver function technique) is that a strong teleseismic mother phase (e.g. P, S, PP or SKS) incident from below on any seismic discontinuity beneath a station produces a converted phase (Ps or Sp) which indicates its depth and properties. We discuss details of this technique. A sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought. An intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves. This confirms earlier results from controlled source observations (Thybo and Perchuc 1997). We discuss possible interpretations of this shallow low velocity zone in cratonic regions.

  10. Paleoproterozoic, High-Metamorphic, Metasedimentary Units of Siberian Craton

    Institute of Scientific and Technical Information of China (English)

    Lena URMANTSEVA; Olga TURKINA

    2009-01-01

    Sensitive, high-resointion ion microprobe zircon U-Pb ages of Paleoproterozoic, high-grade,metasedimentary rocks from the south-western part of the Siberian Craton are reported. Early Precambrian, high-grade complexes, including garnet-biotite, hypersthene-biotite, and cordierite-bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift. Protoliths of studied gneisses correspond to terrigenous sediments, ranging from greywacke to shale. The paragneiss model Nd ages of 2.4-3.1 Ga indicate Archean-to-Paleoproterozoic source provinces. Zircons from gneisses show core-rim textures in cathodoluminescence (CL) image. Round or irregular shaped cores indicate detrital origin. Structureless rims with low Th/U are metamorphic in origin. The three age groups of detrital cores are: ≥2.7, -2.3, and 1.95-2 Ga. The ages of metamorphic rims range from 1.86 to 1.85 Ga;therefore, the sediments were deposited between 1.95 and 1.86 Ga and derived from Archean and Paleoproterozoic source rocks. It should be noted that Paleoproterozoic metasedimentary rocks of the Irkut Block are not unique. High-grade metaterrigenons sediments, with model Nd ages ranging from 2.3 to 2.5 Ga, are widely distributed within the AIdan and Anabar Shields of the Siberian Craton. The same situation is observed in the North China Craton, where metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 to 2.1 Ga (Wan et al., 2006). All of these sedimentary units were subjected to Late Paleoproterozoic metamorphism. In the Siberian Craton, the Paleoproterozoic sedimentary deposits are possibly marked passive margins of the Early Precambrian crustal blocks, and their high-grade metamorphism was related to the consolidation of the Siberian Craton.

  11. EarthScope in Midcontinent North America: Investigating the Architecture and Tectonic History of Cratonic-Platform Lithosphere

    Science.gov (United States)

    Marshak, S.; Larson, T.; Hamburger, M. W.; Pavlis, G. L.; Gilbert, H. J.; Parke, M.

    2010-12-01

    The transportable array of EarthScope will sweep across the Midcontinent of North America during 2011 and 2012. The central portion of this swath, between latitudes 36°N and 38°N, covers a "type example" of cratonic-platform lithosphere, where a veneer of Paleozoic sedimentary strata overlies Precambrian crystalline basement. In anticipating this scientific opportunity, we have compiled a unique suite of geologic, geophysical, subsurface, and topographic data sets for this area. The maps emphasize that, in spite of low topographic relief, the region has large subsurface structural relief. Specifically, its western portion includes a large intracratonic uplift (the Ozark Plateau), whereas its central portion includes a major intracratonic basin (the Illinois Basin). The elevation difference between the Cambrian-Precambrian unconformity at the crest of the Ozark Plateau and the same horizon at the base of the Illinois Basin (< 100 km to the east) is over 7.5 km. The region also includes the northern end of the Mississippi embayment (an anomalous depression), three major Proterozoic lithosphere accretionary boundaries (borders of the Yavapai, Mazatzal, and Grenville belts), one of the world's largest anorogenic igneous provinces (the Eastern Granite-Rhyolite Province), pronounced gravity and magnetic anomalies, and numerous fault-and-fold zones. Many of the zones remain active, both within and outside the notorious New Madrid seismic zone, making the central Midcontinent one of the most seismically active examples of cratonic platform lithosphere anywhere. As part of the USArray deployment in this region, a number of research groups (some of whom met at an EarthScope Workshop held in Urbana) have proposed dense, Flex-Array networks that would densify the sparser Transportable Array network. We propose an experiment that would span the Ozark Dome and the Illinois Basin, the Rough Creek Graben and other fault zones including the Wabash Valley seismic zone. This

  12. Synsedimentary deformation and the paleoseismic record in Marinoan cap carbonate of the southern Amazon Craton, Brazil

    Science.gov (United States)

    Soares, Joelson Lima; Nogueira, Afonso César Rodrigues; Domingos, Fábio; Riccomini, Claudio

    2013-12-01

    Event Layers in Neoproterozoic cap carbonates of Brazil's southwestern Amazon Craton record post-Marinoan synsedimentary seismicity. The 35 m-thick cap carbonates overlie glaciogenic sediments related to the Marinoan glaciation (635 Ma) and are comprised of two units: the lower cap consists of dolomite (˜15 m thick) and the upper cap is limestone (˜25 m thick). The cap dolomite includes pinkish crystalline dolostone with even parallel lamination, stratiform stromatolites, eventual tube structures and megaripple bedded peloidal dolostone interpreted as shallow (euphotic) platform deposits. The cap limestone onlaps the cap dolomite and consists of red marl, gray to black bituminous lime mudstone, bituminous shale with abundant calcite crystal fans (pseudomorphs after aragonite) and even parallel lamination interpreted as moderately deep to deep platform deposits. Five successive events of synsedimentary deformation were recognized in the cap carbonates exposed at Mirassol d'Oeste and Tangará da Serra, in Central Brazil: Event 1 - large to small-scale load cast structures in the contact between dolostones and glaciogenic sediments; Event 2 - stromatolitic lamination truncated by tube structures; Event 3 - vertical to subvertical fractures and faults, and large-scale synclines and anticlines with chevron folds; Event 4 - conglomerate and breccia filling neptunian dykes limited by undeformed beds; and Event 5 - slump and sliding deposits found only in the upper part of the cap limestone. Event 1 was produced by hydroplastic dynamics likely induced by isostatic rebound during ice cap melting in the final stages of the Marinoan glaciation. Events 2 and 5 are autocyclic in nature, and related to depositional processes. Event 2 is linked to fluid and methane escape from organic degradation of microbial mats and domes that formed tubestones; Event 5 is associated to collapse and sliding/slumping in the platform and slope. The reliable orientations of synsedimentary faults

  13. Multi-stage crustal growth and cratonization of the North China Craton

    Institute of Scientific and Technical Information of China (English)

    Mingguo Zhai

    2014-01-01

    The North China Craton (NCC) has a complicated evolutionary history with multi-stage crustal growth, recording nearly all important geological events in the early geotectonic history of the Earth. Our studies propose that the NCC can be divided into six micro-blocks with >w3.0e3.8 Ga old continental nuclei that are surrounded by Neoarchean greenstone belts (GRB). The micro-blocks are also termed as high-grade regions (HGR) and are mainly composed of orthogneisses with minor gabbros and BIF-bearing supracrustal beds or lenses, all of which underwent strong deformation and metamorphism of granu-lite-to high-grade amphibolite-facies. The micro-blocks are, in turn, from east to west, the Jiaoliao (JL), Qianhuai (QH), Ordos (ODS), Ji’ning (JN) and Alashan (ALS) blocks, and Xuchang (XCH) in the south. Recent studies led to a consensus that the basement of the NCC was composed of different blocks/ter-ranes that were finally amalgamated to form a coherent craton at the end of Neoarchean. Zircon U-Pb data show that TTG gneisses in the HGRs have two prominent age peaks at ca. 2.9e2.7 and 2.6e2.5 Ga which may correspond to the earliest events of major crustal growth in the NCC. Hafnium isotopic model ages range from ca. 3.8 to 2.5 Ga and mostly are in the range of 3.0e2.6 Ga with a peak at 2.82 Ga. Recent studies revealed a much larger volume of TTG gneisses in the NCC than previously considered, with a dominant ca. 2.7 Ga magmatic zircon ages. Most of the ca. 2.7 Ga TTG gneisses un-derwent metamorphism in 2.6e2.5 Ga as indicated by ubiquitous metamorphic rims around the cores of magmatic zircon in these rocks. Abundant ca. 2.6e2.5 Ga orthogneisses have Hf-in-zircon and Nd whole-rock model ages mostly around 2.9e2.7 Ga and some around 2.6e2.5 Ga, indicating the timing of pro-tolith formation or extraction of the protolith magma was from the mantle. Therefore, it is suggested that the 2.6e2.5 Ga TTGs probably represent a coherent event of continental accretion and major

  14. On the Origin of Cratonic Sag Basins: Did They Sag?

    Science.gov (United States)

    Morgan, Jason P.

    2015-04-01

    Cratonic sag basins are regions of long-lived, extremely slow (~20-30 m/Myr) shallow water and terrestrial sediment accumulation that have no striking signs of tectonic activity (cf. Allen and Armitage, 2012). In their evolution, hundreds of Myr-long periods of slow sediment accumulation are separated by unconformities. The mechanisms for their formation resist geodynamic characterization by other common hypotheses for basin subsidence because of their extremely slow subsidence and lack of evident tectonic activity. I propose their dynamics are better understood within the geodynamic context of continental cratons that ride over a ~250km-deep sub-asthenospheric mantle with lateral temperature variations between a few wide and persistent 1000s-km broad ~1400C 'superplume' upwelling mantle structures (e.g. currently beneath S. African Atlantic and French Polynesia) and prevalent surrounding ~1150C average temperature sub-asthenospheric mantle. When continents pass over typical mantle plumes, buoyant plume material tends to drain beneath the continent along junctions between cratons where the lithosphere is relatively thin, keeping the lithosphere over regions where plume material drains hotter than the average temperature of ~250km-deep mantle. (e.g., the Cameroon Line.) Regions where melting of plume material occurs during decompression associated with either plume ascent or lateral drainage beneath continents are associated with the addition of a buoyant rind of more depleted mantle to the continent. In addition, regions where plume material can pond in a relatively thin sub-lithospheric 'anti-basin' beneath a continent, or that stay stationary for long times over super plumes will heat to a lithospheric basal temperature of ~1400C instead of ~1150C, with ~700m of associated uplift. (e.g., Southern Africa). In this scenario (cf. Yamamoto, Morgan, and Morgan in "Plumes, Plates, and Paradigms"), it is the relative plume-passage-induced uplift of arches between

  15. Construction and destruction of some North American cratons

    Science.gov (United States)

    Snyder, David B.; Humphreys, Eugene; Pearson, D. Graham

    2017-01-01

    Construction histories of Archean cratons remain poorly understood; their destruction is even less clear because of its rarity, but metasomatic weakening is an essential precursor. By assembling geophysical and geochemical data in 3-D lithosphere models, a clearer understanding of the geometry of major structures within the Rae, Slave and Wyoming cratons of central North America is now possible. Little evidence exists of subducted slab-like geometries similar to modern oceanic lithosphere in these construction histories. Underthrusting and wedging of proto-continental lithosphere is inferred from multiple dipping discontinuities, emphasizing the role of lateral accretion. Archean continental building blocks may resemble the modern lithosphere of oceanic plateau, but they better match the sort of refractory crust expected to have formed at Archean ocean spreading centres. Radiometric dating of mantle xenoliths provides estimates of rock types and ages at depth beneath sparse kimberlite occurrences, and these ages can be correlated to surface rocks. The 3.6-2.6 Ga Rae, Slave and Wyoming cratons stabilized during a granitic bloom at 2.61-2.55 Ga. This stabilization probably represents the final differentiation of early crust into a relatively homogeneous, uniformly thin (35-42 km), tonalite-trondhjemite-granodiorite crust with pyroxenite layers near the Moho atop depleted lithospheric mantle. Peak thermo-tectonic events at 1.86-1.7 Ga broadly metasomatized, mineralized and recrystallized mantle and lower crustal rocks, apparently making mantle peridotite more 'fertile' and more conductive by introducing or concentrating sulfides or graphite at 80-120 km depths. This metasomatism may have also weakened the lithosphere or made it more susceptible to tectonic or chemical erosion. Late Cretaceous flattening of Farallon lithosphere that included the Shatsky Rise conjugate appears to have weakened, eroded and displaced the base of the Wyoming craton below 140-160 km. This

  16. Anisotropic Lithospheric layering in the North American craton, revealed by Bayesian inversion of short and long period data

    Science.gov (United States)

    Roy, Corinna; Calo, Marco; Bodin, Thomas; Romanowicz, Barbara

    2016-04-01

    Competing hypotheses for the formation and evolution of continents are highly under debate, including the theory of underplating by hot plumes or accretion by shallow subduction in continental or arc settings. In order to support these hypotheses, documenting structural layering in the cratonic lithosphere becomes especially important. Recent studies of seismic-wave receiver function data have detected a structural boundary under continental cratons at 100-140 km depths, which is too shallow to be consistent with the lithosphere-asthenosphere boundary, as inferred from seismic tomography and other geophysical studies. This leads to the conclusion that 1) the cratonic lithosphere may be thinner than expected, contradicting tomographic and other geophysical or geochemical inferences, or 2) that the receiver function studies detect a mid-lithospheric discontinuity rather than the LAB. On the other hand, several recent studies documented significant changes in the direction of azimuthal anisotropy with depth that suggest layering in the anisotropic structure of the stable part of the North American continent. In particular, Yuan and Romanowicz (2010) combined long period surface wave and overtone data with core refracted shear wave (SKS) splitting measurements in a joint tomographic inversion. A question that arises is whether the anisotropic layering observed coincides with that obtained from receiver function studies. To address this question, we use a trans-dimensional Markov-chain Monte Carlo (MCMC) algorithm to generate probabilistic 1D radially and azimuthal anisotropic shear wave velocity profiles for selected stations in North America. In the algorithm we jointly invert short period (Ps Receiver Functions, surface wave dispersion for Love and Rayleigh waves) and long period data (SKS waveforms). By including three different data types, which sample different volumes of the Earth and have different sensitivities to 
structure, we overcome the problem of

  17. Seismic Creep

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden erupture associated with an earthquake. It is a usually slow deformation...

  18. THE RECENT STRUCTURE AND THE ASSUMED HISTORY OF FORMATION OF THE CRUST IN THE SOUTH-EASTERN SEGMENT OF THE NORTH ASIAN CRATON ALONG REFERENCE PROFILE 3-DV

    Directory of Open Access Journals (Sweden)

    E. Yu. Goshko

    2015-09-01

    Full Text Available The article presents results of specialized processing of the deep seismic profile along a part of Reference Profile 3-DV which crosses the Aldan-Stanovoi shield in the meridian direction and goes across its buried northern slope. The study is aimed at determining frequency-energy characteristics of the seismic wave field which are related to physical conditions of geological features of the crust. Based on analysis and interpretation of the dynamic profiles, it is possible to reveal and contour the Archean cores of consolidation of the Aldan shield and its buried continuation that is covered by sediments of the Middle Lena monocline and to input new facts in the proposed geodynamic model showing formation of the crust in the south-eastern segment of the North Asian craton.

  19. Seismic seiches

    Science.gov (United States)

    McGarr, Arthur; Gupta, Harsh K.

    2011-01-01

    Seismic seiche is a term first used by Kvale (1955) to discuss oscillations of lake levels in Norway and England caused by the Assam earthquake of August 15, 1950. This definition has since been generalized to apply to standing waves set up in closed, or partially closed, bodies of water including rivers, shipping channels, lakes, swimming pools and tanks due to the passage of seismic waves from an earthquake.

  20. Possible magmatic underplating beneath the west coast of India and adjoining Dharwar craton: Imprint from Archean crustal evolution to breakup of India and Madagascar

    Science.gov (United States)

    Saikia, Utpal; Das, Ritima; Rai, S. S.

    2017-03-01

    The shear wave velocity of the crust along a ∼660 km profile from the west to the east coast of South India is mapped through the joint inversion of receiver functions and Rayleigh wave group velocity. The profile, consisting of 38 broadband seismic stations, covers the Archean Dharwar craton, Proterozoic Cuddapah basin, and rifted margin and escarpment. The Moho is mapped at a depth of ∼40 km beneath the mid-Archean Western Dharwar Craton (WDC), Cuddapah Basin (CB), and the west and east coasts formed through the rifting process. This is in contrast with a thin (∼35 km) crust beneath the late-Archean Eastern Dharwar Craton (EDC). Along the profile, the average thickness of the upper, middle and lower crust is ∼4 km, 12 ± 4 km and 24 ± 4 km respectively. Above the Moho, we observe a high-velocity layer (HVL, Vs > 4 km/s) of variable thickness increasing from 3 ± 1 km beneath the EDC to 11 ± 3 km beneath the WDC and the CB, and 18 ± 2 km beneath the west coast of India. The seismic wave velocity in this layer is greater than typical oceanic lower crust. We interpret the high-velocity layer as a signature of magmatic underplating due to past tectonic processes. Its significant thinning beneath the EDC may be attributed to crustal delamination or relamination at 2.5 Ga. These results demonstrate the dual signature of the Archean Dharwar crust. The change in the geochemical character of the crust possibly occurred at the end of Archean when Komatiite volcanism ceased. The unusually thick HVL beneath the west coast of India and the adjoining region may represent underplated material formed due to India-Madagascar rifting, which is supported by the presence of seaward dipping reflectors and a 85-90 Ma mafic dyke in the adjoining island.

  1. Pb–Pb zircon ages of Archaean metasediments and gneisses from the Dharwar craton, southern India: Implications for the antiquity of the eastern Dharwar craton

    Indian Academy of Sciences (India)

    B Maibam; J N Goswami; R Srinivasan

    2011-08-01

    207Pb–206Pb ages of zircons in samples of metasediments as well as ortho- and para-gneisses from both the western and the eastern parts of the Dharwar craton have been determined using an ion microprobe. Detrital zircons in metasedimentary rocks from both yielded ages ranging from 3.2 to 3.5 Ga. Zircons from orthogneisses from the two parts also yielded similar ages. Imprints of younger events have been discerned in the ages of overgrowths on older zircon cores in samples collected throughout the craton. Our data show that the evolution of the southwestern part of eastern Dharwar craton involved a significant amount of older crust (< 3.0 Ga). This would suggest that crust formation in both the western and eastern parts of the Dharwar craton took place over similar time interval starting in the Mesoarchaean at ca. 3.5 Ga and continuing until 2.5 Ga. Our data coupled with geological features and geodynamic setting of the Dharwar craton tend to suggest that the eastern Dharwar craton and the western Dharwar craton formed part of a single terrane.

  2. The thermal structure of cratonic lithosphere from global Rayleigh wave attenuation

    Science.gov (United States)

    Dalton, Colleen A.; Bao, Xueyang; Ma, Zhitu

    2017-01-01

    The resolution of and level of agreement between different attenuation models have historically been limited by complexities associated with extracting attenuation from seismic-wave amplitudes, which are also affected by the source, the receiver, and propagation through velocity heterogeneities. For intermediate- and long-period Rayleigh waves, removing the amplitude signal due to focusing and defocusing effects is the greatest challenge. In this paper, three independent data sets of fundamental-mode Rayleigh wave amplitude are analyzed to investigate how three factors contribute to discrepancies between the attenuation models: uncertainties in the amplitude measurements themselves, variable path coverage, and the treatment of focusing effects. Regionalized pure-path and fully two-dimensional attenuation models are derived and compared. The approach for determining attenuation models from real data is guided by an analysis of amplitudes measured from synthetic spectral-element waveforms, for which the input Earth model is perfectly known. The results show that differences in the amplitude measurements introduce only very minor differences between the attenuation models; path coverage and the removal of focusing effects are more important. The pure-path attenuation values exhibit a clear dependence on tectonic region at shorter periods that disappears at long periods, in agreement with pure-path phase-velocity results obtained by inverting Rayleigh wave phase delays. The 2-D attenuation maps are highly correlated with each other to spherical-harmonic degree 16 and can resolve smaller features than the previous generation of global attenuation models. Anomalously low attenuation is nearly perfectly associated with continental cratons. Variations in lithospheric thickness are determined by forward modeling the global attenuation variations as a thermal boundary layer of variable thickness. Temperature profiles that satisfy the attenuation values systematically

  3. Latest Jurassic-early Cretaceous regressive facies, northeast Africa craton

    Energy Technology Data Exchange (ETDEWEB)

    van Houten, F.B.

    1980-06-01

    Nonmarine to paralic detrital deposits accumulated in six large basins between Algeria and the Arabo-Nubian shield during major regression in latest Jurassic and Early Cretaceous time. The Ghadames Sirte (north-central Libya), and Northern (Egypt) basins lay along the cratonic margin of northeastern Africa. The Murzuk, Kufra, and Southern (Egypt) basins lay in the south within the craton. Data for reconstructing distribution, facies, and thickness of relevant sequences are adequate for the three northern basins only. High detrital influx near the end of Jurassic time and in mid-Cretaceous time produced regressive nubian facies composed largely of low-sinuosity stream and fahdelta deposits. In the west and southwest the Ghadames, Murzuk, and Kufra basins were filled with a few hundred meters of detritus after long-continued earlier Mesozoic aggradation. In northern Egypt the regressive sequence succeeded earlier Mesozoic marine sedimentation; in the Sirte and Southern basins correlative deposits accumulated on Precambrian and Variscan terranes after earlier Mesozoic uplift and erosion. Waning of detrital influx into southern Tunisia and adjacent Libya in the west and into Israel in the east initiated an Albian to early Cenomanian transgression of Tethys. By late Cenomanian time it had flooded the entire cratonic margin, and spread southward into the Murzuk and Southern basins, as well as onto the Arabo-Nubian shield. Latest Jurassic-earliest Cretaceous, mid-Cretaceous, and Late Cretaceous transgressions across northeastern Africa recorded in these sequences may reflect worldwide eustatic sea-level rises. In contrast, renewed large supply of detritus during each regression and a comparable subsidence history of intracratonic and marginal basins imply regional tectonic control. 6 figures.

  4. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    Science.gov (United States)

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere.

  5. Seismic Studies

    Energy Technology Data Exchange (ETDEWEB)

    R. Quittmeyer

    2006-09-25

    This technical work plan (TWP) describes the efforts to develop and confirm seismic ground motion inputs used for preclosure design and probabilistic safety 'analyses and to assess the postclosure performance of a repository at Yucca Mountain, Nevada. As part of the effort to develop seismic inputs, the TWP covers testing and analyses that provide the technical basis for inputs to the seismic ground-motion site-response model. The TWP also addresses preparation of a seismic methodology report for submission to the U.S. Nuclear Regulatory Commission (NRC). The activities discussed in this TWP are planned for fiscal years (FY) 2006 through 2008. Some of the work enhances the technical basis for previously developed seismic inputs and reduces uncertainties and conservatism used in previous analyses and modeling. These activities support the defense of a license application. Other activities provide new results that will support development of the preclosure, safety case; these results directly support and will be included in the license application. Table 1 indicates which activities support the license application and which support licensing defense. The activities are listed in Section 1.2; the methods and approaches used to implement them are discussed in more detail in Section 2.2. Technical and performance objectives of this work scope are: (1) For annual ground motion exceedance probabilities appropriate for preclosure design analyses, provide site-specific seismic design acceleration response spectra for a range of damping values; strain-compatible soil properties; peak motions, strains, and curvatures as a function of depth; and time histories (acceleration, velocity, and displacement). Provide seismic design inputs for the waste emplacement level and for surface sites. Results should be consistent with the probabilistic seismic hazard analysis (PSHA) for Yucca Mountain and reflect, as appropriate, available knowledge on the limits to extreme ground

  6. Craton-derived alluvium as a major sediment source in the Himalayan Foreland Basin of India

    DEFF Research Database (Denmark)

    Sinha, R.; Kettanah, Y.; Gibling, M.R.

    2009-01-01

    of the Yamuna. This gray cratonic sediment was probably deposited in part by the Chambal River, which transports high-grade metamorphic minerals from the Banded Gneiss Complex of the Aravalli belt. Cratonic sediment appears to interfinger with Himalayan detritus farther north below the Ganga-Yamuna Interfluve...

  7. Seismic Symphonies

    Science.gov (United States)

    Strinna, Elisa; Ferrari, Graziano

    2015-04-01

    The project started in 2008 as a sound installation, a collaboration between an artist, a barrel organ builder and a seismologist. The work differs from other attempts of sound transposition of seismic records. In this case seismic frequencies are not converted automatically into the "sound of the earthquake." However, it has been studied a musical translation system that, based on the organ tonal scale, generates a totally unexpected sequence of sounds which is intended to evoke the emotions aroused by the earthquake. The symphonies proposed in the project have somewhat peculiar origins: they in fact come to life from the translation of graphic tracks into a sound track. The graphic tracks in question are made up by copies of seismograms recorded during some earthquakes that have taken place around the world. Seismograms are translated into music by a sculpture-instrument, half a seismograph and half a barrel organ. The organ plays through holes practiced on paper. Adapting the documents to the instrument score, holes have been drilled on the waves' peaks. The organ covers about three tonal scales, starting from heavy and deep sounds it reaches up to high and jarring notes. The translation of the seismic records is based on a criterion that does match the highest sounds to larger amplitudes with lower ones to minors. Translating the seismogram in the organ score, the larger the amplitude of recorded waves, the more the seismogram covers the full tonal scale played by the barrel organ and the notes arouse an intense emotional response in the listener. Elisa Strinna's Seismic Symphonies installation becomes an unprecedented tool for emotional involvement, through which can be revived the memory of the greatest disasters of over a century of seismic history of the Earth. A bridge between art and science. Seismic Symphonies is also a symbolic inversion: the instrument of the organ is most commonly used in churches, and its sounds are derived from the heavens and

  8. Spatial-Temporal variability of seismic hazard in Peninsular India

    Indian Academy of Sciences (India)

    Kishor Jaiswal; Ravi Sinha

    2008-11-01

    This paper examines the variability of seismic activity observed in the case of different geological zones of peninsular India (10°N–26°N; 68°E–90°E) based on earthquake catalog between the period 1842 and 2002 and estimates earthquake hazard for the region. With compilation of earthquake catalog in terms of moment magnitude and establishing broad completeness criteria, we derive the seismicity parameters for each geologic zone of peninsular India using maximum likelihood procedure. The estimated parameters provide the basis for understanding the historical seismicity associated with different geological zones of peninsular India and also provide important inputs for future seismic hazard estimation studies in the region. Based on present investigation, it is clear that earthquake recurrence activity in various geologic zones of peninsular India is distinct and varies considerably between its cratonic and rifting zones. The study identifies the likely hazards due to the possibility of moderate to large earthquakes in peninsular India and also presents the influence of spatial rate variation in the seismic activity of this region. This paper presents the influence of source zone characterization and recurrence rate variation pattern on the maximum earthquake magnitude estimation. The results presented in the paper provide a useful basis for probabilistic seismic hazard studies and microzonation studies in peninsular India.

  9. The Ufa indenter: stratigraphic and geophysic evidences for an actual indentation of the Southern Urals by the East European craton

    Science.gov (United States)

    Lefort, Jean-Pierre; Danukalova, Guzel

    2014-07-01

    Study of the altitudes of the lowest part of the Upper Cretaceous-Eocene and Aktschagylian-Quaternary stratigraphic ensembles known on the western slope of the Southern Urals evidences the existence of an East-West elongated dome which follows the N53° latitude. This ridge is superimposed at depth with the remnants of the Sernovodsk-Abdulino Aulacogen and with the Belaya tear fault, which support the existence of a recent rejuvenation of these old structures. North of these disruptions the Southern Urals display a clear bent towards the East. Detailed microstructural studies show that this curvature is associated with a typical stress pattern which suggests the existence of an indentation of the fold belt by the East European craton. The hypothesis of an Ufa indenter is not supported by an equivalent East-West deep fault north of the bend. However, a long N100° magnetic anomaly, interpreted as a shear zone, suggests that the indenter is a reality. Quaternary uplift and crustal thickening at its front as well as seismological data support our interpretation. It is not stressed that the curvature of the Urals observed at 56° latitude results solely from this recent indentation. It is only assumed that the actual indentation is rejuvenating a former unevenness which existed before in the East European craton. Study of the inner part of the indenter shows that this type of structure is not necessarily rigid and undeformed. Some of the structures described on the URSEIS deep seismic line could be much younger than previously expected.

  10. Metallogenic Districts of Yangtze Cratonic Rim at the Edge of Chaos

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Combining the science of complexity with ore geology, the author puts forward a new theory of metallogenesis: "complexity and self-organized criticality of metallogenic dynamic systems", and three fundamental theories are raised for it. The ore genesis and regularity of ore formation of four metallogenic districts around the Yangtze craton in China are studied with this theory. It is found that"metallogenic districts of Yangtze cratonic rim are all at the edge of chaos". This proposition is expounded by four determinative criteria of the edge of chaos for metallogenic districts of Yangtze cratonic rim.

  11. Plume tectonics and cratons formation in the early Earth

    Science.gov (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Fischer, R.; Sizova, E.; Sobolev, S. V.; Whattam, S. A.

    2015-12-01

    Modern geodynamics and continental growth are critically driven by subduction and plate tectonics, however how this tectonic regime started and what geodynamic regime was before remains controversial. Most present-day subduction initiation mechanisms require acting plate forces and/or pre-existing zones of lithospheric weakness, which are themselves the consequence of plate tectonics. Here, we focus on plume-lithosphere interactions and spontaneous plume-induced subduction initiation, which does not require pre-existing lithospheric fabric and is viable for both stagnant lid and mobile/deformable lid conditions. We present results of 2D and 3D numerical modeling of plume-induced deformation and associated crustal growth resulting from tectono-magmatic interaction of ascending mantle plumes with oceanic-type lithosphere. We demonstrate that weakening of the lithosphere by plume-induced magmatism is the key factor allowing for its internal deformation and differentiation resulting in continental crust growth. We also show that plume-lithosphere interaction can enable subduction and rudimentary plate tectonics initiation at the margins of a crustal plateau growing above the plume head. We argue that frequent plume-arc interactions recorded in Archean crust could reflect either short-term plume-induced subduction or plume-induced episodic lithospheric drips. We furthermore suggest a distinct plume-tectonics regime operated on Earth before plate tectonics, which was associated with widespread tectono-magmatic heat and mass exchange between the crust and the mantle. This regime was characterized by weak deformable plates with low topography, massive juvenile crust production from mantle derived melts, mantle-flows-driven crustal deformation, magma-assisted crustal convection and widespread development of lithospheric delamination and crustal drips. Plume tectonics also resulted in growth of hot depleted chemically buoyant subcrustal proto-cratonic mantle layer. Later

  12. Geochemistry of khondalites from the central portion of North China craton (NCC):implications for the continental cratonization in the Neoarchean

    Institute of Scientific and Technical Information of China (English)

    李江海; 钱祥麟; 刘树文

    2000-01-01

    Within the high-grade metamorphic basement, the central portion of North China Craton (NCC), a group of Neoarchean khondalites (KS) is identified. They are characterized by large ion lithophile elements (LILE) enrichment, lower abundances of Zr, Hf and Sr. Their rare earth element (REE) distribution has significant LREE enrichment and negative Eu anomalies. The protoliths of KS are interpreted as feldspathic quartzite, shale or petite and carbonite, deposited in a shallow sea upon cratonic shelf distant from the land. KS’s source region might be dominated by granitic rocks, with a minor amount of TTG, underwent comparatively severe chemical weathering. Considering relevent tectonic constraints, we suggest that khondalites from central portion of NCC, an important metamophosed sedimentary cover, are the most significant exogenetic marker of Neoarchean continental cratonization for NCC.

  13. Major tectonic units of the North China Craton and their Paleoproterozoic assembly

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The basement of the North China Craton can be divided into the Eastern and Western Blocks and the Central Zone (Trans-North China Orogen). The West Block formed by the amalgamation of the Ordos Block in the south and the Yinshan Block in the north 1.9-2.0 Ga ago. In 1.8-1.9 Ga, the Eastern and Western Blocks were amalgamated along the Central Zone to form the North China Craton.

  14. Intra-cratonic melting as a result of delamination of mantle lithosphere - insight from numerical modelling

    Science.gov (United States)

    Gorczyk, W.; Vogt, K.; Gerya, T.; Hobbs, B. E.

    2012-12-01

    It is becoming increasingly apparent that intense deformation, metamorphism and metasomatism occur within continental cratonic blocks far removed form subducting margins Such changes may occur intra-cratonically arising from lithospheric thickening and the development of gravitational instabilities, but mostly occur at the boundary of cratonic blocks. The contact of two cratons is characterized by rheological lateral variations within mantle-lithosphere and overlying crust. Tectonic stresses acting on craton/craton boundaries may lead to thinning or thickening due to delamination of the mantle lithosphere. This is reflected in tectonic deformation, topography evolution, melting and crustal metamorphism. To understand the controls on these processes a number of 2D, coupled petrological thermo-mechanical numerical experiments has been performed to test the response of a laterally weakened zone to a compressional regime. The results indicate that the presence of water-bearing minerals in the lithosphere and lower crust is essential to initiate melting, which in the later stages may expand to dry melting of crust and mantle. In the case of anhydrous crust and lithosphere, no melting occurs. Thus a variety of instabilities, melting behaviour and topographic responses occurs at the base of the lithosphere as well as intensive faulting and buckling in the crust dependent on the strength and "water" content of the lithosphere.

  15. SEISMIC GEOLOGY

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    <正>20091465 Cai Xuelin(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China);Cao Jiamin Preliminary Study on the 3-D Crust Structure for the Longmen Lithosphere and the Genesis of the Huge Wenchuan Earthquake,Sichuan Province,China(Journal of Chengdu University of Technology,ISSN1671-9727,CN51-1634/N,35(4),2008,p.357-365,8 illus.,39 refs.)Key words:deep-seated structures,large earthquakes,Longmenshan Fracture ZoneBased on a structural analysis of many seismic sounding profiles,there are two fault systems in Longmen collisional orogenic belt,Sichuan Province,China.They are both different obviously and correlative closely.One is shallow fault system composed mainly of brittle shear zones in surface crust,and the other is deep fault system composed mainly of crust-mantle ductile shear zones cutting Moho discontinuity.Based on the result of researching geological structure and seismic sounding profiles,

  16. Paleoproterozoic postcollisional magmatic belt of the southern Siberian craton

    Science.gov (United States)

    Salnikova, E. B.; Larin, A. M.; Kotov, A. B.; Levitsky, V. I.; Reznitsky, L. Z.; Kovach, V. P.; Yakovleva, S. Z.

    2003-04-01

    Paleoproterozoic time is characterized by large-scale collisional and postcollisional magmatic activity evidenced in the most of ancient cratons. This global event is related to the Arctic supercontinent assemblage (Rogers, 1996). The formation of postcollisional magmatic belt at 1.9-1.8 Ga within the south-west flanking of the Siberian craton is a remarkable example of these processes happened during overall lithospheric convergence. This belt is extends for about 3000 km from the southern Enisey ridge at the west to the central Aldan shield at the east. Within the central Aldan shield the latest collisional event occurred 1925+/-5 Ma (Kotov et al, 2003) and post-collisional subalkaline S- and I-type granites emplaced at 1916+/-10 Ma (Bibikova et al., 1989), 1901+/-1 Ma (Frost et al., 1998) and 1899+/-6 Ma (Kotov et al, 2003). However at the southern Olekma terrain (western Aldan shield) the syncollisional granites have formed at 1906+/-4 Ma and postcollisional Kodar granitoids were generated at 1876-1873 Ma (Larin et al., 2000). The is a tendency outlined in timing of postcollision processes to the west (in modern coordinates). Ages of postcollisional Kevakta granitoid plutons (1846+/-8 Ma) and volcanics of North-Baikal volcano-plutonic belt (1869+/-6 Ma 1856+/-3 Ma), Baikal folded area, support this tendency. Emplacement of the Primorsky complex postcollisional rapakivi-type granitoids (southern Baikal lake) occurred at 1859+/-16 Ma (Donskaya et al., 2002). New results of U-Pb single zircon and baddeleyite dating demonstrate that formation of late-synkinematic syenite, charnockite and pegmatitic veins (1856±12 Ma, 1853±20 Ma) and calciphyre (1868±2 Ma) within the eastern part of the Sharyzhalgay block (southern Baikal lake) occurred virtually within the same episode. Postcollisional intrusive charnockite of the Shumikha complex from the western Sharyzhalgay block dated at 1861±1 Ma (Donskaya et al., 2001) and 1871±17 Ma (Levitsky et al., 2002). Subalcaline

  17. Seismic Wave Velocities in Deep Sediments in Poland: Borehole and Refraction Data Compilation

    Directory of Open Access Journals (Sweden)

    Polkowski Marcin

    2015-06-01

    Full Text Available Sedimentary cover has significant influence on seismic wave travel times and knowing its structure is of great importance for studying deeper structures of the Earth. Seismic tomography is one of the methods that require good knowledge of seismic velocities in sediments and unfortunately by itself cannot provide detailed information about distribution of seismic velocities in sedimentary cover. This paper presents results of P-wave velocity analysis in the old Paleozoic sediments in area of Polish Lowland, Folded Area, and all sediments in complicated area of the Carpathian Mountains in Poland. Due to location on conjunction of three major tectonic units - the Precambrian East European Craton, the Paleozoic Platform of Central and Western Europe, and the Alpine orogen represented by the Carpathian Mountains the maximum depth of these sediments reaches up to 25 000 m in the Carpathian Mountains. Seismic velocities based on 492 deep boreholes with vertical seismic profiling and a total of 741 vertical seismic profiles taken from 29 seismic refraction profiles are analyzed separately for 14 geologically different units. For each unit, velocity versus depth relations are approximated by second or third order polynomials.

  18. A lithospheric perspective on structure and evolution of Precambrian cratons

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2012-01-01

    the roots of the continents, and moves together with continental plates. Depending on geophysical techniques (and physical properties measured), the lithosphere has different practical definitions. Most of them (i.e., seismic, electrical) are on the basis of a sharp change in temperature-dependent physical...

  19. A lithospheric perspective on structure and evolution of Precambrian cratons

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2012-01-01

    the roots of the continents, and moves together with continental plates. Depending on geophysical techniques (and physical properties measured), the lithosphere has different practical definitions. Most of them (i.e., seismic, electrical) are on the basis of a sharp change in temperature-dependent physical...

  20. Towards a Holistic Model for the Tectonic Evolution of the North China Craton

    Science.gov (United States)

    Kusky, T. M.; Polat, A.; Windley, B. F.; Wang, J.; Deng, H.

    2016-12-01

    The North China Craton (NCC) consists of distinctly different tectonic elements assembled during the late Archean - early Proterozoic. We propose a new tectonic evolution of the NCC. The Eastern Block (EB) consists of small microblocks that resemble a collage of accreted arc-rocks from a sutured archipelago similar to the SW Pacific, accreted between 2.6 and 2.7 Ga. An Atlantic-type margin developed on the western side of the EB by 2.5 Ga, and a >1,300 km long arc/accretionary prism collided with this passive margin at 2.5 Ga, obducting ophiolites and ophiolitic mélanges, and forming a foreland basin. This was followed by arc-polarity reversal, and injection of mantle wedge-derived melts. By 2.43 Ga, the ocean behind the accreted arc closed through the collision of an oceanic plateau. Rifting of the amalgamated craton followed at 2.4-2.35 Ga, with a failed rift arm preserved in the center of the craton, and two that successfully made an ocean along the northern margin. By 2.3 Ga an arc built on older cratonic material collided with this passive margin which soon converted to an Andean-type margin. Andean margin tectonics affected much of the craton from 2.3-1.9 Ga, forming a broad E-W swath of continental margin magmas, and retro-arc sedimentary basins including a superimposed basin over the passive margin on the northern margin. From 1.88-1.79 Ga the craton experienced a craton-wide granulite facies metamorphism and basement reactivation event with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the craton. Early Proterozoic granulites and anatectic melts were generated by high-grade metamorphism and partial melting at mid-crustal levels beneath a collisionally-thickened plateau. This collision of the NCC on its northern margin was with the Columbia (Nuna) Continent. The NCC broke out in the period 1753-1673 Ma, as indicated by the formation of a suite of anorthosite, mangerite, charnockite, and alkali-feldspar granites

  1. Architecture of the Sulu crustal suture between the North China Craton and Yangtze Craton: Constraints from Mesozoic granitoids

    Science.gov (United States)

    Zhao, Rui; Wang, Qingfei; Liu, Xuefei; Wang, Wei; Pan, Ruiguang

    2016-12-01

    The Yangtze Craton (YC) and the North China Craton (NCC) collided in the Triassic, producing the prominent NNE-trending Sulu high-ultrahigh pressure metamorphic belt and associated crustal thickening. Late Jurassic-Early Cretaceous granitic plutons in the Sulu orogenic belt and the Jiaobei terrane to the west were used to investigate the crustal architecture across the suture. Our new data show that the granitoids from these two regions have similar chemical and isotope compositions. They are all characterized by very high Sr and low Y-Yb contents, high Sr/Y and (La/Yb)N ratios, similar ƐNd(t) values from - 18.2 to - 21.4, and similar initial 87Sr/86Sr ratios from 0.7076 to 0.7119. The calculated Nd two-stage model ages (TDM2) based on whole rock data vary from 2415 to 2662 Ma. Co-magmatic zircon crystals from the granitoids have variably negative ƐHf(t) values from - 26.8 to - 12.8, with the calculated Hf TDM2 from 2008 to 2892 Ma. The inherited zircon crystals from these rocks are dominated by Neoproterozoic (800-600 Ma) and Triassic-Early Jurassic ( 220 Ma and 180 Ma) ages. The ƐHf(t) values of the inherited zircon crystals with U-Pb ages between 180 Ma and 800 Ma from Sulu and Jiaobei range from - 21.6 to 4.2 and from - 23 to - 1.9, respectively. They all plot within the field of crustal evolution between 1385 and 2583 Ma. The similar whole rock geochemical signatures and similar inherited zircon data indicate a similar source for the granitoids in these two regions. We propose that the source regions across the suture all belong to the YC. The occurrence of the YC crust beneath the NCC at this location is thought to have resulted from the westward subduction of the YC beneath the NCC and subsequent continental collision in the Triassic. In this model, the abundant 800 to 230 Ma inherited zircon crystals in the granitoids are interpreted to have been derived from the source region whereas the rare older inherited zircon crystals are thought to have been

  2. Quantitative Seismic Amplitude Analysis

    OpenAIRE

    Dey, A. K.

    2011-01-01

    The Seismic Value Chain quantifies the cyclic interaction between seismic acquisition, imaging and reservoir characterization. Modern seismic innovation to address the global imbalance in hydrocarbon supply and demand requires such cyclic interaction of both feed-forward and feed-back processes. Currently, the seismic value chain paradigm is in a feed-forward mode. Modern seismic data now have the potential to yield the best images in terms of spatial resolution, amplitude accuracy, and incre...

  3. Peridotite-melt interaction: A key point for the destruction of cratonic lithospheric mantle

    Institute of Scientific and Technical Information of China (English)

    ZHANG HongFu

    2009-01-01

    This paper presents an overview of recent studies dealing with different ages of mantle peridotitic xenoliths and xenocrysts from the North China Craton, with aim to provide new ideas for further study on the destruction of the North China Craton. Re-Os isotopic studies suggest that the lithospheric mantle of the North China Craton is of Archean age prior to its thinning. The key reason why such a low density and highly refractory Archean lithospheric mantle would be thinned is changes in composition, thermal regime, and physical properties of the lithospheric mantle due to interaction of peridotites with melts of different origins. Inward subducUon of circum craton plates and collision with the North China Craton provided not only the driving force for the destruction of the craton, but also continuous melts derived from partial melting of subducted continental or oceanic crustal materials that resulted in the compositional change of the lithospheric mantle. Regional thermal anomaly at ca. 120 Ma led to the melting of highly modified iithospheric mantle. At the same time or subsequently lithospheric extension and asthenospheric upwelling further reinforced the melting and thinning of the lithospheric mantle. Therefore, the destruction and thinning of the North China Craton is a combined result of peridotite-melt interaction (addition of volatile), enhanced regional thermal anomaly (temperature increase) and lithospheric extension (decompression). Such a complex geological process finally produced a "mixed" lithospheric mantle of highly chemical heterogeneity during the Mesozoic and Cenozoic. It also resulted in significant difference in the composition of mantle peridotitic xenoliths between different regions and times.

  4. Shear wave velocity, seismic attenuation, and thermal structure of the continental upper mantle

    Science.gov (United States)

    Artemieva, I.M.; Billien, M.; Leveque, J.-J.; Mooney, W.D.

    2004-01-01

    Seismic velocity and attenuation anomalies in the mantle are commonly interpreted in terms of temperature variations on the basis of laboratory studies of elastic and anelastic properties of rocks. In order to evaluate the relative contributions of thermal and non-thermal effects on anomalies of attenuation of seismic shear waves, QS-1, and seismic velocity, VS, we compare global maps of the thermal structure of the continental upper mantle with global QS-1 and Vs maps as determined from Rayleigh waves at periods between 40 and 150 S. We limit the comparison to three continental mantle depths (50, 100 and 150 km), where model resolution is relatively high. The available data set does not indicate that, at a global scale, seismic anomalies in the upper mantle are controlled solely by temperature variations. Continental maps have correlation coefficients of temperatures: most cratonic regions show high VS and QS and low T, while most active regions have seismic and thermal anomalies of the opposite sign. The strongest inverse correlation is found at a depth of 100 km, where the attenuation model is best resolved. Significantly, at this depth, the contours of near-zero QS anomalies approximately correspond to the 1000 ??C isotherm, in agreement with laboratory measurements that show a pronounced increase in seismic attenuation in upper mantle rocks at 1000-1100 ??C. East-west profiles of VS, QS and T where continental data coverage is best (50??N latitude for North America and 60??N latitude for Eurasia) further demonstrate that temperature plays a dominant, but non-unique, role in determining the value of lithospheric VS and QS. At 100 km depth, where the resolution of seismic models is the highest, we compare observed seismic VS and QS with theoretical VST and QST values, respectively, that are calculated solely from temperature anomalies and constrained by experimental data on temperature dependencies of velocity and attenuation. This comparison shows that

  5. BRYANSK-KURSK-VORONEZH INTRA-CONTINENTAL COLLISIONAL OROGEN (EAST EUROPEAN CRATON

    Directory of Open Access Journals (Sweden)

    M. V. Mints

    2015-09-01

    Full Text Available The article presents new data on the deep crustal structure, origin and evolution of the Bryansk-Kursk-Voronezh orogen in the south-eastern segment of the East European craton; it is composed of the Paleoproterozoic formations and areas of reworked Archean crust. The purpose of this paper is the development and improvement of ideas on intra-continental orogens. The deep structure of the orogen is presented by the 3D model based on results of geological mapping of the Precambrian basement and interpretations of geophysical fields and seismic images of the crust along geotraverse 1-EB and profile DOBRE. It is established that the orogen originated with riftogenic extension of the crust at 2.6–2.5 Ga, that was repeated at 2.2–2.1 Ga, and formation of wide depressions that were efficiently filled in with volcanosedimentary layers including BIF, which accumulation was followed by high-temperature up to granulite facies metamorphism. Suprasubduction magmatism took place at 2.10–2.08 Ga and resulted in formation of the Lipetsk-Losevka volcano-plutonic complex. The active margin was completely formed at about 2.05 Ga. The short duration of subduction-related magmatic activity and the lack of relics of the oceanic lithosphere suggest short-term and spatially limited developing of the oceanic structure. The tectonothermal activity of collisional and postcollision stages was expressed in emplacement of alkaline ultramafic (2.1–2.0 Ga and gabbro-syenite (1.8–1.7 Ga complexes. It is difficult or impossible to explain specific features of the structure and evolution of the orogen in framework of the model of the Cordilleras type  accretionary orogen. Mafic-ultramafic magmatism and indications of intensive heating of the crust suggest a special role of plume type processes that provided for influx of mantle heat and juvenile mantle derived matter. 

  6. Triassic magmatism and its relation to decratonization in the eastern North China Craton

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Lithospheric removal and destruction of the North China Craton have been hotly discussed recently. It has been confirmed that the timing of a strong lithospheric removal took place in Late Mesozoic; however, little is known about when the lithospheric removal was initiated and how the Late Permian to Early Triassic deep subduction of Yangtze continental crust affected the cratonic destruction. This paper presents an overview on the temporal and spatial framework and geochemical characteristics of the Triassic intrusive rocks in the eastern North China Craton and use these data to trace their sources and petrogenetic processes, in order to constrain the tectonic setting in which they evolved. It is concluded that the destruction of the North China Craton was initiated in the Late Triassic and induced by delamination of the thickened continental crust by deep subduction of Yangtze continental crust and continent-continent collision. This suggests that the subduction of the continental crust and continent-continent collision are possibly interpreted as the inducement of Late Mesozoic decratonization of the North China Craton.

  7. Triassic magmatism and its relation to decratonization in the eastern North China Craton

    Institute of Scientific and Technical Information of China (English)

    YANG JinHui; WU FuYuan

    2009-01-01

    Lithospheric removal and destruction of the North China Craton have been hotly discussed recently.It has been confirmed that the timing of a strong lithospheric removal took place in Late Mesozoic;however,little is known about when the lithospheric removal was initiated and how the Late Permian to Early Triassic deep subduction of Yangtze continental crust affected the cratonic destruction.This paper presents an overview on the temporal and spatial framework and geochemical characteristics of the Triassic intrusive rocks in the eastern North China Craton and use these data to trace their sources and petrogenetic processes,in order to constrain the tectonic setting in which they evolved.It is concluded that the destruction of the North China Craton was initiated in the Late Triassic and induced by delamination of the thickened continental crust by deep subduction of Yangtze continental crust and continent-continent collision.This suggests that the subduction of the continental crust and continent-continent collision are possibly interpreted as the inducement of Late Mesozoic decratonization of the North China Craton.

  8. Group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the eastern Indian craton

    Science.gov (United States)

    Mandal, Prantik

    2017-02-01

    In the past three years, a semi-permanent network of fifteen 3-component broadband seismographs has become operational in the eastern Indian shield region occupying the Archean (∼2.5-3.6 Ga) Singhbhum-Odisha craton (SOC) and the Proterozoic (∼1.0-2.5 Ga) Chotanagpur Granitic Gneissic terrane (CGGT). The reliable and accurate broadband data for the recent 2015 Nepal earthquake sequence from 10 broadband stations of this network enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the region. First, we measure fundamental mode Rayleigh- and Love-wave group velocity dispersion curves in the period range of 7-70 s and then invert these curves to estimate the crustal and upper mantle structure below the eastern Indian craton (EIC). We observe that group velocities of Rayleigh and Love waves in SOC are relatively high in comparison to those of CGGT. This could be attributed to a relatively mafic-rich crust-mantle structure in SOC resulting from two episodes of magmatism associated with the 1.6 Ga Dalma and ∼117 Ma Rajmahal volcanisms. The best model for the EIC from the present study is found to be a two-layered crust, with a 14-km thick upper-crust (UC) of average shear velocity (Vs) of 3.0 km/s and a 26-km thick lower-crust (LC) of average Vs of 3.6 km/s. The present study detects a sharp drop in Vs (∼-2 to 3%) at 120-260 km depths, underlying the EIC, representing the probable seismic lithosphere-asthenosphere boundary (LAB) at 120 km depth. Such sharp fall in Vs below the LAB indicates a partially molten layer. Further, a geothermal gradient extrapolated from the surface heat flow shows that such a gradient would intercept the wet basalt solidus at 88-103 km depths, suggesting a 88-103 km thick thermal lithosphere below the EIC. This could also signal the presence of small amounts of partial melts. Thus, this 2-3% drop in Vs could be attributed to the presence of partial melts in the

  9. Lithospheric structure beneath the central and western North China Craton and adjacent regions from S-receiver function imaging

    Science.gov (United States)

    Yinshuang, A.; Zhang, Y.; Chen, L.

    2016-12-01

    The central and western NCC(CWNCC) only experienced localized lithospheric modification and has remained relatively stable since the Pre-Cambrian in contrast to the fundamental destruction in the east. For better unraveling the tectonic evolution and dynamics of CWNCC, detailed knowledge of lithospheric structure is thus important. However, most of the available seismological observations are dominated by regional seismic tomography and the resolutions are rather low due to the limited data coverage or intrinsic limitation of the methods. S receiver function(RF) contains information from deep velocity discontinuities and is free from the interference of crustal multiples, so it is widely used in subcontinental lithospheric structural studies. We collected teleseismic data from 340 broadband stations in CWNCC, and adopted 2-D wave equation-based poststack migration method to do S-receiver function CCP imaging. Finally, we get 8 migrated profile images in CWNCC and adjacent areas and integrate them for an overview. The most prominent feature of the LAB beneath central NCC is an sudden subsidence to 160km in the southern portion, and the dimension and extension of this deep anomaly is correlated to the lithosphere in Ordos, so we interpret it as a remnant cratonic mantle root. The LAB beneath western NCC can extend to the depth of 150-180 km but appears laterally variable. Western Ordos becomes shallower than its eastern counterpart and there are two obvious deep anomalies beneath the eastern Ordos, divided by a geological boundary at 37°N, which reflects that the lithosphere of Ordos is not so homogeneous or rigid as people thought before. Furthermore, a negative velocity discontinuity is widely identified at the depth of 80- 110 km within the thick lithosphere of CWNCC, and the location is spatially coincide with the modified LAB in ENCC. Although the cause of this mid-lithospheric discontinuity(MLD) is still controversial, mechanically, it may indicate an ancient

  10. Seismic, petrological and geodynamical constraints on thermal and compositional structure of the upper mantle: global thermochemical models

    DEFF Research Database (Denmark)

    Cammarano, Fabio; Tackley, Paul J.; Boschi, Lapo

    2011-01-01

    Mapping the thermal and compositional structure of the upper mantle requires a combined interpretation of geophysical and petrological observations. Based on current knowledge of material properties, we interpret available global seismic models for temperature assuming end-member compositional...... lateral compositional variations does not change significantly the thermal interpretation of seismic models, but gives a more realistic density structure. Modelling a petrological lithosphere gives cratonic temperatures at 150 km depth that are only 100 K hotter than those obtained assuming pyrolite......, and thus less buoyant, continental lithosphere is required to explain gravity data. None of the seismic tomography models we analyse is able to reproduce accurately the thermal structure of the oceanic lithosphere. All of them showtheir lowest seismic velocities at~100 km depth beneathmid-oceanic ridges...

  11. Seismicity and seismotectonics of southern Ghana: lessons for seismic hazard mitigation

    Science.gov (United States)

    Amponsah, Paulina

    2014-05-01

    Ghana is located on the West African craton and is far from the major earthquake zone of the world. It is therefore largely considered a stable region. However, the southern part of the country is seismically active. Records of damaging earthquakes in Ghana date as far back as 1615. A study on the microseismic activity in southern Ghana shows that the seismic activity is linked with active faulting between the east-west trending Coastal boundary fault and a northeast-southwest trending Akwapim fault zone. Epicentres of most of the earthquakes have been located close to the area where the two major faults intersect. This can be related to the level of activity of the faults. Some of the epicentres have been located offshore and can be associated with the level of activity of the coastal boundary fault. A review of the geological and instrumental recordings of earthquakes in Ghana show that earthquakes have occurred in the past and are still liable to occur within the vicinity of the intersection of the Akwapim fault zone and the Coastal boundary fault. Data from both historical and instrumental records indicate that the most seismically active areas in Ghana are the west of Accra, where the Akwapim fault zone and the Coastal boundary fault intersect. There are numerous minor faults in the intersection area between the Akwapim fault zone and the Coastal boundary fault. This mosaic of faults has a major implication for seismic activity in the area. Earthquake disaster mitigation measures are being put in place in recent times to reduce the impact of any major event that may occur in the country. The National Disaster Management Organization has come out with a building guide to assist in the mitigation effort of earthquake disasters and floods in the country. The building guide clearly stipulates the kind of material to be used, the proportion, what should go into the foundation for one or two storey building, the electrical materials to be used and many others.

  12. Studies on seismic waves

    Institute of Scientific and Technical Information of China (English)

    张海明; 陈晓非

    2003-01-01

    The development of seismic wave study in China in the past four years is reviewed. The discussion is divided into several aspects, including seismic wave propagation in laterally homogeneous media, laterally heterogeneous media, anisotropic and porous media, surface wave and seismic wave inversion, and seismic wave study in prospecting and logging problems. Important projects in the current studies on seismic wave is suggested as the development of high efficient numerical methods, and applying them to the studies of excitation and propagation of seismic waves in complex media and strong ground motion, which will form a foundation for refined earthquake hazard analysis and prediction.

  13. At the craton edge: Geodynamic evolution of the southern Canadian Cordillera

    Science.gov (United States)

    DiCaprio, L.; Eaton, D. W. S.

    2016-12-01

    In the southern Canadian Cordillera, the thermal and mechanical interface with the craton may influence the geodynamic evolution of the lithosphere-asthenosphere system. Evidence including recent Rayleigh-wave tomography studies suggest that, beneath the southern Canadian Cordillera, the mantle lithosphere is virtually absent. Here, the boundary between craton and Cordillera also marks a step change in measured surface heat flux and a westward termination of magnetic anomalies. This study provides a numerical simulation of lithospheric-mantle removal by geodynamic processes that include delamination, viscous erosion, and mantle dripping. An additional constraint to the geodynamic model comes from thermochronologic data demonstrating long wavelength uplift of the cordilleran plateau in the Eocene. We have developed a suite of 2D visco-plastic models of a transect through the southern Canadian Cordillera and North American Craton. Sensitivity tests elucidate a range of geodynamic models that are consistent with tomographic results and the observed uplift history.

  14. Detrital Zircon Ages of Hanjiang River:Constraints on Evolution of Northern Yangtze Craton, South China

    Institute of Scientific and Technical Information of China (English)

    Yang Jie; Gao Shan; Yuan Honglin; Gong Hujun; Zhang Hong; Xie Shiwen

    2007-01-01

    Clastic sedimentary rocks are natural samples of the exposed continental crust over large ideal sample for studying the formation and evolution of the northern Yangtze craton. Here we report laser ablation inductively coupled plasma mass spectrometer U-Pb ages of 122 detrital zircons from one sand sample of the Hanjiang River. The 110 concordant zircons reveal four major age groups of 768,444, 212, and 124 Ma, which well correlate with known magmatic events in the northern Yangtze craton. A minor group is present at 1 536 Ma, which is less known in the study area. Only seven zircons have ages of >1 750 Ma. Our results show that the Early Paleozoic, Late Triassic, and Early Cretaceous are important episodes of zircon growth and crustal growth/reworking in addition to the previously documented Neoproterozoic event. Our results suggest very limited exposures of Paleoproterozoic and Archean rocks in the northern parts of the Yangtze craton.

  15. Passive margin asymmetry and its polarity in the presence of a craton

    Science.gov (United States)

    Andres-Martinez, Miguel; Perez-Gussinye, Marta; Neto-Araujo, Mario; Morgan, Jason

    2016-04-01

    When continental lithosphere is extended to break-up it forms two conjugate passive margins. In many instances these margins are asymmetric: while one is wide and extensively faulted, the conjugate thins more abruptly and exhibits little faulting. Recent observational studies have suggested that this asymmetry results from the formation of an oceanward-younging sequential normal fault array on the future wide margin. Numerical models have shown that fault sequentiality arises as a result of asymmetric uplift of the hot mantle towards the hanging wall of the active fault, which weakens this area and promotes the formation of a new oceanward fault. In numerical models the polarity of the asymmetry is random. It results from spontaneous preferential localization of strain in a given fault, a process reinforced by strain weakening effects. Slight changes in the experiments initial grid result in an opposite polarity of the asymmetry. However, along a long stretch of the South Atlantic margins, from the Camamu-Gabon to the North Santos-South Kwanza conjugates, the polarity is not random and is very well correlated with the distance of the rift to nearby cratons. Here, we use numerical experiments to show that the presence of a thick cratonic root inhibits asthenospheric flow from underneath the craton towards the adjacent fold belt, while flow from underneath the fold belt towards the craton is favoured. This enhances and promotes sequential faulting towards the craton and results in a wide faulted margin located in the fold belt and a narrow conjugate margin in the craton side, thereby determining the polarity of the asymmetry, as observed in nature.

  16. Small-scale upper mantle flow during the initiation of craton destruction

    Science.gov (United States)

    Zhao, Liang; Wang, Kun; Xu, Xiaobing

    2017-04-01

    The North China Craton (NCC) is an old craton which has experienced multi-episodic tectonism with surrounding plates. Bordered to the north by Xing'an-Mongolian Orogenic Belt, to the south by Qingling-Dabie-Sulu Orogen and to the far-east by (Paleo-) Pacific plate, the NCC has lost the cratonic properties within its eastern part. Evidently, the initiation and mechanism of craton destruction attract tremendous attention and remain hot debated. During the Mesozoic to the Cenozoic, the northeastern part of the NCC has been intensively revoked, along with the transition from NE shortening to NW-SE extension. The subduction of Paleo-Pacific plate becomes the prime suspect due to the same kinematic direction. Here we present a hybrid shear wave splitting measurement to investigate the mantle deformation of the NCC, and intend to constrain geodynamic process during the initiation of craton destruction. The SKS waveform data is recorded from 60 broadband stations with an average spacing of 15 km. We employ the traditional routine method to obtain fast polarization directions (FPDs, Φ) and delay times (δt) for the teleseismic events with epicenter range in 85°-115°. One may often have troubles in delimiting SKS and S wave with regard to the events at distances NCC, the east-end nearly E-W FPD is possibly owing to the fossil anisotropy in the lithosphere during the N-S shortening in Jurassic. The other is located in the Solonker suture zone beneath where the Moho and lithosphere and asthenosphere boundary (LAB) have sharp variation in depth. It suggests that the subduction of Pacific plate apparently reactivates the upper mantle of the north edge of the NCC but has minor effects westwards. The inconsistency in FPDs may result from small-scale mantle flow in the upper mantle, which could be the dominant operating mode of the Pacific subduction during the initiation of cratonic destruction.

  17. Destruction geodynamics of the North China Craton and its Paleoproterozoic plate tectonics

    Institute of Scientific and Technical Information of China (English)

    ZHU RiXiang; ZHENG TianYu

    2009-01-01

    Much attention has been paid in the last two decades to the physical and chemical processes as well as temporal-spatial variations of the lithospheric mantle beneath the North China Craton. In order to provide insights into the geodynamics of this variation, it is necessary to thoroughly study the state and structure of the lithospheric crust and mantle of the North China Craton and its adjacent regions as an integrated unit. Based on the velocity structure of the crust and upper mantle constrained from seismological studies, this paper presents various available geophysical results regarding the lithosphere thickness, the nature of crust-mantle boundary, the upper mantle structure and deformation characteristics as well as their tectonic features and evolution systematics. Combined with the obtained data from petrology and geochemistry, a mantle flow model is proposed for the tectonic evolution of the North China Craton during the Mesozoic-Cenozoic. We suggest that subduction of the Pacific plate made the mantle underneath the eastern Asian continent unstable and able to flow faster. Such a regional mantle flow system would cause an elevation of melt/fluid content in the upper mantle of the North China Craton and the lithospheric softening, which, subsequently resulted in destruction of the North China Craton in different ways of delamination and thermal erosion in Yanshan, Taihang Mountains and the Tan-Lu Fault zone. Multiple lines of evidence recorded in the crust of the North China Craton, such as the amalgamation of the Archean eastern and western blocks, the subduction of Paleo-oceanic crust and Paleo-continental residue, indicate that the Earth in the Paleoproterozoic had already evolved into the plate tectonic system similar to the present plate tectonics.

  18. Rifting processes in the centre of Siberia revealed by BEST (Baikal Explosion Seismic Transects)

    Science.gov (United States)

    Nielsen, C. A.; Thybo, H.; Jensen, M. M.; Ross, A.; Suvorov, V. D.; Emanov, A.; Seleznev, V.; Tatkov, G.; Perchuc, E.; Gazcynski, E.

    2003-12-01

    The Baikal Rift Zone is located in Siberia at the centre of the world's largest continental area. It offers a unique opportunity for studying the processes of intra-cratonic rifting. The BEST project (Baikal Explosion Seismic Transects) comprises two deep seismic profiles at the southern end of Lake Baikal. The field project was carried out in October 2002 after a pilot project in September 2001. The aim of the project is to determine the crustal and upper mantle seismic velocity structure. The two profiles are: (1) a 360 km long, NS-trending profile across the rift zone from the Mongolian border to Cheremhovo, and (2) a 360 km long EW-trending profile along-strike of the rift zone at the northern shore of the lake into the Tunka depression to the Mongolian border. 180 Texan one-component seismographs were deployed along each profile. The primary seismic sources were 13 explosions in boreholes, each with a 500 to 3000 kg charge. Supplementary sources were airgun shots in the lake (one 100 l airgun on profile 1, one 30 l airgun on profile 2) and the supervibrator located at Babushkin near the cross point between the two profiles at the shore of the lake. We present the preliminary modelling results of the BEST data from tomographic inversion of first arrival times and 2D ray tracing modelling of the seismic velocity structure of the crust and uppermost mantle. The models show: (1) A pronounced sedimentary graben structure to depths of at least 10 km; (2) No significant crustal thinning below the rift zone; (3) Strong seismic reflectivity underneath the rift zone, indicative of pronounced magmatic intrusion into the lower crust, despite the non-volcanic appearance of much of the rift zone; (4) No sign of significant reduction of the seismic Pn wave velocity; and (5) No clear indication of continuation of the cratonic crust underneath the rift zone in disagreement with a recently published model of the rifting process. Instead the model is in agreement with a model in

  19. Quantitative Seismic Amplitude Analysis

    NARCIS (Netherlands)

    Dey, A.K.

    2011-01-01

    The Seismic Value Chain quantifies the cyclic interaction between seismic acquisition, imaging and reservoir characterization. Modern seismic innovation to address the global imbalance in hydrocarbon supply and demand requires such cyclic interaction of both feed-forward and feed-back processes.

  20. Quantitative Seismic Amplitude Analysis

    NARCIS (Netherlands)

    Dey, A.K.

    2011-01-01

    The Seismic Value Chain quantifies the cyclic interaction between seismic acquisition, imaging and reservoir characterization. Modern seismic innovation to address the global imbalance in hydrocarbon supply and demand requires such cyclic interaction of both feed-forward and feed-back processes. Cur

  1. Robotization in Seismic Acquisition

    NARCIS (Netherlands)

    Blacquière, G.; Berkhout, A.J.

    2013-01-01

    The amount of sources and detectors in the seismic method follows "Moore’s Law of seismic data acquisition", i.e., it increases approximately by a factor of 10 every 10 years. Therefore automation is unavoidable, leading to robotization of seismic data acquisition. Recently, we introduced a new

  2. Thermo-chemical structure of the North China Craton from multi-observable probabilistic inversion: extent and causes of cratonic lithosphere modification

    Science.gov (United States)

    Guo, Z.; Afonso, J. C.; Qashqai, M.; Yang, Y.; Chen, J.

    2016-12-01

    Although the North China Craton (NCC) is one of the best documented cases of cratonic lithosphere modification, the actual causes, processes, and extent of lithospheric modification still are a matter of debate. Here, we present the first thermo-chemical model of the NCC from the surface down to 350 km by jointly inverting surface wave phase velocity data, geoid height, surface heat flow and absolute elevation with a novel multi-observable probabilistic inversion method. Our model reveals a thin ( 65-100 km) and chemically fertile lithosphere (8790) lithospheric mantle is imaged beneath the central TNCO and Ordos Block, reaching depths > 260 km. This lithospheric "keel" is surrounded to the east by a high-temperature sublithospheric anomaly that originates at depths > 280 km. The spatial distribution of this anomaly and its correlation with the location of recent volcanism in the region suggest that the anomaly represents a deep mantle upwelling being diverted by the cratonic keel and spreading onto regions of shallow lithosphere. Our results indicate that the present-day thermochemical structure beneath the NCC is the result of a complex interaction between a large-scale return flow associated with the subduction of the Pacific slab and the shallow lithospheric structure.

  3. Seismic Constraints on the Mantle Viscosity Structure beneath Antarctica

    Science.gov (United States)

    Wiens, Douglas; Heeszel, David; Aster, Richard; Nyblade, Andrew; Wilson, Terry

    2015-04-01

    Lateral variations in upper mantle viscosity structure can have first order effects on glacial isostatic adjustment. These variations are expected to be particularly large for the Antarctic continent because of the stark geological contrast between ancient cratonic and recent tectonically active terrains in East and West Antarctica, respectively. A large misfit between observed and predicted GPS rates for West Antarctica probably results in part from the use of a laterally uniform viscosity structure. Although not linked by a simple relationship, mantle seismic velocities can provide important constraints on mantle viscosity structure, as they are both largely controlled by temperature and water content. Recent higher resolution seismic models for the Antarctic mantle, derived from data acquired by new seismic stations deployed in the AGAP/GAMSEIS and ANET/POLENET projects, offer the opportunity to use the seismic velocity structure to place new constraints on the viscosity of the Antarctic upper mantle. We use an Antarctic shear wave velocity model derived from array analysis of Rayleigh wave phase velocities [Heeszel et al, in prep] and examine a variety of methodologies for relating seismic, thermal and rheological parameters to compute a suite of viscosity models for the Antarctic mantle. A wide variety of viscosity structures can be derived using various assumptions, but they share several robust common elements. There is a viscosity contrast of at least two orders of magnitude between East and West Antarctica at depths of 80-250 km, reflecting the boundary between cold cratonic lithosphere in East Antarctica and warm upper mantle in West Antarctica. The region beneath the Ellsworth-Whitmore Mtns and extending to the Pensacola Mtns. shows intermediate viscosity between the extremes of East and West Antarctica. There are also significant variations between different parts of West Antarctica, with the lowest viscosity occurring beneath the Marie Byrd Land (MBL

  4. The nature of cratonic lithosphere: Combining constraints from seismology, mineral physics, and petrology

    Science.gov (United States)

    Dalton, Colleen; Faul, Ulrich; Hirsch, Aaron

    2014-05-01

    In recent years, the prevailing notion of Precambrian continental lithosphere as a thick boundary layer (~200-300 km) with a very depleted composition and temperature structure controlled by steady-state conductive cooling has been challenged by several lines of seismological evidence. One, profiles of shear velocity with depth beneath cratons exhibit lower wave speed at shallow depths and higher wave speed at greater depths than can be explained by temperature alone. These profiles are also characterized by positive or flat velocity gradients with depth in the uppermost mantle and anomalously high attenuation, both of which are difficult to reconcile with the low temperatures and large thermal gradient expected in the thermal boundary layer. Two, body-wave receiver-function studies have detected a mid-lithospheric discontinuity that requires a large and abrupt velocity decrease with depth in cratonic regions that cannot be achieved by thermal gradients alone. We have used a forward-modeling approach to identify the suite of shear-velocity profiles that are consistent with phase-velocity observations made for Rayleigh waves traversing cratons in North America, Africa, and Australia. We have also calculated the range of lithospheric temperatures and compositions that are consistent with the elastic and anelastic seismological models, using laboratory measurements on the sensitivity of velocity and attenuation to temperature, major-element composition, and mineralogy. Finally, we consider the implications of the models for the long-term stability of cratons.

  5. Lateral heterogeneity and vertical stratification of cratonic lithospheric keels: examples from Europe, Siberia, and North America

    DEFF Research Database (Denmark)

    Artemieva, Irina; Cherepanova, Yulia; Herceg, Matija;

    The presentation summarizes geophysical models for Precambrian cratons, including the structure of the crust and the lithospheric mantle. A particular focus is on thermo-compositional heterogeneity of the lithospheric mantle as constrained by different geophysical data sets: (i) thermal structure...... by an increase in mantle density as compared to light and strongly depleted lithospheric mantle of the Archean nuclei....

  6. Major element composition of the lithospheric mantle under the North Atlantic craton

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Stevenson, R.K.

    2003-01-01

    The composition and thermal state of the lithospheric mantle under the North Atlantic craton was investigated using a suite of peridotite xenoliths from the diamond-bearing Sarfartoq kimberlite dike swarm of southwestern Greenland. Elevated olivine and whole-rock Mg# (>0.9) attest to the refracto...

  7. An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization

    Science.gov (United States)

    Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.; Cliff, John B.; Belousova, Elena A.; Sheppard, Stephen

    2017-01-01

    The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as 'cratonization', is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons from several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons. The majority of magmatic zircons from the main magmatic cycles have Hf isotopic compositions that are generally more evolved than CHUR, forming vertical arrays that extend to moderately radiogenic compositions. Complimentary O isotope data, also show a significant variation in composition. However, combined, these data define not only the source components from which the magmas were derived, but also a range of physio-chemical processes that operated during magma transport and emplacement. These data also identify a previously unknown crustal reservoir in the Capricorn Orogen.

  8. Mesoproterozoic evolution of the Rio de la Plata Craton in Uruguay: at the heart of Rodinia?

    DEFF Research Database (Denmark)

    Gaucher, Claudio; Frei, Robert; Chemale, Farid

    2011-01-01

    detrital zircon ages occurring in Ediacaran sandstones of the RPC. If the RPC is fringed at both sides by Mesoproterozoic, Grenville-aged belts it is likely that it occupied a rather central position in Rodinia. A possible location between Laurentia and the Kalahari Craton, and to the south of Amazonia...

  9. Evolution of the mantle beneath the eastern North China Craton during the Cenozoic: Linking geochemical and geophysical observations

    Science.gov (United States)

    Li, Hong-Yan; Xu, Yi-Gang; Ryan, Jeffrey G.; Whattam, Scott A.

    2017-01-01

    Recent discoveries related to the geochemistry of Cenozoic basalts and the geophysics of the deep mantle beneath eastern Eurasia make it possible to place constraints on the relationship between the seismic tomography of subcontinental mantle domains and their geochemical heterogeneities. Basalts with ocean island basalt-like trace elements erupted during (56-23 Ma) and after (≤23 Ma) rifting of the eastern North China Craton (NCC) show evidence for the mixing of an isotopically depleted source and an EMI (Enriched mantle type I) pyroxenitic mantle. NCC rifting-stage basalts exhibit anomalously low MgO and Fe2O3T and high SiO2 and Al2O3, as well as low Dy/Yb and Y/Yb and high ɛHf at a given ɛNd, as compared to the postrifting basalts. Temporal compositional variations and their association with basin subsidence indicate that heterogeneity in the eastern NCC asthenospheric mantle is the primary driver for intraplate magmatism in this region. The specific magmatic sources shifted in terms of depth, related to lithospheric thinning and thickening in the eastern NCC. The NCC EMI mantle domain most likely developed due to ancient events, is persistent through time, and is not related to dehydration of the stagnant Pacific slab in the mantle transition zone. Based on the chemical signatures of postrifting basalts, contributions from the Pacific slab are likely to be carbonatite rich. Mantle metasomatism by carbonatite melts from the Pacific slab and the interaction of these melts at shallower depths with EMI pyroxenitic mantle domains to trigger melting are contributors to the observed low P wave velocity zone beneath eastern Eurasia.

  10. Seismicity in West Iberia: small scale seismicity recording from a Dense Seismic Broadband Deployment in Portugal (WILAS Project)

    Science.gov (United States)

    Afonso Dias, Nuno; Custódio, Susana; Silveira, Graça; Carrilho, Fernando; Haberland, Christian; Lima, Vânia; Rio, Inês; Góngora, Eva; Marreiros, Célia; Morais, Iolanda; Vales, Dina; Fonseca, João; Caldeira, Bento; Villaseñor, Antonio

    2013-04-01

    Over the last years several projects targeted the lithospheric structure and its correlation with the surface topography, e.g. EarthSCOPE/USArray or TOPO-EUROPE. Two projects focused on the Iberian Peninsula, one giving particular attention to the southern collision margin (TOPO-MED) and the other to the central cratonic Massif (TOPO-IBERIA/IBERArray). These projects mostly rely on deployed dense seismic broadband (BB) networks with an average inter-station spacing of 60km, which strongly increases the available network spatial coverage. The seismicity recording in such networks is critical to access current rates of lithospheric deformation. Within the scope of project WILAS - West Iberia Lithosphere and Astenosphere Structure (PTDC/CTE-GIX/097946/2008), a 3-year project funded by the Portuguese Science & Technology Foundation (FCT), we deployed a temporary network of 30 BB stations in Portugal between 2010 and 2012, doubling the total number of operating BB stations. Together with the permanent and TOPO-IBERIA stations, the resulting networks provided a full and dense coverage of the Iberian Peninsula. The majority of the permanent stations in Portugal, aimed at the seismic surveillance, are located in the southern part of the country in result of the active tectonic convergence between Iberia and Africa. Therefore, the temporary stations were mainly deployed in the north of Portugal. These temporary stations allowed an improvement of the earthquake detection threshold. The detection of seismic events was based on the analysis of daily spectrograms of the entire network, the new events detected being analysed and included in the catalogue. The new detected events are located mainly in the north, with magnitudes as low as 0.5 ML and in the offshore in the Estremadura Spur. Some additional events were also located south of Portugal, between the Gorringe Bank and the Gulf of Cadiz, in this case the lower magnitudes being ~2.0ML. Focal mechanisms will also be

  11. Natural Seismicity in NW Australia: Another Look at Continental Intraplate Earthquakes

    Science.gov (United States)

    Revets, S. A.; Keep, M.; Kennett, B. L.

    2007-12-01

    Northwestern Australia hosts a considerable number of smaller seismic events, but also Australia's largest earthquake on record (Meeberrie, 1941, M7.9). In 2005 we deployed a small network of seismometers to record natural seismicity in the region, to understand the amount, magnitude, nature and distribution of these events, and to interpret these events within a tectonic and neotectonic context. The region is largely underlain by Precambrian material, ranging from Archaean craton to Proterozoic mobile belts, and truncated to the west by the lithospheric-scale Darling Fault. This fault separates the Precambrian crustal elements from the younger Palaeozoic-Mesozoic Carnarvon Basin to the east, has a strike length of over 1400 km. It is thought to have been active since at least the Proterozoic. Estimates of slip on some southerly sections of this fault exceed 12 km. We believe that these various crustal elements (basins, cratons, mobile belts) respond differently to seismicity based on their rheology, thickness and deformation history. We supplemented data from our network with traces from some of the instruments of the national network of Australia. This data set proved adequate for the calculation of fault-plane solutions of some 13 mini- and micro- events in the region. The eventsrecorded occurred along or close to known faults, although field data for movement or reactivation on these faults is sparse. Most of our calculated events occur in close proximity to mechanical boundaries between crustal elements, indicating that the mechanical response of these elements controls the location of seismicity. The transitional tectonic setting of this part of the Australian margin---a passive margin sandwiched between two active margin segments---indicates that the term "intraplate" may be an inappropriate description of these seismic events.

  12. Dating Metasomatism in the Lithosphere Beneath North China Craton

    Science.gov (United States)

    Chen, L.; Zhou, X.

    2005-12-01

    Dating of mantle metasomatism had been carried out using zircons in metasomatized mantle xenoliths entrained in kimberlites (Kinny and Dawson, 1992; Rudnick et al., 1999; Konzett et al., 1998, 2000; Liati et al., 2004), because the U-Pb system in zircon can remain closed at high temperature (>900-)(Lee et al., 1997). Here we report a SHRIMP U-Pb dating analysis of zircons from a unique dunite-orthopyroxenite xenolith entrained in Cretaceous high-Mg diorite of Shandong province, which provides a timing constraint for the multi-stage metasomatism in the lithosphere beneath North China craton (NCC). Abundant ultramafic xenoliths had been found in the Tietonggou intrusion, one of the Cretaceous high-Mg diorite-dominated plutons in North China (Chen and Zhou, 2004). The lithology, mineral chemistry, equilibrium temperature (690-790A), and metasomatic characteristics of the ultramafic xenoliths indicate that they might be derived from the shallow lithosphere (the crust-mantle transitional zone or the uppermost lithospheric mantle) and had suffered multi-stage metasomatism (Chen and Zhou, 2004, 2005). Xenolith LW0006 is the most extremely metasomatized sample found so far in the xenolith suite of the Tietonggou pluton. The petrography, mineral chemistry, and major element compositions provide a clear metasomatic record of the composite xenolith: K (and/or Ca) metasomatism, and Si (Na) metasomatism (Chen and Zhou). We found seven zircons range from 100-170 Im in longest dimension, which is reflected in the unusually high Zr content of the bulk rock (49 ppm) of this sample. SHRIMP U-Pb dating reveals that these zircons might be grouped three kinds: Mesozoic (concordia age of 127-A3 Ma, 5 zircons), Paleozoic (430-470 Ma, 1 zircon only) and Mesoproterozoic (1310-1540 Ma, 1 zircon only). Cathodoluminescence (CL) images reveal that a few Mesozoic zircons and the Paleozoic zircons retain oscillatory zoning. The Mesozoic zircons are characterized with high Th, U contents and high

  13. Constraints on Shear Velocity in the Cratonic Upper Mantle From Rayleigh Wave Phase Velocity

    Science.gov (United States)

    Hirsch, A. C.; Dalton, C. A.

    2014-12-01

    In recent years, the prevailing notion of Precambrian continental lithosphere as a thick boundary layer (200-300 km), defined by a depleted composition and a steady-state conductively cooled temperature structure, has been challenged by several lines of seismological evidence. One, profiles of shear velocity with depth beneath cratons exhibit lower wave speed at shallow depths and higher wave speed at greater depths than can be explained by temperature alone. These profiles are also characterized by positive or flat velocity gradients with depth and anomalously high attenuation in the uppermost mantle, both of which are difficult to reconcile with the low temperatures and large thermal gradient expected with a thermal boundary layer. Two, body-wave receiver-function studies have detected a mid-lithospheric discontinuity that requires a large and abrupt velocity decrease with depth in cratonic regions that cannot be achieved by thermal gradients alone. Here, we used forward-modeling to identify the suite of shear-velocity profiles that are consistent with phase-velocity observations made for Rayleigh waves that primarily traversed cratons in North America, South America, Africa, and Australia. We considered two approaches; with the first, depth profiles of shear velocity were predicted from thermal models of the cratonic upper mantle that correspond to a range of assumed values of mantle potential temperature, surface heat flow, and radiogenic heat production in the crust and upper mantle. With the second approach, depth profiles of shear velocity were randomly generated. In both cases, Rayleigh wave phase velocity was calculated from the Earth models and compared to the observed values. We show that it is very difficult to match the observations with an Earth model containing a low-velocity zone in the upper mantle; instead, the best-fit models contain a flat or positive velocity gradient with depth. We explore the implications of this result for the thermal and

  14. Angola Seismicity MAP

    Science.gov (United States)

    Neto, F. A. P.; Franca, G.

    2014-12-01

    The purpose of this job was to study and document the Angola natural seismicity, establishment of the first database seismic data to facilitate consultation and search for information on seismic activity in the country. The study was conducted based on query reports produced by National Institute of Meteorology and Geophysics (INAMET) 1968 to 2014 with emphasis to the work presented by Moreira (1968), that defined six seismogenic zones from macro seismic data, with highlighting is Zone of Sá da Bandeira (Lubango)-Chibemba-Oncócua-Iona. This is the most important of Angola seismic zone, covering the epicentral Quihita and Iona regions, geologically characterized by transcontinental structure tectono-magmatic activation of the Mesozoic with the installation of a wide variety of intrusive rocks of ultrabasic-alkaline composition, basic and alkaline, kimberlites and carbonatites, strongly marked by intense tectonism, presenting with several faults and fractures (locally called corredor de Lucapa). The earthquake of May 9, 1948 reached intensity VI on the Mercalli-Sieberg scale (MCS) in the locality of Quihita, and seismic active of Iona January 15, 1964, the main shock hit the grade VI-VII. Although not having significant seismicity rate can not be neglected, the other five zone are: Cassongue-Ganda-Massano de Amorim; Lola-Quilengues-Caluquembe; Gago Coutinho-zone; Cuima-Cachingues-Cambândua; The Upper Zambezi zone. We also analyzed technical reports on the seismicity of the middle Kwanza produced by Hidroproekt (GAMEK) region as well as international seismic bulletins of the International Seismological Centre (ISC), United States Geological Survey (USGS), and these data served for instrumental location of the epicenters. All compiled information made possible the creation of the First datbase of seismic data for Angola, preparing the map of seismicity with the reconfirmation of the main seismic zones defined by Moreira (1968) and the identification of a new seismic

  15. Dobreflection: An Exceptional Example of Basin Inversion In The East-european Craton

    Science.gov (United States)

    Bayer, U.; Stovba, S.; Maystrenko, Y.; Stephenson, R.; Tolkunov, A.; Dobreflection Working Group

    DOBREflection is a joint project of Ukrainian organisations (Ukrgeofisika and the Institute of Geophysics of the National Academy of Sciences) and an international European consortium that included acquisition of some 250 km of deep seismic re- flection data in 2000 and 2001. The aim was to study the south-eastern continuation of the Dnieper-Donets Basin (DDB) into the coal mining areas of the Donbas Foldbelt (DF), including the sedimentary fill and its deformation as well as the structure of the deeper crust. The DF is the strongly inverted and compressionally deformed part of the DDB, which is a Late Devonian rift basin located on the south-western part of the East-European Craton (EEC) between the Ukrainian Shield (UkS) to the south-west and the Voronezh Massif (VM) to the north-east. DOBREflection reveals that the base of the predominantly Devonian and Carboniferous sedimentary succession in the DF reaches a maximum of about 20-km in its axial part. However, the Donbas area has been much more seriously affected by secondary tectonic events than those parts of the DDB further north. In particular, significant shortening in response to Late Cretaceous Eo-Alpine compression is in evidence. While syn- and post-rift faults with offsets up to more than 3-km disrupt the basement horizon, the shortening (basin inversion) is displayed mainly as folding within the sedimentary succession. The fold patterns sug- gest a detachment surface most likely located within the Upper Devonian sequence, perhaps indicating the presence of salt rich layers. Shortening is also accommodated on two important crustal-scale structures. The first of these is a slightly inclined listric shear zone, or thrust, cutting the entire crust - including the UkS Moho - south of the DF, upwards through the complete sedimentary package ending in the northern part of the DF within an area of reverse faults exposed at the surface. The latter have vertical offsets up to a few kilometres whereas the

  16. Simplified seismic risk analysis

    Energy Technology Data Exchange (ETDEWEB)

    Pellissetti, Manuel; Klapp, Ulrich [AREVA NP GmbH, Erlangen (Germany)

    2011-07-01

    Within the context of probabilistic safety analysis (PSA) for nuclear power plants (NPP's), seismic risk assessment has the purpose to demonstrate that the contribution of seismic events to overall risk is not excessive. The most suitable vehicle for seismic risk assessment is a full scope seismic PSA (SPSA), in which the frequency of core damage due to seismic events is estimated. An alternative method is represented by seismic margin assessment (SMA), which aims at showing sufficient margin between the site-specific safe shutdown earthquake (SSE) and the actual capacity of the plant. Both methods are based on system analysis (fault-trees and event-trees) and hence require fragility estimates for safety relevant systems, structures and components (SSC's). If the seismic conditions at a specific site of a plant are not very demanding, then it is reasonable to expect that the risk due to seismic events is low. In such cases, the cost-benefit ratio for performing a full scale, site-specific SPSA or SMA will be excessive, considering the ultimate objective of seismic risk analysis. Rather, it will be more rational to rely on a less comprehensive analysis, used as a basis for demonstrating that the risk due to seismic events is not excessive. The present paper addresses such a simplified approach to seismic risk assessment which is used in AREVA to: - estimate seismic risk in early design stages, - identify needs to extend the design basis, - define a reasonable level of seismic risk analysis Starting from a conservative estimate of the overall plant capacity, in terms of the HCLPF (High Confidence of Low Probability of Failure), and utilizing a generic value for the variability, the seismic risk is estimated by convolution of the hazard and the fragility curve. Critical importance is attached to the selection of the plant capacity in terms of the HCLPF, without performing extensive fragility calculations of seismically relevant SSC's. A suitable basis

  17. Seismic Catalogue and Seismic Network in Haiti

    Science.gov (United States)

    Belizaire, D.; Benito, B.; Carreño, E.; Meneses, C.; Huerfano, V.; Polanco, E.; McCormack, D.

    2013-05-01

    The destructive earthquake occurred on January 10, 2010 in Haiti, highlighted the lack of preparedness of the country to address seismic phenomena. At the moment of the earthquake, there was no seismic network operating in the country, and only a partial control of the past seismicity was possible, due to the absence of a national catalogue. After the 2010 earthquake, some advances began towards the installation of a national network and the elaboration of a seismic catalogue providing the necessary input for seismic Hazard Studies. This paper presents the state of the works carried out covering both aspects. First, a seismic catalogue has been built, compiling data of historical and instrumental events occurred in the Hispaniola Island and surroundings, in the frame of the SISMO-HAITI project, supported by the Technical University of Madrid (UPM) and Developed in cooperation with the Observatoire National de l'Environnement et de la Vulnérabilité of Haiti (ONEV). Data from different agencies all over the world were gathered, being relevant the role of the Dominican Republic and Puerto Rico seismological services which provides local data of their national networks. Almost 30000 events recorded in the area from 1551 till 2011 were compiled in a first catalogue, among them 7700 events with Mw ranges between 4.0 and 8.3. Since different magnitude scale were given by the different agencies (Ms, mb, MD, ML), this first catalogue was affected by important heterogeneity in the size parameter. Then it was homogenized to moment magnitude Mw using the empirical equations developed by Bonzoni et al (2011) for the eastern Caribbean. At present, this is the most exhaustive catalogue of the country, although it is difficult to assess its degree of completeness. Regarding the seismic network, 3 stations were installed just after the 2010 earthquake by the Canadian Government. The data were sent by telemetry thought the Canadian System CARINA. In 2012, the Spanish IGN together

  18. Magnetotelluric characterization through the Ambargasta-Sumampa Range: The connection between the northern and southern trace of the Río de La Plata Craton - Pampean Terrane tectonic boundary

    Science.gov (United States)

    Peri, V. Gisel; Barcelona, Hernan; Pomposiello, M. Cristina; Favetto, Alicia

    2015-04-01

    The South American Platform was part of the Western Gondwana, a collage of plates of different ages assembled in late Neoproterozoic to Cambrian times. The Transbrasiliano Lineament, a continental shear belt that transversely intersects this platform from NE to SW, has its southern expression in the tectonic boundary between the Río de La Plata Craton and the Pampean Terrane. Magnetotelluric long-period data in a W-E profile (29°30‧ S) that crosses the Ambargasta-Sumampa Range and the Chaco-Pampean Plain were obtained to connect information of this mostly inferred tectonic boundary. A 2-D inversion model shows the Chacoparanense basin, Río Dulce lineament, Ambargasta-Sumampa Range and Salina de Ambargasta in the upper crust. At mid-to-lower crust and 40 km to the east of the Ambargasta-Sumampa Range, a discontinuity (500-2000 Ω m) of 20-km-wide separates two highly resistive blocks, the Río de La Plata Craton (6000-20,000 Ω m) in the east, and the Pampean Terrane (5000-20,000 Ω m) in the west. This discontinuity represents the tectonic boundary between both cratons and could be explained by the presence of graphite. The geometry of the Pampean Terrane suggests an east-dipping paleo-subduction. Our results are consistent with gravimetric and seismicity data of the study area. A more conductive feature beneath the range and the tectonic boundary was associated with the NE-SW dextral transpressive system evidenced by the mylonitic belts exposed in the Eastern Pampean Ranges. This belt represents a conjugate of the mega-shear Transbrasiliano Lineament and could be explained by fluid-rock interaction by shearing during hundreds of years. The eastern border of the Ambargasta-Sumampa Range extends the trace of the Transbrasiliano Lineament. The electrical Moho depth (40 km to the west and 35 km to the east) was identified by a high electrical contrast between the crust and upper mantle. The upper mantle shows a resistive structure beneath the Río de La Plata

  19. Imaging seismic reflections

    NARCIS (Netherlands)

    Op 't Root, Timotheus Johannes Petrus Maria

    2011-01-01

    The goal of reflection seismic imaging is making images of the Earth subsurface using surface measurements of reflected seismic waves. Besides the position and orientation of subsurface reflecting interfaces it is a challenge to recover the size or amplitude of the discontinuities. We investigate tw

  20. Origin and diamond prospectivity of Mesoproterozoic kimberlites from the Narayanpet field, Eastern Dharwar Craton, southern India

    DEFF Research Database (Denmark)

    Chalapathi Rao, N.V.; Paton, Chad; Lehmann, B.

    2012-01-01

    The Mesoproterozoic Narayanpet Kimberlite Field (NKF) is located ~200km north of the well-known Wajrakarur Kimberlite Field (WKF) in the Eastern Dharwar Craton, southern India. Whereas a majority of the WKF occurrences are diamondiferous and contain mantle xenoliths and xenocrysts, their paucity ......-wide, indicates that redox conditions were favourable for diamond prospectivity, and that magmatic emplacement could, instead, have played a major role in their low diamond potential. © 2011 John Wiley & Sons, Ltd.....

  1. Magnetotelluric investigations of the lithosphere beneath the central Rae craton, mainland Nunavut, Canada

    Science.gov (United States)

    Spratt, Jessica E.; Skulski, Thomas; Craven, James A.; Jones, Alan G.; Snyder, David B.; Kiyan, Duygu

    2014-03-01

    New magnetotelluric soundings at 64 locations throughout the central Rae craton on mainland Nunavut constrain 2-D resistivity models of the crust and lithospheric mantle beneath three regional transects. Responses determined from colocated broadband and long-period magnetotelluric recording instruments enabled resistivity imaging to depths of > 300 km. Strike analysis and distortion decomposition on all data reveal a regional trend of 45-53°, but locally the geoelectric strike angle varies laterally and with depth. The 2-D models reveal a resistive upper crust to depths of 15-35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries. Surface projections of the conductive layer coincide with areas of high grade, Archean metasedimentary rocks. Tectonic burial of these rocks and thickening of the crust occurred during the Paleoproterozoic Arrowsmith (2.3 Ga) and Trans-Hudson orogenies (1.85 Ga). Overall, the uppermost mantle of the Rae craton shows resistivity values that range from 3000 Ω m in the northeast (beneath Baffin Island and the Melville Peninsula) to 10,000 Ω m beneath the central Rae craton, to >50,000 Ω m in the south near the Hearne Domain. Near-vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of Hudsonian granites. A regional decrease in resistivities to values of 500 Ω m at depths of 180-220 km, increasing to 300 km near the southern margin of the Rae craton, is interpreted as the lithosphere-asthenosphere boundary.

  2. SOAR Telescope seismic performance II: seismic mitigation

    Science.gov (United States)

    Elias, Jonathan H.; Muñoz, Freddy; Warner, Michael; Rivera, Rossano; Martínez, Manuel

    2016-07-01

    We describe design modifications to the SOAR telescope intended to reduce the impact of future major earthquakes, based on the facility's experience during recent events, most notably the September 2015 Illapel earthquake. Specific modifications include a redesign of the encoder systems for both azimuth and elevation, seismic trigger for the emergency stop system, and additional protections for the telescope secondary mirror system. The secondary mirror protection may combine measures to reduce amplification of seismic vibration and "fail-safe" components within the assembly. The status of these upgrades is presented.

  3. Lithospheric seismic fabrics of Sulu ultrahigh-pressure metamorphic belt

    Institute of Scientific and Technical Information of China (English)

    YANG; Wencai; YANG; Wuyang; JIN; Zhenmin; CHENG; Zhenyan

    2005-01-01

    supercrustal rocks after the Triassic collision between the Yangtze and Sino-Korean cratons; whilst the ductile shearing rock-suites resulted from shearing deformation processes during the subduction and exhumation. The normal velocity below the UHP rock-slice was correlated with Mesozoic extension processes in the area. Through careful calibration of seismic reflectors and analyzing xenoliths, one can find the relationship between the causes of seismic reflectors and corresponding geodynamic processes, offering a new basis for reconstruction of regional dynamic evolution history.

  4. Seismic lamination and anisotropy of the Lower Continental Crust

    Science.gov (United States)

    Meissner, Rolf; Rabbel, Wolfgang; Kern, Hartmut

    2006-04-01

    Seismic lamination in the lower crust associated with marked anisotropy has been observed at various locations. Three of these locations were investigated by specially designed experiments in the near vertical and in the wide-angle range, that is the Urach and the Black Forrest area, both belonging to the Moldanubian, a collapsed Variscan terrane in southern Germany, and in the Donbas Basin, a rift inside the East European (Ukrainian) craton. In these three cases, a firm relationship between lower crust seismic lamination and anisotropy is found. There are more cases of lower-crustal lamination and anisotropy, e.g. from the Basin and Range province (western US) and from central Tibet, not revealed by seismic wide-angle measurements, but by teleseismic receiver function studies with a P-S conversion at the Moho. Other cases of lamination and anisotropy are from exhumed lower crustal rocks in Calabria (southern Italy), and Val Sesia and Val Strona (Ivrea area, Northern Italy). We demonstrate that rocks in the lower continental crust, apart from differing in composition, differ from the upper mantle both in terms of seismic lamination (observed in the near-vertical range) and in the type of anisotropy. Compared to upper mantle rocks exhibiting mainly orthorhombic symmetry, the symmetry of the rocks constituting the lower crust is either axial or orthorhombic and basically a result of preferred crystallographic orientation of major minerals (biotite, muscovite, hornblende). We argue that the generation of seismic lamination and anisotropy in the lower crust is a consequence of the same tectonic process, that is, ductile deformation in a warm and low-viscosity lower crust. This process takes place preferably in areas of extension. Heterogeneous rock units are formed that are generally felsic in composition, but that contain intercalations of mafic intrusions. The latter have acted as heat sources and provide the necessary seismic impedance contrasts. The observed

  5. An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: from subduction magmatism to cratonization

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Simon P.; Korhonen, Fawna; Kirkland, Christopher; Cliff, John B.; Belousova, Elena; Sheppard, Stephen

    2017-01-03

    The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as ‘cratonization’, is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons from several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons.

  6. Magnetic anomalies across Bastar craton and Pranhita–Godavari basin in south of central India

    Indian Academy of Sciences (India)

    I V Radhakrishna Murthy; S Bangaru Babu

    2009-02-01

    Aeromagnetic anomalies over Bastar craton and Pranhita –Godavari (P –G)basin in the south of central India could be attributed to NW –SE striking mafic intrusives in both the areas at variable depths.Such intrusions can be explained considering the collision of the Bastar and Dharwar cratons by the end of the Archaean and the development of tensile regimes that followed in the Paleoproterozoic,facilitating intrusions of mafic dykes into the continental crust.The P –G basin area,being a zone of crustal weakness along the contact of the Bastar and Dharwar cratons, also experienced extensional tectonics.The inferred remanent magnetization of these dykes dips upwards and it is such that the dykes are oriented towards the east of the magnetic north at the time of their formation compared to their present NW –SE strike.Assuming that there was no imprint of magnetization of a later date,it is concluded that the Indian plate was located in the southern hemisphere,either independently or as part of a supercontinent,for some span of time during Paleoproterozoic and was involved in complex path of movement and rotation subsequently. The paper presents a case study of the utility of aeromagnetic anomalies in qualitatively deducing the palaeopositions of the landmasses from the interpreted remanent magnetism of buried intrusive bodies.

  7. Geology and geochemistry of giant quartz veins from the Bundelkhand Craton, central India and their implications

    Indian Academy of Sciences (India)

    J K Pati; S C Patel; K L Pruseth; V P Malviya; M Arima; S Raju; P Pati; K Prakash

    2007-12-01

    Giant quartz veins (GQVs; earlier referred to as `quartz reefs’) occurring in the Archean Bundelkhand Craton (29, 000 km2) represent a gigantic Precambrian (∼2.15 Ga) silica-rich fluid activity in the central Indian shield. These veins form a striking curvilinear feature with positive relief having a preferred orientation NE–SW to NNE–SSW in the Bundelkhand Craton. Their outcrop widths vary from ≤ 1 to 70m and pervasively extend over tens of kilometers along the strike over the entire craton. Numerous younger thin quartz veins with somewhat similar orientation cut across the giant quartz veins. They show imprints of strong brittle to ductile–brittle deformation, and in places are associated with base metal and gold incidences, and pyrophyllite-diaspore mineralization. The geochemistry of giant quartz veins were studied. Apart from presenting new data on the geology and geochemistry of these veins, an attempt has been made to resolve the long standing debate on their origin, in favour of an emplacement due to tectonically controlled polyphase hydrothermal fluid activity.

  8. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction.

    Science.gov (United States)

    Guex, Jean; Pilet, Sebastien; Müntener, Othmar; Bartolini, Annachiara; Spangenberg, Jorge; Schoene, Blair; Sell, Bryan; Schaltegger, Urs

    2016-03-24

    The temporal coincidence between large igneous provinces (LIPs) and mass extinctions has led many to pose a causal relationship between the two. However, there is still no consensus on a mechanistic model that explains how magmatism leads to the turnover of terrestrial and marine plants, invertebrates and vertebrates. Here we present a synthesis of ammonite biostratigraphy, isotopic data and high precision U-Pb zircon dates from the Triassic-Jurassic (T-J) and Pliensbachian-Toarcian (Pl-To) boundaries demonstrating that these biotic crises are both associated with rapid change from an initial cool period to greenhouse conditions. We explain these transitions as a result of changing gas species emitted during the progressive thermal erosion of cratonic lithosphere by plume activity or internal heating of the lithosphere. Our petrological model for LIP magmatism argues that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere before CO2 became the dominant gas. This model offers an explanation of why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere.

  9. Main controlling factors for hydrocarbon reservoir formation and petroleum distribution in Cratonic Area of Tarim Basin

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The Cratonic Area of the Tarim Basin is located in the central part of the basin, developing primarily with Cambrian marine source rocks and secondly Middle to Upper Ordovician marine and Carboniferous-Permian transitional facies source rocks. The source rocks were matured in the changeable period and space, forming multiple hydrocarbon generating centers during the periods. The Cratonic Area experienced multiple tectonic orogenies, forming several palaeouplifts. The matching condition between effective hydrocarbon generating centers and the palaeouplifts in various periods is the main control factor for the formation and distribution of hydrocarbon reservoirs. The palaeouplifts have experienced multiple hydrocarbon-filling phases, several periods of modifications and even breakdown. The palaeouplifts and the adjacent slopes around the effective hydrocarbon generating center compose the most favorable places for hydrocarbon accumulation. The hydrocarbon phase is related with the evolution of the hydrocarbon generating center. In the Tarim Basin's Cratonic Area, reservoirs were mostly formed during late Hercynian. The originally formed hydrocarbon reservoirs which are adjacent to source kitchens and in the good preservation condition are the most favorable prospecting targets. Hydrocarbon is richly accumulated under the regional caprock, surrounding the faulted trends, and over and below the unconformity surfaces. Reservoirs in the Carboniferous sandstone, Ordovician karstic weathered crust and carbonate rock inside the buried hill compose the main intervals for hydrocarbon accumulation. Carboniferous and Silurian sandstone pinchout reservoirs and carbonate lithologic reservoirs with rich fractures and pores are the main targets for further prospecting.

  10. Seismic texture classification. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Vinther, R.

    1997-12-31

    The seismic texture classification method, is a seismic attribute that can both recognize the general reflectivity styles and locate variations from these. The seismic texture classification performs a statistic analysis for the seismic section (or volume) aiming at describing the reflectivity. Based on a set of reference reflectivities the seismic textures are classified. The result of the seismic texture classification is a display of seismic texture categories showing both the styles of reflectivity from the reference set and interpolations and extrapolations from these. The display is interpreted as statistical variations in the seismic data. The seismic texture classification is applied to seismic sections and volumes from the Danish North Sea representing both horizontal stratifications and salt diapers. The attribute succeeded in recognizing both general structure of successions and variations from these. Also, the seismic texture classification is not only able to display variations in prospective areas (1-7 sec. TWT) but can also be applied to deep seismic sections. The seismic texture classification is tested on a deep reflection seismic section (13-18 sec. TWT) from the Baltic Sea. Applied to this section the seismic texture classification succeeded in locating the Moho, which could not be located using conventional interpretation tools. The seismic texture classification is a seismic attribute which can display general reflectivity styles and deviations from these and enhance variations not found by conventional interpretation tools. (LN)

  11. The Seismic Wavefield

    Science.gov (United States)

    Kennett, B. L. N.

    2002-12-01

    The two volumes of The Seismic Wavefield are a comprehensive guide to the understanding of seismograms in terms of physical propagation processes within the Earth. The focus is on the observation of earthquakes and man-made sources on all scales, for both body waves and surface waves. Volume I provides a general introduction and a development of the theoretical background for seismic waves. Volume II looks at the way in which observed seismograms relate to the propagation processes. Volume II also discusses local and regional seismic events, global wave propagation, and the three-dimensional Earth.

  12. Research on seismic stress triggering

    Institute of Scientific and Technical Information of China (English)

    万永革; 吴忠良; 周公威; 黄静; 秦立新

    2002-01-01

    This paper briefly reviews basic theory of seismic stress triggering. Recent development on seismic stress triggering has been reviewed in the views of seismic static and dynamic stress triggering, application of viscoelastic model in seismic stress triggering, the relation between earthquake triggering and volcanic eruption or explosion, other explanation of earthquake triggering, etc. And some suggestions for further study on seismic stress triggering in near future are given.

  13. Reproducibility in Seismic Imaging

    Directory of Open Access Journals (Sweden)

    González-Verdejo O.

    2012-04-01

    Full Text Available Within the field of exploration seismology, there is interest at national level of integrating reproducibility in applied, educational and research activities related to seismic processing and imaging. This reproducibility implies the description and organization of the elements involved in numerical experiments. Thus, a researcher, teacher or student can study, verify, repeat, and modify them independently. In this work, we document and adapt reproducibility in seismic processing and imaging to spread this concept and its benefits, and to encourage the use of open source software in this area within our academic and professional environment. We present an enhanced seismic imaging example, of interest in both academic and professional environments, using Mexican seismic data. As a result of this research, we prove that it is possible to assimilate, adapt and transfer technology at low cost, using open source software and following a reproducible research scheme.

  14. Seismic Fault Preserving Diffusion

    CERN Document Server

    Lavialle, Olivier; Germain, Christian; Donias, Marc; Guillon, Sebastien; Keskes, Naamen; Berthoumieu, Yannick

    2007-01-01

    This paper focuses on the denoising and enhancing of 3-D reflection seismic data. We propose a pre-processing step based on a non linear diffusion filtering leading to a better detection of seismic faults. The non linear diffusion approaches are based on the definition of a partial differential equation that allows us to simplify the images without blurring relevant details or discontinuities. Computing the structure tensor which provides information on the local orientation of the geological layers, we propose to drive the diffusion along these layers using a new approach called SFPD (Seismic Fault Preserving Diffusion). In SFPD, the eigenvalues of the tensor are fixed according to a confidence measure that takes into account the regularity of the local seismic structure. Results on both synthesized and real 3-D blocks show the efficiency of the proposed approach.

  15. Seismic fault preserving diffusion

    Science.gov (United States)

    Lavialle, Olivier; Pop, Sorin; Germain, Christian; Donias, Marc; Guillon, Sebastien; Keskes, Naamen; Berthoumieu, Yannick

    2007-02-01

    This paper focuses on the denoising and enhancing of 3-D reflection seismic data. We propose a pre-processing step based on a non-linear diffusion filtering leading to a better detection of seismic faults. The non-linear diffusion approaches are based on the definition of a partial differential equation that allows us to simplify the images without blurring relevant details or discontinuities. Computing the structure tensor which provides information on the local orientation of the geological layers, we propose to drive the diffusion along these layers using a new approach called SFPD (Seismic Fault Preserving Diffusion). In SFPD, the eigenvalues of the tensor are fixed according to a confidence measure that takes into account the regularity of the local seismic structure. Results on both synthesized and real 3-D blocks show the efficiency of the proposed approach.

  16. BUILDING 341 Seismic Evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Halle, J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-06-15

    The Seismic Evaluation of Building 341 located at Lawrence Livermore National Laboratory in Livermore, California has been completed. The subject building consists of a main building, Increment 1, and two smaller additions; Increments 2 and 3.

  17. Seismic facies; Facies sismicas

    Energy Technology Data Exchange (ETDEWEB)

    Johann, Paulo Roberto Schroeder [PETROBRAS, Rio de Janeiro, RJ (Brazil). Exploracao e Producao Corporativo. Gerencia de Reservas e Reservatorios]. E-mail: johann@petrobras.com.br

    2004-11-01

    The method presented herein describes the seismic facies as representations of curves and vertical matrixes of the lithotypes proportions. The seismic facies are greatly interested in capturing the spatial distributions (3D) of regionalized variables, as for example, lithotypes, sedimentary facies groups and/ or porosity and/or other properties of the reservoirs and integrate them into the 3D geological modeling (Johann, 1997). Thus when interpreted as curves or vertical matrixes of proportions, seismic facies allow us to build a very important tool for structural analysis of regionalized variables. The matrixes have an important application in geostatistical modeling. In addition, this approach provides results about the depth and scale of the wells profiles, that is, seismic data is integrated to the characterization of reservoirs in depth maps and in high resolution maps. The link between the different necessary technical phases involved in the classification of the segments of seismic traces is described herein in groups of predefined traces of two approaches: a) not supervised and b) supervised by the geological knowledge available on the studied reservoir. The multivariate statistical methods used to obtain the maps of the seismic facies units are interesting tools to be used to provide a lithostratigraphic and petrophysical understanding of a petroleum reservoir. In the case studied these seismic facies units are interpreted as representative of the depositional system as a part of the Namorado Turbiditic System, Namorado Field, Campos Basin.Within the scope of PRAVAP 19 (Programa Estrategico de Recuperacao Avancada de Petroleo - Strategic Program of Advanced Petroleum Recovery) some research work on algorithms is underway to select new optimized attributes to apply seismic facies. One example is the extraction of attributes based on the wavelet transformation and on the time-frequency analysis methodology. PRAVAP is also carrying out research work on an

  18. Seismic Consequence Abstraction

    Energy Technology Data Exchange (ETDEWEB)

    M. Gross

    2004-10-25

    The primary purpose of this model report is to develop abstractions for the response of engineered barrier system (EBS) components to seismic hazards at a geologic repository at Yucca Mountain, Nevada, and to define the methodology for using these abstractions in a seismic scenario class for the Total System Performance Assessment - License Application (TSPA-LA). A secondary purpose of this model report is to provide information for criticality studies related to seismic hazards. The seismic hazards addressed herein are vibratory ground motion, fault displacement, and rockfall due to ground motion. The EBS components are the drip shield, the waste package, and the fuel cladding. The requirements for development of the abstractions and the associated algorithms for the seismic scenario class are defined in ''Technical Work Plan For: Regulatory Integration Modeling of Drift Degradation, Waste Package and Drip Shield Vibratory Motion and Seismic Consequences'' (BSC 2004 [DIRS 171520]). The development of these abstractions will provide a more complete representation of flow into and transport from the EBS under disruptive events. The results from this development will also address portions of integrated subissue ENG2, Mechanical Disruption of Engineered Barriers, including the acceptance criteria for this subissue defined in Section 2.2.1.3.2.3 of the ''Yucca Mountain Review Plan, Final Report'' (NRC 2003 [DIRS 163274]).

  19. Seismicity in Northern Germany

    Science.gov (United States)

    Bischoff, Monika; Gestermann, Nicolai; Plenefisch, Thomas; Bönnemann, Christian

    2013-04-01

    Northern Germany is a region of low tectonic activity, where only few and low-magnitude earthquakes occur. The driving tectonic processes are not well-understood up to now. In addition, seismic events during the last decade concentrated at the borders of the natural gas fields. The source depths of these events are shallow and in the depth range of the gas reservoirs. Based on these observations a causal relationship between seismicity near gas fields and the gas production is likely. The strongest of these earthquake had a magnitude of 4.5 and occurred near Rotenburg in 2004. Also smaller seismic events were considerably felt by the public and stimulated the discussion on the underlying processes. The latest seismic event occurred near Langwedel on 22nd November 2012 and had a magnitude of 2.8. Understanding the causes of the seismicity in Northern Germany is crucial for a thorough evaluation. Therefore the Seismological Service of Lower Saxony (NED) was established at the State Office for Mining, Energy and Geology (LBEG) of Lower Saxony in January 2013. Its main task is the monitoring and evaluation of the seismicity in Lower Saxony and adjacent areas. Scientific and technical questions are addressed in close cooperation with the Seismological Central Observatory (SZO) at the Federal Institute for Geosciences and Natural Resources (BGR). The seismological situation of Northern Germany will be presented. Possible causes of seismicity are introduced. Rare seismic events at greater depths are distributed over the whole region and probably are purely tectonic whereas events in the vicinity of natural gas fields are probably related to gas production. Improving the detection threshold of seismic events in Northern Germany is necessary for providing a better statistical basis for further analyses answering these questions. As a first step the existing seismic network will be densified over the next few years. The first borehole station was installed near Rethem by BGR

  20. Cretaceous Apparent Polar Wander Relative to the Major Cratons and Displacement Estimates of Baja British Columbia

    Science.gov (United States)

    Enkin, R. J.

    2004-12-01

    When paleogeographic interpretations derived from independent observations conflict, the methods and results from each discipline come under careful scrutiny, as illustrated by the Baja British Columbia controversy. Cretaceous paleomagnetic data from a large region of the Canadian Cordillera render paleopoles which are far-sided with respect to cratonic North American poles, suggesting this region, designated Baja British Columbia, translated northward during Late Cretaceous - Paleogene time. Criticism of this interpretation based on other geological reasoning prompted me to perform new reviews of Cretaceous to Eocene paleomagnetic results from the Cordillera and from the major cratons of the globe. The global review follows the method of Besse and Courtillot (1991; 2002). One difference between our methods is that I compiled paleomagnetic results from highly studied rock units to single results to balance data weightings spatially and temporally, thus reducing the number of individual results. For the period 160 to 40 Ma, 51 poles were included compared to 92 poles by Besse and Courtillot (2002). Differences between apparent polar wander paths in their and my analyses are never significant at 95% confidence, however mean pole positions differ by up to 500 km, which is important for paleogeographic analysis. The global distribution of sampling localities and the tight clustering of the paleomagnetic poles after plate reconstruction provide invaluable confirmation of plate tectonically derived Euler rotations, the reliability of paleomagnetic remanence directions, and the geocentric dipole geometry of the geomagnetic field. My Cordilleran review shows that paleolatitudes derived from plutons and remagnetized rocks are significantly more scattered than those derived from bedded rocks. Using bedded rocks only, the paleomagnetic record shows that Baja British Columbia sat 2100 ± 500 km south of its present position with respect to cratonic North America during the

  1. Peaceful Nuclear Explosion Datasets for Seismic Research and Nuclear Test Monitoring

    Science.gov (United States)

    Smithson, S. B.; Morozov, I. B.; Morozova, E. A.; Richards, P. G.; Solodilov, L. N.

    2001-12-01

    Within the next four years, IRIS databases will receive from the University of Wyoming and GEON recordings from nine ultra-long range Deep Seismic Sounding (DSS) projects conducted between 1970-1989 in the former Soviet Union: QUARTZ, CRATON, KIMBERLITE, METEORITE, RIFT, RUBY, BATHOLIT, BAZALT, and AGATE. Jointly sponsored by the Department of Defense and National Science Foundation, this effort will bring the unique recordings of 22 Peaceful Nuclear Explosions (PNEs) and hundreds of crustal-scale chemical shots to the broad seismological and monitoring research communities. A grid of reversed PNE profiles (plus fan recording for RUBY) covers the East European Platform, the Ural Mountains, the West Siberian Platform, the Siberian craton, and the Baikal Rift. Dense, 3-component, short-period recordings along these profiles provide a valuable source of seismic information for seismic calibration of these vast aseismic regions. DSS recordings offer unique opportunities to study propagation effects of body waves and regional seismic phases, to examine their correlation with geologic and tectonic features, to develop unusually well constrained models of the structure of the crust and upper mantle to 600-700 km depth, and to explore the variability of explosion discriminants such as spectral ratios of P- and S-waves. Though the data principally concern properties of the crust and upper mantle, some of the profiles also show strong reflections from the core-mantle boundary. We summarize the recent findings from the analysis of PNE datasets in Northern Eurasia. These results include (1) unusually detailed velocity and attenuation structure of the crust and uppermost mantle, (2) characterization of crustal attenuation through coda measurements, (3) constraints on seismic scattering from within the crust and uppermost mantle, (4) detailed imaging of the crustal basement using receiver functions, (5) continuous observations of the regional phases from the PNEs within 0

  2. Hydrothermal alteration at the Panorama Formation, North Pole Dome, Pilbara Craton, Western Australia

    CERN Document Server

    Brown, Adrian J; Walter, Malcolm R

    2014-01-01

    An airborne hyperspectral remote sensing dataset was obtained of the North Pole Dome region of the Pilbara Craton in October 2002. It has been analyzed for indications of hydrothermal minerals. Here we report on the identification and mapping of hydrothermal minerals in the 3.459 Ga Panorama Formation and surrounding strata. The spatial distribution of a pattern of subvertical pyrophyllite rich veins connected to a pyrophyllite rich palaeohorizontal layer is interpreted to represent the base of an acid-sulfate epithermal system that is unconformably overlain by the stromatolitic 3.42 Ga Strelley Pool Chert.

  3. Eclogite-High-Pressure Granulite Belt in Northern Edge of the Archean North China Craton

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    The discovery of retrograded eclogites and high-pressure basic granulites in the joining region of Hebei-Shanxi-Inner Mongolia (HSIM) abandon the old thoughts that Archean granulites in the North China craton are of middle or low pressure facies and promote the reconsideration of Early Precambrian cratonization tectonic process, and reveal the geological fact that the scale, rigid behavior and geological structure of Archean cratonic blocks have strong similarities to the present fundamental plate tectonics, which suggest new tectonic mechanism to understand the early continental evolution of the North China craton. (1) The retrograded eclogites and high-pressure granulites constitute a ENE-NE-striking structure-rock zone termed as the Sanggan structural belt. (2) The retrograded eclogites are closely associated with high-pressure granulites. We can call this belt a transitional eclogite-granulite facies metamorphic belt. Petrographically three metamorphic stages, at least, in the retrograded eclogite can be distinguished. ① The main mineral assemblage is composed of garnet+clinopyroxene+quartz+rutile. The mineral inclusions in garnet are fine-grained quartz, rutile and small inclusions of fine-grained second stage mineral aggregate. This aggregate consists of hypersthene+albite, and has the typical texture of small hypersthene core surrounded by albite micro-grained grains. ② The second mineral assemblage is represented by corona of garnet and symplectite of clinopyroxene. The corona of garnet is composed of hypersthene+plagioclase+clinopyroxene+a minor amount of quartz and magnetite. The symplectite of clinopyroxene is composed of hypersthene + albite+clinopyroxene. The secondary mineral assemblage along boundaries between quartz and garnet (or clinopyroxene) is fine-grained aggregate of hypersthene and clinopyroxene. ③ The third retrograded metamorphic minerals are mainly amphiboles replacing pyroxenes and plagioclases replacing garnets. The estimated

  4. Compositional variations in the Mesoarchean chromites of the Nuggihalli schist belt, Western Dharwar Craton (India)

    DEFF Research Database (Denmark)

    Mukherjee, Ria; Mondal, Sisir Kanti; Rosing, Minik Thorleif

    2010-01-01

    -98)) and pyroxene grains (Mg-numbers = 97-99). Compositional variability on the scale of a single chromite grain occurs in the form of zoning, and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite. In the zoned grains, the composition of the core is modified...... has been used to compute the nature of the parental melt. The parental melt calculations indicate derivation from a high-Mg komatiitic basalt that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the Western Dharwar Craton. Tectonic discrimination...

  5. DOBRE studies evolution of inverted intra-cratonic rifts in Ukraine

    Science.gov (United States)

    DOBREflection-2000 Working Groups,; DOBREfraction'99 Working Groups,

    Donbas Refraction and Reflection (DOBRE) is a multinational study of the Donbas Foldbelt (DF) of Ukraine (Figure l). The DF is the uplifted and deformed part of the more than 20-km-thick Dniepr-Donets Basin (DDB) that formed due to Late Devonian rifting of the East European Craton (EEC) in eastern Ukraine and southern Russia. The DF; especially its southern margin, was uplifted in Early Permian times in a (trans) tensional tectonic stress regime. Folding and reverse faulting occurred later, during the Triassic and Late Cretaceous.

  6. Microstructural analysis of calcite-filled fractures inherited from basement structures, southern Ontario, Canada: long term instability of the craton?

    Science.gov (United States)

    Spalding, Jennifer; Schneider, David

    2016-04-01

    Intra-cratonic regions are generally characterized by tectonic stability and low seismicity. In southern Ontario, Canada, moderate levels of seismicity have been recorded over the last few decades reaching magnitudes of 5 MN, indicating that the geosphere is not as stable as predicted. The stratigraphy of the region consists of Ordovician limestone with a thickness of ~200 m that unconformably overlays the Mesoproterozoic crystalline Grenville Province. Subsequent tectonism including repeated Paleozoic orogenies and rifting along the east coast of North America has reactivated Proterozoic structures that have propagated into the overlying carbonate platform forming mesoscopic-scale brittle structures. Exposed along the shores of Lake Ontario are decameter-scale fracture zones, with a fracture spacing of 0.5 to 10 meters. The dominant fracture set trends E-W, and often forms conjugate sets with less prominent NNE-oriented fractures. More locally, an older NW-oriented fracture set is cross cut by the E-W and NNE oriented fractures. Regionally, there have been six directions of maximum horizontal stress in southern Ontario since the Precambrian, with the current orientation of maximum stress oriented ENE as a consequence of far field Atlantic ridge-push forces generated at distant plate boundaries. Calcite mineralization along fractured surfaces locally form sub-horizontal slickenside fabrics which are covered by a layer of euhedral calcite crystals, suggesting that fracture dilation (and fluid flow) occurred after fracture slip to allow the growth of calcite crystals. Due to the proximity of the carbonate units to the crystalline basement, we expect the calcitic veins to be enriched in rare earth elements and are presently conducting geochemical analyses. The calcite veins and surfaces vary from 2.5 cm to 1 mm thicknesses, often with larger calcite crystals in the center of the vein and smaller crystals at the vein boundaries, likely representing nucleation on small

  7. Landslide seismic magnitude

    Science.gov (United States)

    Lin, C. H.; Jan, J. C.; Pu, H. C.; Tu, Y.; Chen, C. C.; Wu, Y. M.

    2015-11-01

    Landslides have become one of the most deadly natural disasters on earth, not only due to a significant increase in extreme climate change caused by global warming, but also rapid economic development in topographic relief areas. How to detect landslides using a real-time system has become an important question for reducing possible landslide impacts on human society. However, traditional detection of landslides, either through direct surveys in the field or remote sensing images obtained via aircraft or satellites, is highly time consuming. Here we analyze very long period seismic signals (20-50 s) generated by large landslides such as Typhoon Morakot, which passed though Taiwan in August 2009. In addition to successfully locating 109 large landslides, we define landslide seismic magnitude based on an empirical formula: Lm = log ⁡ (A) + 0.55 log ⁡ (Δ) + 2.44, where A is the maximum displacement (μm) recorded at one seismic station and Δ is its distance (km) from the landslide. We conclude that both the location and seismic magnitude of large landslides can be rapidly estimated from broadband seismic networks for both academic and applied purposes, similar to earthquake monitoring. We suggest a real-time algorithm be set up for routine monitoring of landslides in places where they pose a frequent threat.

  8. Studies on seismic source

    Institute of Scientific and Technical Information of China (English)

    李世愚; 陈运泰

    2003-01-01

    During the period of 1999~2002, the Chinese seismologists made a serious of developments in the study on seismic sources including observations, experiments and theory. In the field of observation, the methods of the accuracy location of earthquake sources, the inversion of seismic moment tensor and the mechanism of earthquake source are improved and developed. A lot of important earthquake events are studied by using these methods. The rupture processes of these events are inverted and investigated combined with the local stress fields and the tectonic moment by using the measurements of surface deformation. In the fields of experiments and theory, many developments are obtained in cause of seismic formation, condition of stress and tectonics, dynamics of earthquake rupture, rock fracture and nucleation of strong earthquakes.

  9. Les organismes du Précambrien terminal du craton ouest africain

    Directory of Open Access Journals (Sweden)

    E. Eboureau

    1983-12-01

    Full Text Available THE ORGANISMS OF THE TERMINAL PRECAMBRIAN OF THE WESTERN AFRICAN CRATON The terminal Precamhrian (Lipalian of the western African Craton, in the Adrar of Mauritania, has provided, especially in the Guelb er Richát, many organisms with an archaic structure, often very simple. It concerns some coccoides, often grouped in more or less complex spheroides according to an evolutionary pattern that could be accurately established. The understanding of fossil forms from the Precambrian is, to a great extent, the result of an interpretation made of an included ‘black spot', which one adopted for the emissions of substance produced by these forms. Compared to the present species, the Precambrian organisms recall the coccoid Bacteria and the Cyanophyceae. These microorganisms are oolithes in origin and are by no means mineral, since they contain stain-sensitive glucides with Schiff’s reagent following the action of periodic acid. These forms, usually spherical, are classified amongst the Oncolithes. These organisms are also responsible for the massive calcareous or dolomitic reefs reaching considerable thickness and containing some known stromatolites in many parts of the world. Stromatolites are Conophyton. Collenia . . . They are spherical, lamellate or columnar. These reef formations of Africa reach a thickness of 3 000 m in the Adoudounian of Collenia of the Anti-Atlas, of 600 m in the Zemmour, of 150 m in the Adrar of Mauritania, of 100 m in the cliff of Hank in the north of the Taoudeni Basin.

  10. Abnormal lithium isotope composition from the ancient lithospheric mantle beneath the North China Craton.

    Science.gov (United States)

    Tang, Yan-Jie; Zhang, Hong-Fu; Deloule, Etienne; Su, Ben-Xun; Ying, Ji-Feng; Santosh, M; Xiao, Yan

    2014-03-04

    Lithium elemental and isotopic compositions of olivines in peridotite xenoliths from Hebi in the North China Craton provide direct evidence for the highly variable δ(7)Li in Archean lithospheric mantle. The δ(7)Li in the cores of olivines from the Hebi high-Mg# peridotites (Fo > 91) show extreme variation from -27 to +21, in marked deviation from the δ(7)Li range of fresh MORB (+1.6 to +5.6) although the Li abundances of the olivines are within the range of normal mantle (1-2 ppm). The Li abundances and δ(7)Li characteristics of the Hebi olivines could not have been produced by recent diffusive-driven isotopic fractionation of Li and therefore the δ(7)Li in the cores of these olivines record the isotopic signature of the subcontinental lithospheric mantle. Our data demonstrate that abnormal δ(7)Li may be preserved in the ancient lithospheric mantle as observed in our study from the central North China Craton, which suggest that the subcontinental lithospheric mantle has experienced modification of fluid/melt derived from recycled oceanic crust.

  11. Correlations between the North China Craton and the Indian Shield: Constraints from regional metallogeny

    Directory of Open Access Journals (Sweden)

    Caifeng Li

    2015-11-01

    Full Text Available The correlation between the North China Craton (NCC and the Indian Shield (IND has been a hot topic in recent years. On the basis of ore deposit databases, the NCC and IND have shown broad similarity in metallogenesis from the middle Archaean to the Mesoproterozoic. The two blocks both have three major metallogenic systems: (1 the Archaean BIF metallogenic system; (2 the Paleoproterozoic Cu-Pb-Zn metallogenic system; and (3 the Mesoproterozoic Fe-Pb-Zn system. In the north margin of the NCC and the west margin of the IND, the Archaean BIF-Au-Cu-Pb-Zn deposits had the same petrogenesis and host rocks, the Paleoproterozoic Cu-Pb-Zn deposits were controlled by active belts, and the Mesoproterozoic Fe-Pb-Zn deposits were mainly related to multi-stage rifting. Matching regional mineralization patterns and geological features has established the continental assembly referred to as “NCWI”, an acronym for the north margin of the NCC (NC and the west margin of the IND (WI during the middle Archaean to the Mesoproterozoic. In this assembly, the available geological and metallogenic data from the Eastern Block and active belts of NC fit those from the Dharwar craton and the Aravalli–Delhi–Vindhyan belt of WI, respectively. Moreover, the depositional model and environment of Paleoproterozoic metasedimentary manganese deposits in NCWI implied that the assembly may be located at low latitudes, where the conditions were favorable for dissolving ice and precipitating manganese deposits.

  12. Les organismes du Précambrien terminal du craton ouest africain

    Directory of Open Access Journals (Sweden)

    E. Eboureau

    1983-12-01

    Full Text Available THE ORGANISMS OF THE TERMINAL PRECAMBRIAN OF THE WESTERN AFRICAN CRATON The terminal Precamhrian (Lipalian of the western African Craton, in the Adrar of Mauritania, has provided, especially in the Guelb er Richát, many organisms with an archaic structure, often very simple. It concerns some coccoides, often grouped in more or less complex spheroides according to an evolutionary pattern that could be accurately established. The understanding of fossil forms from the Precambrian is, to a great extent, the result of an interpretation made of an included ‘black spot', which one adopted for the emissions of substance produced by these forms. Compared to the present species, the Precambrian organisms recall the coccoid Bacteria and the Cyanophyceae. These microorganisms are oolithes in origin and are by no means mineral, since they contain stain-sensitive glucides with Schiff’s reagent following the action of periodic acid. These forms, usually spherical, are classified amongst the Oncolithes. These organisms are also responsible for the massive calcareous or dolomitic reefs reaching considerable thickness and containing some known stromatolites in many parts of the world. Stromatolites are Conophyton. Collenia . . . They are spherical, lamellate or columnar. These reef formations of Africa reach a thickness of 3 000 m in the Adoudounian of Collenia of the Anti-Atlas, of 600 m in the Zemmour, of 150 m in the Adrar of Mauritania, of 100 m in the cliff of Hank in the north of the Taoudeni Basin.

  13. Organic matter in the Neoproterozoic cap carbonate from the Amazonian Craton, Brazil

    Science.gov (United States)

    Sousa Júnior, Gustavo R.; Nogueira, Afonso C. R.; Santos Neto, Eugênio V.; Moura, Candido A. V.; Araújo, Bruno Q.; Reis, Francisco de A. M.

    2016-12-01

    Bitumen found in Neoproterozoic carbonates from the southern Amazonian Craton, Brazil, represents a great challenge for its geochemical characterization (origin, thermal maturity and the degree of preservation) within a context of petroleum system. This organic material occurs in the basal Araras Group, considered as a Neoproterozoic cap carbonate, composed of dolostones (Mirassol d'Oeste Formation) overlaid by limestones and shales (Guia Formation). Geochemical analyses in samples of carbonate with bitumen from two open pits (Terconi and Tangará quarries) have shown low to very low total organic carbon content. Analyses of representative samples of Guia and Mirassol d'Oeste formations allowed us to obtain Gas chromatography (GC) traces and diagnostic biomarkers. n-C14 to n-C37 alkane distribution patterns in all samples suggests a major contribution of marine algae. Mid-chain monomethyl alkanes (C14sbnd C25) identified in both sets of samples were also reported in all mid to late Proterozoic oils and source rocks. However, there are significant differences among terpane distribution between the Mirassol d'Oeste and Tangará da Serra regions. The integration of organic geochemistry data and geological information suggests an indigenous origin for studied bitumen, primarily accumulated as hydrocarbon fluids migrated to carbonate rocks with higher porosity and permeability, and afterwards, altered to bitumen or migrabitumen. Although further investigations are required, this work provides a significant contribution to the knowledge about the remnant of this hypothetical Neoproterozoic petroleum system developed in the Southern Amazonian Craton.

  14. Seismic Disaster Reduction in China

    Institute of Scientific and Technical Information of China (English)

    Ministry of Construction

    2001-01-01

    @@ Great accomplishments have been made in seismic disaster reduction in China's engineering construction and city construction projects during the past decade (1990~2000). A new national map on the division of seismic intensity has been promulgated, and a series of anti-seismic standards and norms have been drafted or revised, which has further improved the country's technical code system on anti-seismic engineering measures.

  15. B341 Seismic Evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Halle, J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2014-01-02

    The Seismic Evaluation of Building 341 located at Lawrence Livermore National Laboratory in Livermore, California has been completed. The subject building consists of a main building, Increment 1, and two smaller additions; Increments 2 and 3. Based on our evaluation the building does not meet a Life Safety performance level for the BSE- 1E earthquake ground shaking hazard. The BSE-1E is the recommended seismic hazard level for evaluation of existing structures and is based on a 20% probability of exceedence in 50 years.

  16. Induced Seismicity Monitoring System

    Science.gov (United States)

    Taylor, S. R.; Jarpe, S.; Harben, P.

    2014-12-01

    There are many seismological aspects associated with monitoring of permanent storage of carbon dioxide (CO2) in geologic formations. Many of these include monitoring underground gas migration through detailed tomographic studies of rock properties, integrity of the cap rock and micro seismicity with time. These types of studies require expensive deployments of surface and borehole sensors in the vicinity of the CO2 injection wells. Another problem that may exist in CO2 sequestration fields is the potential for damaging induced seismicity associated with fluid injection into the geologic reservoir. Seismic hazard monitoring in CO2 sequestration fields requires a seismic network over a spatially larger region possibly having stations in remote settings. Expensive observatory-grade seismic systems are not necessary for seismic hazard deployments or small-scale tomographic studies. Hazard monitoring requires accurate location of induced seismicity to magnitude levels only slightly less than that which can be felt at the surface (e.g. magnitude 1), and the frequencies of interest for tomographic analysis are ~1 Hz and greater. We have developed a seismo/acoustic smart sensor system that can achieve the goals necessary for induced seismicity monitoring in CO2 sequestration fields. The unit is inexpensive, lightweight, easy to deploy, can operate remotely under harsh conditions and features 9 channels of recording (currently 3C 4.5 Hz geophone, MEMS accelerometer and microphone). An on-board processor allows for satellite transmission of parameter data to a processing center. Continuous or event-detected data is kept on two removable flash SD cards of up to 64+ Gbytes each. If available, data can be transmitted via cell phone modem or picked up via site visits. Low-power consumption allows for autonomous operation using only a 10 watt solar panel and a gel-cell battery. The system has been successfully tested for long-term (> 6 months) remote operations over a wide range

  17. Seismic Hazard Assessment in Stable Continental Regions of Northen Eurasia

    Science.gov (United States)

    Levshenko, V.; Yunga, S.

    2009-04-01

    critical infrastructures of Novovoronezh, Kursk, Smolensk, Kalinin and Leningrad regions are located on the East European craton. Bilibino critical infrastructure is located in the Mesozoic Verkhoyansk-Chukotka fold belt. For capable faults within the investigated territories microearthquake registration is carried out. Automatic phase pickers are designed for seismogram processing based on STA/LTA ratios jointly with polarization analysis. Neotectonic bending strain rate and the seismotectonic strain rate, which depend on the Mmax, and seismicity parameters are determined. Maximum magnitudes for all the above mentioned sites are found to be in the range 4-4.5 The intensity I of strong shaking is less than 5 balls. Three different approaches were applied in estimating target response spectrum. Generalized response spectrum was calculated based on West Europe seismic records. Parametrisation of Eurocode 8 (1998) as well as standart spectrum spectra from Russian Guideline NP-031-01 (2002) were used. Ground time history acceleration was synthesized on a basis of standard generalized ground spectra. Acknowledgments. This work was partly supported by RFBR, № 07-05-00436.

  18. High-resolution 3D seismic model of the crustal and uppermost mantle structure in Poland

    Science.gov (United States)

    Grad, Marek; Polkowski, Marcin; Ostaficzuk, Stanisław R.

    2016-01-01

    In the area of Poland a contact between the Precambrian and Phanerozoic Europe and the Carpathians has a complicated structure and a complex P-wave velocity of the sedimentary cover, crystalline crust, Moho depth and the uppermost mantle. The geometry of the uppermost several kilometers of sediments is relatively well recognized from over 100,000 boreholes. The vertical seismic profiling (VSP) from 1188 boreholes provided detailed velocity data for regional tectonic units and for stratigraphic successions from Permian to the Tertiary and Quaternary deposits. These data, however, do not provide information about the velocity and basement depth in the central part of the Trans-European suture zone (TESZ) and in the Carpathians. So, the data set is supplemented by 2D velocity models from 32 deep seismic sounding refraction profiles which also provide information about the crust and uppermost mantle. Together with the results of other methods: vertical seismic profiling, magnetotelluric, allow for the creation of a detailed, high-resolution 3D model for the entire Earth's crust and the uppermost mantle down to a depth of 60 km. The thinnest sedimentary cover in the Mazury-Belarus anteclise is only 0.3 to 1 km thick, which increases to 7 to 8 km along the East European Craton (EEC) margin, and 9 to 12 km in the TESZ. The Variscan domain is characterized by a 1-4 km thick sedimentary cover, while the Carpathians are characterized by very thick sedimentary layers, up to about 20 km. The crystalline crust is differentiated and has a layered structure. The crust beneath the West European Platform (WEP; Variscan domain) is characterized by P-wave velocities of 5.8-6.6 km/s. The upper and middle crusts beneath the EEC are characterized by velocities of 6.1-6.6 km/s, and are underlain by a high velocity lower crust with a velocity of about 7 km/s. A general decrease in velocity is observed from the older to the younger tectonic domains. The TESZ is associated with a steep dip

  19. Imaging the continental lithosphere: Perspectives from global and regional anisotropic seismic tomography

    Science.gov (United States)

    Lebedev, Sergei; Schaeffer, Andrew

    2016-04-01

    Azimuthal seismic anisotropy, the dependence of seismic wave speeds on propagation azimuth, is largely due to fabrics within the Earth's crust and mantle, produced by deformation. It thus provides constraints on the distribution and evolution of deformation within the upper mantle. Lateral variations in isotropic-average seismic velocities reflect variations in the temperature of the rocks at depth. Seismic tomography thus also provides a proxy for lateral changes in the temperature and thickness of the lithosphere. It can map the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our new global, anisotropic, 3D tomographic models of the upper mantle and the crust are constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provide improved resolution of the lithosphere at the global scale, compared to other available models. The most prominent high-velocity anomalies, seen down to around 200 km depths, indicate the cold, thick, stable mantle lithosphere beneath Precambrian cratons. The tomography resolves the deep boundaries of the cratons even where they are not exposed and difficult to map at the surface. Our large waveform dataset, with complementary large global networks and high-density regional array data, also produces improved resolution of azimuthal anisotropy patterns, so that regional-scale variations related to lithospheric deformation and mantle flow can be resolved, in particular in densely sampled regions. The depth of the boundary between the cold, rigid lithosphere (preserving ancient, frozen anisotropic fabric) and the rheologically weak asthenosphere (characterized by fabric developed recently) can be inferred from the depth layering of seismic anisotropy and its comparison to the past and present plate motions. Beneath oceans, the lithosphere-asthenosphere boundary (LAB) is defined clearly by the layering of anisotropy, with a dependence on

  20. Nonstructural seismic restraint guidelines

    Energy Technology Data Exchange (ETDEWEB)

    Butler, D.M.; Czapinski, R.H.; Firneno, M.J.; Feemster, H.C.; Fornaciari, N.R.; Hillaire, R.G.; Kinzel, R.L.; Kirk, D.; McMahon, T.T.

    1993-08-01

    The Nonstructural Seismic Restraint Guidelines provide general information about how to secure or restrain items (such as material, equipment, furniture, and tools) in order to prevent injury and property, environmental, or programmatic damage during or following an earthquake. All SNL sites may experience earthquakes of magnitude 6.0 or higher on the Richter scale. Therefore, these guidelines are written for all SNL sites.

  1. Understanding induced seismicity

    NARCIS (Netherlands)

    Elsworth, Derek; Spiers, Christopher J.; Niemeijer, Andre R.

    2016-01-01

    Fluid injection–induced seismicity has become increasingly widespread in oil- and gas-producing areas of the United States (1–3) and western Canada. It has shelved deep geothermal energy projects in Switzerland and the United States (4), and its effects are especially acute in Oklahoma, where seismi

  2. Understanding induced seismicity

    NARCIS (Netherlands)

    Elsworth, Derek; Spiers, Christopher J.; Niemeijer, Andre R.

    2016-01-01

    Fluid injection–induced seismicity has become increasingly widespread in oil- and gas-producing areas of the United States (1–3) and western Canada. It has shelved deep geothermal energy projects in Switzerland and the United States (4), and its effects are especially acute in Oklahoma, where

  3. Mobile seismic exploration

    Science.gov (United States)

    Dräbenstedt, A.; Cao, X.; Polom, U.; Pätzold, F.; Zeller, T.; Hecker, P.; Seyfried, V.; Rembe, C.

    2016-06-01

    Laser-Doppler-Vibrometry (LDV) is an established technique to measure vibrations in technical systems with picometer vibration-amplitude resolution. Especially good sensitivity and resolution can be achieved at an infrared wavelength of 1550 nm. High-resolution vibration measurements are possible over more than 100 m distance. This advancement of the LDV technique enables new applications. The detection of seismic waves is an application which has not been investigated so far because seismic waves outside laboratory scales are usually analyzed at low frequencies between approximately 1 Hz and 250 Hz and require velocity resolutions in the range below 1 nm/s/√Hz. Thermal displacements and air turbulence have critical influences to LDV measurements at this low-frequency range leading to noise levels of several 100 nm/√Hz. Commonly seismic waves are measured with highly sensitive inertial sensors (geophones or Micro Electro-Mechanical Sensors (MEMS)). Approaching a laser geophone based on LDV technique is the topic of this paper. We have assembled an actively vibration-isolated optical table in a minivan which provides a hole in its underbody. The laser-beam of an infrared LDV assembled on the optical table impinges the ground below the car through the hole. A reference geophone has detected remaining vibrations on the table. We present the results from the first successful experimental demonstration of contactless detection of seismic waves from a movable vehicle with a LDV as laser geophone.

  4. Mobile seismic exploration

    Energy Technology Data Exchange (ETDEWEB)

    Dräbenstedt, A., E-mail: a.draebenstedt@polytec.de, E-mail: rembe@iei.tu-clausthal.de, E-mail: ulrich.polom@liag-hannover.de; Seyfried, V. [Research & Development, Polytec GmbH, Waldbronn (Germany); Cao, X.; Rembe, C., E-mail: a.draebenstedt@polytec.de, E-mail: rembe@iei.tu-clausthal.de, E-mail: ulrich.polom@liag-hannover.de [Institute of Electrical Information Technology, TU Clausthal, Clausthal-Zellerfeld (Germany); Polom, U., E-mail: a.draebenstedt@polytec.de, E-mail: rembe@iei.tu-clausthal.de, E-mail: ulrich.polom@liag-hannover.de [Leibniz Institute of Applied Geophysics, Hannover (Germany); Pätzold, F.; Hecker, P. [Institute of Flight Guidance, TU Braunschweig, Braunschweig (Germany); Zeller, T. [Clausthaler Umwelttechnik Institut CUTEC, Clausthal-Zellerfeld (Germany)

    2016-06-28

    Laser-Doppler-Vibrometry (LDV) is an established technique to measure vibrations in technical systems with picometer vibration-amplitude resolution. Especially good sensitivity and resolution can be achieved at an infrared wavelength of 1550 nm. High-resolution vibration measurements are possible over more than 100 m distance. This advancement of the LDV technique enables new applications. The detection of seismic waves is an application which has not been investigated so far because seismic waves outside laboratory scales are usually analyzed at low frequencies between approximately 1 Hz and 250 Hz and require velocity resolutions in the range below 1 nm/s/√Hz. Thermal displacements and air turbulence have critical influences to LDV measurements at this low-frequency range leading to noise levels of several 100 nm/√Hz. Commonly seismic waves are measured with highly sensitive inertial sensors (geophones or Micro Electro-Mechanical Sensors (MEMS)). Approaching a laser geophone based on LDV technique is the topic of this paper. We have assembled an actively vibration-isolated optical table in a minivan which provides a hole in its underbody. The laser-beam of an infrared LDV assembled on the optical table impinges the ground below the car through the hole. A reference geophone has detected remaining vibrations on the table. We present the results from the first successful experimental demonstration of contactless detection of seismic waves from a movable vehicle with a LDV as laser geophone.

  5. Discovery of Late Paleozoic retrograded eclogites from the middle part of the northern margin of North China Craton

    Institute of Scientific and Technical Information of China (English)

    NI Zhiyao; ZHAI Mingguo; WANG Renmin; TONG Ying; SHU Guiming; HAl Xiuling

    2004-01-01

    The retrograded eciogites have been discovered in the middle part of the northern margin of the North China Craton, which occur as lens or boudin within biotite-plagioclase gneisses in Paleoproterozoic Hongqiyingzi Group. The peak eclogite facies (P > 1.40-1.50 GPa, T = 680-730℃) mineral assemblage is composed of garnet, omphacite and rutile (+ quartz), which was overprinted by the granulite facies mineral assemblage of vermicular symplectite of sodic clinopyroxene and plagioclase which replaced the precursory omphacite, and then amphibolite facies retrograded minerals with characterization of Amp+Pl kelyphitic rim and symplectite, and amphibole replaced clinopyroxene. The protolith of retrograded eclogites is oceanic basalt formed at 438 + 11 Ma. The peak eclogite facies metamorphic age of the retrograded eclogite is 325 + 4 Ma. These relict eclogites may be formed by the subduction of Paleo-Asian oceanic crust beneath the North China Craton during Late Paleozoic. The discovery of relict eclogite in this paper provides a new insight into farther understanding of tectonic evolution of the northern margin of the North China Craton, and the relationship between the Paleo-Asian Ocean and the North China Craton.

  6. Geophysics and Seismic Hazard Reduction

    Institute of Scientific and Technical Information of China (English)

    YuGuihua; ZhouYuanze; YuSheng

    2003-01-01

    The earthquake is a natural phenomenon, which often brings serious hazard to the human life and material possession. It is a physical process of releasing interior energy of the earth, which is caused by interior and outer forces in special tectonic environment in the earth, especially within the lithosphere. The earthquake only causes casualty and loss in the place where people inhabit. Seismic hazard reduction is composed of four parts as seismic prediction, hazard prevention and seismic engineering, seismic response and seismic rescuing, and rebuilding.

  7. Mountain building at northeastern boundary of Tibetan Plateau and craton reworking at Ordos block from joint inversion of ambient noise tomography and receiver functions

    Science.gov (United States)

    Guo, Zhen; Chen, Yongshun John

    2017-04-01

    We have obtained a high resolution 3-D crustal and uppermost mantle velocity model of the Ordos block and its surrounding areas by joint inversion of ambient noise tomography and receiver functions using seismic recordings from 320 stations. The resulting model shows wide-spread low velocity zone (Vs ≤ 3.4 km/s) in the mid-to-lower crust beneath northeastern Tibet Plateau, which may favor crustal ductile flow within the plateau. However, our model argues against the eastward crustal ductile flow beneath the Qinling belt from the Tibetan Plateau. We find high velocities in the middle part of Qinling belt which separate the low velocities in the mid-to-lower crust of the eastern Qinling belt from the low velocity zone in eastern Tibetan Plateau. More importantly, we observe significant low velocities and thickened lower crust at the Liupanshan thrust belt as the evidence for strong crustal shortening at this boundary between the northeastern Tibetan Plateau and Ordos block. The most important finding of our model is the upper mantle low velocity anomalies surrounding the Ordos block, particularly the one beneath the Trans North China Craton (TNCO) that is penetrating into the southern margin of the Ordos block for ∼100 km horizontally in the depth range of ∼70 km and at least 100 km. We propose an on-going lithospheric mantle reworking at the southernmost boundary of the Ordos block due to complicated mantle flow surrounding the Ordos block, that is, the eastward asthenospheric flow from the Tibet Plateau proposed by recent SKS study and mantle upwelling beneath the TNCO from mantle transition zone induced by the stagnant slabs of the subducted Pacific plate.

  8. Sources and mobility of carbonate melts beneath cratons, with implications for deep carbon cycling, metasomatism and rift initiation

    Science.gov (United States)

    Tappe, Sebastian; Romer, Rolf L.; Stracke, Andreas; Steenfelt, Agnete; Smart, Katie A.; Muehlenbachs, Karlis; Torsvik, Trond H.

    2017-05-01

    Kimberlite and carbonatite magmas that intrude cratonic lithosphere are among the deepest probes of the terrestrial carbon cycle. Their co-existence on thick continental shields is commonly attributed to continuous partial melting sequences of carbonated peridotite at >150 km depths, possibly as deep as the mantle transition zone. At Tikiusaaq on the North Atlantic craton in West Greenland, approximately 160 Ma old ultrafresh kimberlite dykes and carbonatite sheets provide a rare opportunity to study the origin and evolution of carbonate-rich melts beneath cratons. Although their Sr-Nd-Hf-Pb-Li isotopic compositions suggest a common convecting upper mantle source that includes depleted and recycled oceanic crust components (e.g., negative ΔεHf coupled with > + 5 ‰ δ7Li), incompatible trace element modelling identifies only the kimberlites as near-primary low-degree partial melts (0.05-3%) of carbonated peridotite. In contrast, the trace element systematics of the carbonatites are difficult to reproduce by partial melting of carbonated peridotite, and the heavy carbon isotopic signatures (-3.6 to - 2.4 ‰ δ13C for carbonatites versus -5.7 to - 3.6 ‰ δ13C for kimberlites) require open-system fractionation at magmatic temperatures. Given that the oxidation state of Earth's mantle at >150 km depth is too reduced to enable larger volumes of 'pure' carbonate melt to migrate, it is reasonable to speculate that percolating near-solidus melts of carbonated peridotite must be silicate-dominated with only dilute carbonate contents, similar to the Tikiusaaq kimberlite compositions (e.g., 16-33 wt.% SiO2). This concept is supported by our findings from the North Atlantic craton where kimberlite and other deeply derived carbonated silicate melts, such as aillikites, exsolve their carbonate components within the shallow lithosphere en route to the Earth's surface, thereby producing carbonatite magmas. The relative abundances of trace elements of such highly

  9. High Voltage Seismic Generator

    Science.gov (United States)

    Bogacz, Adrian; Pala, Damian; Knafel, Marcin

    2015-04-01

    This contribution describes the preliminary result of annual cooperation of three student research groups from AGH UST in Krakow, Poland. The aim of this cooperation was to develop and construct a high voltage seismic wave generator. Constructed device uses a high-energy electrical discharge to generate seismic wave in ground. This type of device can be applied in several different methods of seismic measurement, but because of its limited power it is mainly dedicated for engineering geophysics. The source operates on a basic physical principles. The energy is stored in capacitor bank, which is charged by two stage low to high voltage converter. Stored energy is then released in very short time through high voltage thyristor in spark gap. The whole appliance is powered from li-ion battery and controlled by ATmega microcontroller. It is possible to construct larger and more powerful device. In this contribution the structure of device with technical specifications is resented. As a part of the investigation the prototype was built and series of experiments conducted. System parameter was measured, on this basis specification of elements for the final device were chosen. First stage of the project was successful. It was possible to efficiently generate seismic waves with constructed device. Then the field test was conducted. Spark gap wasplaced in shallowborehole(0.5 m) filled with salt water. Geophones were placed on the ground in straight line. The comparison of signal registered with hammer source and sparker source was made. The results of the test measurements are presented and discussed. Analysis of the collected data shows that characteristic of generated seismic signal is very promising, thus confirms possibility of practical application of the new high voltage generator. The biggest advantage of presented device after signal characteristics is its size which is 0.5 x 0.25 x 0.2 m and weight approximately 7 kg. This features with small li-ion battery makes

  10. The record of the Amazon craton in two supercontinents: Paleomagnetic and geological constraints for Mesoproterozoic to Paleozoic times

    Science.gov (United States)

    Tohver, E.

    2008-05-01

    The Amazon craton plays a fundamental role in the evolution of two supercontinents, the late Mesoproterozoic Rodinia, the break-up of which led to thethe late Neoproterozoic-early Paleozoic formation of Gondwana. A recent review of the paleomagnetic database for South America and Africa highlights the different role of the principal elements of western Gondwana elements Amazonia, conjoined with West Africa, versus the more centrally- located pieces of Gondwana; -Congo-São Francisco, Kalahari, the Rio de Plata, and the accreted terranes of the Arabia-Nubia shield. Whereas the Amazon-West Africa conjoined craton appears to have been alongside Laurentia within the framework of Rodinia, the other "central Gondwana" cratons were not part of Rodinia. New paleomagnetic data from the SW Amazon craton demonstrate the transpressive evolution of the Grenvillian collision, which resulted in thousands of kilometers of along-strike between the Amazon and Laurentia cratons. Portions of Amazonian crust stranded within the North American craton, notably the Blue Ridge province of the southern Appalachians, is evidence for this long-lived motion. An extensive review of recent thermochronological data from the North American Grenville Province and new data from the SW Amazon belts of "Grenvillian" age reveals the effects of differential post-orogenic exhumation. Restoration of this exhumation gives us a crustal-scale cross-section of the synorogenic structure, marked by thrust-related imbrication on the North American side, and large-scale, strike-slip faults on the Amazon side. It is this asymmetric structure that accounts for the differences in tectonic style between the two cratons. The timing of the break-up of Rodinia is still mostly unconstrained by geochronological data from rift-related sediments from the Amazon side. The Paraguai belt that marks the SE margin of the Amazon craton is a curved, fold-and-thrust belt that affected the late Neoproterozoic-Cambrian sediments that

  11. Cover sequences at the northern margin of the Antongil Craton, NE Madagascar

    Science.gov (United States)

    Bauer, W.; Walsh, G.J.; De Waele, B.; Thomas, Ronald J.; Horstwood, M.S.A.; Bracciali, L.; Schofield, D.I.; Wollenberg, U.; Lidke, D.J.; Rasaona, I.T.; Rabarimanana, M.H.

    2011-01-01

    The island of Madagascar is a collage of Precambrian, generally high-grade metamorphic basement domains, that are locally overlain by unmetamorphosed sedimentary rocks and poorly understood low-grade metasediments. In the Antalaha area of NE Madagascar, two distinct cover sequences rest on high-grade metamorphic and igneous basement rocks of the Archaean Antongil craton and the Neoproterozoic Bemarivo belt. The older of these two cover sequences, the Andrarona Group, consists of low-grade metasedimentary rocks. The younger sequence, the newly defined Ampohafana Formation, consists of unmetamorphosed sedimentary rocks. The Andrarona Group rests on Neoarchaean granites and monzogranites of the Antongil craton and consists of a basal metagreywacke, thick quartzites and an upper sequence of sericite-chlorite meta-mudstones, meta-sandstones and a volcaniclastic meta-sandstone. The depositional age of the volcaniclastic meta-sandstone is constrained in age by U–Pb laser-ablation ICP-MS analyses of euhedral zircons to 1875 ± 8 Ma (2σ). Detrital zircons of Archaean and Palaeoproterozoic age represent an input from the Antongil craton and a newly defined Palaeoproterozoic igneous unit, the Masindray tonalite, which underlies the Andrarona Group, and yielded a U–Pb zircon age of 2355 ± 11 Ma (2σ), thus constraining the maximum age of deposition of the basal part of the Andrarona Group. The Andrarona Group shows a low-grade metamorphic overprint in the area near Antalaha; illite crystallinity values scatter around 0.17°Δ2Θ CuKα, which is within the epizone. The Ampohafana Formation consists of undeformed, polymict conglomerate, cross-bedded sandstone, and red mudstone. An illite crystallinity value of >0.25°Δ2Θ CuKα obtained from the rocks is typical of the diagenetic zone. Occurrences of rhyodacite pebbles in the Ampohafana Formation and the intrusion of a basaltic dyke suggest a deposition in a WSW-ENE-trending graben system during the opening of the Indian

  12. Cretaceous mantle of the Congo craton: Evidence from mineral and fluid inclusions in Kasai alluvial diamonds

    Science.gov (United States)

    Kosman, Charles W.; Kopylova, Maya G.; Stern, Richard A.; Hagadorn, James W.; Hurlbut, James F.

    2016-11-01

    Alluvial diamonds from the Kasai River, Democratic Republic of the Congo (DRC) are sourced from Cretaceous kimberlites of the Lucapa graben in Angola. Analysis of 40 inclusion-bearing diamonds provides new insights into the characteristics and evolution of ancient lithospheric mantle of the Congo craton. Silicate inclusions permitted us to classify diamonds as peridotitic, containing Fo91-95 and En92-94, (23 diamonds, 70% of the suite), and eclogitic, containing Cr-poor pyrope and omphacite with 11-27% jadeite (6 diamonds, 18% of the suite). Fluid inclusion compositions of fibrous diamonds are moderately to highly silicic, matching compositions of diamond-forming fluids from other DRC diamonds. Regional homogeneity of Congo fibrous diamond fluid inclusion compositions suggests spatially extensive homogenization of Cretaceous diamond forming fluids within the Congo lithospheric mantle. In situ cathodoluminescence, secondary ion mass spectrometry and Fourier transform infrared spectroscopy reveal large heterogeneities in N, N aggregation into B-centers (NB), and δ13C, indicating that diamonds grew episodically from fluids of distinct sources. Peridotitic diamonds contain up to 2962 ppm N, show 0-88% NB, and have δ13C isotopic compositions from - 12.5‰ to - 1.9‰ with a mode near mantle-like values. Eclogitic diamonds contain 14-1432 ppm N, NB spanning 29%-68%, and wider and lighter δ13C isotopic compositions of - 17.8‰ to - 3.4‰. Fibrous diamonds on average contain more N (up to 2976 ppm) and are restricted in δ13C from - 4.1‰ to - 9.4‰. Clinopyroxene-garnet thermobarometry suggests diamond formation at 1350-1375 °C at 5.8 to 6.3 GPa, whereas N aggregation thermometry yields diamond residence temperatures between 1000 and 1280 °C, if the assumed mantle residence time is 0.9-3.3 Ga. Integrated geothermobaromtery indicates heat fluxes of 41-44 mW/m2 during diamond formation and a lithosphere-asthenosphere boundary (LAB) at 190-210 km. The hotter

  13. Plate Motions Predicted from Global Dynamic Models and Seismic Tomography: The Problem of North American Plate Motion

    Science.gov (United States)

    Liu, S.; King, S. D.; Adam, C. M.

    2016-12-01

    Seismic tomography is a snapshot of the mantle convection system and provides important constraints on Earth's internal dynamics. An increasing number of global seismic tomography models along with various rheological structures have been used to compute mantle flow pattern and the resulting surface expressions, including dynamic topography and geoid. Accurately predicting the plate motion from the mantle dynamic models is a challenge particularly with the newest generation of seismic tomography models (e.g., S40RTS, SAVANI), especially for the North American plate which only has a little subduction along it's boundary. The difficulties include the uncertainty of the velocity-to-density scaling, discrepancies between different seismic tomography models, and the computational technology to solve for global mantle flow with observationally constrained high resolution models. We use the code ASPECT (Advanced Solver for Problems in Earth CovecTion) to make a series of tests to derive mantle flow pattern from different global seismic tomography models and rheological structures. We further make a quantitative statistical comparison between the modeled and observed plate motions in terms of flow magnitude, flow direction, and plateness within each plate area. We investigate how the velocity-to-density scaling, the features of seismic tomography models, and the lateral rheological structures of the lithosphere and upper mantle influence the modeled plate motions. We find that the velocity-to-density scaling mainly changes the flow magnitude and has little impact on the flow direction. The results of different seismic tomography models are similar broadly but can be quite different in some regions. The presence of lateral viscosity variations including stiff cratons, weak plate boundary zones, and high viscosity slabs along with density variations from seafloor age and subducting slabs can improve the fit to observed plate motions. With a very small fraction of subduction

  14. Problems of seismic hazard estimation in regions with few large earthquakes: Examples from eastern Canada

    Science.gov (United States)

    Basham, P. W.; Adams, John

    1989-10-01

    Seismic hazard estimates and seismic zoning maps are based on an assessment of historical and recent seismieity and any correlations with geologic and tectonic features that might define the earthquake potential. Evidence is accumulating that the large earthquakes in eastern Canada ( M ~ 7) may be associated with the rift systems hat surround or break the integrity of the North American craton. The problem for seismic hazard estimation is that the larger historical earthquakes are not uniformly distributed along the Paleozoic St. Lawrence-Ottawa rift system and are too rare on the Mesozoic eastern margin rift to assess the overall seismogenic potential. Multiple source zone models for hazard estimation could include hypotheses of future M = 7 earthquakes at any location along these rift systems, but at a moderate probability (such as that used in the Canadian zoning maps) the resultant hazard will be so diluted that it will not result in adequate design against the near-source effects of such earthquakes. The near-source effects of large, rare earthquakes can, however, be accommodated in conservative codes and standards for critical facilities, if society is willing to pay the price.

  15. Broadband seismic deployments in East Antarctica: IPY contribution to monitoring the Earth’s interiors

    Directory of Open Access Journals (Sweden)

    Masaki Kanao

    2014-06-01

    Full Text Available “Deployment of broadband seismic stations on the Antarctica continent” is an ambitious project to improve the spatial resolution of seismic data across the Antarctic Plate and surrounding regions. Several international collaborative programs for the purpose of geomonitoring were conducted in Antarctica during the International Polar Year (IPY 2007-2008. The Antarctica’s GAmburtsev Province (AGAP; IPY #147, the GAmburtsev Mountain SEISmic experiment (GAMSEIS, a part of AGAP, and the Polar Earth Observing Network (POLENET; IPY #185 were major contributions in establishing a geophysical network in Antarctica. The AGAP/GAMSEIS project was an internationally coordinated deployment of more than 30 broadband seismographs over the crest of the Gambursev Mountains (Dome-A, Dome-C and Dome-F area. The investigations provide detailed information on crustal thickness and mantle structure; provide key constraints on the origin of the Gamburtsev Mountains; and more broadly on the structure and evolution of the East Antarctic craton and subglacial environment. From GAMSEIS and POLENET data obtained, local and regional seismic signals associated with ice movements, oceanic loading, and local meteorological variations were recorded together with a significant number of teleseismic events. In this chapter, in addition to the Earth’s interiors, we will demonstrate some of the remarkable seismic signals detected during IPY that illustrate the capabilities of broadband seismometers to study the sub-glacial environment, particularly at the margins of Antarctica. Additionally, the AGAP and POLENET stations have an important role in the Federation of Digital Seismographic Network (FDSN in southern high latitude.

  16. Seismic anisotropy and mantle dynamics beneath the central and western United States

    Science.gov (United States)

    Yang, Bin

    Various tectonic features and the recent availability of high-quality broadband seismic data from the USArray and other seismic stations in the central and western United States (CWUS) provide a distinct opportunity to test different anisotropy-forming mechanisms. For the first part of the study, a total of 4138 pairs of well-defined shear wave splitting (SWS) parameters observed at 445 stations on the northern Great Plains show systematic spatial variations of anisotropic characteristics. Azimuthally invariant fast orientations subparallel to the absolute plate motion (APM) direction are observed at most of the stations on the Superior Craton and the southern Yavapai province, indicating that a single layer of anisotropy with a horizontal axis of symmetry is sufficient to explain the anisotropic structure. Based on the splitting measurements and previous results from seismic tomography and geodynamic modeling, we propose a model involving deflecting of asthenosphere flow by the bottom of the lithosphere and channeling flow by a zone of thinned lithosphere approximately along the northern boundary of the Yavapai province. The second part of the study created an up-to-date SWS database for CWUS in the area of 125° W to 90° W, 26° N to 52° N to upgrade a previous database [Liu et al., 2014]. A total of 7452 pairs of high-quality measurements recorded by 1202 digital broadband seismic stations (both permanent and portable seismic networks) over the period of 1989-2014 is obtained. The current version includes 23448 pairs of well-defined splitting parameters in three phases, i.e. PKS, SKKS and SKS. The dissertation is a combination of two journal papers published in 2014 and 2016, respectively.

  17. The Formation of Laurentia: Evidence from Shear Wave Splitting and Seismic Tomography

    Science.gov (United States)

    Liddell, M. V.; Bastow, I. D.; Gilligan, A.; Darbyshire, F. A.; Pugh, S.

    2016-12-01

    Earth conditions during the Precambrian, and their effect on plate tectonic processes during that era, are not fully understood; how the fast wave-speed cratonic roots, or keels, often found beneath these regions were formed is also debated. The geological record of northern Hudson Bay includes the 1.8Ga TransHudson Orogen (THO) terrane, a remnant of the Paleoproterozoic collision of the Archean Rae and Churchill domains that overlies one of Earth's largest cratonic keels. This region is thus an ideal natural laboratory for the study of Precambrian processes. We use broadband seismological data recorded at 65 stations in northern Hudson Bay to address questions regarding the manner and scale of plate deformation during Precambrian assembly of the region. To explore these questions, we conduct a study of mantle seismic anisotropy using SKS splitting. Our study constitutes the most complete shear wave splitting analysis of northern Canada to date utilising up to 11 years of data for some stations. Anisotropic fast directions (φ) and delay times (δt) are determined using a modified Silver and Chan (1991) method. In the Hudson Strait, φ directions parallel the THO, while the islands in northern Hudson Bay show changes in φ over length scales short enough to indicate lithospheric origin. Complex anisotropy patterns are observed in the central Rae craton and southern Baffin Island, suggesting multiple sources. Several possible sources of anisotropy are explored, including basal drag of the North American plate, mantle flow deflected by the Laurentian keel, and discontinuities associated with possible two-stage keel development P and S-wave relative arrival-time tomographic velocity models are also presented. Waveforms are aligned using the adaptive stacking routine of Rawlinson et al. (2004), and models are produced using the Fast Marching Tomography inversion code of Rawlinson et al. (2006). The THO is modeled as a low velocity feature relative to the neighbouring

  18. The 3.1 Ga Nuggihalli chromite deposits, Western Dhawar craton (India)

    DEFF Research Database (Denmark)

    Mukherjee, Ria; Mondal, Sisir K.; Frei, Robert

    2012-01-01

    , therefore melting and mixing of the eclogite component with depleted mantle melts resulted in distinct HFSE enrichment in the Nuggihalli rocks. Alternatively, melting of a HFSE-enriched eclogitic slab and the surrounding depleted mantle within an active subduction zone is another possible mechanism, however......The Nuggihalli greenstone belt is part of the older greenstone belts (3.4 - 3.0 Ga) in the Western Dharwar Craton, southern India. This greenstone sequence consists of conformable metavolcanic and metasedimentary supracrustal rock assemblages that belong to the Sargur Group. Sill-like ultramafic......-mafic plutonic bodies are present within these supracrustal rocks (schist rocks) which are in turn enclosed by tonalite-trondhjemite-granodiorite gneiss (TTG). The sill-like ultramafic-mafic rocks are cumulates derived from a high-Mg parental magma that are represented by chromitite-hosted serpentinite...

  19. The Montesbelos mass-flow (southern Amazonian craton, Brazil): a Paleoproterozoic volcanic debris avalanche deposit?

    Science.gov (United States)

    Roverato, M.

    2016-07-01

    The present contribution documents the extremely well-preserved Paleoproterozoic architecture of the Montesbelos breccia (named here for the first time), which is interpreted as a rare example of a subaerial paleoproterozoic (>1.85 Ga) granular-dominated mass-flow deposit, few of which are recorded in the literature. Montesbelos deposit is part of the andesitic Sobreiro Formation located in the São Felix do Xingu region, southern Amazonian craton, northern Brazil. The large volume, high variability of textural features, presence of broken clasts, angular low sphericity fragments, mono- to heterolithic character, and the size of the outcrops point to a volcanic debris avalanche flow. Fluviatile sandy material and debris flows are associated with the deposit as a result of post-depositional reworking processes.

  20. Tectonic Evolution of an Early Precambrian High-Pressure Granulite Belt in the North China Craton

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A large-scale high-pressure granulite belt (HPGB), more than 700 km long, is recognized within the metamorphic basement of the North China craton. In the regional tectonic framework, the Hengshan-Chengde HPGB is located in the central collision belt between the western block and eastern block, and represents the deep crustal structural level. The typical high-pressure granulite (HPG) outcrops are distributed in the Hengshan and Chengde areas. HPGs commonly occur as mafic xenoliths within ductile shear zones, and underwent multipile deformations. To the south, the Hengshan-Chengde HPGB is juxtaposed with the Wutai greenstone belt by several strike-slip shear zones. Preliminary isotopic age dating indicates that HPGs from North China were mainly generated at the end of the Neoarchaean, assocaited with tectonic assembly of the western and esatern blocks.

  1. Discovery of the Early Mesozoic granulite xenoliths in North China Craton

    Institute of Scientific and Technical Information of China (English)

    邵济安[1; 韩庆军[2; 李惠民[3

    2000-01-01

    The discovery of the Early Mesozoic basic granulite xenoliths in the Harqin area of the Inner Mongolia Autonomous Region (for short Inner Mongolia) is reported for the first time in this paper. According to the mineral assemblage the xenoliths include two-pyroxene granulite, clinopyroxene granulite, and hypersthene granulite. Their protolytes are mainly gabbroite rocks. The zircon U-Pb age of the granulite xenoliths is 251 Ma, and K-Ar age of the hypersthene is 229 Ma. They represent the times of metamorphism and cooling of the granulite facies respectively. The host rock of the xenoliths is Early Mesozoic biotite-quartz diorites, whose whole-rock K-Ar age is 219 Ma. This discovery confirms existence of an Early Mesozoic underplating in the North China Craton, which is of much importance in research on the Early Mesozoic mantle-crust interaction in the concerned area.

  2. The paleomagnetism and geological significance of Meso- proterozoic dyke swarms in the central North China Craton

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The Mesoproterozoic mafic dyke swarms are extensively distributedin the central North China Craton(NCC) including North Shanxi, Wutai and Lüliang areas, which are not deformed and metamorphic but high magnetic, so the dyke swarms become the mark to compare the high meta-morphic rock areas in magnetism. Based on the analysis of paleomagnetism of mafic dyke swarms in North Shanxi, Wutai and Lüliang areas, NCC inclined southward about 18° so that North Shanxi lifted up and rotated 10° left to Wutai area. The dyke swarms in Lüliang developed later than in North Shanxi and Wutai area. The NNW-trending and WNW-trending dyke swarms developed in Lüliang while the North China Plate moved northward consistently so that the paleomagnetism of dyke swarms in Lüliang is greatly different from North Shanxi and Wutai area.

  3. Nitrogen isotope and content record of Mesozoic orogenic gold deposits surrounding the North China craton

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    As an effective tracer, nitrogen isotopes have been used to determine the source of ore materials in recent years. In this study, the nitrogen isotopes and contents were measured on K- feldspar and sericite of gold deposits and some related granitic intrusions in Jiaodong, Xiaoqinling-Xiong'ershan, west Qinling, the west part of North Qilian and the Zhangjiakou-Xuanhua district around the North China craton (NCC). Although the gold deposits around the NCC are hosted in Precambrian metamorphic rocks, Phanerozoic sedimentary rocks, mafic volcanic rocks or granite, comparison of which with the nitrogen contents and isotope data of previous studies on mantle-derived rocks, granites, metamorphic rocks and gold deposits indicates that those deposits are closely related to granitic rocks. In addition, mantle-derived materials may have been involved in the ore-forming processes to a certain degree. This conclusion is consistent with the result of previous hydrogen, oxygen and carbon isotopic studies of those gold deposits.

  4. A review of the tectonic evolution of the Sunsás belt, SW Amazonian Craton

    Science.gov (United States)

    Teixeira, Wilson; Geraldes, Mauro Cesar; Matos, Ramiro; Ruiz, Amarildo Salina; Saes, Gerson; Vargas-Mattos, Gabriela

    2010-01-01

    The Sunsás-Aguapeí province (1.20-0.95 Ga), SW Amazonian Craton, is a key area to study the heterogeneous effects of collisional events with Laurentia, which shows evidence of the Grenvillian and Sunsás orogens. The Sunsás orogen, characterized by an allochthonous collisional-type belt (1.11-1.00 Ga), is the youngest and southwesternmost of the events recorded along the cratonic fringe. Its evolution occurred after a period of long quiescence and erosion of the already cratonized provinces (>1.30 Ga), that led to sedimentation of the Sunsás and Vibosi groups in a passive margin setting. The passive margin stage was roughly contemporary with intraplate tectonics that produced the Nova Brasilândia proto-oceanic basin (aborted rifts that evolved to the Huanchaca-Aguapeí basin (1.17-1.15 Ga). The Sunsás belt is comprised by the metamorphosed Sunsás and Vibosi sequences, the Rincón del Tigre mafic-ultramafic sill and granitic intrusive suites. The latter rocks yield ɛNd(t) signatures (-0.5 to -4.5) and geochemistry (S, I, A-types) suggesting their origin associated with a continental arc setting. The Sunsás belt evolution is marked by "tectonic fronts" with sinistral offsets that was active from c. 1.08 to 1.05 Ga, along the southern edge of the Paraguá microcontinent where K/Ar ages (1.27-1.34 Ga) and the Huanchaca-Aguapeí flat-lying cover attest to the earliest tectonic stability at the time of the orogen. The Sunsás dynamics is coeval with inboard crustal shortening, transpression and magmatism in the Nova Brasilândia belt (1.13-1.00 Ga). Conversely, the Aguapeí aulacogen (0.96-0.91 Ga) and nearby shear zones (0.93-0.91 Ga) are the late tectonic offshoots over the cratonic margin. The post-tectonic to anorogenic stages took place after ca. 1.00 Ga, evidenced by the occurrences of intra-plate A-type granites, pegmatites, mafic dikes and sills, as well as of graben basins. Integrated interpretation of the available data related to the Sunsás orogen

  5. Comparison of seismic sources for shallow seismic: sledgehammer and pyrotechnics

    Directory of Open Access Journals (Sweden)

    Brom Aleksander

    2015-10-01

    Full Text Available The pyrotechnic materials are one of the types of the explosives materials which produce thermal, luminous or sound effects, gas, smoke and their combination as a result of a self-sustaining chemical reaction. Therefore, pyrotechnics can be used as a seismic source that is designed to release accumulated energy in a form of seismic wave recorded by tremor sensors (geophones after its passage through the rock mass. The aim of this paper was to determine the utility of pyrotechnics for shallow seismic engineering. The work presented comparing the conventional method of seismic wave excitation for seismic refraction method like plate and hammer and activating of firecrackers on the surface. The energy released by various sources and frequency spectra was compared for the two types of sources. The obtained results did not determine which sources gave the better results but showed very interesting aspects of using pyrotechnics in seismic measurements for example the use of pyrotechnic materials in MASW.

  6. Pre-plate tectonics and structure of the Archean mantle lithosphere imaged by seismic anisotropy - inferences from the LAPNET array in northern Fennoscandia

    Science.gov (United States)

    Plomerova, Jaroslava; Vecsey, Ludek; Babuska, Vladislav; Lapnet Working Group

    2013-04-01

    Various studies of seismic anisotropy clearly demonstrate the Archean mantle lithosphere consists of domains with different fabrics reflecting fossil anisotropic structures. We detect anisotropic signal both in the P-wave travel-time deviations and shear-wave splitting recorded by the LAPNET array (2007-2009) in the Archean craton of Fennoscandia (Plomerova et al., 2011). The anisotropic parameters change across the array and stations with similar characteristics form groups. The geographical variations of seismic-wave anisotropy delimit individual sharply bounded domains of the mantle lithosphere, each of them having a consistent fabric. The domains can be modelled in 3D by peridotite aggregates with dipping lineation a, or foliation (a,c). Also radial anisotropy of the Archean lithosphere derived from surface waves indicates inclined structure of all the cratonic regions of the continents, though with less detailed lateral resolution in comparison with body-wave anisotropy. These findings allow us to interpret the domains as micro-plate fragments retaining fossil fabrics in the mantle lithosphere, reflecting thus an olivine LPO created before the micro-plates assembled. Successive subductions of oceanic lithosphere is a mechanism which can work in modern-style plate tectonics as we know it now, being considered as widespread since 2.7 Ga. Though the modern plate tectonics is the most distinct tectonic style acting up to now, we have to consider a mechanism creating oriented structures (fabrics) in a pre-plate-tectonic style. The early lithosphere formed in dynamic conditions far from simple cooling which would result in sub-horizontal layered structure of the lithosphere. Earlier tectonic modes in a hotter and more dynamic Earth might be similar in some respects to those of the modern-plate tectonics. Basaltic "rockbergs" on convecting magma ocean in the Hadean Earth are supposed to turn to either proto-plate tectonics with platelets and supercratonal, or, to

  7. REGULATION OF SEISMIC LOAD ON BUILDINGS SEISMIC DEVICES

    Directory of Open Access Journals (Sweden)

    Kh. N. Mazhiev

    2013-01-01

    Full Text Available The issues of regulation of seismic loads on structures using kinematic supports of highstrength concrete on the impregnated coarse aggregate and seismic isolation bearings Belleville. The results of experimental studies related to the obtaining of a new coarse aggregate and construction of seismic isolation bearings. Addresses the issues of interaction forces in thehemispherical supports vibration process.

  8. Stutter seismic source

    Energy Technology Data Exchange (ETDEWEB)

    Gumma, W. H.; Hughes, D. R.; Zimmerman, N. S.

    1980-08-12

    An improved seismic prospecting system comprising the use of a closely spaced sequence of source initiations at essentially the same location to provide shorter objective-level wavelets than are obtainable with a single pulse. In a preferred form, three dynamite charges are detonated in the same or three closely spaced shot holes to generate a downward traveling wavelet having increased high frequency content and reduced content at a peak frequency determined by initial testing.

  9. Principle and Program of Evaluating Diffuse Seismicity

    Institute of Scientific and Technical Information of China (English)

    Chang Xiangdong

    2001-01-01

    Concept and origin of the term "the diffuse seismicity" are illustrated. Some different viewpoints regarding the diffuse seismicity and the influence characteristics on determining seismic design basis of engineering from the seismicity are analyzed. Principle and program for evaluating diffuse seismicity are studied and discussed base on over contents.

  10. Establishing seismic design criteria to achieve an acceptable seismic margin

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, R.P. [RPK Structural Mechanics Consulting, Inc., Yorba Linda, CA (United States)

    1997-01-01

    In order to develop a risk based seismic design criteria the following four issues must be addressed: (1) What target annual probability of seismic induced unacceptable performance is acceptable? (2). What minimum seismic margin is acceptable? (3) Given the decisions made under Issues 1 and 2, at what annual frequency of exceedance should the Safe Shutdown Earthquake ground motion be defined? (4) What seismic design criteria should be established to reasonably achieve the seismic margin defined under Issue 2? The first issue is purely a policy decision and is not addressed in this paper. Each of the other three issues are addressed. Issues 2 and 3 are integrally tied together so that a very large number of possible combinations of responses to these two issues can be used to achieve the target goal defined under Issue 1. Section 2 lays out a combined approach to these two issues and presents three potentially attractive combined resolutions of these two issues which reasonably achieves the target goal. The remainder of the paper discusses an approach which can be used to develop seismic design criteria aimed at achieving the desired seismic margin defined in resolution of Issue 2. Suggestions for revising existing seismic design criteria to more consistently achieve the desired seismic margin are presented.

  11. Seismic hazard assessment of Iran

    Directory of Open Access Journals (Sweden)

    M. Ghafory-Ashtiany

    1999-06-01

    Full Text Available The development of the new seismic hazard map of Iran is based on probabilistic seismic hazard computation using the historical earthquakes data, geology, tectonics, fault activity and seismic source models in Iran. These maps have been prepared to indicate the earthquake hazard of Iran in the form of iso-acceleration contour lines, and seismic hazard zoning, by using current probabilistic procedures. They display the probabilistic estimates of Peak Ground Acceleration (PGA for the return periods of 75 and 475 years. The maps have been divided into intervals of 0.25 degrees in both latitudinal and longitudinal directions to calculate the peak ground acceleration values at each grid point and draw the seismic hazard curves. The results presented in this study will provide the basis for the preparation of seismic risk maps, the estimation of earthquake insurance premiums, and the preliminary site evaluation of critical facilities.

  12. Seismic Imager Space Telescope

    Science.gov (United States)

    Sidick, Erkin; Coste, Keith; Cunningham, J.; Sievers,Michael W.; Agnes, Gregory S.; Polanco, Otto R.; Green, Joseph J.; Cameron, Bruce A.; Redding, David C.; Avouac, Jean Philippe; Ampuero, Jean Paul; Leprince, Sebastien; Michel, Remi

    2012-01-01

    A concept has been developed for a geostationary seismic imager (GSI), a space telescope in geostationary orbit above the Pacific coast of the Americas that would provide movies of many large earthquakes occurring in the area from Southern Chile to Southern Alaska. The GSI movies would cover a field of view as long as 300 km, at a spatial resolution of 3 to 15 m and a temporal resolution of 1 to 2 Hz, which is sufficient for accurate measurement of surface displacements and photometric changes induced by seismic waves. Computer processing of the movie images would exploit these dynamic changes to accurately measure the rapidly evolving surface waves and surface ruptures as they happen. These measurements would provide key information to advance the understanding of the mechanisms governing earthquake ruptures, and the propagation and arrest of damaging seismic waves. GSI operational strategy is to react to earthquakes detected by ground seismometers, slewing the satellite to point at the epicenters of earthquakes above a certain magnitude. Some of these earthquakes will be foreshocks of larger earthquakes; these will be observed, as the spacecraft would have been pointed in the right direction. This strategy was tested against the historical record for the Pacific coast of the Americas, from 1973 until the present. Based on the seismicity recorded during this time period, a GSI mission with a lifetime of 10 years could have been in position to observe at least 13 (22 on average) earthquakes of magnitude larger than 6, and at least one (2 on average) earthquake of magnitude larger than 7. A GSI would provide data unprecedented in its extent and temporal and spatial resolution. It would provide this data for some of the world's most seismically active regions, and do so better and at a lower cost than could be done with ground-based instrumentation. A GSI would revolutionize the understanding of earthquake dynamics, perhaps leading ultimately to effective warning

  13. Seismic capacity of a reinforced concrete frame structure without seismic detailing and limited ductility seismic design in moderate seismicity

    Energy Technology Data Exchange (ETDEWEB)

    Kim, J. K.; Kim, I. H. [Seoul National Univ., Seoul (Korea, Republic of)

    1999-10-01

    A four-story reinforced concrete frame building model is designed for the gravity loads only. Static nonlinear pushover analyses are performed in two orthogonal horizontal directions. The overall capacity curves are converted into ADRS spectra and compared with demand spectra. At several points the deformed shape, moment and shear distribution are calculated. Based on these results limited ductility seismic design concept is proposed as an alternative seismic design approach in moderate seismicity resign.

  14. Thermal modeling and geomorphology of the south border of the Sao Francisco Craton: thermochronology by fission tracks in apatites;Modelagem termica e geomorfologia da borda sul do Craton do Sao Francisco: termocronologia por tracos de fissao em apatita

    Energy Technology Data Exchange (ETDEWEB)

    Hackspacher, Peter Christian [UNESP, Rio Claro, SP (Brazil). Inst. de Geociencias e Ciencias Exatas; Godoy, Daniel Francoso de; Franco, Ana Olivia Barufi [UNESP, Rio Claro, SP (Brazil). Pos-Graduacao em Geologia Regional; Ribeiro, Luiz Felipe Brandini [NUCLEARGEO, Rio Claro, SP (Brazil); Hadler Neto, Julio Cesar [Universidade Estadual de Campinas (IFGW/UNICAMP), SP (Brazil). Inst. de Fisica Gleb Wataghin

    2007-12-15

    Recent developments in Fission Track thermochronology associated to mesozoic-cenozoic erosion and tectonic presented trough thematic maps (isotemperature), permit to model the landscape evolution in the southern border of the Sao Francisco craton, southeastern Brazil. Paleotemperature, obtained by fission track analysis in apatite, is closely related to geomorphologic interpretations. The area suffered a complex imprint of endogenous and exogenous processes resulting diversified and differentiated relieves. The landscape is strongly controlled by exhumation between Jurassic and Lower Cretaceous, uplift with tectonic denudation related to crustal heating at the Upper Cretaceous and reactivation of faults until the Miocene. This scenario is a result of reactivations of different brittle structures that accommodate the deformation in the southern border of the Sao Francisco craton. The landscape reflects denudations of up to 3 km with preserved remains of erosive surfaces in the topographical tops and chronocorrelates deposits in the basins of the region. (author)

  15. Modelling of NW Himalayan Seismicity

    Science.gov (United States)

    Bansal, A. R.; Dimri, V. P.

    2014-12-01

    The northwest Himalaya is seismicity active region due to the collision of Indian and Eurasian plates and experienced many large earthquakes in past. A systematic analysis of seismicity is useful for seismic hazard estimation of the region. We analyzed the seismicity of northwestern Himalaya since 1980. The magnitude of completeness of the catalogue is carried out using different methods and found as 3.0. A large difference in magnitude of completeness is found using different methods and a reliable value is obtained after testing the distribution of magnitudes with time. The region is prone to large earthquake and many studied have shown that seismic activation or quiescence takes place before large earthquakes. We studied such behavior of seismicity based on Epidemic Type Aftershock Sequence (ETAS) model and found that a stationary ETAS model is more suitable for modelling the seismicity of this region. The earthquake catalogue is de-clustered using stochasting approach to study behavior of background and triggered seismicity. The triggered seismicity is found to have shallower depths as compared to the background events.

  16. Flat lens for seismic waves

    CERN Document Server

    Brule, Stephane; Guenneau, Sebastien

    2016-01-01

    A prerequisite for achieving seismic invisibility is to demonstrate the ability of civil engineers to control seismic waves with artificially structured soils. We carry out large-scale field tests with a structured soil made of a grid consisting of cylindrical and vertical holes in the ground and a low frequency artificial source (< 10 Hz). This allows the identification of a distribution of energy inside the grid, which can be interpreted as the consequence of an effective negative refraction index. Such a flat lens reminiscent of what Veselago and Pendry envisioned for light opens avenues in seismic metamaterials to counteract the most devastating components of seismic signals.

  17. Neural networks in seismic discrimination

    Energy Technology Data Exchange (ETDEWEB)

    Dowla, F.U.

    1995-01-01

    Neural networks are powerful and elegant computational tools that can be used in the analysis of geophysical signals. At Lawrence Livermore National Laboratory, we have developed neural networks to solve problems in seismic discrimination, event classification, and seismic and hydrodynamic yield estimation. Other researchers have used neural networks for seismic phase identification. We are currently developing neural networks to estimate depths of seismic events using regional seismograms. In this paper different types of network architecture and representation techniques are discussed. We address the important problem of designing neural networks with good generalization capabilities. Examples of neural networks for treaty verification applications are also described.

  18. Seismic hazard estimation of northern Iran using smoothed seismicity

    Science.gov (United States)

    Khoshnevis, Naeem; Taborda, Ricardo; Azizzadeh-Roodpish, Shima; Cramer, Chris H.

    2017-07-01

    This article presents a seismic hazard assessment for northern Iran, where a smoothed seismicity approach has been used in combination with an updated seismic catalog and a ground motion prediction equation recently found to yield good fit with data. We evaluate the hazard over a geographical area including the seismic zones of Azerbaijan, the Alborz Mountain Range, and Kopeh-Dagh, as well as parts of other neighboring seismic zones that fall within our region of interest. In the chosen approach, seismic events are not assigned to specific faults but assumed to be potential seismogenic sources distributed within regular grid cells. After performing the corresponding magnitude conversions, we decluster both historical and instrumental seismicity catalogs to obtain earthquake rates based on the number of events within each cell, and smooth the results to account for the uncertainty in the spatial distribution of future earthquakes. Seismicity parameters are computed for each seismic zone separately, and for the entire region of interest as a single uniform seismotectonic region. In the analysis, we consider uncertainties in the ground motion prediction equation, the seismicity parameters, and combine the resulting models using a logic tree. The results are presented in terms of expected peak ground acceleration (PGA) maps and hazard curves at selected locations, considering exceedance probabilities of 2 and 10% in 50 years for rock site conditions. According to our results, the highest levels of hazard are observed west of the North Tabriz and east of the North Alborz faults, where expected PGA values are between about 0.5 and 1 g for 10 and 2% probability of exceedance in 50 years, respectively. We analyze our results in light of similar estimates available in the literature and offer our perspective on the differences observed. We find our results to be helpful in understanding seismic hazard for northern Iran, but recognize that additional efforts are necessary to

  19. Seismic hazard estimation of northern Iran using smoothed seismicity

    Science.gov (United States)

    Khoshnevis, Naeem; Taborda, Ricardo; Azizzadeh-Roodpish, Shima; Cramer, Chris H.

    2017-03-01

    This article presents a seismic hazard assessment for northern Iran, where a smoothed seismicity approach has been used in combination with an updated seismic catalog and a ground motion prediction equation recently found to yield good fit with data. We evaluate the hazard over a geographical area including the seismic zones of Azerbaijan, the Alborz Mountain Range, and Kopeh-Dagh, as well as parts of other neighboring seismic zones that fall within our region of interest. In the chosen approach, seismic events are not assigned to specific faults but assumed to be potential seismogenic sources distributed within regular grid cells. After performing the corresponding magnitude conversions, we decluster both historical and instrumental seismicity catalogs to obtain earthquake rates based on the number of events within each cell, and smooth the results to account for the uncertainty in the spatial distribution of future earthquakes. Seismicity parameters are computed for each seismic zone separately, and for the entire region of interest as a single uniform seismotectonic region. In the analysis, we consider uncertainties in the ground motion prediction equation, the seismicity parameters, and combine the resulting models using a logic tree. The results are presented in terms of expected peak ground acceleration (PGA) maps and hazard curves at selected locations, considering exceedance probabilities of 2 and 10% in 50 years for rock site conditions. According to our results, the highest levels of hazard are observed west of the North Tabriz and east of the North Alborz faults, where expected PGA values are between about 0.5 and 1 g for 10 and 2% probability of exceedance in 50 years, respectively. We analyze our results in light of similar estimates available in the literature and offer our perspective on the differences observed. We find our results to be helpful in understanding seismic hazard for northern Iran, but recognize that additional efforts are necessary to

  20. The influence of backfill on seismicity

    CSIR Research Space (South Africa)

    Hemp, DA

    1990-09-01

    Full Text Available , that the seismicity has been reduced in areas where backfill had been placed. A factor complicating the evaluation of backfill on seismicity is the effect of geological structures on seismicity....

  1. Seismic velocity structure of the crust and shallow mantle of the Central and Eastern United States by seismic surface wave imaging

    Science.gov (United States)

    Pollitz, Fred; Mooney, Walter D.

    2016-01-01

    Seismic surface waves from the Transportable Array of EarthScope's USArray are used to estimate phase velocity structure of 18 to 125 s Rayleigh waves, then inverted to obtain three-dimensional crust and upper mantle structure of the Central and Eastern United States (CEUS) down to ∼200 km. The obtained lithosphere structure confirms previously imaged CEUS features, e.g., the low seismic-velocity signature of the Cambrian Reelfoot Rift and the very low velocity at >150 km depth below an Eocene volcanic center in northwestern Virginia. New features include high-velocity mantle stretching from the Archean Superior Craton well into the Proterozoic terranes and deep low-velocity zones in central Texas (associated with the late Cretaceous Travis and Uvalde volcanic fields) and beneath the South Georgia Rift (which contains Jurassic basalts). Hot spot tracks may be associated with several imaged low-velocity zones, particularly those close to the former rifted Laurentia margin.

  2. Sm-Nd age dating of high- pressure granulites and amphi- bolite from Sanggan area, North China craton

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The high pressure (HP) metamorphic age has been dated to HP rocks from the Sanggan area, North China craton. We have got garnet+whole rock isochron ages of (1 842±38) Ma for HP granulite, and (1 856 ± 26) Ma for HP amphibolite. The Sm-Nd whole rock isochron of HP granulites give out an age of (1 870±150) Ma with Nd deplet-ed mantle model age of (2 402-2 482) Ma. Considering the Nd isotope homogenization during the peak metamorphism of the HP granulite, Sm-Nd closure temperature and the retention of Nd isotopic memory in garnets partially broken down during decompression, all these isochron ages are thought to be HP metamorphic age. Furthermore, we pro-posed that the HP metamorphism took place at the end of Paleoproterozoic during the large-scale collision and assem-bly of the North China craton.

  3. Heat flow, heat generation and crustal thermal structure of the northern block of the South Indian Craton

    Science.gov (United States)

    Gupta, Mohan L.; Sharma, S. R.; Sundar, A.

    1988-01-01

    Heat flow values and heat generation data calculated from the concentration of heat producing radioactive elements, U, Th and K in surface rocks were analyzed. The South Indian Craton according to Drury et al., can be divided into various blocks, separated by late Proterozoic shear belts. The northern block comprises Eastern and Western Dharwar Cratons of Rogers (1986), Naqvi and Rogers (1987) and a part of the South Indian granulite terrain up to a shear system occupying the Palghat-Cauvery low lands. The geothermal data analysis clearly demonstrates that the present thermal characteristics of the above two Archaean terrains of the Indian and Australian Shields are quite similar. Their crustal thermal structures are likely to be similar also.

  4. The Zimbabwe Craton in Mozambique: A brief review of its geochronological pattern and its relation to the Mozambique Belt

    Science.gov (United States)

    Chaúque, F. R.; Cordani, U. G.; Jamal, D. L.; Onoe, A. T.

    2017-05-01

    The eastern margin of the Zimbabwe Craton, along the Mozambique-Zimbabwe border, includes the oldest rocks of west-central Mozambique constituting a large terrain of granite-greenstone type dated between 3000 and 2500 Ma. These rocks consist mainly of gneisses and granitoid rocks of tonalitic-trondhjemitic-granodioritic composition belonging to the Mudzi Metamorphic Complex in the northern part and to the Mavonde Complex in the southern part. The latter is associated with a granite-greenstone terrain, which includes the eastern part of Mutare-Odzi-Manica greenstone belt. A volcano-sedimentary sequences cover, belonging to the apparently Mesoproterozoic and Paleoproterozoic Umkondo and Gairezi groups respectively was deposited along the eastern margin of the craton and is exposed in the territory of Mozambique. The Umkondo minimum age is marked by intrusive dolerite in Zimbabwe dated at 1100 Ma while for the Ghairezi it is still not well established. The Gairezi Group was subjected to progressive metamorphism of Pan-African age. At the margin of the Zimbabwe Craton, in its northern part, metasedimentary units occur representing a passive margin of Neoproterozoic age. They make up the Rushinga Group, which includes felsic metavolcanic rocks dated at ca.800 Ma. Granulites and medium- to high-grade paragneisses, and migmatites of the Chimoio, Macossa and Mungari Groups of Neoproterozoic metamorphic age, overly the ortho-metamorphic pre-existing rock of ca. 1100 Ma, which belongs to the Báruè Magmatic Arc. They characterize the N-S trend Mozambique Belt, which appears to the east of the craton tectonically juxtaposed on the Archean rocks. The maximum age of deposition of these rocks, indicated by U-Pb dating of detrital zircons, is ca. 700 Ma and their minimum age is limited by a few monzonitic Cambrian intrusions dated at ca. 500 Ma. The Neoproterozoic bimodal Guro Suite, dated at ca. 850 Ma and composed of felsic and mafic members characterizes the east

  5. Bayesian seismic AVO inversion

    Energy Technology Data Exchange (ETDEWEB)

    Buland, Arild

    2002-07-01

    A new linearized AVO inversion technique is developed in a Bayesian framework. The objective is to obtain posterior distributions for P-wave velocity, S-wave velocity and density. Distributions for other elastic parameters can also be assessed, for example acoustic impedance, shear impedance and P-wave to S-wave velocity ratio. The inversion algorithm is based on the convolutional model and a linearized weak contrast approximation of the Zoeppritz equation. The solution is represented by a Gaussian posterior distribution with explicit expressions for the posterior expectation and covariance, hence exact prediction intervals for the inverted parameters can be computed under the specified model. The explicit analytical form of the posterior distribution provides a computationally fast inversion method. Tests on synthetic data show that all inverted parameters were almost perfectly retrieved when the noise approached zero. With realistic noise levels, acoustic impedance was the best determined parameter, while the inversion provided practically no information about the density. The inversion algorithm has also been tested on a real 3-D dataset from the Sleipner Field. The results show good agreement with well logs but the uncertainty is high. The stochastic model includes uncertainties of both the elastic parameters, the wavelet and the seismic and well log data. The posterior distribution is explored by Markov chain Monte Carlo simulation using the Gibbs sampler algorithm. The inversion algorithm has been tested on a seismic line from the Heidrun Field with two wells located on the line. The uncertainty of the estimated wavelet is low. In the Heidrun examples the effect of including uncertainty of the wavelet and the noise level was marginal with respect to the AVO inversion results. We have developed a 3-D linearized AVO inversion method with spatially coupled model parameters where the objective is to obtain posterior distributions for P-wave velocity, S

  6. Seismic failure modes and seismic safety of Hardfill dam

    Institute of Scientific and Technical Information of China (English)

    Kun XIONG; Yong-hong WENG; Yun-long HE

    2013-01-01

    Based on microscopic damage theory and the finite element method, and using the Weibull distribution to characterize the random distribution of the mechanical properties of materials, the seismic response of a typical Hardfill dam was analyzed through numerical simulation during the earthquakes with intensities of 8 degrees and even greater. The seismic failure modes and failure mechanism of the dam were explored as well. Numerical results show that the Hardfill dam remains at a low stress level and undamaged or slightly damaged during an earthquake with an intensity of 8 degrees. During overload earthquakes, tensile cracks occur at the dam surfaces and extend to inside the dam body, and the upstream dam body experiences more serious damage than the downstream dam body. Therefore, under the seismic conditions, the failure pattern of the Hardfill dam is the tensile fracture of the upstream regions and the dam toe. Compared with traditional gravity dams, Hardfill dams have better seismic performance and greater seismic safety.

  7. The paleomagnetism and geological significance of Meso- proterozoic dyke swarms in the central North China Craton

    Institute of Scientific and Technical Information of China (English)

    HOU; Guiting

    2001-01-01

    [1]Ma Xinghua, Zhang Zhengkun, Paleomagnetism and its application to plate tectonics, in The Basic Problems of Plate Tectonics (in Chinese), Beijing: Seismology Press, 1985, 119-142.[2]Zhang Wenzhi, Li Pu, The paleomagnetic characteristics of Sub-Sinian Erathem in Jixian of China, Bulletin of the Chinese Academy of Geological Science, Branch Bulletin of Geological Institute of Tianjin, 1980, 1(1): 111[3]Halls, H. C., Paleomagnetism, structure and longitudinal correlation of middle Precambrian dykes from northwestern Ontario and Minnesota, Can. J. Earth Sci., 1985, 23: 142.[4]Qian Xianglin, Chen Yaping, Late Precambrian mafic swarms of the north China Craton, in Mafic Dyke Swarms, Geological Association of Canada (eds. Halls, H. C., Fahrig, W. F.), 1987, Special Paper, 34: 385.[5]Chen Yaping, Qian Xianglin, The paleomagnetism study of Late Precambrian mafic dyke swarms in Lüliang inlier of Shanxi, Acta Scientiarum Naturalium Universitatis Pekinensis (in Chinese), 1987, 2: 87.[6]Ernst, R. E., Head, J. W., Parfitt, E. et al, Giant radiating dyke swarms on Earth and Venus, Earth-Science Reviews, 1995, 4: 229[7]Radhakrishns, T., Joseph. M., Proterozoic palaeomagnetism of the mafic dyke swarms is the high-grade region of southern India, Precambrian Research, 1996, 76: 31.[8]Li Jianghai, Qian Xianglin, Zhai Mingguo, The tectonic classification of granulite facies of North China and its Early Precambrian tectonic evolution, Scientia Geologica Sinica (in Chinese), 1997, 32: 254.[9]Hou Guiting, Zhang Chen, Qian Xianglin, The formation mechanism and tectonic stress field of Mesoproterozoic mafic dyke swarms in the North China Craton, Geological Review (in Chinese), 1998, 44(3): 309.[10]Li Jianghai, He Wenyuan, Qian Xianglin, Genetic mechanism and tectonic setting of Proterozoic mafic dyke swarm: its implication for paleoplate reconstruction, Geological Journal of China University (in Chinese), 1997, 3(3): 272.[11]Hou Guiting, Mu

  8. Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

    Energy Technology Data Exchange (ETDEWEB)

    Bob A. Hardage; Milo M. Backus; Michael V. DeAngelo; Sergey Fomel; Khaled Fouad; Robert J. Graebner; Paul E. Murray; Randy Remington; Diana Sava

    2006-07-31

    The purpose of our research has been to develop and demonstrate a seismic technology that will provide the oil and gas industry a better methodology for understanding reservoir and seal architectures and for improving interpretations of hydrocarbon systems. Our research goal was to expand the valuable science of seismic stratigraphy beyond the constraints of compressional (P-P) seismic data by using all modes (P-P, P-SV, SH-SH, SV-SV, SV-P) of a seismic elastic wavefield to define depositional sequences and facies. Our objective was to demonstrate that one or more modes of an elastic wavefield may image stratal surfaces across some stratigraphic intervals that are not seen by companion wave modes and thus provide different, but equally valid, information regarding depositional sequences and sedimentary facies within that interval. We use the term elastic wavefield stratigraphy to describe the methodology we use to integrate seismic sequences and seismic facies from all modes of an elastic wavefield into a seismic interpretation. We interpreted both onshore and marine multicomponent seismic surveys to select the data examples that we use to document the principles of elastic wavefield stratigraphy. We have also used examples from published papers that illustrate some concepts better than did the multicomponent seismic data that were available for our analysis. In each interpretation study, we used rock physics modeling to explain how and why certain geological conditions caused differences in P and S reflectivities that resulted in P-wave seismic sequences and facies being different from depth-equivalent S-wave sequences and facies across the targets we studied.

  9. Seismic risk perception test

    Science.gov (United States)

    Crescimbene, Massimo; La Longa, Federica; Camassi, Romano; Pino, Nicola Alessandro

    2013-04-01

    The perception of risks involves the process of collecting, selecting and interpreting signals about uncertain impacts of events, activities or technologies. In the natural sciences the term risk seems to be clearly defined, it means the probability distribution of adverse effects, but the everyday use of risk has different connotations (Renn, 2008). The two terms, hazards and risks, are often used interchangeably by the public. Knowledge, experience, values, attitudes and feelings all influence the thinking and judgement of people about the seriousness and acceptability of risks. Within the social sciences however the terminology of 'risk perception' has become the conventional standard (Slovic, 1987). The mental models and other psychological mechanisms which people use to judge risks (such as cognitive heuristics and risk images) are internalized through social and cultural learning and constantly moderated (reinforced, modified, amplified or attenuated) by media reports, peer influences and other communication processes (Morgan et al., 2001). Yet, a theory of risk perception that offers an integrative, as well as empirically valid, approach to understanding and explaining risk perception is still missing". To understand the perception of risk is necessary to consider several areas: social, psychological, cultural, and their interactions. Among the various research in an international context on the perception of natural hazards, it seemed promising the approach with the method of semantic differential (Osgood, C.E., Suci, G., & Tannenbaum, P. 1957, The measurement of meaning. Urbana, IL: University of Illinois Press). The test on seismic risk perception has been constructed by the method of the semantic differential. To compare opposite adjectives or terms has been used a Likert's scale to seven point. The test consists of an informative part and six sections respectively dedicated to: hazard; vulnerability (home and workplace); exposed value (with reference to

  10. Passive seismic experiment.

    Science.gov (United States)

    Latham, G V; Ewing, M; Press, F; Sutton, G; Dorman, J; Nakamura, Y; Toksöz, N; Wiggins, R; Derr, J; Duennebier, F

    1970-01-30

    Seismometer operation for 21 days at Tranquillity Base revealed, among strong signals produced by the Apollo 11 lunar module descent stage, a small proportion of probable natural seismic signals. The latter are long-duration, emergent oscillations which lack the discrete phases and coherence of earthquake signals. From similarity with the impact signal of the Apollo 12 ascent stage, they are thought to be produced by meteoroid impacts or shallow moonquakes. This signal character may imply transmission with high Q and intense wave scattering, conditions which are mutually exclusive on earth. Natural background noise is very much smaller than on earth, and lunar tectonism may be very low.

  11. Tectonic setting of the Helong Block: Implications for the northern boundary of the eastern North China Craton

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yanbin; WU Fuyuan; ZHAI Mingguo; LU Xiaoping

    2005-01-01

    LA-ICP-MS zircon U-Pb dating indicates that the Bailiping granitic pluton was emplaced during Late Paleozoic to Early Cretaceous (285―116 Ma) by four distinct magmatic episodes, arguing against the previous thought that the Bailiping granites were emplaced during Archean, Proterozoic or Early Paleozoic. It is suggested that the so-called Archean Jinchengdong granite-greenstone belt, mainly composed of Bailiping granites, should be broken down. Sr-Nd isotopic compositions of the Bailiping granites are similar to those of the Phanerozoic granites in the Xing'an-Mongolian orogenic belt, suggesting that their parental magmas were mainly derived from a juvenile crust with some contamination of ancient crustal materials during magma rising and/or emplacement. Therefore, the basement of the Helong Block is similar to that in the northern Xing'an-Mongolian Orogenic Belt, but different from that of the North China Craton. It is proposed that the Archean Jinchengdong complex in this area is probably an exotic slice from the North China Craton, which indicates that the Fu'erhe-Gudonghe Fault, located in northern part of the Helong area, is not the boundary between the North China Craton and the Xing'an-Mongolian Orogenic Belt. The possible boundary should be located further southward more than 50 km and near the Baitoushan volcano.

  12. The new occurrence of Marinoan cap carbonate in Brazil: The expansion of snowball Earth events to the southwesternmost Amazon Craton

    Science.gov (United States)

    Gaia, Valber do Carmo de Souza; Nogueira, Afonso César Rodrigues; Domingos, Fábio Henrique Garcia; Sans-Jofre, Pierre; Bandeira, José Cavalcante da Silva; Oliveira, José Guilherme Ferreira de; Sial, Alcides Nóbrega

    2017-07-01

    Carbonate deposits exposed in the border of the Pimenta Bueno and Colorado grabens, western part of Parecis Basin, southwestern Amazon Craton, Brazil, have been previously considered as Paleozoic record. These deposits lying unconformably on Mesoproterozoic crystalline rocks, the basement of the grabens, and consist predominantly by pinkish dolomite overlying glacial diamictites, with average negative values of δ13C of -3,10‰VPDB. The contact between the dolostone and diamictites is sharp and deformed similarly with others Neoproterozoic cap carbonates occurrences in the Amazon Craton, also related to the Marinoan Glaciation (635 Ma). This new occurrence of Marinoan cap carbonate is composed by two facies associations. Facies Association 1 consists of pinkish peloidal dolostone with even parallel and quasi-planar laminations, wavy and megarriple bedding, macropeloid lenses associated with low-angle truncations, interpreted as fairwhether- and storm-influenced shallow platform deposits. Facies association 2 consists in dolostone rhythmically interbedded with shale underlaid by 5 m-thick laminated siltstones, interpreted as moderately deep platform deposits. This retrogradational succession is overlaid in angular unconformity by Early Paleozoic diamictites and locally by Mesozoic volcanic rocks. This cap carbonate precedes the Paleozoic deposits of Parecis Basin and represents a post-glacial event linked to the Marinoan glaciation, extending to the southwesternmost Amazon Craton the phenomena of the Snowball Earth hypothesis.

  13. Emplacement and deformation of the A-type Madeira granite (Amazonian Craton, Brazil)

    Science.gov (United States)

    Siachoque, Astrid; Salazar, Carlos Alejandro; Trindade, Ricardo

    2017-04-01

    The Madeira granite is one of the Paleoproterozoic (1.82 Ga) A-type granite intrusions in the Amazonian Craton. It is elongated in the NE-SW direction and is composed of four facies. Classical structural techniques and the anisotropy of magnetic susceptibility (AMS) method were applied to the study of its internal fabric. Magnetic susceptibility measurements, thermomagnetic curves, remanent coercivity spectra, optical microscopy and SEM (scanning electron microscopy) analyses were carried out on the earlier and later facies of the Madeira granite: the rapakivi granite (RG) and the albite granite (AG) respectively. The last one is subdivided into the border albite granite (BAG) and the core albite granite (CAG) subfacies. AMS fabric pattern is controlled by pure magnetite in all facies, despite significant amounts of hematite in the BAG subfacies. Microstructural observations show that in almost all sites, magnetic fabric correlates to magmatic state fabrics that are defined by a weak NE-SW orientation of mafic and felsic silicates. However, strain mechanisms in both subfacies of AG also exhibit evidence for solid-state deformation at high to moderate temperatures. Pegmatite dyke, strike slip fault (SFA-B-C), hydrothermal vein, normal fault (F1-2) and joint (J) structures were observed and their orientation and kinematics is consistent with the magmatic and solid-state structures. Dykes, SFA-C and F1, are usually orientated along the N70°E/40°N plane, which is nearly parallel to the strike of AMS and magmatic foliations. In contrast, veins, SFB, F2 and some J are oriented perpendicular to the N70°E trend. Kinematic analysis in these structures shows evidence for a dextral sense of movement in the system in the brittle regime. The coherent structural pattern for the three facies of Madeira granite suggests that the different facies form a nested pluton. The coherence in orientation and kinematics from magmatic to high-temperature solid-state, and into the brittle

  14. A historical overview of Moroccan magmatic events along northwest edge of the West African Craton

    Science.gov (United States)

    Ikenne, Moha; Souhassou, Mustapha; Arai, Shoji; Soulaimani, Abderrahmane

    2017-03-01

    Located along the northwestern edge of the West African Craton, Morocco exhibits a wide variety of magmatic events from Archean to Quaternary. The oldest magmatic rocks belong to the Archean Reguibat Shield outcrops in the Moroccan Sahara. Paleoproterozoic magmatism, known as the Anti-Atlas granitoids, is related to the Eburnean orogeny and initial cratonization of the WAC. Mesoproterozoic magmatism is represented by a small number of mafic dykes known henceforth as the Taghdout mafic volcanism. Massive Neoproterozoic magmatic activity, related to the Pan-African cycle, consists of rift-related Tonian magmatism associated with the Rodinia breakup, an Early Cryogenian convergent margin event (760-700 Ma), syn-collisional Bou-Azzer magmatism (680-640 Ma), followed by widespread Ediacaran magmatism (620-555 Ma). Each magmatic episode corresponded to a different geodynamic environment and produced different types of magma. Phanerozoic magmatism began with Early Cambrian basaltic (rift?) volcanism, which persisted during the Middle Cambrian, and into the Early Ordovician. This was succeeded by massive Late Devonian and Carboniferous, pre-Variscan tholeiitic and calc-alkaline (Central Morocco) volcanic flows in basins of the Moroccan Meseta. North of the Atlas Paleozoic Transform Zone, the Late Carboniferous Variscan event was accompanied by the emplacement of 330-300 Ma calc-alkaline granitoids in upper crustal shear zones. Post-Variscan alkaline magmatism was associated with the opening of the Permian basins. Mesozoic magmatism began with the huge volumes of magma emplaced around 200 Ma in the Central Atlantic Magmatic Province (CAMP) which was associated with the fragmentation of Pangea and the subsequent rifting of Central Atlantic. CAMP volcanism occurs in all structural domains of Morocco, from the Anti-Atlas to the External Rif domain with a peak activity around 199 Ma. A second Mesozoic magmatic event is represented by mafic lava flows and gabbroic intrusions in

  15. Magnesium isotopic heterogeneity across the cratonic lithosphere in eastern China and its origins

    Science.gov (United States)

    Wang, Ze-Zhou; Liu, Sheng-Ao; Ke, Shan; Liu, Yi-Can; Li, Shu-Guang

    2016-10-01

    Available data in the literature have demonstrated a broad magnesium (Mg) isotope range for mantle and lower continental crustal rocks, implying an isotopically heterogeneous continental lithosphere, but its origin has not been thoroughly understood. Here, to investigate the primary cause of lithospheric Mg isotopic heterogeneity, we report major-trace elements, Sr and Mg isotope data for thirty deep-seated mafic xenoliths, which sampled different lithospheric depths in the southeastern North China Craton (NCC). The xenoliths are classified into three types based upon petrology and mineralogy, sampling from middle continental crust (Group I), lower continental crust (Group II) and lithospheric mantle (Group III), respectively. The Group I xenoliths have mantle-like to slightly high δ26Mg values (- 0.32 ‰ to + 0.01 ‰), whereas some of the Group II xenoliths have very low δ26Mg values (- 0.93 ‰ to - 0.07 ‰), reflecting substantial reaction with intracrustal carbonate-derived fluids. Combined with data in the literature, the results suggest that the Mg isotopic composition of the lower continental crust is much more heterogeneous and lighter on average relative to the middle continental crust. Except for one sample, the Group III xenoliths have extremely low δ26Mg values (- 1.23 ‰ to - 0.73 ‰), the lightest among values already reported for mantle-derived rocks including peridotites and basalts. They also have highly variable 87Sr/86Sr ratios, of 0.70387 to 0.71675. The covariation of Mg and Sr isotopes in Group III xenoliths can be explained by Mg and Sr isotopic exchange reactions during mantle metasomatism, implying that the sub-continental mantle has been significantly modified by fluids derived from recycled carbonate-pelite bearing oceanic crust. Together with the metasomatism age of ∼400 Ma obtained for one Group III xenolith, the results provide new evidence for the presence of extremely low-δ26Mg rocks in the lithosphere and indicate ancient

  16. Seismic Data Gathering and Validation

    Energy Technology Data Exchange (ETDEWEB)

    Coleman, Justin [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-02-01

    Three recent earthquakes in the last seven years have exceeded their design basis earthquake values (so it is implied that damage to SSC’s should have occurred). These seismic events were recorded at North Anna (August 2011, detailed information provided in [Virginia Electric and Power Company Memo]), Fukushima Daichii and Daini (March 2011 [TEPCO 1]), and Kaswazaki-Kariwa (2007, [TEPCO 2]). However, seismic walk downs at some of these plants indicate that very little damage occurred to safety class systems and components due to the seismic motion. This report presents seismic data gathered for two of the three events mentioned above and recommends a path for using that data for two purposes. One purpose is to determine what margins exist in current industry standard seismic soil-structure interaction (SSI) tools. The second purpose is the use the data to validated seismic site response tools and SSI tools. The gathered data represents free field soil and in-structure acceleration time histories data. Gathered data also includes elastic and dynamic soil properties and structural drawings. Gathering data and comparing with existing models has potential to identify areas of uncertainty that should be removed from current seismic analysis and SPRA approaches. Removing uncertainty (to the extent possible) from SPRA’s will allow NPP owners to make decisions on where to reduce risk. Once a realistic understanding of seismic response is established for a nuclear power plant (NPP) then decisions on needed protective measures, such as SI, can be made.

  17. Procedures for computing site seismicity

    Science.gov (United States)

    Ferritto, John

    1994-02-01

    This report was prepared as part of the Navy's Seismic Hazard Mitigation Program. The Navy has numerous bases located in seismically active regions throughout the world. Safe effective design of waterfront structures requires determining expected earthquake ground motion. The Navy's problem is further complicated by the presence of soft saturated marginal soils that can significantly amplify the levels of seismic shaking as evidenced in the 1989 Loma Prieta earthquake. The Naval Facilities Engineering Command's seismic design manual, NAVFAC P355.l, requires a probabilistic assessment of ground motion for design of essential structures. This report presents the basis for the Navy's Seismic Hazard Analysis procedure that was developed and is intended to be used with the Seismic Hazard Analysis computer program and user's manual. This report also presents data on geology and seismology to establish the background for the seismic hazard model developed. The procedure uses the historical epicenter data base and available geologic data, together with source models, recurrence models, and attenuation relationships to compute the probability distribution of site acceleration and an appropriate spectra. This report discusses the developed stochastic model for seismic hazard evaluation and the associated research.

  18. Key aspects governing induced seismicity

    Science.gov (United States)

    Buijze, Loes; Wassing, Brecht; Fokker, Peter

    2013-04-01

    In the past decades numerous examples of earthquakes induced by human-induced changes in subsurface fluid pressures have been reported. This poses a major threat to the future development of some of these operations and calls for an understanding and quantification of the seismicity generated. From geomechanical considerations and insights from laboratory experiments the factors controlling induced seismicity may be grouped into 4 categories; the magnitude of the stress disturbance, the pre-existing stress conditions, the reservoir/fault rock properties and the local geometry. We investigated whether the (relative) contributions of these factors and their influence on magnitudes generated could be recognized by looking at the entire dataset of reported cases of induced seismicity as a whole, and what this might imply for future developments. An extensive database has been built out of over a 160 known cases of induced seismicity worldwide, incorporating the relevant geological, seismological and fluid-related parameters. The cases studied include hydrocarbon depletion and secondary recovery, waste water injection, (enhanced) geothermal systems and hydraulic fracturing with observed magnitudes ranging from less than -1.5 to 7. The parameters taken into account were based on the theoretical background of the mechanisms of induced seismicity and include the injection/depletion-related parameters, (spatial) characteristics of seismicity, lithological properties and the local stress situation. Correlations between the seismic response and the geological/geomechanical characteristics of the various sites were investigated. The injected/depleted volumes and the scale of the activities are major controlling factors on the maximum magnitudes generated. Spatial signatures of seismicity such as the depth and lateral spread of the seismicity were observed to be distinct for different activities, which is useful when considering future operations. Where available the local

  19. Advances in Rotational Seismic Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Pierson, Robert [Applied Technology Associates, Albuquerque, NM (United States); Laughlin, Darren [Applied Technology Associates, Albuquerque, NM (United States); Brune, Robert [Applied Technology Associates, Albuquerque, NM (United States)

    2016-10-19

    Rotational motion is increasingly understood to be a significant part of seismic wave motion. Rotations can be important in earthquake strong motion and in Induced Seismicity Monitoring. Rotational seismic data can also enable shear selectivity and improve wavefield sampling for vertical geophones in 3D surveys, among other applications. However, sensor technology has been a limiting factor to date. The US Department of Energy (DOE) and Applied Technology Associates (ATA) are funding a multi-year project that is now entering Phase 2 to develop and deploy a new generation of rotational sensors for validation of rotational seismic applications. Initial focus is on induced seismicity monitoring, particularly for Enhanced Geothermal Systems (EGS) with fracturing. The sensors employ Magnetohydrodynamic (MHD) principles with broadband response, improved noise floors, robustness, and repeatability. This paper presents a summary of Phase 1 results and Phase 2 status.

  20. Flat vs. Normal subduction, Central Chile: insights from regional seismic tomography and rock type modeling

    Science.gov (United States)

    Marot, Marianne; Monfret, Tony; Gerbault, Muriel; Nolet, Guust; Ranalli, Giorgio; Pardo, Mario

    2013-04-01

    The Central Chilean subduction zone (27-35°S) is host to a multitude of unexplained phenomena, all likely linked to one another. Here, the 35 Ma oceanic Nazca plate is subducting beneath South America with a well developed, highly seismic flat slab, very well correlated with the subducting Juan Fernandez seamount Ridge (JFR) track, and also with the absence of volcanism at the surface. The upper plate, currently under compression, is composed of a series of accreted terranes of various origins and ages. Although no general consensus on the formation of this flat slab has been yet achieved, there may have been influence of overthickened oceanic crust, delayed eclogitization and consequent fluid retain within the slab, and slab suction due to the high convergence rate with the thick Rio de Plata craton. Therefore, the main questions we address are: Does the slab dehydrate along the flat subducting segment? If so, how hydrated is the slab, at what depth does slab dehydration occur, where are the fluids transported to, and where are they stored? Is magmatism still active beneath the now inactive arc? Are accreted terranes and suture zones important attributes of this subduction zone? Do they possess their own mantle entities? To answer these questions, we analyzed recorded local seismicity and performed regional 3D seismic tomography for Vp and Vs. Combining seismic tomography with 2D instantaneous thermo-mechanical modeling for the regions of flat and normal subduction, we predict rock compositions for these two regions based on published mineral and rock elastic properties. Here, we present a comparison between the normal subduction zone to the south, reflecting typical and expected features, and the flat slab region to the north, exhibiting heterogeneities. Our results agree with other studies for a dry and cold continental mantle above the flat slab. We distinguish the Cuyania terrane with overthickened crust and/or abnormal mantle beneath it. We notice that the

  1. Seismic moulin tremor

    Science.gov (United States)

    Roeoesli, Claudia; Walter, Fabian; Ampuero, Jean-Paul; Kissling, Edi

    2016-08-01

    Through glacial moulins, meltwater is routed from the glacier surface to its base. Moulins are a main feature feeding subglacial drainage systems and thus influencing basal motion and ice dynamics, but their geometry remains poorly known. Here we show that analysis of the seismic wavefield generated by water falling into a moulin can help constrain its geometry. We present modeling results of hour-long seimic tremors emitted from a vertical moulin shaft, observed with a seismometer array installed at the surface of the Greenland Ice Sheet. The tremor was triggered when the moulin water level exceeded a certain height, which we associate with the threshold for the waterfall to hit directly the surface of the moulin water column. The amplitude of the tremor signal changed over each tremor episode, in close relation to the amount of inflowing water. The tremor spectrum features multiple prominent peaks, whose characteristic frequencies are distributed like the resonant modes of a semiopen organ pipe and were found to depend on the moulin water level, consistent with a source composed of resonant tube waves (water pressure waves coupled to elastic deformation of the moulin walls) along the water-filled moulin pipe. Analysis of surface particle motions lends further support to this interpretation. The seismic wavefield was modeled as a superposition of sustained wave radiation by pressure sources on the side walls and at the bottom of the moulin. The former was found to dominate the wave field at close distance and the latter at large distance to the moulin.

  2. seismic-py: Reading seismic data with Python

    Directory of Open Access Journals (Sweden)

    2008-08-01

    Full Text Available The field of seismic exploration of the Earth has changed
    dramatically over the last half a century. The Society of Exploration
    Geophysicists (SEG has worked to create standards to store the vast
    amounts of seismic data in a way that will be portable across computer
    architectures. However, it has been impossible to predict the needs of the
    immense range of seismic data acquisition systems. As a result, vendors have
    had to bend the rules to accommodate the needs of new instruments and
    experiment types. For low level access to seismic data, there is need for a
    standard open source library to allow access to a wide range of vendor data
    files that can handle all of the variations. A new seismic software package,
    seismic-py, provides an infrastructure for creating and managing drivers for
    each particular format. Drivers can be derived from one of the known formats
    and altered to handle any slight variations. Alternatively drivers can be
    developed from scratch for formats that are very different from any previously
    defined format. Python has been the key to making driver development easy
    and efficient to implement. The goal of seismic-py is to be the base system
    that will power a wide range of experimentation with seismic data and at the
    same time provide clear documentation for the historical record of seismic
    data formats.

  3. Evolution of a Paleoproterozoic “weak type” orogeny in the West African Craton (Ivory Coast)

    Science.gov (United States)

    Vidal, M.; Gumiaux, C.; Cagnard, F.; Pouclet, A.; Ouattara, G.; Pichon, M.

    2009-11-01

    The Paleoproterozoic domain of the Ivory Coast lies in the central part of the West African Craton (WAC) and is mainly constituted by TTG, greenstones, supracrustal rocks and leucogranites. A compilation of metamorphic and radiometric data highlights that: i) metamorphic conditions are rather homogeneous through the domain, without important metamorphic jumps, ii) HP-LT assemblages are absent and iii) important volumes of magmas emplaced during the overall Paleoproterozoic orogeny suggesting the occurrence of long-lived rather hot geotherms. Results of the structural analysis, focused on three areas within the Ivory Coast, suggest that the deformation is homogeneous and distributed through the Paleoproterozoic domain. In details, results of this study point out the long-lived character of vertical movements during the Eburnean orogeny with a two folds evolution. The first stage is characterized by the development of "domes and basins" geometries without any boundary tectonic forces and the second stage is marked by coeval diapiric movements and horizontal regional-scale shortening. These features suggest that the crust is affected by vertical movements during the overall orogeny. The Eburnean orogen can then be considered as an example of long-lived Paleoproterozoic "weak type" orogen.

  4. The late Paleoproterozoic extension event:aulacogens and dyke Swarms in the North China craton

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The extension structures and tectonic implication in the North China Craton (NCC) are discussed in this paper based on the mafic dyke swarms and geochronology, combining with the geochronology of aulacogens. The late Paleoproterozoic time is the important turning point in the Precambrian evolution of the NCC. The extension system (e. g. aulacogens and dyke swarms) is widespread in the NCC, which marks the carbonization of the NCC with the rigid characteristic similar to the modern plate. The paleostress field modeling suggests that the dyke swarms and aulacogens are arogenic extension marking the start of the supercontinent, not synorogenic and postorogenic extension. The mafic dyke swarms in the NCC mainly ranged from 1.83 to 1.77 Ga. The extension of the NCC is very limited brittle extension, the average extension ratio is only 0.35 % given by mafic dyke swarms extension calculation, so most of extension in the NCC is contributed by the aulacogens. The mafic dyke swarms are related with the aulacogens in the origin.

  5. Eclogite-melt/peridotite reaction: Experimental constrains on the destruction mechanism of the North China Craton

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    To study the mechanism of melt-peridotite reaction pertinent to the destruction of the North China Craton (NCC) lithosphere, a series of experiments were performed at a pressure of 2.0 GPa and temperatures from 1250 to 1400°C using Bixiling eclogite and Damaping peridotite as starting materials. The experimental results show that the reaction between eclogite melt and peridotite causes dissolution of olivine and orthopyroxene and precipitation of clinopyroxene in the melt. The experimental run products, characterized by a lherzolite/pyroxenite/garnet-pyroxenite sequence, are consistent with the mantle xenoliths in the Neogene Hannuoba basalt of the NCC found by Liu et al. (2005). It suggests that the mafic lower continental crust was probably recycled into the mantle during the Mesozoic Era. In the experiments conducted at 1300 and 1350°C, the resulting melts have a high Mg# andesite signature, indicating that the melt-peridotite reaction may have played a major role in the generation of high Mg# andesite. Our experimental results support the hypothesis that melts derived from foundered eclogite in the asthenosphere will consume the lithospheric peridotites. Therefore, melt-peridotite reaction is an important mechanism for the destruction/thinning of the lithosphere.

  6. Metallogenic Systems on the Paleocontinental Margin of the North China Craton

    Institute of Scientific and Technical Information of China (English)

    ZHAI Yusheng; DENG Jun; TANG Zhongli; XIAO Rongge; SONG Honglin; PENG Runmin; SUN Zhongshi; WANG Jianping

    2004-01-01

    The North China Craton (NCC) is one of the largest blocks composing the continent. Different types of continental margins well developed around the NCC, along with lots of metallogenic systems of different metals and different times. Based on the study on the structural evolution of the NCC, the authors made a new division of tectonic units of the NCC. Through an analysis of the data of 1:25000 geochemical survey on stream sediments, regional geochemical features of main ore-forming elements including Au, Ag, Cu, Pb, Zn, W, Ni, Co and Mo of the NCC are discussed in the paper. Then different metallogenic systems and their forming processes and geodynamics are discussed in detail. At last, temporal and spatial distribution regularities are summarized and ten favorable ore-control factors on the paleocontinental margins are put forward, including (1) abundance of ore sources; (2) rendezvous of ore-forming fluids; (3) high thermo-dynamic anomaly; (4) remarkable Earth crust-mantle interaction; (5) cluster of macroscopic structures and their long activities; (6) diversity of ore-forming environments; (7) long geohistory; (8) multiforms of critical transitional ore-forming mechanisms; (9) multi-staged and superimposed ore-formation; and (10) suitable preservation condition.

  7. Is the outcrop topology of dolerite dikes of the Precambrian Singhbhum Craton fractal?

    Indian Academy of Sciences (India)

    Nibir Mandal; Atin Kumar Mitra; Santanu Misra; Chandan Chakraborty

    2006-12-01

    In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW–SE and NE–SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in nonlinear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation and coalescence of fractures.

  8. On the nature and origin of highly-refractory Archean lithosphere: Petrological and geophysical constraints from the Tanzanian craton

    Science.gov (United States)

    Gibson, S. A.; McMahon, S. C.; Day, J. A.; Dawson, J. B.

    2012-12-01

    The nature and timescales of garnet formation are important to understanding how subcontinental lithospheric mantle (SCLM) has evolved since the Archean, and also to mantle dynamics, because the presence of garnet greatly influences the density of the lower lithosphere and hence the long-term stability of thick (150 to 220 km) subcratonic lithosphere. Nevertheless, the widespread occurrence of garnet in the SCLM remains one of the 'holy grails' of mantle petrology. Garnets found in mantle xenoliths from the eastern margin of the Tanzanian Craton (Lashaine) have diverse compositions and provide major constraints on how the underlying deep (120 to 160 km) mantle evolved during the last 3 billion years. Certain harzburgite members of the xenolith suite contain the first reported occurrence of pyrope garnets with rare-earth element patterns similar to hypothetical garnets proposed to have formed in the Earth's SCLM during the Archean, prior to metasomatism [Stachel et al., 2004]. These rare ultradepleted low-Cr garnets occur in low temperature (~1050 oC) xenoliths derived from depths of ~120 km and coexist in chemical and textural equilibrium with highly-refractory olivine (Fo95.4) and orthopyroxene (Mg#=96.4). These phases are all more magnesian than generally encountered in global mantle harzburgites and diamond inclusions. The ultradepleted garnets form interconnecting networks around grains of orthopyroxene which give the rocks a banded appearance: we propose that the increase in pressure associated with cratonization may have caused isochemical exsolution of ultradepleted garnet from orthopyroxene. These unique garnets have not previously been identified in global suites of mantle xenoliths or diamond inclusions. We believe they are rare because their low concentrations of trace elements make them readily susceptible to geochemical overprinting. This highly-refractory low-density peridotite may be common in the 'shallow' SCLM but not normally brought to the

  9. Updated Colombian Seismic Hazard Map

    Science.gov (United States)

    Eraso, J.; Arcila, M.; Romero, J.; Dimate, C.; Bermúdez, M. L.; Alvarado, C.

    2013-05-01

    The Colombian seismic hazard map used by the National Building Code (NSR-98) in effect until 2009 was developed in 1996. Since then, the National Seismological Network of Colombia has improved in both coverage and technology providing fifteen years of additional seismic records. These improvements have allowed a better understanding of the regional geology and tectonics which in addition to the seismic activity in Colombia with destructive effects has motivated the interest and the need to develop a new seismic hazard assessment in this country. Taking advantage of new instrumental information sources such as new broad band stations of the National Seismological Network, new historical seismicity data, standardized global databases availability, and in general, of advances in models and techniques, a new Colombian seismic hazard map was developed. A PSHA model was applied. The use of the PSHA model is because it incorporates the effects of all seismic sources that may affect a particular site solving the uncertainties caused by the parameters and assumptions defined in this kind of studies. First, the seismic sources geometry and a complete and homogeneous seismic catalog were defined; the parameters of seismic rate of each one of the seismic sources occurrence were calculated establishing a national seismotectonic model. Several of attenuation-distance relationships were selected depending on the type of seismicity considered. The seismic hazard was estimated using the CRISIS2007 software created by the Engineering Institute of the Universidad Nacional Autónoma de México -UNAM (National Autonomous University of Mexico). A uniformly spaced grid each 0.1° was used to calculate the peak ground acceleration (PGA) and response spectral values at 0.1, 0.2, 0.3, 0.5, 0.75, 1, 1.5, 2, 2.5 and 3.0 seconds with return periods of 75, 225, 475, 975 and 2475 years. For each site, a uniform hazard spectrum and exceedance rate curves were calculated. With the results, it is

  10. Midget Seismic in Sandbox Models

    Science.gov (United States)

    Krawczyk, C. M.; Buddensiek, M. L.; Philipp, J.; Kukowski, N.; Oncken, O.

    2008-12-01

    Analog sandbox simulation has been applied to study geological processes to provide qualitative and quantitative insights into specific geological problems. In nature, the structures, which are simulated in those sandbox models, are often inferred from seismic data. With the study introduced here, we want to combine the analog sandbox simulation techniques with seismic physical modeling of those sandbox models. The long-term objectives of this approach are (1) imaging of seismic and seismological events of actively deforming and static 3D analogue models, and (2) assessment of the transferability of the model data to field data in order to improve field data acquisition and interpretation according to the addressed geological problem. To achieve this objective, a new midget-seismic facility for laboratory use was designed and developed, comprising a seismic tank, a PC control unit including piezo-electric transducers, and a positioning system. The first experiments are aimed at studying the wave field properties of the piezo- transducers in order to investigate their feasibility for seismic profiling. The properties investigated are their directionality and the change of waveform due to their size (5-12 mm) compared to the wavelengths (material properties and the effects of wave propagation in an-/isotropic media by physical studies, before we finally start using different seismic imaging and processing techniques on static and actively deforming 3D analog models.

  11. Seismic hazard assessment: Issues and alternatives

    Science.gov (United States)

    Wang, Z.

    2011-01-01

    Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used inter-changeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been pro-claimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications. ?? 2010 Springer Basel AG.

  12. Seismic modeling of carbonate outcrops

    Energy Technology Data Exchange (ETDEWEB)

    Stafleu, J.; Schlager, W.; Campbell, E.; Everts, A.J. (Vrije Universiteit, Amsterdam (Netherlands))

    1993-09-01

    Traditionally, seismic modeling has concentrated on one-dimensional borehole modeling and two-dimensional forward modeling of basic structural-stratigraphic schemes, which are directly compared with real seismic data. Two-dimensional seismic models based on outcrop observations may aid in bridging the gap between the detail of the outcrop and the low resolution of seismic lines. Examples include the Dolomites (north Italy), the High Atlas (Morocco), the Vercors (southeast France) and the Last chance Canyon (New Mexico). The seismic models generally are constructed using the following procedure: (1) construction of a detailed lithological model based on direct outcrop observations; (2) division of the lithological model into lithostratigraphic units, using master bedding planes and important facies transitions as boundaries; (3) assignment of petrophysical properties of these lithostratigraphic units; (4) computation of time sections of reflectivity, using different modeling techniques; and (5) convolution with source wavelets of different frequencies. The lithological detail modeled in the case studies lead to some striking results, particularly the discovery of pseudo-unconformities. Pseudo-unconformities are unconformities in seismics, but correspond to rapid changes of dip and facies in outcrop. None of the outcrop geometries studied were correctly portrayed seismically at 25 Hz frequency. However, in some instances the true relationship would emerge gradually at frequencies of 50 to 100 Hz. These results demonstrate that detailed, outcrop-derived/seismic models can reveal what stratigraphic relationships and features are likely to be resolved under ideal or less ideal conditions, and what pitfalls may befall the interpreter of real seismic data.

  13. Integrated system for seismic evaluations

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J.; Philippacopoulos, A.J.; Miller, C.A.; Costantino, C.J.; Graves, H.

    1989-01-01

    This paper describes the various features of the Seismic Module of the CARES system (Computer Analysis for Rapid Evaluation of Structures). This system was developed by Brookhaven National Laboratory (BNL) for the US Nuclear Regulatory Commission to perform rapid evaluations of structural behavior and capability of nuclear power plant facilities. The CARES is structured in a modular format. Each module performs a specific type of analysis i.e., static or dynamic, linear or nonlinear, etc. This paper describes the features of the Seismic Module in particular. The development of the Seismic Module of the CARES system is based on an approach which incorporates all major aspects of seismic analysis currently employed by the industry into an integrated system that allows for carrying out interactively computations of structural response to seismic motions. The code operates on a PC computer system and has multi-graphics capabilities. It has been designed with user friendly features and it allows for interactive manipulation of various analysis phases during the seismic design process. The capabilities of the seismic module include (a) generation of artificial time histories compatible with given design ground response spectra, (b) development of Power Spectral Density (PSD) functions associated with the seismic input, (c) deconvolution analysis using vertically propagating shear waves through a given soil profile, and (d) development of in-structure response spectra or corresponding PSD's. It should be pointed out that these types of analyses can also be performed individually by using available computer codes such as FLUSH, SAP, etc. The uniqueness of the CARES, however, lies on its ability to perform all required phases of the seismic analysis in an integrated manner. 5 refs., 6 figs.

  14. Seismic anisotropy: an original tool to understand the geodynamic evolution of the Italian peninsula

    Directory of Open Access Journals (Sweden)

    A. Amato

    1997-06-01

    Full Text Available Anisotropy is a common property of the Earth's crust and the upper mantle; it is related to the strain field of the medium and therefore to geodynamics. In this paper we describe the different possible origins of anisotropic behavior of the seismic waves and the seismological techniques used to define anisotropic bodies. In general it is found that the fast polarization direction is parallel to the absolute plate motion in cratonic areas, to the spreading direction near rifts or extensional zones, and to the main structural features in transpressive regimes. The delay times between fast and slow waves reflect the relative strength and penetration at depth of the deformation field. The correspondence between surface structural trends and anisotropy in the upper mantle, found in many regions of the world, strongly suggest that orogenic processes involve not only the shallow crust but the entire lithosphere. Recently in Italy both shear wave splitting analysis and Pn inversion were applied to define the trend of seismic anisotropy. Along the Northern Appeninic arc fast directions follow the strike of the arc (i.e., parallel to the strike of the Miocene-Pleistocene compressional features, whereas in the Tyrrhenian zone fast directions are about E-W SW-NE; parallel to the post-Miocene extension that is thought to have reoriented the mantle minerals fabric in the astenosphere.

  15. Seismic calm predictors of rockburst

    Science.gov (United States)

    Zmushko, Tatjana; Turuntaev, Sergey; Kulikov, Vladimir

    2013-04-01

    The method of "seismic calm" is widely used for forecasting of strong natural earthquakes (Sobolev G.A., Ponomarev A.V., 2003). The "seismic calm" means that during some time period before the main earthquake, the smaller events (with energies of several order smaller than that of the main earthquake) don't occur. In the presented paper the applicability of the method based on the idea of seismic calm for forecasting rockburst is considered. Three deposits (with seismicity induced by mining) are analyzed: Tashtagol iron deposit (Altai, Russia), Vorkuta (North Ural, Russia) and Barentsburg (Spitsbergen, Norway) coalmines. Local seismic monitoring networks are installed on each of them. The catalogues of seismic events were processed and strong events (rockbursts) were studied (Vorkuta M=2,3; Barentsburg M=1,8; Tashtagol M=1,9÷2,2). All catalogues cover at least two years (Vorkuta - 2008-2011, Barentsburg - 2011-2012, Tashtagol - 2002-2012). It was found that the number of seismic events with magnitudes M=0,5÷1 decreased in a month before the main strong event at Vorkuta coalmines. This event was not directly related with coal mining, its epicenter was located aside of the area of coal mining. In Barentsburg mine the rockburst wasn't so strong as in Vorkuta. The number of events with energies M=0,5 decreased slightly before the rockburst, but not so obviously as in Vorkuta case. The seismic events with high energies occur often at Tashtagol iron deposit. Mining methods used there differ from the coal deposit mining. At coalmines the mining combine runs from edge to edge of the wall, cutting off the coal. The considered iron deposit is developed by a method of block blasting. Not all rockbursts occur immediately after the blasting, so, the problem of the rockburst prediction is important for mining safety. To find rockburst precursors it is necessary to separate the events occurred due to the block blasting from the seismic events due to relocation of stresses in

  16. Automating Shallow Seismic Imaging

    Energy Technology Data Exchange (ETDEWEB)

    Steeples, Don W.

    2004-12-09

    This seven-year, shallow-seismic reflection research project had the aim of improving geophysical imaging of possible contaminant flow paths. Thousands of chemically contaminated sites exist in the United States, including at least 3,700 at Department of Energy (DOE) facilities. Imaging technologies such as shallow seismic reflection (SSR) and ground-penetrating radar (GPR) sometimes are capable of identifying geologic conditions that might indicate preferential contaminant-flow paths. Historically, SSR has been used very little at depths shallower than 30 m, and even more rarely at depths of 10 m or less. Conversely, GPR is rarely useful at depths greater than 10 m, especially in areas where clay or other electrically conductive materials are present near the surface. Efforts to image the cone of depression around a pumping well using seismic methods were only partially successful (for complete references of all research results, see the full Final Technical Report, DOE/ER/14826-F), but peripheral results included development of SSR methods for depths shallower than one meter, a depth range that had not been achieved before. Imaging at such shallow depths, however, requires geophone intervals of the order of 10 cm or less, which makes such surveys very expensive in terms of human time and effort. We also showed that SSR and GPR could be used in a complementary fashion to image the same volume of earth at very shallow depths. The primary research focus of the second three-year period of funding was to develop and demonstrate an automated method of conducting two-dimensional (2D) shallow-seismic surveys with the goal of saving time, effort, and money. Tests involving the second generation of the hydraulic geophone-planting device dubbed the ''Autojuggie'' showed that large numbers of geophones can be placed quickly and automatically and can acquire high-quality data, although not under rough topographic conditions. In some easy

  17. Advanced Seismic While Drilling System

    Energy Technology Data Exchange (ETDEWEB)

    Robert Radtke; John Fontenot; David Glowka; Robert Stokes; Jeffery Sutherland; Ron Evans; Jim Musser

    2008-06-30

    A breakthrough has been discovered for controlling seismic sources to generate selectable low frequencies. Conventional seismic sources, including sparkers, rotary mechanical, hydraulic, air guns, and explosives, by their very nature produce high-frequencies. This is counter to the need for long signal transmission through rock. The patent pending SeismicPULSER{trademark} methodology has been developed for controlling otherwise high-frequency seismic sources to generate selectable low-frequency peak spectra applicable to many seismic applications. Specifically, we have demonstrated the application of a low-frequency sparker source which can be incorporated into a drill bit for Drill Bit Seismic While Drilling (SWD). To create the methodology of a controllable low-frequency sparker seismic source, it was necessary to learn how to maximize sparker efficiencies to couple to, and transmit through, rock with the study of sparker designs and mechanisms for (a) coupling the sparker-generated gas bubble expansion and contraction to the rock, (b) the effects of fluid properties and dynamics, (c) linear and non-linear acoustics, and (d) imparted force directionality. After extensive seismic modeling, the design of high-efficiency sparkers, laboratory high frequency sparker testing, and field tests were performed at the University of Texas Devine seismic test site. The conclusion of the field test was that extremely high power levels would be required to have the range required for deep, 15,000+ ft, high-temperature, high-pressure (HTHP) wells. Thereafter, more modeling and laboratory testing led to the discovery of a method to control a sparker that could generate low frequencies required for deep wells. The low frequency sparker was successfully tested at the Department of Energy Rocky Mountain Oilfield Test Center (DOE RMOTC) field test site in Casper, Wyoming. An 8-in diameter by 26-ft long SeismicPULSER{trademark} drill string tool was designed and manufactured by TII

  18. Mechanisms for strain localization within Archaean craton: A structural study from the Bundelkhand Tectonic Zone, north-central India

    Science.gov (United States)

    Sarkar, Saheli; Patole, Vishal; Saha, Lopamudra; Pati, Jayanta Kumar; Nasipuri, Pritam

    2015-04-01

    The transformation of palaeo-continents involve breakup, dispersal and reassembly of cratonic blocks by collisional suturing that develop a network of orogenic (mobile) belts around the periphery of the stable cratons. The nature of deformation in the orogenic belt depends on the complex interaction of fracturing, plastic deformation and diffusive mass transfer. Additionally, the degree and amount of melting during regional deformation is critical as the presence of melt facilitates the rate of diffusive mass transfer and weakens the rock by reducing the effective viscosity of the deformed zone. The nature of strain localization and formation of ductile shear zones surrounding the cratonic blocks have been correlated with Proterozoic-Palaeozoic supercontinent assembly (Columbia, Rodinia and Gondwana reconstruction). Although, a pre-Columbia supercontinent termed as Kenorland has been postulated, there is no evidence that supports the notion due to lack of the presence of shear zones within the Archaean cratonic blocks. In this contribution, we present the detailed structural analysis of ductile shear zones within the Bundelkhand craton. The ductlile shear zone is termed as Bundelkhand Tectonic Zone (BTZ) that extends east-west for nearly 300 km throughout the craton with a width of two-three kilometer . In the north-central India, the Bundelkhand craton is exposed over an area of 26,000 sq. The craton is bounded by Central Indian Tectonic zone in the south, the Great Boundary fault in the west and by the rocks of Lesser Himalaya in the north. A series of tonalite-trondjhemite-granodiorite gneiss are the oldest rocks of the Bundelkhand craton that also contains a succession of metamorphosed supracrustal rocks comprising of banded iron formation, quartzite, calc-silicate and ultramafic rocks. K-feldspar bearing granites intrude the tonalite-trondjhemite-granodiorite and the supracrustal rocks during the time span of 2.1 to 2.5 Ga. The TTGs near Babina, in central

  19. Reevaluation of the Seismicity and seismic hazards of Northeastern Libya

    Science.gov (United States)

    Ben Suleman, abdunnur; Aousetta, Fawzi

    2014-05-01

    Libya, located at the northern margin of the African continent, underwent many episodes of orogenic activities. These episodes of orogenic activities affected and shaped the geological setting of the country. This study represents a detailed investigation that aims to focus on the seismicity and its implications on earthquake hazards of Northeastern Libya. At the end of year 2005 the Libyan National Seismological Network starts functioning with 15 stations. The Seismicity of the area under investigation was reevaluated using data recorded by the recently established network. The Al-Maraj earthquake occurred in May 22nd 2005was analyzed. This earthquake was located in a known seismically active area. This area was the sight of the well known 1963 earthquake that kills over 200 people. Earthquakes were plotted and resulting maps were interpreted and discussed. The level of seismic activity is higher in some areas, such as the city of Al-Maraj. The offshore areas north of Al-Maraj seem to have higher seismic activity. It is highly recommended that the recent earthquake activity is considered in the seismic hazard assessments for the northeastern part of Libya.

  20. Validating induced seismicity forecast models - Induced Seismicity Test Bench

    CERN Document Server

    Kiraly-Proag, Eszter; Gischig, Valentin; Wiemer, Stefan; Karvounis, Dimitrios; Doetsch, Joseph

    2016-01-01

    Induced earthquakes often accompany fluid injection, and the seismic hazard they pose threatens various underground engineering projects. Models to monitor and control induced seismic hazard with traffic light systems should be probabilistic, forward-looking, and updated as new data arrive. In this study, we propose an Induced Seismicity Test Bench to test and rank such models; this test bench can be used for model development, model selection, and ensemble model building. We apply the test bench to data from the Basel 2006 and Soultz-sous-For\\^ets 2004 geothermal stimulation projects, and we assess forecasts from two models: Shapiro and Smoothed Seismicity (SaSS) and Hydraulics and Seismics (HySei). These models incorporate a different mix of physics-based elements and stochastic representation of the induced sequences. Our results show that neither model is fully superior to the other. Generally, HySei forecasts the seismicity rate better after shut-in, but is only mediocre at forecasting the spatial distri...

  1. Microstructures, deformation mechanisms and seismic properties of a Palaeoproterozoic shear zone: The Mertz shear zone, East-Antarctica

    Science.gov (United States)

    Lamarque, Gaëlle; Bascou, Jérôme; Maurice, Claire; Cottin, Jean-Yves; Riel, Nicolas; Ménot, René-Pierre

    2016-06-01

    The Mertz shear zone (MSZ) is a lithospheric scale structure that recorded mid-crustal deformation during the 1.7 Ga orogeny. We performed a microstructural and crystallographic preferred orientation (CPO) study of samples from both mylonites and tectonic boudins that constitute relics of the Terre Adélie Craton (TAC). The deformation is highly accommodated in the MSZ by anastomosed shear bands, which become more scattered elsewhere in the TAC. Most of the MSZ amphibolite-facies mylonites display similar CPO, thermal conditions, intensity of deformation and dominant shear strain. Preserved granulite-facies boudins show both coaxial and non-coaxial strains related to the previous 2.45 Ga event. This former deformation is more penetrative and less localized and shows a deformation gradient, later affected by a major phase of recrystallization during retrogression at 2.42 Ga. Both MSZ samples and granulite-facies tectonic boudins present microstructures that reflect a variety of deformation mechanisms associated with the rock creep that induce contrasted CPO of minerals (quartz, feldspar, biotite, amphibole and orthopyroxene). In particular, we highlight the development of an "uncommon" CPO in orthopyroxene from weakly deformed samples characterized by (010)-planes oriented parallel to the foliation plane, [001]-axes parallel to the stretching lineation and clustering of [100]-axes near the Y structural direction. Lastly, we computed the seismic properties of the amphibolite and granulite facies rocks in the MSZ area in order to evaluate the contribution of the deformed intermediate and lower continental crust to the seismic anisotropy recorded above the MSZ. Our results reveal that (i) the low content of amphibole and biotite in the rock formations of the TAC, and (ii) the interactions between the CPO of the different mineralogical phases, generate a seismically isotropic crust. Thus, the seismic anisotropy recorded by the seismic stations of the TAC, including the

  2. Mesozoic(?) lithosphere-scale buckling of the East European Craton in southern Ukraine

    DEFF Research Database (Denmark)

    Starostenko, V.; Janik, T.; Lysynchuk, D.

    2013-01-01

    tectonic units to the SW. Therefore, on purely seismic grounds it is not possible to distinguish major tectonic units known from the surface. The Moho is, however, clearly delineated by a velocity contrast of ca. 1.3–1.7 km s−1. A specific feature of the velocity model are waveform successive changes......In order to study the lithospheric structure in southern Ukraine, a seismic wide-angle reflection/refraction project DOBRE-4 was conducted. The 500-km-long profile starts in the SW from the Alpine/Variscan North Dobrudja Fold-Thrust Belt, being part of the Trans-European Suture Zone. It runs...... modelling of the P- and S-wave velocity structure along the profile. Two methods were used for the modelling of the seismic data. At first, ray tracing trial-and-error modelling was developed using arrivals of major refracted and reflected P- and S-wave phases. Next, the amplitudes of the recorded phases...

  3. Earthquake Activity - SEISMIC_DATA_IN: Seismic Refraction Data for Indiana (Indiana Geological Survey, Point Shapefile)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — SEISMIC_DATA_IN is a point shapefile created from a shapefile named SEISMIC_DATA, which was derived from a Microsoft Excel spreadsheet named SEISMIC_DECODED. The...

  4. null Seismic Creep, null Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden rupture associated with an earthquake. It is a usually slow deformation...

  5. Static behaviour of induced seismicity

    CERN Document Server

    Mignan, Arnaud

    2015-01-01

    The standard paradigm to describe seismicity induced by fluid injection is to apply nonlinear diffusion dynamics in a poroelastic medium. I show that the spatiotemporal behaviour and rate evolution of induced seismicity can, instead, be expressed by geometric operations on a static stress field produced by volume change at depth. I obtain laws similar in form to the ones derived from poroelasticity while requiring a lower description length. Although fluid flow is known to occur in the ground, it is not pertinent to the behaviour of induced seismicity. The proposed model is equivalent to the static stress model for tectonic foreshocks generated by the Non- Critical Precursory Accelerating Seismicity Theory. This study hence verifies the explanatory power of this theory outside of its original scope.

  6. Worldwide Marine Seismic Reflection Profiles

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NGDC maintains a large volume of both Analog and Digital seismic reflection data. Currently only a limited number of lines are available online. Digital data include...

  7. Sulfide Mineralization In The Marble Bar Greenstone Belt Around Mount Edger Batholith, Pilbara Craton, Western Australia

    Science.gov (United States)

    Kitazono, S.; Nedachi, M.; Taguchi, S.

    2004-12-01

    Pilbara Craton is one of the most important regions in the world to understand the evolution of early Earth, because the geological history is well preserved through the metamorphism of low grade. Pilbara Craton, Western Australia, consists of two different tectonic components formed 3.6 and 2.8 Ga; an older Archean granite occupying the east Pilbara and greenstone belt. In the east Pilbara, the most conspicuous structures are broad domal granitoid complex separated by narrow synformal greenstone belts, and a model of continuous lithostratigraphy in the greenstones in which the dominant structures were produced by multi-stage granitoid diapirism. The Marble Bar greenstone belt is distributed around the Mount Edgar of granitoid pluton, and numerous hydrothermal gold veins are distributed in the greenstone near the boundary of pluton. Also base-metal veins and volcanogenic sedimentary type deposits are located in the same area. In this study, we examined the hydrothermal mineralization observed in the core samples of the Marble Bar greenstone belt, drilled at the Salgash area by the Archean Biosphere Drilling Project (ABDP). The Salgash drill hole is composed of tuff breccias with numerous fragments of black shale of 100 m in thickness, alternation of sandstone and shale of 40 m in thickness, basaltic lava and tuff of 30 m in thickness, and shale and sandstone of 110m in thickness with some sills of basalt and ultramafic rock. The rocks had been metamorphosed, and the grade is near the boundary between green schist and amphibolite facies. Low REE content (43 to 88 ppm), low La/Yb ratio (6.3 to 14.3), and high Eu/Eu* ratio (0.9 to 1.3) of the volcanic rocks are ordinal as the basaltic rock in Archean greenstone belts. On the other hand, these rocks show extremely high values of Cr (1500ppm), Ni (700ppm), Co (70 ppm), and Zn (600 ppm). The C isotopic ratios of carbonate in the volcanic rocks are around -3.8 permil. The clastic sediment sandstone and black shale show

  8. Joint land-sea seismic survey and research on the deep structures of the Bohai Sea areas

    Institute of Scientific and Technical Information of China (English)

    HAO Tianyao; HAN Guozhong; YOU Qingyu; LIU Lihua; LV Chuanchuan; XU Ya; LI Zhiwei; ZHAO Chunlei; ZHENG Yanpeng; LIU Chenguang

    2013-01-01

    This paper presents the survey and research work of two land-sea profiles in the Bohai Sea, China, carried out in 2010-2011, including the seismic sources on land and in the sea, the ocean bottom seismographs (OBS) and their recovery, the coupling of OBS and the environment noise in sea area, the data quality of OBSs, and the result of data analysis. We focused on the investigation of crustal structures revealed by the two NE\\EW-trending joint land-sea profiles. In combination with the Pn-velocity distribution and gravity-magnetic inversion results in the North China Craton, we propose that the undulation of the Moho interface in the Bohai and surrounding areas is not strong, and the lithospheric thinning is mainly caused by the thinning of its mantle part. The research result indicates that obvious lateral variations of Moho depth and seismic velocity appear nearby all the large-scale faults in Bohai Sea, and there is evidence of underplating and reforming of the lower crust by mantle material in the Bohai area. However, geophysical evidence does not appear to support the“mantle plume”or“delamination”model for the North China Craton destruction. The crustal structure of the Bohai Sea revealed“a relatively normal crust and obviously thinned mantle lid”, local velocity anomalies and instability phenomena in the crust. These features may represent a combined effect of North China-Yangtze collision at an early stage and the remote action of Pacific plate subduction at a late stage.

  9. Textural and microstructural development of the Barro Alto Complex: implications for seismic anisotropy

    Science.gov (United States)

    Silveira, Camila; Lagoeiro, Leonardo; Barbosa, Paola; Cavalcante, Geane Carolina; Ferreira, Filippe; Suita, Marcos; Conte, Thailli

    2017-04-01

    Crustal rheology is associated with the behavior of its constituents in response to stress and strain, while the seismic anisotropy is a property that can correlate these parameters. Seismic properties are strongly related to the microstructures and crystallographic preferred orientation (CPO) of the rocks. In this work, we study CPO-derived seismic anisotropy of metamorphosed gabbro-norites from the Barro Alto (Brazil central) layered complex. The EBSD technique was employed to analyze the crystallographic orientation of the main mineral assembly, diopside and feldspar. The Barro Alto complex belongs to the Tocantins Structural Province, developed between the Amazon and São Francisco cratons, during the Neoproterozoic Brasiliano orogenic cycle. This complex was formed by a mafic-ultramafic layered intrusion mylonitized and metamorphosed under granulite facies conditions. The mylonitic foliation shows compositional segregation into felsic and mafic bands. The samples are composed of porphyroclasts of plagioclase and diopside in a fine matrix of plagioclase, clinopyroxene, orthopyroxene and, less commonly, amphibole and biotite. The plagioclase porphyroclasts exhibit undulose extinction and core-mantle structure. In fine matrix samples the poles to a(100), b(010) and c(001) are randomly distributed in both phases. However, for increasing matrix grain size plagioclase grains shows maxima of a(100) poles sub-parallel to the foliation and b(010) normal to the foliation. The low value of the J index (2.4 for plagioclase and 1.8 for diopside) indicates poorly developed fabric. Misorientation profiles showing high frequency of small angle boundaries are typical of recrystallization by subgrain rotation mechanisms. The microstructural and CPO analyses suggest deformation controlled by diffusive processes. The CPO models were compared to models described in the literature, based on the anorthite + diopside assembly, since these are the major phases, and thus control the

  10. Probabilistic Seismic Hazard assessment for Sultanate of Oman

    Science.gov (United States)

    El Hussain, I. W.; Deif, A.; El-Hady, S.; Toksoz, M. N.; Al-Jabri, K.; Al-Hashmi, S.; Al-Toubi, K. I.; Al-Shijbi, Y.; Al-Saifi, M.

    2010-12-01

    Seismic hazard assessment for Oman is conducted utilizing probabilistic approach. Probabilistic Seismic Hazard Assessment (PSHA) has been performed within a logic tree framework. An earthquake catalogue for Oman was compiled and declustered to include only independent earthquakes. The declustered catalogue was used to define seismotectonic source model with 26 source zones that characterize earthquakes in the tectonic environments in and around Oman. The recurrence parameters for all the seismogenic zones are determined using the doubly bounded exponential distribution except the seismogenic zones of Makran subduction zone which were modeled using the characteristic distribution. The maximum earthquakes on known faults were determined geologically and the remaining zones were determined statistically from the compiled catalogue. Horizontal ground accelerations in terms of geometric mean were calculated using ground-motion prediction relationships that were developed from seismic data obtained from the shallow active environment, stable craton environment, and from subduction earthquakes. In this analysis, we have used alternative seismotectonic source models, maximum magnitude, and attenuation models and weighted them to account for the epistemic uncertainty. The application of this methodology leads to the definition of 5% damped seismic hazard maps at rock sites for 72, 475, and 2475 year return periods for spectral accelerations at periods of 0.0 (corresponding to peak ground acceleration), 0.1, 0.2, 0.3, 1.0 and 2.0 sec. Mean and 84th percentile acceleration contour maps were represented. The results also were displayed as uniform hazard spectra for rock sites in the cities of Khasab, Diba, Sohar, Muscat, Nizwa, Sur, and Salalah in Oman and the cities of Abu Dhabi and Dubai in UAE. The PGA across Oman ranges from 20 cm/sec2 in the Mid-West and 115 cm/sec2 at the northern part for 475 years return period and between 40 cm/sec2 and 180 cm/sec2 for 2475 years

  11. Neoproterozoic extension in the greater dharwar craton: A reevaluation of the "betsimisaraka suture" in madagascar

    Science.gov (United States)

    Tucker, R.D.; Roig, J.-Y.; Delor, C.; Amlin, Y.; Goncalves, P.; Rabarimanana, M.H.; Ralison, A.V.; Belcher, R.W.

    2011-01-01

    The Precambrian shield of Madagascar is reevaluated with recently compiled geological data and new U-Pb sensitive high-resolution ion microprobe (SHRIMP) geochronology. Two Archean domains are recognized: the eastern Antongil-Masora domain and the central Antananarivo domain, the latter with distinctive belts of metamafic gneiss and schist (Tsaratanana Complex). In the eastern domain, the period of early crust formation is extended to the Paleo-Mesoarchean (3.32-3.15 Ga) and a supracrustal sequence (Fenerivo Group), deposited at 3.18 Ga and metamorphosed at 2.55 Ga, is identified. In the central domain, a Neoarchean period of high-grade metamorphism and anatexis that affected both felsic (Betsiboka Suite) and mafic gneisses (Tsaratanana Complex) is documented. We propose, therefore, that the Antananarivo domain was amalgamated within the Greater Dharwar Craton (India + Madagascar) by a Neoarchean accretion event (2.55-2.48 Ga), involving emplacement of juvenile igneous rocks, high-grade metamorphism, and the juxtaposition of disparate belts of mafic gneiss and schist (metagreenstones). The concept of the "Betsimisaraka suture" is dispelled and the zone is redefined as a domain of Neoproterozoic metasedimentary (Manampotsy Group) and metaigneous rocks (Itsindro-Imorona Suite) formed during a period of continental extension and intrusive igneous activity between 840 and 760 Ma. Younger orogenic convergence (560-520 Ma) resulted in east-directed overthrusting throughout south Madagascar and steepening with local inversion of the domain in central Madagascar. Along part of its length, the Manampotsy Group covers the boundary between the eastern and central Archean domains and is overprinted by the Angavo-Ifanadiana high-strain zone that served as a zone of crustal weakness throughout Cretaceous to Recent times.

  12. Chemical transfers along slowly eroding catenas developed on granitic cratons in southern Africa

    Science.gov (United States)

    Khomo, Lesego; Bern, Carleton R.; Hartshorn, Anthony S.; Rogers, Kevin H.; Chadwick, Oliver A.

    2013-01-01

    A catena is a series of distinct but co-evolving soils arrayed along a slope. On low-slope, slowly eroding catenas the redistribution of mass occurs predominantly as plasma, the dissolved and suspended constituents in soil water. We applied mass balance methods to track how redistribution via plasma contributed to physical and geochemical differentiation of nine slowly eroding (~ 5 mm ky− 1) granitic catenas. The catenas were arrayed in a 3 × 3 climate by relief matrix and located in Kruger National Park, South Africa. Most of the catenas contained at least one illuviated soil profile that had undergone more volumetric expansion and less mass loss, and these soils were located in the lower halves of the slopes. By comparison, the majority of slope positions were eluviated. Soils from the wetter climates (550 and 730 mm precipitation yr− 1) generally had undergone greater collapse and lost more mass, while soils in the drier climate (470 mm yr− 1) had undergone expansion and lost less mass. Effects of differences in catena relief were less clear. Within each climate zone, soil horizon mass loss and strain were correlated, as were losses of most major elements, illustrating the predominant influence of primary mineral weathering. Nevertheless, mass loss and volumetric collapse did not become extreme because of the skeleton of resistant primary mineral grains inherited from the granite. Colloidal clay redistribution, as traced by the ratio of Ti to Zr in soil, suggested clay losses via suspension from catena eluvial zones. Thus illuviation of colloidal clays into downslope soils may be crucial to catena development by restricting subsurface flow there. Our analysis provides quantitative support for the conceptual understanding of catenas in cratonic landscapes and provides an endmember reference point in understanding the development of slowly eroding soil landscapes.

  13. A primitive mantle source for the Neoarchean mafic rocks from the Tanzania Craton

    Institute of Scientific and Technical Information of China (English)

    Y.A. Cook; I.V. Sanislav; J. Hammerli; T.G. Blenkinsop; P.H.G.M. Dirks

    2016-01-01

    Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.%MgO). This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modeling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf ¼ 32e35, Ti/Zr ¼ 107e147), producing flat REE and HFSE profiles [(La/Yb)pm ¼ 0.9 e1.3], with abundances of 3e10 times primitive mantle and with minor negative anomalies of Nb [(Nb/La)pm ¼ 0.6e0.8] and Th [(Th/La)pm ¼ 0.6e0.9]. Initial isotope compositions (3Nd) range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping w50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between w2830 and w2820 Ma; are compo-sitionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.

  14. Ultrahigh-temperature metamorphism under isobaric heating: New evidence from the North China Craton

    Science.gov (United States)

    Yang, Qiong-Yan; Santosh, M.; Tsunogae, Toshiaki

    2014-12-01

    The Khondalite Belt within Inner Mongolia Suture Zone (IMSZ) in the North China Craton (NCC) preserves evidence for extreme crustal metamorphism under ultra-high temperature (UHT) conditions at ca. 1.92 Ga, associated with the subduction-collision tectonics between the Yinshan and Ordos Blocks. Here we report a new locality in Hongsigou where cordierite- and spinel-bearing granulites record UHT metamorphism. The prograde, peak, and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as: Bt1 + Grt1 + Sil1 + Kfs1 + Pl1 + Ilm + Qtz1, Grt1 + Sil2 + Kfs2 + Pl2 + Spl + Ilm + Qtz2 + Liq, and Crd + Grt2 + Sil3 + Kfs2 + Pl2 + Ilm + Qtz2 respectively. The peak metamorphic conditions of the pelitic granulite were estimated as 930-1050 °C and 6.5-7.5 kbar based on pseudosection analysis in the system NCKFMASHTO, suggesting extreme thermal metamorphism. We report LA-ICPMS zircon U-Pb data from the granulite which show weighted mean 207Pb/206Pb age of 1881 ± 6.6 Ma, marking the timing of UHT metamorphism. Lu-Hf analyses of the zircons show εHf(t) values within a restricted range of -4.2 to 0.3 and together with Hf model ages, a Paleoproterozoic arc magmatic source is inferred for the detrital zircons. The estimated P-T path for the UHT granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory, different from the anti-clockwise P-T paths defined in earlier studies for the 1.92 Ga UHT rocks from the IMSZ. The younger age and the isobaric heating trajectory suggest that the Hongsigou UHT rocks are related to heat input from underplated mafic magmas following continental collision.

  15. Visualization of volumetric seismic data

    Science.gov (United States)

    Spickermann, Dela; Böttinger, Michael; Ashfaq Ahmed, Khawar; Gajewski, Dirk

    2015-04-01

    Mostly driven by demands of high quality subsurface imaging, highly specialized tools and methods have been developed to support the processing, visualization and interpretation of seismic data. 3D seismic data acquisition and 4D time-lapse seismic monitoring are well-established techniques in academia and industry, producing large amounts of data to be processed, visualized and interpreted. In this context, interactive 3D visualization methods proved to be valuable for the analysis of 3D seismic data cubes - especially for sedimentary environments with continuous horizons. In crystalline and hard rock environments, where hydraulic stimulation techniques may be applied to produce geothermal energy, interpretation of the seismic data is a more challenging problem. Instead of continuous reflection horizons, the imaging targets are often steep dipping faults, causing a lot of diffractions. Without further preprocessing these geological structures are often hidden behind the noise in the data. In this PICO presentation we will present a workflow consisting of data processing steps, which enhance the signal-to-noise ratio, followed by a visualization step based on the use the commercially available general purpose 3D visualization system Avizo. Specifically, we have used Avizo Earth, an extension to Avizo, which supports the import of seismic data in SEG-Y format and offers easy access to state-of-the-art 3D visualization methods at interactive frame rates, even for large seismic data cubes. In seismic interpretation using visualization, interactivity is a key requirement for understanding complex 3D structures. In order to enable an easy communication of the insights gained during the interactive visualization process, animations of the visualized data were created which support the spatial understanding of the data.

  16. Seismic properties of polyphase rocks

    Science.gov (United States)

    Wang, Qin

    2005-11-01

    Knowledge about the seismic properties of polyphase rocks is fundamental for interpreting seismic refraction and reflection data and for establishing lithospheric structure and composition models. This study aims to obtain more precise relationships between seismic properties of rocks and controlling factors (e.g., pressure, temperature, mineralogical and chemical compositions, microstructure of rocks), particularly for those rocks imprinted by ultrahigh-pressure (UHP) metamorphism. These relationships will be very helpful to extrapolate calculated and measured seismic properties of rocks to depths of interest and to engender interpretations relevant to petrological composition and tectonic process. An Internet Database of Rock Seismic Properties (DRSP) was set up and a Handbook of Seismic Properties of Minerals, Rocks and Ores was published. They comprise almost all data available in the literature during the past 4 decades and can serve as a convenient, comprehensive and concise information source on physical properties of rocks to the earth sciences and geotechnical communities. Statistical results of the DRSP reveal the dependence of seismic properties on density, porosity, humidity, and mineralogical and chemical compositions. Using 16 different averaging methods, we calculated P-wave velocities of 696 dry samples according to the volume fraction and elastic constants of each constituent mineral. Although only 22 common minerals were taken into account in the computation, the calculated P-wave velocities agree well with laboratory values measured at about 300 MPa, where most microcracks are closed and the mean Vp of a polymineralic rock is exclusively controlled by its modal composition. However, none of these mixture rules can simultaneously fit measured P-wave velocities for all lithologies or at all pressures. Therefore, more prudence is required in selecting an appropriate mixture rule for calculation of seismic velocities of different rock types.

  17. Integrated geologic and geophysical studies of North American continental intraplate seismicity

    Science.gov (United States)

    Van Lanen, X.; Mooney, W.D.

    2007-01-01

    The origin of earthquakes within stable continental regions has been the subject of debate over the past thirty years. Here, we examine the correlation of North American stable continental region earthquakes using five geologic and geophysical data sets: (1) a newly compiled age-province map; (2) Bouguer gravity data; (3) aeromagnetic anomalies; (4) the tectonic stress field; and (5) crustal structure as revealed by deep seismic-reflection profiles. We find that: (1) Archean-age (3.8-2.5 Ga) North American crust is essentially aseismic, whereas post-Archean (less than 2.5 Ga) crust shows no clear correlation of crustal age and earthquake frequency or moment release; (2) seismicity is correlated with continental paleorifts; and (3) seismicity is correlated with the NE-SW structural grain of the crust of eastern North America, which in turn reflects the opening and closing of the proto- and modern Atlantic Ocean. This structural grain can be discerned as clear NE-SW lineaments in the Bouguer gravity and aeromagnetic anomaly maps. Stable continental region seismicity either: (1) follows the NE-SW lineaments; (2) is aligned at right angles to these lineaments; or (3) forms clusters at what have been termed stress concentrators (e.g., igneous intrusions and intersecting faults). Seismicity levels are very low to the west of the Grenville Front (i.e., in the Archean Superior craton). The correlation of seismicity with NE-SW-oriented lineaments implies that some stable continental region seismicity is related to the accretion and rifting processes that have formed the North American continental crust during the past 2 b.y. We further evaluate this hypothesis by correlating stable continental region seismicity with recently obtained deep seismic-reflection images of the Appalachian and Grenville crust of southern Canada. These images show numerous faults that penetrate deep (40 km) into the crust. An analysis of hypocentral depths for stable continental region earthquakes

  18. Shear Wave Velocity Structure of Southern African Crust: Evidence for Compositional Heterogeneity within Archaean and Proterozoic Terrains

    Energy Technology Data Exchange (ETDEWEB)

    Kgaswane, E M; Nyblade, A A; Julia, J; Dirks, P H H M; Durrheim, R J; Pasyanos, M E

    2008-11-11

    Crustal structure in southern Africa has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities for 89 broadband seismic stations spanning much of the Precambrian shield of southern Africa. 1-D shear wave velocity profiles obtained from the inversion yield Moho depths that are similar to those reported in previous studies and show considerable variability in the shear wave velocity structure of the lower part of the crust between some terrains. For many of the Archaean and Proterozoic terrains in the shield, S velocities reach 4.0 km/s or higher over a substantial part of the lower crust. However, for most of the Kimberley terrain and adjacent parts of the Kheis Province and Witwatersrand terrain, as well as for the western part of the Tokwe terrain, mean shear wave velocities of {le} 3.9 km/s characterize the lower part of the crust along with slightly ({approx}5 km) thinner crust. These findings indicate that the lower crust across much of the shield has a predominantly mafic composition, except for the southwest portion of the Kaapvaal Craton and western portion of the Zimbabwe Craton, where the lower crust is intermediate-to-felsic in composition. The parts of the Kaapvaal Craton underlain by intermediate-to-felsic lower crust coincide with regions where Ventersdorp rocks have been preserved, and thus we suggest that the intermediate-to-felsic composition of the lower crust and the shallower Moho may have resulted from crustal melting during the Ventersdorp tectonomagmatic event at c. 2.7 Ga and concomitant crustal thinning caused by rifting.

  19. Newberry Seismic Deployment Fieldwork Report

    Energy Technology Data Exchange (ETDEWEB)

    Wang, J; Templeton, D C

    2012-03-21

    This report summarizes the seismic deployment of Lawrence Livermore National Laboratory (LLNL) Geotech GS-13 short-period seismometers at the Newberry Enhanced Geothermal System (EGS) Demonstration site located in Central Oregon. This Department of Energy (DOE) demonstration project is managed by AltaRock Energy Inc. AltaRock Energy had previously deployed Geospace GS-11D geophones at the Newberry EGS Demonstration site, however the quality of the seismic data was somewhat low. The purpose of the LLNL deployment was to install more sensitive sensors which would record higher quality seismic data for use in future seismic studies, such as ambient noise correlation, matched field processing earthquake detection studies, and general EGS microearthquake studies. For the LLNL deployment, seven three-component seismic stations were installed around the proposed AltaRock Energy stimulation well. The LLNL seismic sensors were connected to AltaRock Energy Gueralp CMG-DM24 digitizers, which are powered by AltaRock Energy solar panels and batteries. The deployment took four days in two phases. In phase I, the sites were identified, a cavity approximately 3 feet deep was dug and a flat concrete pad oriented to true North was made for each site. In phase II, we installed three single component GS-13 seismometers at each site, quality controlled the data to ensure that each station was recording data properly, and filled in each cavity with native soil.

  20. seismicity and seismotectonics of Libya

    Science.gov (United States)

    Ben Suleman, abdunnur

    2015-04-01

    Libya, located at the central Mediterranean margin of the African shield, underwent many episodes of orogenic activity that shaped its geological setting. The present day deformation of Libya is the result of the Eurasia-Africa continental collision. The tectonic evolution of Libya has yielded a complex crustal structure that is composed of a series of basins and uplifts. This study aims to explain in detail the seismicity and seismotectonics of Libya using new data recorded by the recently established Libyan National Seismograph Network (LNSN) incorporating other available geophysical and geological information. Detailed investigations of the Libyan seismicity indicates that Libya has experienced earthquakes of varying magnitudes The seismic activity of Libya shows dominant trends of Seismicity with most of the seismic activity concentrated along the northern coastal areas. Four major clusters of Seismicity were quit noticeable. Fault plane solution was estimated for 20 earthquakes recorded by the Libyan National Seismograph Network in northwestern and northeastern Libya. Results of fault plane solution suggest that normal faulting was dominant in the westernmost part of Libya; strike slip faulting was dominant in northern-central part of Libya. The northern-eastern part of the country suggests that dip-dip faulting were more prevalent.

  1. Seismic stratigraphy of the Bahamas

    Energy Technology Data Exchange (ETDEWEB)

    Ladd, J.W.; Sheridan, R.E.

    1987-06-01

    Seismic reflection profiles from the Straits of Florida, Northwest Providence Channel, Tongue of the Ocean, and Exuma Sound reveal a seismic stratigraphy characterized by a series of prograding Upper Cretaceous and Tertiary seismic sequences with seismic velocities generally less than 4 km/sec overlying a Lower Cretaceous section of low-amplitude reflections which are more nearly horizontal than the overlying prograding clinoforms and have seismic velocities greater than 5 km/sec. The prograding units are detrital shallow-water carbonates shed from nearby carbonate banks into deep intrabank basins that were established in the Late Cretaceous. The Lower Cretaceous units are probably shallow-water carbonate banks that were drowned in the middle Cretaceous but which, during the Early Cretaceous, extended from Florida throughout the Bahamas region. The seismic reflection profiles reveal a sharp angular unconformity at 5-sec two-way traveltime in northwest Tongue of the Ocean, suggesting a rift-drift unconformity and deposition on thinned continental crust. No such unconformity is seen in central and southeast Tongue of the Ocean or in Exuma Sound, suggesting that these areas are built on oceanic crust.

  2. Seismic risk perception in Italy

    Science.gov (United States)

    Crescimbene, Massimo; La Longa, Federica; Camassi, Romano; Pino, Nicola Alessandro; Peruzza, Laura

    2014-05-01

    Risk perception is a fundamental element in the definition and the adoption of preventive counter-measures. In order to develop effective information and risk communication strategies, the perception of risks and the influencing factors should be known. This paper presents results of a survey on seismic risk perception in Italy conducted from January 2013 to present . The research design combines a psychometric and a cultural theoretic approach. More than 7,000 on-line tests have been compiled. The data collected show that in Italy seismic risk perception is strongly underestimated; 86 on 100 Italian citizens, living in the most dangerous zone (namely Zone 1), do not have a correct perception of seismic hazard. From these observations we deem that extremely urgent measures are required in Italy to reach an effective way to communicate seismic risk. Finally, the research presents a comparison between groups on seismic risk perception: a group involved in campaigns of information and education on seismic risk and a control group.

  3. Seismicity of the Jalisco Block

    Science.gov (United States)

    Nunez-Cornu, F. J.; Rutz, M.; Camarena-Garcia, M.; Trejo-Gomez, E.; Reyes-Davila, G.; Suarez-Plascencia, C.

    2002-12-01

    In April 2002 began to transmit the stations of the first phase of Jalisco Telemetric Network located at the northwest of Jalisco Block and at the area of Volcan de Fuego (Colima Volcano), in June were deployed four additional MarsLite portable stations in the Bahia de Banderas area, and by the end of August one more portable station at Ceboruco Volcano. The data of these stations jointly with the data from RESCO (Colima Telemetric Network) give us the minimum seismic stations coverage to initiate in a systematic and permanent way the study of the seismicity in this very complex tectonic region. A preliminary analysis of seismicity based on the events registered by the networks using a shutter algorithm, confirms several important features proposed by microseismicity studies carried out between 1996 and 1998. A high level of seismicity inside and below of Rivera plate is observed, this fact suggest a very complex stress pattern acting on this plate. Shallow seismicity at south and east of Bahia de Banderas also suggest a complex stress pattern in this region of the Jalisco Block, events at more than 30 km depth are located under the mouth of the bay and in face of it, a feature denominated Banderas Boundary mark the change of the seismic regime at north of this latitude (20.75°N), however some shallow events were located at the region of Nayarit.

  4. Seismic pattern treatment method through calculation of seismic density at grid nodes

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Analysis of seismic data and seismicity characteristics in China, we gave a method to deal with seismic patterns by calculating density at grid nodes. Number of earthquakes and epicenter distribution are considered comprehen-sively in this method. Effect of datum accuracy is stressed on parameter confirmation. Seismic patterns from this method are stable and can reflect seismic characteristics reliably. These seismic patterns are the base of quantita-tive analysis of seismicity. It can be applied in seismic tendency analysis and medium-long term earthquake pre-diction, earthquake countermeasure and risk mitigation.

  5. Assessment of Undiscovered Petroleum Resources of the North and East Margins of the Siberian Craton, Russian Federation

    Science.gov (United States)

    Klett, T.R.

    2008-01-01

    Four geologic provinces located along the north and east margins of the Siberian craton were assessed for undiscovered crude oil, natural gas, and natural gas liquids/condensates resources as part of the U.S. Geological Survey's (USGS) Circum-Arctic Oil and Gas Resource Appraisal. Using a geology-based methodology, the USGS estimated the mean undiscovered, conventional petroleum resources in these provinces to be approximately 28 billion barrels of oil equivalent, including approximately 8 billion barrels of crude oil, 106 trillion cubic feet of natural gas, and 3 billion barrels of natural gas liquids.

  6. REE geochemistry of auriferous quartz carbonate veins of Neoarchean Ajjanahalli gold deposit, Chitradurga schist belt, Dharwar Craton, India

    Directory of Open Access Journals (Sweden)

    S. Sarangi

    2013-03-01

    Full Text Available REE composition of the carbonates of the auriferous quartz carbonate veins (QCVs of the Neoarchean Ajjanahalli gold deposit, Chitradurga schist belt, Dharwar Craton, is characterized by U-shaped chondrite normalized REE patterns with both LREE and HREE enrichment and a distinct positive Eu anomaly. As positive Eu anomaly is associated with low oxygen fugacity, we propose that the auriferous fluids responsible for gold mineralization at Ajjanahalli could be from an oxygen depleted fluid. The observed positive Eu anomaly is interpreted to suggest the derivation of the auriferous fluids from a mantle reservoir. The location of Ajjanahalli gold deposit in a crustal scale shear zone is consistent with this interpretation.

  7. Discussion: The timing of gold mineralization across the eastern Yilgarn Craton using U-Pb geochronology of hydrothermal phosphate minerals

    Science.gov (United States)

    Bateman, Roger; Jones, Sarah

    2015-10-01

    The presentation of recent geochronological work on orogenic gold deposits in the Eastern Goldfields of the Yilgarn Craton, Western Australia, claims to prove that there is a single broad event of gold mineralization and that structural work demonstrating that there are a number of discrete gold mineralization events is wrong. This new data demonstrates no such thing, as this data, no doubt the best that can currently be produced, shows a very wide and inconsistent range in ages. Geochronology is not yet able to reliably separate these events, which appear to be spread over an interval of perhaps 30 Ma, up to ˜2635 Ma.

  8. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: Occurrence of Archean oceanic plateau

    Science.gov (United States)

    El Atrassi, Fatima; Debaille, Vinciane; Mattielli, Nadine; Berger, Julien

    2015-04-01

    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African craton in Mauritania (Amsaga area). The Amsaga Archean crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. We report the results of a combined petrologic, Sm-Nd isotopic, major element and rare earth element (REE) study of the Archean amphibolites in the West African craton. This study was conducted in order to characterize these rocks, to constrain the time of their formation and to evaluate their tectonic setting and their possible mantle source. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. They are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. These amphibolites have tholeiitic basalt composition. On a primitive mantle-normalized diagram, they display fairly flat patterns without negative anomalies for either Eu or Nb-Ta. We have shown using Sm-Nd whole rock isotopic data that these amphibolites formed at 3.3 ±0.075 Ga. They have positive ɛNdi values (+5.2 ± 1.6). These samples show isotopically juvenile features, which rule out the possibility of significant contamination of the protolith magmas by ancient continental crust. Based on these geochemical data we propose that the tholeiitic basalts were formed in an oceanic plateau tectonic setting from a mantle plume source and that they have a

  9. Hyperspectral imaging spectroscopy of a Mars analogue environment at the North Pole Dome, Pilbara Craton, Western Australia

    CERN Document Server

    Brown, Adrian J; Cudahy, Thomas

    2014-01-01

    A visible and near infrared (VNIR) to shortwave infrared (SWIR) hyperspectral dataset of the Early Archaean North Pole Dome, Pilbara Craton, Western Australia, has been analysed for indications of hydrothermal alteration. Occurrence maps of hydrothermal alteration minerals were produced. It was found that using a spatial resolution on the ground of approximately 5 m and spectral coverage from 0.4 to 2.5 mm was sufficient to delineate several hydrothermal alteration zones and associated veins, including phyllic, serpentinitic and chloritic alteration. These results suggest this level of spectral and spatial resolution would be ideal for localising shallow epithermal activity, should such activity have existed, on the surface of Mars.

  10. Modern-style Subduction Processes in the Archean:Evidence from the Shangyi Complex in North China Craton

    Institute of Scientific and Technical Information of China (English)

    WANG Renmin; WAN Yusheng; CHENG Suhua; FENG Yonggang

    2009-01-01

    Three fragments of the Arehean oceanic crust have been found between the Archean granulite belt and the Paleo-Proterozoic Hongqiyingzi group in North China craton,which spread and geochronology evidence of the ancient oceanic fragments.The magma crystallizing age of the tonalite in the Shangyi complex is 2512+19 Ma and the geochemical characteristics suggest that the Nb-enriched basalts may be related to crustal contamination and formed in the intra-oceanic arc of the supra subduction zone setting.

  11. Brittle Deformation in the Ordos Basin in response to the Mesozoic destruction of the North China Craton

    Science.gov (United States)

    Wang, Q.; Jiang, L.

    2012-12-01

    Craton is continental block that has been tectonically stable since at least Proterozoic. Some cratons, however, become unstable for some geodynamic reasons. The North China Craton (NCC) is an example. Structure geological, geochemical, and geophysical works have revealed that the NCC was destructed in Cretaceous and that lithosphere thickness beneath the eastern NCC were thinned by 120 km. The present study will focus on deformation of the western NCC, and to understand the effect of the Mesozoic destruction of the North China Craton (NCC). Structural partitioning of the Ordos Basin, which is located in the western NCC, from the eastern NCC occurred during the Mesozoic. Unlike the eastern NCC where many Cretaceous metamorphic core complexes developed, sedimentary cover of the NCC remains nearly horizontal and deformation is manifested by joint. We visited 216 sites of outcrops and got 1928 joints measurements, among which 270 from Jurassic sandstones, 1378 from the Upper Triassic sandstones, 124 from the Middle and Lower Triassic sandstones, and 156 from Paleozoic sandstones. In the interior of the Ordos Basin, joints developed quite well in the Triassic strata, while joints in the Jurassic stata developed weakly and no joint in the Cretaceous strata. The Mesozoic stratigraphic thickness are: 1000 meters for the Lower Triassic, the Middle Triassic sandstone with thickness of 800 meters, 3000 meters for the Upper Triassic, 4000 meters for the Jurassic, and 1100 meters for the Lower Cretaceous. The vertical difference in joint development might be related to the burying depth of the strata: the higher the strata, the smaller the lithostatic stress, and then the weaker the joint. Joints in all stratigraphic levels showed a similar strain direction with the sigma 1 (the maximum pressure stress) vertical and the sigma 3 (the minimum pressure stress) horizontal and running N-S. The unconformity below the Cretaceous further indicates that joints in Jurassic and Triassic

  12. Petrogenesis and Tectonic Implications of Paleoproterozoic Metapelitic Rocks in the Archean Kongling Complex from the Northern Yangtze Craton, South China

    Science.gov (United States)

    Li, Y.; Zheng, J.; Wang, W.; Xiong, Q.

    2015-12-01

    The Archean Kongling Complex in the northern Yangtze Craton is an ideal target to investigate the Precambrian accretion and evolution of continental crust in South China. This study aims to unravel the crustal evolution and tectonic setting of the Yangtze Craton during the Paleoproterozoic time, using integrated studies of petrography, zircon U-Pb and Hf isotopes and whole-rock geochemistry of Paleoproterozoic metapelitic rocks in the Kongling Complex. These rocks contain garnet, sillimanite, biotite, plagioclase, minor graphite and ilmenite. Zircons from the samples show nebulous sector-zoning and rim-core structure, suggesting both metamorphic origin and detrital origin with metamorphic overprints. The metamorphic zircons and metamorphic overprints have concordant 207Pb/206Pb age at ~2.0 Ga, while detrital grains yield three distinct concordant-age populations of >2.5 Ga, 2.4-2.2 Ga and 2.2-2.1 Ga. The age patterns indicate that the depositional age of the metasedimentary rocks was 2.1-2.0 Ga. Those 2.2-2.1 Ga detrital zircons with variable ɛHf(t) values (-7.28 to 2.97) suggest the addition of juvenile materials from depleted mantle to the crust during 2.2-2.1 Ga. The 2.4-2.2 Ga zircons have Hf model ages (TDM2) of ~2.6-3.5 Ga and >2.5 Ga zircons have TDM2 ages varying from 2.9 Ga to 3.3 Ga. The new data suggest that the Kongling Complex was originally a Paleoarchean (old up to 3.5 Ga) continental nucleus, which experienced multiple episodes of growth and reworking events at 3.3-3.2 Ga, 2.9 Ga, 2.7-2.6 Ga, 2.4-2.2 Ga and 2.2-2.1 Ga. In combination with available data, the new results in this study suggest a continent-arc-continent evolution model to explain the tectonic evolution of the Yangtze Craton during the Paleoproterozoic time: the western margin of Yangtze Craton was originally an individual continent, which underwent a reworking event during 2.4-2.2 Ga and a crust growth event caused by continent-arc collision during 2.2-2.1 Ga; it subsequently collided

  13. Romanian Educational Seismic Network Project

    Science.gov (United States)

    Tataru, Dragos; Ionescu, Constantin; Zaharia, Bogdan; Grecu, Bogdan; Tibu, Speranta; Popa, Mihaela; Borleanu, Felix; Toma, Dragos; Brisan, Nicoleta; Georgescu, Emil-Sever; Dobre, Daniela; Dragomir, Claudiu-Sorin

    2013-04-01

    Romania is one of the most active seismic countries in Europe, with more than 500 earthquakes occurring every year. The seismic hazard of Romania is relatively high and thus understanding the earthquake phenomena and their effects at the earth surface represents an important step toward the education of population in earthquake affected regions of the country and aims to raise the awareness about the earthquake risk and possible mitigation actions. In this direction, the first national educational project in the field of seismology has recently started in Romania: the ROmanian EDUcational SEISmic NETwork (ROEDUSEIS-NET) project. It involves four partners: the National Institute for Earth Physics as coordinator, the National Institute for Research and Development in Construction, Urban Planning and Sustainable Spatial Development " URBAN - INCERC" Bucharest, the Babeş-Bolyai University (Faculty of Environmental Sciences and Engineering) and the software firm "BETA Software". The project has many educational, scientific and social goals. The main educational objectives are: training students and teachers in the analysis and interpretation of seismological data, preparing of several comprehensive educational materials, designing and testing didactic activities using informatics and web-oriented tools. The scientific objective is to introduce into schools the use of advanced instruments and experimental methods that are usually restricted to research laboratories, with the main product being the creation of an earthquake waveform archive. Thus a large amount of such data will be used by students and teachers for educational purposes. For the social objectives, the project represents an effective instrument for informing and creating an awareness of the seismic risk, for experimentation into the efficacy of scientific communication, and for an increase in the direct involvement of schools and the general public. A network of nine seismic stations with SEP seismometers

  14. Crustal Structure Across the Okavango Rift Zone, Botswana: Initial Results From the PRIDE-SEISORZ Active-Source Seismic Profile

    Science.gov (United States)

    Canales, J. P.; Moffat, L.; Lizarralde, D.; Laletsang, K.; Harder, S. H.; Kaip, G.; Modisi, M.

    2015-12-01

    The PRIDE project aims to understand the processes of continental rift initiation and evolution by analyzing along-axis trends in the southern portion of the East Africa Rift System, from Botswana through Zambia and Malawi. The SEISORZ active-source seismic component of PRIDE focused on the Okavango Rift Zone (ORZ) in northwestern Botswana, with the main goal of imaging the crustal structure across the ORZ. This will allow us to estimate total crustal extension, determine the pattern and amount of thinning, assess the possible presence of melt within the rift zone, and assess the contrasts in crustal blocks across the rift, which closely follows the trend of a fold belt. In November 2014 we conducted a crustal-scale, 450-km-long seismic refraction/wide-angle reflection profile consisting of 19 sources (shots in 30-m-deep boreholes) spaced ~25 km apart from each other, and 900 receivers (IRIS/PASSCAL "Texan" dataloggers and 4.5Hz geophones) with ~500 m spacing. From NW to SE, the profile crosses several tectonic domains: the Congo craton, the Damara metamorphic belt and the Ghanzi-Chobe fold belt where the axis of the ORZ is located, and continues into the Kalahari craton. The record sections display clear crustal refraction (Pg) and wide-angle Moho reflection (PmP) phases for all 17 of the good-quality shots, and a mantle refraction arrival (Pn), with the Pg-PmP-Pn triplication appearing at 175 km offset. There are distinct changes in the traveltime and amplitude of these phases along the transect, and on either side of the axis, that seem to correlate with sharp transitions across tectonic terrains. Initial modeling suggests: (1) the presence of a sedimentary half-graben structure at the rift axis beneath the Okavango delta, bounded to the SE by the Kunyere-Thamalakane fault system; (2) faster crustal Vp in the domains to the NW of the ORZ; and (3) thicker crust (45-50 km) at both ends of the profile within the Congo and Kalahari craton domains than at the ORZ and

  15. Seismic failure modes and seismic safety of Hardfill dam

    Directory of Open Access Journals (Sweden)

    Kun XIONG

    2013-04-01

    Full Text Available Based on microscopic damage theory and the finite element method, and using the Weibull distribution to characterize the random distribution of the mechanical properties of materials, the seismic response of a typical Hardfill dam was analyzed through numerical simulation during the earthquakes with intensities of 8 degrees and even greater. The seismic failure modes and failure mechanism of the dam were explored as well. Numerical results show that the Hardfill dam remains at a low stress level and undamaged or slightly damaged during an earthquake with an intensity of 8 degrees. During overload earthquakes, tensile cracks occur at the dam surfaces and extend to inside the dam body, and the upstream dam body experiences more serious damage than the downstream dam body. Therefore, under the seismic conditions, the failure pattern of the Hardfill dam is the tensile fracture of the upstream regions and the dam toe. Compared with traditional gravity dams, Hardfill dams have better seismic performance and greater seismic safety.

  16. Is subduction really in the plate tectonics driving seat, or do two other global mechanisms do the driving? A review in the 'deep-keeled cratons' frame for global dynamics

    Science.gov (United States)

    Osmaston, M. F.

    2012-04-01

    of the upper mantle? Nature 319, 309-310. [7] Hirth G. & Kohlstedt D. L. (1996) Water in the oceanic upper mantle: implication for rheology, melt extraction, and the evolution of the lithosphere. EPSL 144, 93-108. [8] Osmaston M. F. (2010) On the actual variety of plate dynamical mechanisms and how mantle evolution affected them through time, from core formation to the Indian collision. Geophys. Res. Abstr. 12, EGU2010-6101. [9] Osmaston M. F. (1995) A straightness mechanism for MORs: a new view of ocean plate genesis and evolution XXI IUGG, Abstracts p. A472. [10] Osmaston M. (2005) The ridge push mechanism of MORs as the agent of seismic coupling, tsunami, convergence partitioning and landward thrusting at subduction zones; insights on an interactive family of mostly-jerky mechanisms. IASPEI 2005 Gen. Assy, Santiago, Chile, Abstr. No 303. [11] Osmaston M. F. (2008) Basal subduction tectonic erosion (STE), butter mélanges and the construction and exhumation of HP-UHP belts: the Alps example and some comparisons. Internat. Geol. Rev. 50(8), 685-754 DOI: 10.2747/00206814.50.8.685. [12] Osmaston M. F. (2012) Did clockwise rotation of Antarctica cause the break-up of Gondwanaland? An investigation in the 'deep-keeled cratons' frame for global dynamics. GD6.1. Geophys. Res. Abstr. 14, EGU2012-2170.

  17. Comparison of mantle-derived matierals from different spatiotemporal settings: Implications for destructive and accretional processes of the North China Craton

    Institute of Scientific and Technical Information of China (English)

    ZHENG JianPing

    2009-01-01

    Cratonic destruction or lithospheric thinning beneath North China makes it as one of the most ideal areas for the studying on the formation and evolution of continent. However, the mechanism, time, range and dynamic setting of the destruction, even the lithospheric status before the destruction, are contentious. The comparison among mantle xenoliths in the volcanic rocks from different captured times (e.g. Paleozoic, Mesozoic and Cenozoic) and locations (e.g. Intra-plate or its rim, the translithospheric Tanlu fault or the North-South Gravity Line), and peridotitic massifs within the Sulu-Dabie ultrahigh-pressure metamorphism belt along the southern margin of the North China Craton, indicates that (1) the cratonic lithosphere is heterogeneous in structure and composition, and contains mantle weak zones; and (2) the Mesozoic-Cenozoic lithospheric thinning process is complex, including lateral spreading of lithosphere, interaction between melt and peridotite, non-even asthenospheric erosion (huge lithospheric thinning), and the limited lithospheric accretion and thus thickening, which resulted in the final replacement of the refractory cratonic lithosphere by juvenile fertile mantle. In early Mesozoic, the integrity of the North China Craton was interrupted, even destroyed by subduction and collision of the Yangtze block. The mantle wedge of the North China Craton was also metasomatized and modified by melt/fluids revealed from the subducted Yangtze continent. Lithospheric mantle extension and tectonic intrusion of the North China Craton also occurred, accompanied by the asthenospheric upwelling that due to the detachement of the subducted Yangtze continent (orogenic root). During early Cretaceous-early Tertiary, the huge thinning of lithosphere was triggered by the upwelling asthenosphere due to the subduction of the Pacific plate. Since late Tertiary, the cooling of the upwelling asthenosphere resulted in the replacement of the mantle in existence by the newly

  18. National Seismic Network of Georgia

    Science.gov (United States)

    Tumanova, N.; Kakhoberashvili, S.; Omarashvili, V.; Tserodze, M.; Akubardia, D.

    2016-12-01

    Georgia, as a part of the Southern Caucasus, is tectonically active and structurally complex region. It is one of the most active segments of the Alpine-Himalayan collision belt. The deformation and the associated seismicity are due to the continent-continent collision between the Arabian and Eurasian plates. Seismic Monitoring of country and the quality of seismic data is the major tool for the rapid response policy, population safety, basic scientific research and in the end for the sustainable development of the country. National Seismic Network of Georgia has been developing since the end of 19th century. Digital era of the network started from 2003. Recently continuous data streams from 25 stations acquired and analyzed in the real time. Data is combined to calculate rapid location and magnitude for the earthquake. Information for the bigger events (Ml>=3.5) is simultaneously transferred to the website of the monitoring center and to the related governmental agencies. To improve rapid earthquake location and magnitude estimation the seismic network was enhanced by installing additional 7 new stations. Each new station is equipped with coupled Broadband and Strong Motion seismometers and permanent GPS system as well. To select the sites for the 7 new base stations, we used standard network optimization techniques. To choose the optimal sites for new stations we've taken into account geometry of the existed seismic network, topographic conditions of the site. For each site we studied local geology (Vs30 was mandatory for each site), local noise level and seismic vault construction parameters. Due to the country elevation, stations were installed in the high mountains, no accessible in winter due to the heavy snow conditions. To secure online data transmission we used satellite data transmission as well as cell data network coverage from the different local companies. As a result we've already have the improved earthquake location and event magnitudes. We

  19. A study on seismicity and seismic hazard for Karnataka State

    Indian Academy of Sciences (India)

    T G Sitharam; Naveen James; K S Vipin; K Ganesha Raj

    2012-04-01

    This paper presents a detailed study on the seismic pattern of the state of Karnataka and also quantifies the seismic hazard for the entire state. In the present work, historical and instrumental seismicity data for Karnataka (within 300 km from Karnataka political boundary) were compiled and hazard analysis was done based on this data. Geographically, Karnataka forms a part of peninsular India which is tectonically identified as an intraplate region of Indian plate. Due to the convergent movement of the Indian plate with the Eurasian plate, movements are occurring along major intraplate faults resulting in seismic activity of the region and hence the hazard assessment of this region is very important. Apart from referring to seismotectonic atlas for identifying faults and fractures, major lineaments in the study area were also mapped using satellite data. The earthquake events reported by various national and international agencies were collected until 2009. Declustering of earthquake events was done to remove foreshocks and aftershocks. Seismic hazard analysis was done for the state of Karnataka using both deterministic and probabilistic approaches incorporating logic tree methodology. The peak ground acceleration (PGA) at rock level was evaluated for the entire state considering a grid size of 0.05° × 0.05°. The attenuation relations proposed for stable continental shield region were used in evaluating the seismic hazard with appropriate weightage factors. Response spectra at rock level for important Tier II cities and Bangalore were evaluated. The contour maps showing the spatial variation of PGA values at bedrock are presented in this work.

  20. Seismic behaviour of geotechnical structures

    Directory of Open Access Journals (Sweden)

    F. Vinale

    2002-06-01

    Full Text Available This paper deals with some fundamental considerations regarding the behaviour of geotechnical structures under seismic loading. First a complete definition of the earthquake disaster risk is provided, followed by the importance of performing site-specific hazard analysis. Then some suggestions are provided in regard to adequate assessment of soil parameters, a crucial point to properly analyze the seismic behaviour of geotechnical structures. The core of the paper is centered on a critical review of the analysis methods available for studying geotechnical structures under seismic loadings. All of the available methods can be classified into three main classes, including the pseudo-static, pseudo-dynamic and dynamic approaches, each of which is reviewed for applicability. A more advanced analysis procedure, suitable for a so-called performance-based design approach, is also described in the paper. Finally, the seismic behaviour of the El Infiernillo Dam was investigated. It was shown that coupled elastoplastic dynamic analyses disclose some of the important features of dam behaviour under seismic loading, confirmed by comparing analytical computation and experimental measurements on the dam body during and after a past earthquake.

  1. Geophysical Character and Geochemical Evolution of the Mesoproterozoic Figueira Branca Intrusive Suite, SW Amazon Craton (Brazil)

    Science.gov (United States)

    Louro, Vinicius; Cawood, Peter; Mantovani, Marta

    2016-04-01

    The Jauru Terrain hosts the Figueira Branca Intrusive Suite (FBS) in the SW of the Amazon Craton (Brazil). The FBS is a series of 1425 Ma layered mafic intrusions, previously interpreted as anorogenic. The FBS area is located in foreland to the Santa Helena orogen, formed by the subduction of the Rio Alegre Terrain under the Jauru Terrain. Potential field methods (magnetic and gravity), gamma-ray spectrometry, geochemical and isotope data were used to characterize and to model the extent of FBS magmatism, the distribution of faults and shear zones in the area, to evaluate affinities of the magmatic activity, and the relation between the FBS and the Santa Helena orogen. The geophysical methods identified three anomalies corresponding with FBS outcrops. A fourth anomaly with significantly higher amplitude was observed to the north of the three anomalies. From south to north, the anomalies were named Indiavaí, Azteca, Figueira Branca and Jauru. These anomalies were modeled and indicated a northwest-southeast trend, parallel to regional shear zones. The gamma-ray data enabled the collection of 50 samples from the FBS rocks, the Alto Jauru group that hosts the FBS, from nearby intrusive suites, and the Rio Alegre Terrain. The 30 freshest samples were analyzed by X-ray fluorescence for oxides and some trace elements, 20 by ICP-MS for Rare-Earth Elements and 10 for Nd-Sr isotope analyses. The FBS samples were gabbros and gabbro-norites with Nb/Yb-Th/Yb and TiO2/Yb-Nb/Yb ratios indicating varying degrees of crustal interaction. The TiO2/Yb-Nb/Yb data suggested a subduction related component and the ɛNd-ɛSr indicated a juvenile source. Samples from coeval adjacent intermediate magma suites displayed similar characteristics, which suggest derivation from a bimodal source probably related with the subduction of the Rio Alegre Terrain. We interpreted the tectonic setting of the FBS as a result of a roll-back of the subducted slab, which resulted in rejuvenation of the

  2. Tectono-metamorphic evolution of the Paleoproterozoic ultra-high temperatures Khondalite Belt, North China Craton.

    Science.gov (United States)

    Lobjoie, Cyril; Trap, Pierre; Lin, Wei; Goncalves, Philippe; Marquer, Didier

    2016-04-01

    In the North China Craton, the Khondalite belt is a famous Paleoproterozoic domain where ultra-high temperatures (UHT) metamorphism was extensively documented over an area of 1000 square kilometers. Numerous petrological analyses argue for P-T conditions around 0.6-0.8GPa for temperature above 900°C for peak metamorphism. Unfortunately, the scarcity of available structural data prevents any discussion about thermo-mechanical behavior of the orogenic crust suffering high thermal regime. In this contribution, we present a detail structural analysis of the Khondalite belt that allowed to distinguish two main deformation events, named D1 and D2. The deformation D1 led to the formation of the S1 foliation that dips weakly toward the South-East. S1 holds a N70°E trending mineral and stretching L1 lineation that is sub-horizontal or plunges weakly to the East. The D1 fabrics is reworked by the dextral transpressional D2 deformation responsible for the development of km-scale S2-C2-C'2 system. The N30°E trending S2 foliation is sub-vertical to highly dipping toward the East. Kilometer-scale C2 and C'2 shear zones are sub-vertical and trend N70°E and N90-100°E, respectively. Petrological study and phase diagram modeling suggest that both D1 and D2 developed at UHT conditions. Garnet and spinel-bearing migmatites recording D1 fabric yield 0.7GPa for ca. 950-1015°C P-T conditions. Within D2 shear zones, numerous granitoids and mafic bodies are injected. Mafic intrusions are responsible for UHT contact metamorphism that can occur at low pressure as recorded in an olivine-bearing migmatite. This may suggest that the D2 S-C-C' system form an interconnected network of kilometer scale shear zones that act as pathways for percolation of mafic magmas from the mantle up to the base of the upper crust. Our results allow to discuss the role of localized heat advection along crustal-scale shear zones as a possible mechanism responsible for UHT metamorphism at regional scale, with

  3. Multifractal spatial organisation in hydrothermal gold systems of the Archaean Yilgarn craton, Western Australia

    Science.gov (United States)

    Munro, Mark; Ord, Alison; Hobbs, Bruce

    2015-04-01

    A range of factors controls the location of hydrothermal alteration and gold mineralisation in the Earth's crust. These include the broad-scale lithospheric architecture, availability of fluid sources, fluid composition and pH, pressure-temperature conditions, microscopic to macroscopic structural development, the distribution of primary lithologies, and the extent of fluid-rock interactions. Consequently, the spatial distribution of alteration and mineralization in hydrothermal systems is complex and often considered highly irregular. However, despite this, do they organize themselves in a configuration that can be documented and quantified? Wavelets, mathematical functions representing wave-like oscillations, are commonly used in digital signals analysis. Wavelet-based multifractal analysis involves incrementally scanning a wavelet across the dataset multiple times (varying its scale) and recording its degree of fit to the signal at each interval. This approach (the wavelet transform modulus maxima method) highlights patterns of self-similarity present in the dataset and addresses the range of scales over which these patterns replicate themselves (expressed by their range in 'fractal dimension'). Focusing on seven gold ore bodies in the Archaean Yilgarn craton of Western Australia, this study investigates whether different aspects of hydrothermal gold systems evolve to organize themselves spatially as multifractals. Four ore bodies were selected from the Sunrise Dam deposit (situated in the Laverton tectonic zone of the Kurnalpi terrane) in addition to the Imperial, Majestic and Salt Creek gold prospects, situated in the Yindarlgooda dome of the Mount Monger goldfield (approximately 40km due east of Kalgoorlie). The Vogue, GQ, Cosmo East and Astro ore bodies at Sunrise Dam were chosen because they exhibit different structural geometries and relationships between gold and associated host-rock alteration styles. Wavelet-based analysis was conducted on 0.5m and 1m

  4. Paleoproterozoic andesitic volcanism in the southern Amazonian craton (northern Brazil); lithofacies analysis and geodynamic setting

    Science.gov (United States)

    Roverato, Matteo; Juliani, Caetano; Capra, Lucia; Dias Fernandes, Carlos Marcelo

    2016-04-01

    Precambrian volcanism played an important role in geological evolution and formation of new crust. Most of the literature on Precambrian volcanic rocks describes settings belonging to subaqueous volcanic systems. This is likely because subaerial volcanic rocks in Proterozoic and Archean volcano-sedimentary succession are poorly preserved due to erosive/weathering processes. The late Paleoproterozoic Sobreiro Formation (SF) here described, seems to be one of the rare exceptions to the rule and deserves particular attention. SF represents the subaerial expression of an andesitic magmatism that, linked with the upper felsic Santa Rosa F., composes the Uatumã Group. Uatumã Group is an extensive magmatic event located in the Xingú region, southwestern of Pará state, Amazonian Craton (northern Brazil). The Sobreiro volcanism is thought to be related to an ocean-continent convergent margin. It is characterized by ~1880 Ma well-preserved calc-alkaline basaltic/andesitic to andesitic lava flows, pyroclastic rocks and associated reworked successions. The superb preservation of its rock-textures allowed us to describe in detail a large variety of volcaniclastic deposits. We divided them into primary and secondary, depending if they result from a direct volcanic activity (pyroclastic) or reworked processes. Our study reinforces the importance of ancient volcanic arcs and rocks contribution to the terrestrial volcaniclastic sedimentation and evolution of plate tectonics. The volcanic activity that produced pyroclastic rocks influenced the amount of detritus shed into sedimentary basins and played a major role in the control of sedimentary dispersal patterns. This study aims to provide, for the first time, an analysis of the physical volcanic processes for the subaerial SF, based in field observation, lithofacies analysis, thin section petrography and less geochemical data. The modern volcanological approach here used can serve as a model about the evolution of Precambrian

  5. Large Calcium Isotopic Variation in Peridotitic Xenoliths from North China Craton

    Science.gov (United States)

    Huang, S.; Zhao, X.; Zhang, Z.

    2016-12-01

    Calcium is the fifth most abundant element in the Earth. The Ca isotopic composition of the Earth is important in many aspects, ranging from tracing the Ca cycle on the Earth to comparing the Earth to other terrestrial planets. There is large mass-dependent Ca isotopic variation, measured as δ44/40Ca relative to a standard sample, in terrestrial igneous rocks: about 2 per mil in silicate rocks, compared to 3 per mil in carbonates. Therefore, a good understanding of the Ca isotopic variation in igneous rocks is necessary. Here we report Ca isotopic data on a series of peridotitic xenoliths from North China Craton (NCC). There is about 1 per mil δ44/40Ca variation in these NCC peridotites: The highest δ44/40Ca is close to typical mantle values, and the lowest δ44/40Ca is found in an Fe-rich peridotite, -1.13 relative to normal mantle (or -0.08 on the SRM 915a scale). This represents the lowest δ44/40Ca value ever reported for igneous rocks. Combined with published Fe isotopic data on the same samples, our data show a positive linear correlation between δ44/40Ca and δ57/54Fe in NCC peridotites. This trend is inconsistent with mixing a low-δ44/40Ca and -δ57/54Fe sedimentary component with a normal mantle component. Rather, it is best explained as the result of kinetic isotopic effect caused by melt-peridotite reaction on a time scale of several hundreds of years. In detail, basaltic melt reacts with peridotite, replaces orthopyroxene with clinopyroxene, and increases the Fo number of olivine. Consistent with this interpretation, our on-going Mg isotopic study shows that low-δ44/40Ca and -δ57/54Fe NCC peridotites also have heavier Mg isotopes compared to normal mantle. Our study shows that mantle metasomatism plays an important role generating stable isotopic variations within the Earth's mantle.

  6. Paleoproterozoic crustal evolution of the Hengshan–Wutai–Fuping region, North China Craton

    Directory of Open Access Journals (Sweden)

    Chunjing Wei

    2014-07-01

    Full Text Available An arguable point regarding the Neoarchean and Paleoproterozoic crustal evolution of the North China Craton (NCC is whether the tectonic setting in the central belt during the mid-Paleoproterozoic (2.35–2.0 Ga was dominated by an extensional regime or an oceanic subduction–arc regime. A review of the mid-Paleoproterozoic magmatism and sedimentation for the Hengshan–Wutai–Fuping region suggests that a back-arc extension regime was dominant in this region. This conclusion is consistent with the observation that the 2.35–2.0 Ga magmatism shows a typical bimodal distribution where the mafic rocks mostly have arc affinities and the acidic rocks mainly comprise highly-fractioned calc-alkaline to alkaline (or A-type granites, and that this magmatism was coeval with development of extensional basins characteristic of transgressive sequences with volcanic interlayers such as in the Hutuo Group. Although the final amalgamation of the NCC was believed to occur at ∼1.85 Ga, recent zircon U–Pb age dating for mica schist in the Wutai Group suggests a collisional event may have occurred at ∼1.95 Ga. The metamorphic ages of ∼1.85 Ga, obtained mostly from the high-grade rocks using the zircon U–Pb approach, most probably indicate uplifting and cooling of these high-grade terranes. This is because (i phase modeling suggests that newly-grown zircon grains in high-grade rocks with a melt phase cannot date the age of peak pressure and temperature stages, but the age of melt crystallization in cooling stages; (ii the metamorphic P–T paths with isobaric cooling under 6–7 kb for the Hengshan and Fuping granulites suggest their prolonged stay in the middle–lower crust; and (iii the obtained metamorphic age data show a continuous distribution from 1.95 to 1.80 Ga. Thus, an alternative tectonic scenario for the Hengshan–Wutai–Fuping region involves: (i formation of a proto-NCC at ∼2.5 Ga; (ii back-arc extension during 2.35–2.0

  7. Fluid-induced martitization of magnetite in BIFs from the Dharwar Craton, India.

    Science.gov (United States)

    Wagner, Christiane; Orberger, Beate; Tudryn, Alina; Wirth, Richard; Morgan, Rachael

    2013-04-01

    Banded iron formations (BIFs) represent the largest iron deposits on Earth, which mainly formed in the Late Archean and Early Proterozoic. The complex geological history of BIFs makes it difficult to reconstruct the primary mineralogy and thus the initial depositional environment. Magnetite and hematite are the most important iron oxide minerals in BIFs. Magnetite (FeOFe2O3) comprising of both ferrous and ferric iron, easily undergoes transformation at low temperature. Hematite (α-Fe2O3) is often a result of the pseudomorphic replacement of magnetite, in the processus called martitisation. Despite the process of martitization having been widely studied, in both synthetic and natural magnetites, the mechanics of the transformation are poorly understood. What is generally agreed is that the transformation from magnetite to hematite occurs via a maghemite (g-Fe2O3) intermediate. The 2.9 Ga BIF from the Western Dharwar Craton, Southern India (a 500 m thick Archean BIF), is characterized by millimetric to centrimetric alternating white quartz and grey Fe-oxide bands. The Fe-oxide bands consist of martite crystals (~20µm) which represent the hematitisation of euhedral magnetite. The hematite crystals are in part euhedral, cubic shaped pointing to the replacement of magnetite. The crystals show a trellis pattern. Magnetite patches occur within the hematite. Raman spectroscopy, X-Ray diffraction, Curie balance and magnetic hysteresis analyses and FIB-TEM investigation indicate the presence of maghemite, and the presence of subhedral magnetite and interstitial hematite crystal. The latter are characterized by dislocation with fluid inclusions and high porosity zones. The magnetite grains contain lamellae and the interfaces between magnetite-maghemite and hematite are curved suggesting grain boundary migrations with the growth of hematite at the expense of magnetite and maghemite. It is thus suggested that martite result from low-T exsolutions along cleavage resulting in

  8. Provenance of zircon of the lowermost sedimentary cover, Estonia, East-European Craton

    Directory of Open Access Journals (Sweden)

    Konsa, M.

    1999-12-01

    Cambrian sequence, zircons resembling those of local basement sources are very rare or absent. Obviously, basal Vendian/Cambrian sedimentary rocks sealed off the basement as a source of zircon. Therefore a distant source, probably outside the Svecofennian Domain, could be supposed for the bulk clastic minerals and zircons of the upperpart of the Vendian and the lower part of the Cambrian. Probably, studies of isotopic ages of different typological varieties of zircons, both of obviously local and distant origin, could provide new information on respective source rock ages and areas, and on the general palaeogeographic pattern of the Vendian and Cambrian epicratonic sedimentary basins of the East-European Craton.

  9. Deciphering relative timing of fabric development in granitoids with similar absolute ages based on AMS study (Dharwar Craton, South India)

    Science.gov (United States)

    Bhatt, Sandeep; Rana, Virendra; Mamtani, Manish A.

    2017-01-01

    Anisotropy of Magnetic Susceptibility (AMS) data are presented from the Koppal Granitoid (Dharwar Craton, South India) that has U-Pb zircon age of 2528 ± 9 Ma. The magnetic fabric is oriented in NNE-SSW direction. This is parallel to the planar structures that developed during regional D3 deformation, but oblique to the NNW-SSE oriented magnetic foliation as well as field foliation (D1/D2 deformation) recorded in the country rock Peninsular Gneiss. Variation in the intensity of fabric within the granitoid is mapped. It is inferred that the emplacement of Koppal Granitoid took place by ballooning and fabric development within the pluton was syntectonic with regional D3. These results are compared with the time-relationship between emplacement/fabric development and regional deformation reported from the Mulgund Granite (2555 ± 6 Ma; U-Pb zircon), which is also located in the Dharwar Craton and is equivalent to the Koppal Granitoid in age. This granite is known to have emplaced syntectonically with regional D1/D2 deformation, and is thus not related to the same deformation event as the Koppal Granitoid, despite their similar absolute ages. It is argued that in the study area, D3 is ≤2537 Ma, while D1/D2 is ≥2549 Ma in age. Thus, this study highlights the use of AMS in (a) deciphering the relative timing of regional deformation and emplacement of granitoids of equivalent age and (b) constraining the timing of regional superposed deformation events.

  10. Paleoproterozoic high-pressure metamorphism in the northern North China Craton and implications for the Nuna supercontinent.

    Science.gov (United States)

    Wan, Bo; Windley, Brian F; Xiao, Wenjiao; Feng, Jianyun; Zhang, Ji'en

    2015-09-21

    The connection between the North China Craton (NCC) and contiguous cratons is important for the configuration of the Nuna supercontinent. Here we document a new Paleoproterozoic high-pressure (HP) complex dominated by garnet websterite on the northern margin of the NCC. The peak metamorphism of the garnet websterite was after ∼1.90 Ga when it was subducted to eclogite facies at ∼2.4 GPa, then exhumed back to granulite facies at ∼0.9 GPa before ∼1.82 Ga. The rock associations with their structural relationships and geochemical affinities are comparable to those of supra-subduction zone ophiolites, and supported by subduction-related signatures of gabbros and basalts. We propose that a ∼1.90 Ga oceanic fragment was subducted and exhumed into an accretionary complex along the northern margin of the NCC. Presence of the coeval Sharyzhalgai complex with comparable HP garnet websterites in the southern Siberian active margin favours juxtaposition against the NCC in the Paleoproterozoic.

  11. No coincidence? Exploring the connection between the Great Oxidation Event and craton stabilization during the Archean-Proterozoic transition

    Science.gov (United States)

    Kump, L. R.

    2014-12-01

    As geochronological constraints on the timing of the Great Oxidation Event (here defined as the passage of atmospheric oxygen levels through the proposed upper limit of 10-5 of present) have improved, it has become increasingly clear that this event is somehow tied to the tectonic factors that have defined the Archean-Proterozoic boundary for decades, namely the stabilization of continental cratons allowing for the growth of large continents. We have proposed two connections in the past: 1) elevated late Archean mantle plume activity brought oxidized material from the lithospheric graveyard to the upper mantle, reducing the oxygen fugacity of post-Archean volcanism, and 2) that the stabilization of the cratons allowed for a proportional increase in less-reducing, subaerial volcanism at the expense of more reducing, submarine volcanism. Critiques of these two proposals will be addressed in the context of subsequent work by the geosciences community on the geodynamics and geochemistry of the Archean-Proterozoic transition, and a synthetic hypothesis for a tectonic driver for atmospheric oxygenation will be presented.

  12. The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution

    Directory of Open Access Journals (Sweden)

    Ruiz Amarildo S.

    2004-01-01

    Full Text Available Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0. In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7. Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1 The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2 T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga continental margin. (3 The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time.

  13. Paleoproterozoic Greenstone-Granite Belts in Northern Brazil and the Former Guyana Shield - West African Craton Province

    Directory of Open Access Journals (Sweden)

    Ian McReath

    2006-03-01

    Full Text Available The mainly meta-volcano-sedimentary Vila Nova Group and associated granites constitute separate belts, which formpart of a large paleoproterozoic (mainly rhyacian province in the Guyana Shield of which northern Brazil forms a part, andthe West African Craton. In Brazil the southwestern Serra do Ipitinga and Serra Tumucumaque-Serra do Navio belts have noobvious geometrical extensions in the Guyanas or Venezuela, and may represent deposits formed at penecontemporaneouspassive continental margins and ocean floor spreading centres. To the Northeast the Serra Lombarda-Tartarugalzinho andOiapoque belts are continuations of Guianese belts. In the former the igneous rocks have geochemical characteristics ofsuprasubduction environments. Belts in the Guyana Shield and West African Craton have many similar features. Themegaprovince evolved in a number of stages, which may have started at about 2.3 Ga, and continued with diminished activityafter 2.11 Ga. Both major juvenile additions and (possibly minor reworking of earlier crust contributed to the growth of theprovince. The major transcurrent deformation, responsible for the present structure of the belts, probably occurred duringthe later stages of evolution of the province, but metamorphism and deformation are registered even in the oldest rocks.

  14. TECHNICAL NOTES SEISMIC SOIL-STRUCTURE INTERACTION ...

    African Journals Online (AJOL)

    dell

    SEISMIC SOIL-STRUCTURE INTERACTION AS A POTENTIAL TOOL FOR. ECONOMICAL SEISMIC ... inherent in the system as in any other material like the superstructure itself. ..... [9] Gazetas, G., “Analysis of Machine. Foundation Vibration: ...

  15. SEG Advances in Rotational Seismic Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Pierson, Robert; Laughlin, Darren; Brune, Bob

    2016-10-17

    Significant advancements in the development of sensors to enable rotational seismic measurements have been achieved. Prototypes are available now to support experiments that help validate the utility of rotational seismic measurements.

  16. Seismic scanning tunneling macroscope - Theory

    KAUST Repository

    Schuster, Gerard T.

    2012-09-01

    We propose a seismic scanning tunneling macroscope (SSTM) that can detect the presence of sub-wavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of λ/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the point scatterer is in the near-field region; if the sub-wavelength scatterer is a spherical impedance discontinuity then the resolution will also be limited by the radius of the sphere. Therefore, superresolution imaging can be achieved as the scatterer approaches the source. This is analogous to an optical scanning tunneling microscope that has sub-wavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by imaging of near-field seismic energy.

  17. The Apollo passive seismic experiment

    Science.gov (United States)

    Latham, G. V.; Dorman, H. J.; Horvath, P.; Ibrahim, A. K.; Koyama, J.; Nakamura, Y.

    1979-01-01

    The completed data set obtained from the 4-station Apollo seismic network includes signals from approximately 11,800 events of various types. Four data sets for use by other investigators, through the NSSDC, are in preparation. Some refinement of the lunar model based on seismic data can be expected, but its gross features remain as presented two years ago. The existence of a small, molten core remains dependent upon the analysis of signals from a single, far-side impact. Analysis of secondary arrivals from other sources may eventually resolve this issue, as well as continued refinement of the magnetic field measurements. Evidence of considerable lateral heterogeneity within the moon continues to build. The mystery of the much meteoroid flux estimate derived from lunar seismic measurements, as compared with earth-based estimates, remains; although, significant correlations between terrestrial and lunar observations are beginning to emerge.

  18. Ambient noise tomography of the East African Rift in Mozambique

    Science.gov (United States)

    Domingues, Ana; Silveira, Graça; Ferreira, Ana M. G.; Chang, Sung-Joon; Custódio, Susana; Fonseca, João F. B. D.

    2016-03-01

    Seismic ambient noise tomography is applied to central and southern Mozambique, located in the tip of the East African Rift (EAR). The deployment of MOZART seismic network, with a total of 30 broad-band stations continuously recording for 26 months, allowed us to carry out the first tomographic study of the crust under this region, which until now remained largely unexplored at this scale. From cross-correlations extracted from coherent noise we obtained Rayleigh wave group velocity dispersion curves for the period range 5-40 s. These dispersion relations were inverted to produce group velocity maps, and 1-D shear wave velocity profiles at selected points. High group velocities are observed at all periods on the eastern edge of the Kaapvaal and Zimbabwe cratons, in agreement with the findings of previous studies. Further east, a pronounced slow anomaly is observed in central and southern Mozambique, where the rifting between southern Africa and Antarctica created a passive margin in the Mesozoic, and further rifting is currently happening as a result of the southward propagation of the EAR. In this study, we also addressed the question concerning the nature of the crust (continental versus oceanic) in the Mozambique Coastal Plains (MCP), still in debate. Our data do not support previous suggestions that the MCP are floored by oceanic crust since a shallow Moho could not be detected, and we discuss an alternative explanation for its ocean-like magnetic signature. Our velocity maps suggest that the crystalline basement of the Zimbabwe craton may extend further east well into Mozambique underneath the sediment cover, contrary to what is usually assumed, while further south the Kaapval craton passes into slow rifted crust at the Lebombo monocline as expected. The sharp passage from fast crust to slow crust on the northern part of the study area coincides with the seismically active NNE-SSW Urema rift, while further south the Mazenga graben adopts an N-S direction

  19. THE SOUTHERN FRAGMENT OF THE SIBERIAN CRATON: “LANDSCAPE” HISTORY OVER TWO BILLION YEARS

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    Arkady M. Stanevich

    2015-09-01

    Full Text Available In the state-of-the-art geology, concepts of evolution of interrelated geodynamic and biotic events throughout the history of the Earth have been developed (Fig. 1. Research results on sediments, bio-stratigraphy and geodynamics of the southern fragment of the Siberian craton (SSC, Fig. 2 provide for more or less reliable assessments of the status and evolution of ancient landscapes and biotas from the Lower Proterozoic to the Cenozoic.In the Lower Proterozoic, the geodynamic regime of the Urik-Iyskiy graben was similar to those of the westernpacific island-arc systems, which resulted in the orogen formation and established post-orogen granitoids of 1.86 bln years of age. At the beginning of the Early Riphean, volcano-sedimentary masses were accumulated in continental basins (Fig. 2, 3A. Collision orogenesis also resulted in the occurrence of the terrigeno-volcanogenic complex of the Akitkanskaya suite in the Western Pribaikalie and the transecting Irelskiy granitoids, aged 1.86 bln years, at the edge of the craton. Later on, most probably before the Riphean, peneplanation took place, and a shallow peripheral sea was formed with highly-mature sediments of the Purpolskaya suite. Different environments are reconstructed in the KodarUdokan zone. Sediments of the Udokanskaya suite, varying in thicknesses from 11 to 14 km, suggest a complicated evolution of sedimentation in the peripheral marine basin. Dozens of radiochronological datings of granitoids of the Chuiskiy and Kodarskiy complex which transect the Udokanskaya suite are within the range from 1.7 to 2.0 bln years. From the deposit composition and texture, it can be suggested that the middle, Chineiskaya sub-suite was formed under island-arc conditions; and glacial phenomena occurred in the late Udokan time.Further geological history of the SSC can be described only within the period after the Late Riphean sedimentations (see Fig. 3Б, В. The SSC evolution in the Neo-Proterozoic began with

  20. Time-Dependent Seismic Tomography

    Science.gov (United States)

    Julian, B. R.

    2008-12-01

    Temporal changes in seismic wave speeds in the Earth's crust have been measured at several locations, notably The Geysers geothermal area in California, in studies that used three-dimensional seismic tomography. These studies have used conventional tomography methods to invert multiple seismic-wave arrival time data sets independently and assumed that any differences in the derived structures reflect real temporal variations. Such an assumption is dangerous because the results of repeated tomography experiments would differ even if the structure did not change, simply because of variation in the seismic ray distribution caused by the natural variation in earthquake locations. This problem can be severe when changes in the seismicity distribution are systematic, as, for example, at the onset of an aftershock sequence. The sudden change in the ray distribution can produce artifacts that mimic changes in the seismic wave speeds at the time of a large earthquake. Even if the source locations did not change (if only explosion data were used, for example), derived structures would inevitably differ because of observational errors. A better approach to determining what temporal changes are truly required by the data is to invert multiple data sets simultaneously, imposing constraints to minimize differences between the models for different epochs. This problem is similar to that of seeking models similar to some a priori initial assumption, and a method similar to "damped least squares" can solve it. The order of the system of normal equations for inverting data from two epochs is twice as large as that for a single epoch, and solving it by standard methods requires eight times the computational labor. We present an algorithm for reducing this factor to two, so that inverting multiple epochs simultaneously is comparable in difficulty to inverting them independently, and illustrate its performance using synthetic arrival times and observed data from several areas in

  1. USGS National Seismic Hazard Maps

    Science.gov (United States)

    Frankel, A.D.; Mueller, C.S.; Barnhard, T.P.; Leyendecker, E.V.; Wesson, R.L.; Harmsen, S.C.; Klein, F.W.; Perkins, D.M.; Dickman, N.C.; Hanson, S.L.; Hopper, M.G.

    2000-01-01

    The U.S. Geological Survey (USGS) recently completed new probabilistic seismic hazard maps for the United States, including Alaska and Hawaii. These hazard maps form the basis of the probabilistic component of the design maps used in the 1997 edition of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, prepared by the Building Seismic Safety Council arid published by FEMA. The hazard maps depict peak horizontal ground acceleration and spectral response at 0.2, 0.3, and 1.0 sec periods, with 10%, 5%, and 2% probabilities of exceedance in 50 years, corresponding to return times of about 500, 1000, and 2500 years, respectively. In this paper we outline the methodology used to construct the hazard maps. There are three basic components to the maps. First, we use spatially smoothed historic seismicity as one portion of the hazard calculation. In this model, we apply the general observation that moderate and large earthquakes tend to occur near areas of previous small or moderate events, with some notable exceptions. Second, we consider large background source zones based on broad geologic criteria to quantify hazard in areas with little or no historic seismicity, but with the potential for generating large events. Third, we include the hazard from specific fault sources. We use about 450 faults in the western United States (WUS) and derive recurrence times from either geologic slip rates or the dating of pre-historic earthquakes from trenching of faults or other paleoseismic methods. Recurrence estimates for large earthquakes in New Madrid and Charleston, South Carolina, were taken from recent paleoliquefaction studies. We used logic trees to incorporate different seismicity models, fault recurrence models, Cascadia great earthquake scenarios, and ground-motion attenuation relations. We present disaggregation plots showing the contribution to hazard at four cities from potential earthquakes with various magnitudes and

  2. Historical Seismicity of Central Panama

    Science.gov (United States)

    Camacho, E.

    2013-05-01

    Central Panama lies in the Panama microplate, neighboring seismically active regions of Costa Rica and Colombia. This region, crossed by the Panama Canal, concentrates most of the population and economic activity of the Republic of Panama. Instrumental observation of earthquakes in Panama began on 1882 by the Compagnie Universelle du Canal Interocéanique de Panama and continued from 1904 to 1977 by the Panama Canal Company. From October 1997 to March 1998 the USGS deployed a temporary digital seismic network. Since 2003 this region is monitored by a digital seismic network operated by the Panama Canal Authority and I complemented by the broad band stations of the University of Panama seismic network. The seismicity in this region is very diffuse and the few events which are recorded have magnitudes less than 3.0. Historical archives and antique newspapers from Spain, Colombia, Panama and the United Sates have been searched looking for historical earthquake information which could provide a better estimate of the seismicity in this region. We find that Panama City has been shaken by two destructive earthquakes in historical times. One by a local fault (i.e. Pedro Miguel fault) on May 2, 1621 (I=Vlll MM), and a subduction event from the North Panama Deformed Belt (NPDB) on September 7, 1882 (I=Vll MM). To test these findings two earthquakes scenarios were generated, using SELENA, for Panama City Old Quarter. Panama City was rebuilt on January 21, 1673, on a rocky point facing the Pacific Ocean after the sack by pirate Morgan on January 28, 1671. The pattern of damage to calicanto (unreinforced colonial masonry) and wood structures for a crustal local event are higher than those for an event from the NPDB and seem to confirm that the city has not been shaken by a major local event since May 2, 1621 and a subduction event since September 7, 1882

  3. A Review of Seismicity in 2008

    Institute of Scientific and Technical Information of China (English)

    Li Gang; Liu Jie; Yu Surong

    2009-01-01

    @@ 1 SURVEY OF GLOBE SEISMICITY IN 2008 A total of 19 strong earthquakes with Ms≥7.0 occurred in the world in 2008 according to the Chinese Seismic Station Network (Table 1 ). The strongest earthquake was the Wenchuan earthquake with Ms8.0 on May 12,2008 (Fig.1). Earthquake frequency was apparently lower and the energy release remarkably attenuated in 2008, compared to seismicity in 2007. The characteristics of seismicity are as follows:

  4. Seismic detection of meteorite impacts on Mars

    OpenAIRE

    Teanby, N.A.; Wookey, J.

    2011-01-01

    Abstract Meteorite impacts provide a potentially important seismic source for probing Mars? interior. It has recently been shown that new craters can be detected from orbit using high resolution imaging, which means the location of any impact-related seismic event could be accurately determined thus improving the constraints that could be placed on internal structure using a single seismic station. This is not true of other seismic sources on Mars such as sub-surface faulting, whic...

  5. Time-lapse seismic within reservoir engineering

    OpenAIRE

    Oldenziel, T.

    2003-01-01

    Time-lapse 3D seismic is a fairly new technology allowing dynamic reservoir characterisation in a true volumetric sense. By investigating the differences between multiple seismic surveys, valuable information about changes in the oil/gas reservoir state can be captured. Its interpretation involves different disciplines, of which the main three are: reservoir management, rock physics, and seismics. The main challenge is expressed as "How to optimally benefit from time-lapse seismic". The chall...

  6. Robustness of timber structures in seismic areas

    OpenAIRE

    Neves, Luís A.C.; Branco, Jorge M.

    2011-01-01

    Major similarities between robustness assessment and seismic design exist, and significant information can be brought from seismic design to robustness design. As will be discussed, although some methods and limitations considered in seismic design can improve robustness, the capacity of the structure to sustain limited damage without disproportionate effects is significantly more complex. In fact, seismic design can either improve or reduce the resistance of structures to unfo...

  7. Development of seismic analysis model of LMFBR and seismic time history response analysis

    Energy Technology Data Exchange (ETDEWEB)

    Koo, K. H.; Lee, J. H.; Yoo, B. [KAERI, Taejon (Korea, Republic of)

    2001-05-01

    The main objective of this paper is to develop the seismic analysis model of KALIMER reactor structures including the primary coolant of sodium and to evaulate the seismic responses of the maximum peak acceleration and the relative displacements by the time history seismic response analysis. The seismic time history response analyses were carried out for both cases of the seismic isolation design and the non-isolation one to verify the seismic isolation performance. From the results of seismic response analysis using the developed seismic analysis model, it is clearly verified that the seismic isolation design gives very significantly reduced seismic responses compared with the non-isolation design. All design criteria for the relative displacement repsonse were satisfied for KALIMER reactor structures.

  8. Advanced Seismic While Drilling System

    Energy Technology Data Exchange (ETDEWEB)

    Robert Radtke; John Fontenot; David Glowka; Robert Stokes; Jeffery Sutherland; Ron Evans; Jim Musser

    2008-06-30

    A breakthrough has been discovered for controlling seismic sources to generate selectable low frequencies. Conventional seismic sources, including sparkers, rotary mechanical, hydraulic, air guns, and explosives, by their very nature produce high-frequencies. This is counter to the need for long signal transmission through rock. The patent pending SeismicPULSER{trademark} methodology has been developed for controlling otherwise high-frequency seismic sources to generate selectable low-frequency peak spectra applicable to many seismic applications. Specifically, we have demonstrated the application of a low-frequency sparker source which can be incorporated into a drill bit for Drill Bit Seismic While Drilling (SWD). To create the methodology of a controllable low-frequency sparker seismic source, it was necessary to learn how to maximize sparker efficiencies to couple to, and transmit through, rock with the study of sparker designs and mechanisms for (a) coupling the sparker-generated gas bubble expansion and contraction to the rock, (b) the effects of fluid properties and dynamics, (c) linear and non-linear acoustics, and (d) imparted force directionality. After extensive seismic modeling, the design of high-efficiency sparkers, laboratory high frequency sparker testing, and field tests were performed at the University of Texas Devine seismic test site. The conclusion of the field test was that extremely high power levels would be required to have the range required for deep, 15,000+ ft, high-temperature, high-pressure (HTHP) wells. Thereafter, more modeling and laboratory testing led to the discovery of a method to control a sparker that could generate low frequencies required for deep wells. The low frequency sparker was successfully tested at the Department of Energy Rocky Mountain Oilfield Test Center (DOE RMOTC) field test site in Casper, Wyoming. An 8-in diameter by 26-ft long SeismicPULSER{trademark} drill string tool was designed and manufactured by TII

  9. Community Seismic Network (CSN)

    Science.gov (United States)

    Clayton, R. W.; Heaton, T. H.; Kohler, M. D.; Cheng, M.; Guy, R.; Chandy, M.; Krause, A.; Bunn, J.; Olson, M.; Faulkner, M.; Liu, A.; Strand, L.

    2012-12-01

    We report on developments in sensor connectivity, architecture, and data fusion algorithms executed in Cloud computing systems in the Community Seismic Network (CSN), a network of low-cost sensors housed in homes and offices by volunteers in the Pasadena, CA area. The network has over 200 sensors continuously reporting anomalies in local acceleration through the Internet to a Cloud computing service (the Google App Engine) that continually fuses sensor data to rapidly detect shaking from earthquakes. The Cloud computing system consists of data centers geographically distributed across the continent and is likely to be resilient even during earthquakes and other local disasters. The region of Southern California is partitioned in a multi-grid style into sets of telescoping cells called geocells. Data streams from sensors within a geocell are fused to detect anomalous shaking across the geocell. Temporal spatial patterns across geocells are used to detect anomalies across regions. The challenge is to detect earthquakes rapidly with an extremely low false positive rate. We report on two data fusion algorithms, one that tessellates the surface so as to fuse data from a large region around Pasadena and the other, which uses a standard tessellation of equal-sized cells. Since September 2011, the network has successfully detected earthquakes of magnitude 2.5 or higher within 40 Km of Pasadena. In addition to the standard USB device, which connects to the host's computer, we have developed a stand-alone sensor that directly connects to the internet via Ethernet or wifi. This bypasses security concerns that some companies have with the USB-connected devices, and allows for 24/7 monitoring at sites that would otherwise shut down their computers after working hours. In buildings we use the sensors to model the behavior of the structures during weak events in order to understand how they will perform during strong events. Visualization models of instrumented buildings ranging

  10. Seismic Physical Modeling Technology and Its Applications

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This paper introduces the seismic physical modeling technology in the CNPC Key Lab of Geophysical Exploration. It includes the seismic physical model positioning system, the data acquisition system, sources, transducers,model materials, model building techniques, precision measurements of model geometry, the basic principles of the seismic physical modeling and experimental methods, and two physical model examples.

  11. Seismic processing in the inverse data space

    NARCIS (Netherlands)

    Berkhout, A.J.

    2006-01-01

    Until now, seismic processing has been carried out by applying inverse filters in the forward data space. Because the acquired data of a seismic survey is always discrete, seismic measurements in the forward data space can be arranged conveniently in a data matrix (P). Each column in the data matrix

  12. Relationship between Precambrian North Korean Peninsula and the North China Craton: Evidence from LA-ICP-MS U-Pb ages of detrital zircons from Neoproterozoic tillites of North Korea and Southern North China Craton

    Science.gov (United States)

    Hu, B.; Zhai, M.; Peng, P.; Zhang, Y.; Wu, J.; Jia, X.; Zhang, H.; Lei, W.; Zhuang, G.

    2016-12-01

    Relationship between Precambrian Korean Peninsula and the North China Craton (NCC) is focus of attention. There are Neoproterozoic tillites in Phyongnam Basin, Nangrim massif, North Korea (NK) and Southern NCC. Nangrim massif was regarded as a part of the NCC according to similar Precambrian basements between Nangrim massif and Longgang massif in the Northeast NCC. But the comparation of Neoproterozoic rocks is lacked between NK and NCC. Detrital zircon LA-ICP-MS U-Pb ages of 2 pebbly phyllite samples of Pirangdong Series in Phyongnam Basin and 2 argillaceous cemented mix-conglomeate samples of Luoquan Series in Southern NCC was analyzed in this research. Detrital zircon ages of pebbly phyllites of Pirangdong Series distribute mainly at 1.85 Ga, 1.8 Ga, 1.6 Ga, 1.4 Ga and 1.2 Ga. A small number of them are at 3.2 Ga, 2.6 - 2.5 Ga, 2.3 Ga, 2.1 Ga and 900 - 860 Ma. Detrital zircon ages of mix-conglomeates of Luoquan Series mainly focus on 2.5 Ga, 2.2 Ga, 2.0 Ga, 1.8 Ga and 1.6 Ga. Minor of them distribute at 1.12 Ga. The similar age distribution of Pirangdong and Luoquan Series of 2.6 - 2.5 Ga, 2.1 - 2.0 Ga, 1.85 - 1.8 Ga and 1.6 Ga corresponds to Precambrian significant tectonic- magmatic- thermal events of the NCC, which indicates that the Precambrian basement rocks of the NCC are main provenances of both Pirangdong and Luoquan Series. This also confirm that the Phyongnam Basin is a part of Neoproterozoic sedimentary covers of the NCC. It is worth to mention that 1.2 - 1.0 Ga and 900 - 850 Ma magmatic rocks in the NCC are seldom reported which relate to the assemblage and breakup of Rodinia Supercontinent. whereas they crop out widely in the South China Craton (SCC) and was always regarded as a mark distingusing the two craton. 1.2 - 1.0 Ga and 900 - 850 Ma zircon ages preserved in sedimentary rocks not only in North Korea and Southern NCC but also in Northeast NCC and East NCC provide data to compare Neoproterozoic strata between NCC and SCC and important clues to

  13. Simplified seismic performance assessment and implications for seismic design

    Science.gov (United States)

    Sullivan, Timothy J.; Welch, David P.; Calvi, Gian Michele

    2014-08-01

    The last decade or so has seen the development of refined performance-based earthquake engineering (PBEE) approaches that now provide a framework for estimation of a range of important decision variables, such as repair costs, repair time and number of casualties. This paper reviews current tools for PBEE, including the PACT software, and examines the possibility of extending the innovative displacement-based assessment approach as a simplified structural analysis option for performance assessment. Details of the displacement-based s+eismic assessment method are reviewed and a simple means of quickly assessing multiple hazard levels is proposed. Furthermore, proposals for a simple definition of collapse fragility and relations between equivalent single-degree-of-freedom characteristics and multi-degree-of-freedom story drift and floor acceleration demands are discussed, highlighting needs for future research. To illustrate the potential of the methodology, performance measures obtained from the simplified method are compared with those computed using the results of incremental dynamic analyses within the PEER performance-based earthquake engineering framework, applied to a benchmark building. The comparison illustrates that the simplified method could be a very effective conceptual seismic design tool. The advantages and disadvantages of the simplified approach are discussed and potential implications of advanced seismic performance assessments for conceptual seismic design are highlighted through examination of different case study scenarios including different structural configurations.

  14. Expanding Conventional Seismic Stratigrphy into the Multicomponent Seismic Domain

    Energy Technology Data Exchange (ETDEWEB)

    Innocent Aluka

    2008-08-31

    Multicomponent seismic data are composed of three independent vector-based seismic wave modes. These wave modes are, compressional mode (P), and shear modes SV and SH. The three modes are generated using three orthogonal source-displacement vectors and then recorded using three orthogonal vector sensors. The components travel through the earth at differing velocities and directions. The velocities of SH and SV as they travel through the subsurface differ by only a few percent, but the velocities of SV and SH (Vs) are appreciably lower than the P-wave velocity (Vp). The velocity ratio Vp/Vs varies by an order of magnitude in the earth from a value of 15 to 1.5 depending on the degree of sedimentary lithification. The data used in this study were acquired by nine-component (9C) vertical seismic profile (VSP), using three orthogonal vector sources. The 9C vertical seismic profile is capable of generating P-wave mode and the fundamental S-wave mode (SH-SH and SV-SV) directly at the source station and permits the basic components of elastic wavefield (P, SH-SH and SV-SV) to be separated from one another for the purposes of imaging. Analysis and interpretations of data from the study area show that incident full-elastic seismic wavefield is capable of reflecting four different wave modes, P, SH , SV and C which can be utilized to fully understand the architecture and heterogeneities of geologic sequences. The conventional seismic stratigraphy utilizes only reflected P-wave modes. The notation SH mode is the same as SH-SH; SV mode means SV-SV and C mode which is a converted shear wave is a special SV mode and is the same as P-SV. These four wave modes image unique geologic stratigraphy and facies and at the same time reflect independent stratal surfaces because of the unique orientation of their particle-displacement vectors. As a result of the distinct orientation of individual mode's particle-displacement vector, one mode may react to a critical subsurface sequence

  15. Chapter 27: Geology and petroleum potential of the north and east margins of the Siberian Craton, north of the Arctic Circle

    Science.gov (United States)

    Klett, T.R.; Wandrey, C.J.; Pitman, J.K.

    2011-01-01

    The Siberian Craton consists of crystalline rocks and superimposed Precambrian sedimentary rocks deposited in rift basins. Palaeozoic rocks, mainly carbonates, were deposited along the margins of the craton to form an outwardly younger concentric pattern that underlies an outward-thickening Mesozoic sedimentary section. The north and east margins of the Siberian Craton subsequently became foreland basins created by compressional deformation during collision with other tectonic plates. The Tunguska Basin developed as a Palaeozoic rift/sag basin over Proterozoic rifts. The geological provinces along the north and east margins of the Siberian Craton are immature with respect to exploration, so exploration-history analysis alone cannot be used for assessing undiscovered petroleum resources. Therefore, other areas from around the world having greater petroleum exploration maturity and similar geological characteristics, and which have been previously assessed, were used as analogues to aid in this assessment. The analogues included those of foreland basins and rift/sag basins that were later subjected to compression. The US Geological Survey estimated the mean undiscovered, technically recoverable conventional petroleum resources to be approximately 28 billion barrels of oil equivalent, including approximately 8 billion barrels of crude oil, 103 trillion cubic feet of natural gas and 3 billion barrels of natural gas liquids. ?? 2011 The Geological Society of London.

  16. Early Precambrian Crustal Evolution in the Northern Margin of the North China Craton: Constraints from Zircon U-Pb and Lu-Hf Isotopes

    Institute of Scientific and Technical Information of China (English)

    LIU Shu-wen; Lü Yong-jun; LI Qiu-gen

    2008-01-01

    @@ Northern Hebei province, one of important Precambrian metamorphic areas, is located in the middle segment of northern margin of the North China Craton. Precambrian rocks in this area are subdivided into two units by the Chaiwopu-Dantazi ductile shear zone.

  17. Crustal evolution and the eclogite to granulite phase transition in xenoliths from the West African Craton

    Science.gov (United States)

    Haggerty, S. E.; Hills, D. V.; Toft, P. B.

    1988-01-01

    A suite of eclogite and granulite facies xenoliths from kimberlite pipes in the Archean Man Shield of West Africa is described. The xenoliths include lithologies ranging in composition from komatiite to anorthosite and appear to be geochemically, petrologically, and geophysically related. The suite may represent fractionation of felsic material separated from ancient mantle and added to early Archean crust. The samples can be used to define a xenolith geotherm, which may represent an ancient episode of high heat flow. The samples also imply that the crust-mantle boundary is a gradational and possibly interlayered geochemical, mineralogical, and seismic transition. It is speculated that the depleted subcontinental mantle required by diamond bearing coalescence of smaller depletion cells formed by extraction of ancient crustal components. These depleted zones are surrounded by fertile asthenospheric mantle, which may have given rise to later flood basalts such as the Karroo and Parana Provinces.

  18. Timing of the granulite facies metamorphism in the Sanggan area, North China craton: zircon U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    GUO; Jinghui

    2001-01-01

    [1]Lu, L. Z., Jin, S. Q., P-T-t paths and tectonic history of an early Precambrian granulite facies terrane, Jining District, south-eastern Inner Mongolia, China, J. Metamorphic Geol., 1993, 11: 483-498.[2]Liu, F. L., Shen, Q. H., Retrogressive textures and metamorphic reaction features of Al-rich gneisses in the granulite facies belt from northwestern Hebei province, Acta Petrologia Sinica (in Chinese with English abstract), 1999, 15(4): 505-517.[3]Zhai, M. G., Guo, J. H., Yan, Y. H. et al., Discovery of high-pressure basic granulite terrain in North China Archaean craton and preliminary study, Science in China, Ser. B, 1993, 36(11): 1402-1408.[4]Guo, J. H., Zhai, M. G., Zhang, Y. G. et al., Early Precambrian Manjinggou high-pressure granulite melange belt on the south edge of the Huaian complex, North China craton: geological features, petrology and isotopic geochronology, Acta Petrologica Sinica (in Chinese with English abstract), 1993, 9(4): 329-341.[5]Liu, S. W., Shen, Q. H., Geng, Y. S., Metamorphic evolution of two types of garnet-granulites in Northwestern Hebei province and analyses by Gibbs method, Acta Petrologica Sinica (in Chinese with English abstract), 1996, 12(2): 261-275.[6]Wang, R. M., Some evidence of the late Archaean collision zone in the northwestern Hebei Province, in Geological Evolution of the Granulite Terrane in North Part of the North China Craton (eds. Qian, X., Wang, R.), Beijing: Seismolgical Press. 1994, 7-20.[7]Liu, D. Y., Geng, Y. S., Song, B., Late Archean crustal accretion and reworking in northwest Hebei Province: geochronological evidence, Acta Geoscientia Sinica (in Chinese with English abstract), 1997, 18(3): 226-232.[8]Geng, Y. S., Liu, D. Y., Song, B., Chronological framework of the early Precambrian important events of the north-western Hebei granulite terrain, Acta Geologica Sinica (in Chinese with English abstract), 1997, 71:316-327.[9]Guo, J. H., Zhai, M. G., Sm-Nd age dating of high

  19. Aeromagnetic signatures reveal a back-arc basin imposed upon the inherited rifted margin of the East Antarctic craton

    Science.gov (United States)

    Armadillo, E.; Ferraccioli, F.; Jordan, T. A.; Bozzo, E.

    2009-12-01

    The Wilkes Subglacial Basin (WSB) represents a largely unexplored, approximately 1400 km-long and up to 600 km-wide subglacial depression, buried beneath the over 3 km-thick East Antarctic Ice Sheet. During the 2005-06 austral summer an extensive aerogeophysical survey was flown to investigate the WSB adjacent to northern Victoria Land (NVL), and included the acquisition of new airborne radar, aeromagnetic and aerogravity data. Several contrasting models for the origin of the basin have been previously proposed, and are based primarily on relatively sparse gravity data. These range from Cenozoic flexure, to distributed crustal extension of unknown age (possibly Mesozoic to Cenozoic), and even compression along the margin of craton. Our recent aeromagnetic data reveal that the basin is structurally controlled and has a tectonic origin, at least adjacent to NVL. The eastern margin of the basin is imposed upon an Early Paleozoic thrust fault belt, which can be traced under the ice using aeromagnetic signatures from exposures in Oates Land and the Ross Sea coast. Aeromagnetic patterns reveal that the western margin of the basin is imposed upon a Proterozoic-age shear zone mapped in the Mertz Glacier, and that is interpreted from geological studies to represent the continuation of a coeval shear zone in Australia. The broad aeromagnetic and satellite magnetic low over the WSB contrasts with the high over the un-reworked Proterozoic craton to the west of the basin, and is interpreted to reflect Neoproterozoic-age sediments deposited along the rifted margin of the craton. Magnetic intrusions within the WSB are interpreted as back-arc plutons that formed later in response to Cambrian-Ordovician age subduction along the paleo-Pacific margin of Gondwana. The aeromagnetic interpretation for a former broad back-arc basin in the WSB is supported by the occurrence of low-grade metasedimentary rocks of back-arc affinity in Oates Land, and also by the similarity in long

  20. Seismic link at plate boundary

    Indian Academy of Sciences (India)

    Faical Ramdani; Omar Kettani; Benaissa Tadili

    2015-06-01

    Seismic triggering at plate boundaries has a very complex nature that includes seismic events at varying distances. The spatial orientation of triggering cannot be reduced to sequences from the main shocks. Seismic waves propagate at all times in all directions, particularly in highly active zones. No direct evidence can be obtained regarding which earthquakes trigger the shocks. The first approach is to determine the potential linked zones where triggering may occur. The second step is to determine the causality between the events and their triggered shocks. The spatial orientation of the links between events is established from pre-ordered networks and the adapted dependence of the spatio-temporal occurrence of earthquakes. Based on a coefficient of synchronous seismic activity to grid couples, we derive a network link by each threshold. The links of high thresholds are tested using the coherence of time series to determine the causality and related orientation. The resulting link orientations at the plate boundary conditions indicate that causal triggering seems to be localized along a major fault, as a stress transfer between two major faults, and parallel to the geothermal area extension.

  1. Seismic hazard studies in Egypt

    Science.gov (United States)

    Mohamed, Abuo El-Ela A.; El-Hadidy, M.; Deif, A.; Abou Elenean, K.

    2012-12-01

    The study of earthquake activity and seismic hazard assessment of Egypt is very important due to the great and rapid spreading of large investments in national projects, especially the nuclear power plant that will be held in the northern part of Egypt. Although Egypt is characterized by low seismicity, it has experienced occurring of damaging earthquake effect through its history. The seismotectonic sitting of Egypt suggests that large earthquakes are possible particularly along the Gulf of Aqaba-Dead Sea transform, the Subduction zone along the Hellenic and Cyprean Arcs, and the Northern Red Sea triple junction point. In addition some inland significant sources at Aswan, Dahshour, and Cairo-Suez District should be considered. The seismic hazard for Egypt is calculated utilizing a probabilistic approach (for a grid of 0.5° × 0.5°) within a logic-tree framework. Alternative seismogenic models and ground motion scaling relationships are selected to account for the epistemic uncertainty. Seismic hazard values on rock were calculated to create contour maps for four ground motion spectral periods and for different return periods. In addition, the uniform hazard spectra for rock sites for different 25 periods, and the probabilistic hazard curves for Cairo, and Alexandria cities are graphed. The peak ground acceleration (PGA) values were found close to the Gulf of Aqaba and it was about 220 gal for 475 year return period. While the lowest (PGA) values were detected in the western part of the western desert and it is less than 25 gal.

  2. Seismic amplitude recovery with curvelets

    NARCIS (Netherlands)

    Moghaddam, P.P.; Herrmann, F.J.; Stolk, C.C.

    2007-01-01

    A non-linear singularity-preserving solution to the least-squares seismic imaging problem with sparseness and continuity constraints is proposed. The applied formalism explores curvelets as a directional frame that, by their sparsity on the image, and their invariance under the imaging operators,

  3. Quantifying Similarity in Seismic Polarizations

    Science.gov (United States)

    Eaton, D. W. S.; Jones, J. P.; Caffagni, E.

    2015-12-01

    Measuring similarity in seismic attributes can help identify tremor, low S/N signals, and converted or reflected phases, in addition to diagnosing site noise and sensor misalignment in arrays. Polarization analysis is a widely accepted method for studying the orientation and directional characteristics of seismic phases via. computed attributes, but similarity is ordinarily discussed using qualitative comparisons with reference values. Here we introduce a technique for quantitative polarization similarity that uses weighted histograms computed in short, overlapping time windows, drawing on methods adapted from the image processing and computer vision literature. Our method accounts for ambiguity in azimuth and incidence angle and variations in signal-to-noise (S/N) ratio. Using records of the Mw=8.3 Sea of Okhotsk earthquake from CNSN broadband sensors in British Columbia and Yukon Territory, Canada, and vertical borehole array data from a monitoring experiment at Hoadley gas field, central Alberta, Canada, we demonstrate that our method is robust to station spacing. Discrete wavelet analysis extends polarization similarity to the time-frequency domain in a straightforward way. Because histogram distance metrics are bounded by [0 1], clustering allows empirical time-frequency separation of seismic phase arrivals on single-station three-component records. Array processing for automatic seismic phase classification may be possible using subspace clustering of polarization similarity, but efficient algorithms are required to reduce the dimensionality.

  4. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    Energy Technology Data Exchange (ETDEWEB)

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2003-12-01

    We have developed and tested technology for a new type of direct hydrocarbon detection. The method uses inelastic rock properties to greatly enhance the sensitivity of surface seismic methods to the presence of oil and gas saturation. These methods include use of energy absorption, dispersion, and attenuation (Q) along with traditional seismic attributes like velocity, impedance, and AVO. Our approach is to combine three elements: (1) a synthesis of the latest rock physics understanding of how rock inelasticity is related to rock type, pore fluid types, and pore microstructure, (2) synthetic seismic modeling that will help identify the relative contributions of scattering and intrinsic inelasticity to apparent Q attributes, and (3) robust algorithms that extract relative wave attenuation attributes from seismic data. This project provides: (1) Additional petrophysical insight from acquired data; (2) Increased understanding of rock and fluid properties; (3) New techniques to measure reservoir properties that are not currently available; and (4) Provide tools to more accurately describe the reservoir and predict oil location and volumes. These methodologies will improve the industry's ability to predict and quantify oil and gas saturation distribution, and to apply this information through geologic models to enhance reservoir simulation. We have applied for two separate patents relating to work that was completed as part of this project.

  5. Seismic isolation for Advanced LIGO

    CERN Document Server

    Abbott, R; Allen, G; Cowley, S; Daw, E; Debra, D; Giaime, J; Hammond, G; Hammond, M; Hardham, C; How, J; Hua, W; Johnson, W; Lantz, B; Mason, K; Mittleman, R; Nichol, J; Richman, S; Rollins, J; Shoemaker, D; Stapfer, G; Stebbins, R

    2002-01-01

    The baseline design concept for a seismic isolation component of the proposed 'Advanced LIGO' detector upgrade has been developed with proof-of-principle experiments and computer models. It consists of a two-stage in-vacuum active isolation platform that is supported by an external hydraulic actuation stage. Construction is underway for prototype testing of a full-scale preliminary design.

  6. Seismicity dynamics and earthquake predictability

    Directory of Open Access Journals (Sweden)

    G. A. Sobolev

    2011-02-01

    Full Text Available Many factors complicate earthquake sequences, including the heterogeneity and self-similarity of the geological medium, the hierarchical structure of faults and stresses, and small-scale variations in the stresses from different sources. A seismic process is a type of nonlinear dissipative system demonstrating opposing trends towards order and chaos. Transitions from equilibrium to unstable equilibrium and local dynamic instability appear when there is an inflow of energy; reverse transitions appear when energy is dissipating. Several metastable areas of a different scale exist in the seismically active region before an earthquake. Some earthquakes are preceded by precursory phenomena of a different scale in space and time. These include long-term activation, seismic quiescence, foreshocks in the broad and narrow sense, hidden periodical vibrations, effects of the synchronization of seismic activity, and others. Such phenomena indicate that the dynamic system of lithosphere is moving to a new state – catastrophe. A number of examples of medium-term and short-term precursors is shown in this paper. However, no precursors identified to date are clear and unambiguous: the percentage of missed targets and false alarms is high. The weak fluctuations from outer and internal sources play a great role on the eve of an earthquake and the occurrence time of the future event depends on the collective behavior of triggers. The main task is to improve the methods of metastable zone detection and probabilistic forecasting.

  7. The Rondonian-San Ignacio Province in the SW Amazonian Craton: An overview

    Science.gov (United States)

    Bettencourt, Jorge Silva; Leite, Washington Barbosa; Ruiz, Amarildo Salina; Matos, Ramiro; Payolla, Bruno Leonelo; Tosdal, Richard M.

    2010-01-01

    .50 Ga), Santo Antonio Intrusive Suite (1.40-1.36 Ga), and the Teotônio Intrusive Suite (1.38 Ga). Magmatism of these types also occur at the end of the Rondonian-San Ignacio Orogeny, and are represented by the Alto Candeias Intrusive Suite (1.34-1.36 Ga), and the São Lourenço-Caripunas Intrusive Suite (1.31-1.30 Ga). The cratonization of the province occurred between 1.30 and 1.25 Ga.

  8. Boron isotopes reveal multiple metasomatic events in the mantle beneath the eastern North China Craton

    Science.gov (United States)

    Li, Hong-Yan; Zhou, Zhou; Ryan, Jeffrey G.; Wei, Gang-Jian; Xu, Yi-Gang

    2016-12-01

    Linkages inferred between the geochemical heterogeneity of the mantle beneath eastern Eurasia and the stagnant Pacific slab documented geophysically in its mantle transition zone are as yet not clearly characterized. In this paper we report new elemental and isotopic data for boron (B) on a suite of well-characterized Cenozoic basalts (alkali basalts, basanites and nephelinites), with ocean island basalt (OIB)-like trace element signatures from western Shandong of the eastern North China Craton (NCC). Correlations between major elements (e.g., FeOT versus SiO2), trace elements (e.g., CeN/PbN versus BaN/ThN) and radiogenic isotopes (e.g., 206Pb/204Pb versus 87Sr/86Sr) suggest these basalts are derived via the mixing of melts from two mantle components: a fluid mobile element (FME; such as Ba, K, Pb and Sr) enriched component, which is most evident in the alkali basalts, and a FME depleted mantle component that is more evident in the basanites and nephelinites. The alkali basalts in this study have lower B concentrations (1.4-2.2 μg/g) but higher δ11B (-4.9 to -1.4) values than the basanites and nephelinites (B = 2.1-5.0 μg/g; δ11B = -6.9 to -3.9), and all the samples have nearly constant B/Nb ratios between 0.03 and 0.07, similar to the observed range in B/Nb for intraplate lavas. Our high-SiO2 samples have higher δ11B than that of our low SiO2 samples, indicating that the B isotopic differences among our samples do not result from the addition of a continental crustal component in the mantle source, or direct crustal assimilation during the eruption process. The positive B versus Nb correlation suggests the B isotopic compositions of the western Shandong basalts primarily reflect the pre-eruptive compositions of their mantle sources. Correlations among B, Nd and Sr isotope signatures of the western Shandong basalts differ from those among basalts from plume settings (e.g., Azores and Hawaii), and are inconsistent with models suggesting single-step metasomatic

  9. Gold distribution in Archean continental crust: Evaluating the effects of intracrustal differentiation in the Tanzanian Craton

    Science.gov (United States)

    Long, K.; Rudnick, R. L.; McDonough, W. F.; Manya, S.

    2013-12-01

    We have evaluated the vertical distribution of gold in variably metamorphosed igneous rocks in the Tanzanian Craton: 2.6 Ga upper-crustal greenschist-facies greenstone belt basalts and andesites from the Lake Victoria Gold Field of northern Tanzania, and compositionally similar 2.6 Ga lower-crustal mafic granulite-facies xenoliths that were carried in rift-related basalts that erupted nearby. We implemented the preconcentration method of Pitcairn et al. (2006), which utilizes chromatographic separation of gold from acid-digested rocks using diisobutyl ketone (DIBK), followed by standard addition ICP-MS to determine the distribution of gold in the crust. Repeat analyses of the certified reference material TDB-1, a whole-rock powder diabase dike from Tremblay Lake, Saskatchewan, Canada (certified gold concentration = 6.3 × 1.0 ng/g), yielded an average gold concentration of 6.5 × 1.1 ng/g. Results were reproducible to within 17% for rock powder aliquots between 200-600 mg (n=38), where 400 mg sample aliquots were reproducible to within 6% (n=9), and 600 mg aliquots were reproducible to within 4.5% (n=4). Better reproducibility for the greater sample aliquots likely reflects the 'nugget' effect. Rock samples in the 0.1-0.8 ng/g gold concentration range reproduced to within 27% for 400-600 mg sample aliquots. Although the lavas come from an area containing gold deposits, all were more than 5 km from any gold mine. The Tanzanian greenstone belt basalts have the highest gold concentrations (9 ng/g to 62 μg/g, ave. = 40 (+68/-25) ng/g, 1σ (n=10)), followed by the greenstone belt andesites (0.4 to 120 ng/g, ave. = 1.1 (+0.9/-0.5) ng/g, 1σ (n=14)). The lowest concentrations were observed in the granulite-facies lower-crustal xenoliths (0.1 to 3.3 ng/g, ave. = 0.3 (+0.3/-0.1) ng/g, 1σ (n=21)). Gold is incompatible in silicates and can partition into hydrothermal and/or magmatic fluid or vapour during high-grade metamorphic dehydration reactions or partial melting

  10. Seismic Imaging of Sandbox Models

    Science.gov (United States)

    Buddensiek, M. L.; Krawczyk, C. M.; Kukowski, N.; Oncken, O.

    2009-04-01

    Analog sandbox simulations have been applied to study structural geological processes to provide qualitative and quantitative insights into the evolution of mountain belts and basins. These sandbox simulations provide either two-dimensional and dynamic or pseudo-three-dimensional and static information. To extend the dynamic simulations to three dimensions, we combine the analog sandbox simulation techniques with seismic physical modeling of these sandbox models. The long-term objective of this approach is to image seismic and seismological events of static and actively deforming 3D analog models. To achieve this objective, a small-scale seismic apparatus, composed of a water tank, a PC control unit including piezo-electric transducers, and a positioning system, was built for laboratory use. For the models, we use granular material such as sand and glass beads, so that the simulations can evolve dynamically. The granular models are required to be completely water saturated so that the sources and receivers are directly and well coupled to the propagating medium. Ultrasonic source frequencies (˜500 kHz) corresponding to wavelengths ˜5 times the grain diameter are necessary to be able to resolve small scale structures. In three experiments of different two-layer models, we show that (1) interfaces of layers of granular materials can be resolved depending on the interface preparation more than on the material itself. Secondly, we show that the dilation between the sand grains caused by a string that has been pulled through the grains, simulating a shear zone, causes a reflection that can be detected in the seismic data. In the third model, we perform a seismic reflection survey across a model that contains both the prepared interface and a shear zone, and apply 2D-seismic reflection processing to improve the resolution. Especially for more complex models, the clarity and penetration depth need to be improved to study the evolution of geological structures in dynamic

  11. Statistical Seismology and Induced Seismicity

    Science.gov (United States)

    Tiampo, K. F.; González, P. J.; Kazemian, J.

    2014-12-01

    While seismicity triggered or induced by natural resources production such as mining or water impoundment in large dams has long been recognized, the recent increase in the unconventional production of oil and gas has been linked to rapid rise in seismicity in many places, including central North America (Ellsworth et al., 2012; Ellsworth, 2013). Worldwide, induced events of M~5 have occurred and, although rare, have resulted in both damage and public concern (Horton, 2012; Keranen et al., 2013). In addition, over the past twenty years, the increase in both number and coverage of seismic stations has resulted in an unprecedented ability to precisely record the magnitude and location of large numbers of small magnitude events. The increase in the number and type of seismic sequences available for detailed study has revealed differences in their statistics that previously difficult to quantify. For example, seismic swarms that produce significant numbers of foreshocks as well as aftershocks have been observed in different tectonic settings, including California, Iceland, and the East Pacific Rise (McGuire et al., 2005; Shearer, 2012; Kazemian et al., 2014). Similarly, smaller events have been observed prior to larger induced events in several occurrences from energy production. The field of statistical seismology has long focused on the question of triggering and the mechanisms responsible (Stein et al., 1992; Hill et al., 1993; Steacy et al., 2005; Parsons, 2005; Main et al., 2006). For example, in most cases the associated stress perturbations are much smaller than the earthquake stress drop, suggesting an inherent sensitivity to relatively small stress changes (Nalbant et al., 2005). Induced seismicity provides the opportunity to investigate triggering and, in particular, the differences between long- and short-range triggering. Here we investigate the statistics of induced seismicity sequences from around the world, including central North America and Spain, and

  12. Time-dependent seismic tomography

    Science.gov (United States)

    Julian, B.R.; Foulger, G.R.

    2010-01-01

    Of methods for measuring temporal changes in seismic-wave speeds in the Earth, seismic tomography is among those that offer the highest spatial resolution. 3-D tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations. This assumption is dangerous because the results of independent inversions would differ even if the structure in the Earth did not change, due to observational errors and differences in the seismic ray distributions. The latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences, and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant. A better approach, which makes it possible to assess what changes are truly required by the data, is to invert multiple data sets simultaneously, minimizing the difference between models for different epochs as well as the rms arrival-time residuals. This problem leads, in the case of two epochs, to a system of normal equations whose order is twice as great as for a single epoch. The direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions. We present an algorithm, tomo4d, that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require. No claim to original US government works Journal compilation ?? 2010 RAS.

  13. Seismic evaluation methods for existing buildings

    Energy Technology Data Exchange (ETDEWEB)

    Hsieh, B.J.

    1995-07-01

    Recent US Department of Energy natural phenomena hazards mitigation directives require the earthquake reassessment of existing hazardous facilities and general use structures. This applies also to structures located in accordance with the Uniform Building Code in Seismic Zone 0 where usually no consideration is given to seismic design, but where DOE specifies seismic hazard levels. An economical approach for performing such a seismic evaluation, which relies heavily on the use of preexistent structural analysis results is outlined below. Specifically, three different methods are used to estimate the seismic capacity of a building, which is a unit of a building complex located on a site considered low risk to earthquakes. For structures originally not seismically designed, which may not have or be able to prove sufficient capacity to meet new arbitrarily high seismic design requirement and which are located on low-seismicity sites, it may be very cost effective to perform detailed site-specific seismic hazard studies in order to establish the true seismic threat. This is particularly beneficial, to sites with many buildings and facilities to be seismically evaluated.

  14. Assessment of seismic loss dependence using copula.

    Science.gov (United States)

    Goda, Katsuichiro; Ren, Jiandong

    2010-07-01

    The catastrophic nature of seismic risk is attributed to spatiotemporal correlation of seismic losses of buildings and infrastructure. For seismic risk management, such correlated seismic effects must be adequately taken into account, since they affect the probability distribution of aggregate seismic losses of spatially distributed structures significantly, and its upper tail behavior can be of particular importance. To investigate seismic loss dependence for two closely located portfolios of buildings, simulated seismic loss samples, which are obtained from a seismic risk model of spatially distributed buildings by taking spatiotemporally correlated ground motions into account, are employed. The characterization considers a loss frequency model that incorporates one dependent random component acting as a common shock to all buildings, and a copula-based loss severity model, which facilitates the separate construction of marginal loss distribution functions and nonlinear copula function with upper tail dependence. The proposed method is applied to groups of wood-frame buildings located in southwestern British Columbia. Analysis results indicate that the dependence structure of aggregate seismic losses can be adequately modeled by the right heavy tail copula or Gumbel copula, and that for the considered example, overall accuracy of the proposed method is satisfactory at probability levels of practical interest (at most 10% estimation error of fractiles of aggregate seismic loss). The developed statistical seismic loss model may be adopted in dynamic financial analysis for achieving faster evaluation with reasonable accuracy.

  15. Seismic Risk Perception compared with seismic Risk Factors

    Science.gov (United States)

    Crescimbene, Massimo; La Longa, Federica; Pessina, Vera; Pino, Nicola Alessandro; Peruzza, Laura

    2016-04-01

    The communication of natural hazards and their consequences is one of the more relevant ethical issues faced by scientists. In the last years, social studies have provided evidence that risk communication is strongly influenced by the risk perception of people. In order to develop effective information and risk communication strategies, the perception of risks and the influencing factors should be known. A theory that offers an integrative approach to understanding and explaining risk perception is still missing. To explain risk perception, it is necessary to consider several perspectives: social, psychological and cultural perspectives and their interactions. This paper presents the results of the CATI survey on seismic risk perception in Italy, conducted by INGV researchers on funding by the DPC. We built a questionnaire to assess seismic risk perception, with a particular attention to compare hazard, vulnerability and exposure perception with the real data of the same factors. The Seismic Risk Perception Questionnaire (SRP-Q) is designed by semantic differential method, using opposite terms on a Likert scale to seven points. The questionnaire allows to obtain the scores of five risk indicators: Hazard, Exposure, Vulnerability, People and Community, Earthquake Phenomenon. The questionnaire was administered by telephone interview (C.A.T.I.) on a statistical sample at national level of over 4,000 people, in the period January -February 2015. Results show that risk perception seems be underestimated for all indicators considered. In particular scores of seismic Vulnerability factor are extremely low compared with house information data of the respondents. Other data collected by the questionnaire regard Earthquake information level, Sources of information, Earthquake occurrence with respect to other natural hazards, participation at risk reduction activities and level of involvement. Research on risk perception aims to aid risk analysis and policy-making by

  16. Seismic wave velocity of Archaeozoic felsic rocks from North China and its existing location in the crust

    Institute of Scientific and Technical Information of China (English)

    SUN Jun-xiu; XIE Yi-han; ZHANG You-nan

    2000-01-01

    This paper contains two contents. The first is seismic velocity of felsic crystalline rocks of North China at room temperature and high pressures and at both high temperatures and pressures. The second is heating acoustic emission of felsic rocks at atmosphere pressure and the temperature of the quartz a -b transition. The results of these experiments show that velocities of the felsic crystalline rocks are obviously lower than that of the basic rocks and no visible relationship with metamorphic phase. The velocity curves of rocks containing quartz display peaks of the a -b phase reaction, which are different from other rocks in configuration. When the heating temperature is up to the phase transition temperature of quartz at the atmosphere pressure, felsic hypometamorphic rocks and magma granite produce acoustic emission. While the other kind of the granite generated by metasomatism does not produce acoustic emission. These results have the following implications. It explains the crustal constitution of the North China craton in combination with other geoscientific data, and clarifies the existing space of a quartz and b quartz. It also indicates that the a -b quartz transition and dehydration melting of amphibole and biotite in the lower crustal rocks of the Cenozoic tectonic subsidence area are likely associated with faulting (tensional fault) and seismic activities.

  17. Timing of the granulite facies metamorphism in the Sanggan area, North China craton: zircon U-Pb geochronology

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Zircon U-Pb ages are reported for three samples of intrusive rocks in Khondalite series in the Sanggan area, North China craton. The age of meta-granite is dated as 2005±9 Ma, implying that the sedimentary sequences in Khondalites series formed before 2.0Ga. The age of 1921 ±1Ma for the meta-diorite constrain the age of granulite facies metamorphism younger than this date. The age of 1892±10 Ma for garnet granite is obtained, but the granite crystallization age seems a little younger than the date considering the morphology of zircons. On the basis of these dates and of a concise review of previous age data, it is inferred that the Khondalite series was subjected to granulite facies metamorphism at about 1.87Ga together with tonalitic granulites and HP basic granulites in the Sanggan area.

  18. Comparison of mantle lithosphere beneath early Triassic kimberlite fields in Siberian craton reconstructed from deep-seated xenocrysts

    Directory of Open Access Journals (Sweden)

    I.V. Ashchepkov

    2016-07-01

    Kharamai mantle clinopyroxenes represent three geochemical types: (1 harzburgitic with inclined linear REE, HFSE troughs and elevated Th, U; (2 lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements; (3 eclogitic with Eu troughs, Pb peak and high LILE content. Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction. Clinopyroxenes from Ary-Mastakh fields show less inclined REE patterns with HMREE troughs and an increase of incompatible elements. Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba, U, Pb and Sr, similar to those in ophiolitic harzburgites. The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe#Ol upward and slightly reduced thickness of the mantle keel of the Siberian craton, resulting from the influence of the Permian–Triassic superplume, but with no signs of delamination.

  19. Geological and geochemical evolution of the Trincheira Complex, a Mesoproterozoic ophiolite in the southwestern Amazon craton, Brazil

    Science.gov (United States)

    Rizzotto, Gilmar José; Hartmann, Léo Afraneo

    2012-09-01

    We document the first-known Mesoproterozoic ophiolite from the southwestern part of the Amazon craton, corresponding to the Trincheira Complex of Calymmian age, and propose a tectonic model that explains many previously enigmatic features of the Precambrian history of this key craton, and discuss its role in the reconstruction of the Columbia supercontinent. The complex comprises extrusive rocks (fine-grained amphibolites derived from massive and pillowed basalts), mafic-ultramafic intrusive rocks, chert, banded iron formation (BIFs), pelites, psammitic and a smaller proportion of calc-silicate rocks. This sequence was deformed, metasomatized and metamorphosed during the development of the Alto Guaporé Belt, a Mesoproterozoic accretionary orogen. The rocks were deformed by a single tectonic event, which included isoclinal folding and metamorphism of the granulite-amphibolite facies. Layered magmatic structures were preserved in areas of low strain, including amygdaloidal and cumulate structures. Metamorphism was pervasive and reached temperatures of 780-853 °C in mafic granulites and 680-720 °C in amphibolites under an overall pressure of 6.8 kbar. The geochemical composition of the extrusive and intrusive rocks indicates that all noncumulus mafic-ultramafic rocks are tholeiitic basalts. The mafic-ultramafic rocks display moderate to strong fractionation of light rare earth elements (LREE), near-flat heavy rare earth element (HREE) patterns and moderate to strong negative high field strength element (HFSE) anomalies (especially Nb), a geochemical signature typical of subduction zones. The lowest units of mafic granulites and porphyroblastic amphibolites in the Trincheira ophiolite are similar to the modern mid-ocean ridge basalt (MORB), although they locally display small Ta, Ti and Nb negative anomalies, indicating a small subduction influence. This behavior changes to an island arc tholeiite (IAT) signature in the upper units of fine-grained amphibolites and

  20. Composition and Thermal History of the Lower Crust Beneath the Tanzania Craton and the Adjacent Mozambique Belt

    Science.gov (United States)

    Mansur, A. T.; Manya, S.; Rudnick, R. L.

    2006-05-01

    The Tanzanian craton has undergone little deformation since its formation 2.6 Ga ago, but Archaean crust of the adjacent Mozambique Belt (MB) has been reworked by at least two high-grade metamorphic events. An old, thick (~~200-km) lithospheric keel appears to have stabilized the craton during these deformational events. Although a thick keel appears to be absent beneath the MB today, ancient mantle lithosphere is preserved beneath much of the MB and the original thickness of this lithosphere is uncertain. Studies of the present-day lower crust can help to constrain the compositional and thermal evolution of this region. Granulite xenoliths from the Labait volcano (craton margin) are exclusively mafic and are mostly two pyroxene granulites, but also include gt-opx granulites and a gt-cpx-spinel-corundum anorthosite. Most samples also have orthoclase as a major phase. Two-pyroxene thermometry yields temperatures of 710 to 810°C for an estimated lower crustal pressure of 1 GPa; whereas the anorthosite appears to have equilibrated at a somewhat hotter temperature (gt-cpx T = 970°C). All Labait xenoliths exhibit high K2O (0.8 to 2.6 wt., excluding the anorthosite), Ba (530 to 6730 ppm), Sr (440 to 1040 ppm) and Ni contents (100 to 400 ppm) and relatively high Mg# (47 to 63). The combined high Ni, Mg# and alkali and alkaline-earth elements may reflect an unusual igneous protolith (e.g., adakitic magma) or mafic cumulates that have been metasomatically enriched in the lower crust. Granulite xenoliths from Lashaine (MB) are also exclusively mafic and form two groups: 1) anorthositic, high Al2O3 (17 to 23 wt. %) and Mg#, plag-ky-cpx-gt granulites, which are enriched in Sr and have positive Eu anomalies and 2) lower Al2O3 (13 wt. %), two pyroxene ± gt granulites, which are enriched in Ti, K, P and Ni. The latter may be meta-cumulates from alkaline magmas. Temperatures for Lashaine granulites range from 770 to 980°C. Unlike Labait and Lashaine, the Naibor Soito

  1. Complex evolution of the lower crust beneath the southeastern North China Craton: The Junan xenoliths and xenocrysts: Reply

    Science.gov (United States)

    Tang, Huayun; Zheng, Jianping; Griffin, William L.; O‧Reilly, Suzanne Y.; Yu, Chunmei; Pearson, Norman J.; Ping, Xianquan; Xia, Bing; Yang, Huaben

    2015-10-01

    In our paper, we suggested that the Junan granulite xenoliths and xenocrysts record evolution of the Precambrian lower crust beneath the southeastern North China Craton (NCC). Yuan and Xia (2015) disagree with us. However, they have not fully considered the evolutional histories of the NCC lithosphere, and geochemical and isotopic compositions of the Junan xenoliths. We also contend that they have misinterpreted the available geophysical data. Synthesizing the geochronological characteristics of the NCC lower crust, nature of the Junan granulite xenoliths, and reinterpretation of the resistivity profile, we again emphasize that the Junan granulite xenoliths are tectonically affiliated to the NCC lower crust, and the Junan zircon data could reflect the complex evolution of the lower crust beneath the southeastern NCC.

  2. Geochronology of middle Neoproterozoic volcanic deposits in Yangtze Craton interior of South China and its implications to tectonic settings

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Here we report new SHRIMP dating results of the crystal tuff in Ejiaao Formation of middle Banxi Group in northern Guizhou. The results indicate that the volcanic deposition occurred at ~780 Ma. We also suggests that the igneous activities across Yangtze Craton with diabase dyke swarms and basal volcanic rocks during middle Banxi time are indicative of the episodic, extensive and vigorous great bimodal igneous events during middle Neoproterozoic (825-720 Ma) in South China. The characteristics of the igneous series are contrary to the model claiming they are of island-arc origin, but suggest that they are the records of rifting process and may be related to the episodic plume activities leading to the break-up of Rodinia.

  3. Thermodynamic evolution of lithosphere of the North China craton: Records from lower crust and upper mantle xenoliths from Hannuoba

    Institute of Scientific and Technical Information of China (English)

    LIU Yongsheng; GAO Shan; LIU Xiaoming; CHEN Xiaoming; ZHANG Wenlan; WANG Xuance

    2003-01-01

    Major element compositions of garnet, clinopyroxene, orthopyroxene andspinel in the garnet-bearing lower crust and upper mantle xenoliths from Hannuoba, North China craton are analyzed by the electron microprobe (EMP). The pressure-temperature estimates reveal the increasing temperature and pressure from core to rim for granulites. In contrast, mantle xenoliths with core temperature > 930℃ recorded a history of decrease in temperature and pressure. However, those with core temperature < 930℃ show a negligible change. The final pressures recorded by these xenoliths cluster at 0.9-1.5 GPa. The presence of high- Na2O cpx in granulite xenoliths suggests that they are products of the transition from granulite to eclogite metamorphism corresponding to the increasing temperature andpressure. Together with previous studies, it is suggested that the P-T changes preserved in the xenoliths are related to lithospheric thickening and subsequentthinning prior to their eruption in the Cenozoic.

  4. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: What Is the Message?

    Science.gov (United States)

    El Atrassi, F.; Debaille, V.; Mattielli, N. D. C.; Berger, J.

    2014-12-01

    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African Craton in Mauritania (Amsaga area). The Amsaga Archean Crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. Our main objectives aim to the identification of the mafic lithology origin and a better understanding of their role in the continental crust emplacement. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. The amphibolites are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. Two groups are distinct in their geochemical characteristics (major and trace elements), although both have tholeiitic basalt composition. The first group show LREE-enriched patterns and negative Nb-Ta anomalies. The second group is characterized by near-flat LREE patterns and flat HREE patterns. This second group clearly shows no Nb-Ta anomalies. The first group could be related to arc-like basalts, as it is many similarities with some Archean amphibolites probably formed in a supra-subduction zone, for instance the volcanic rocks from the southern edge of the Isua Supracrustal Belt. On the contrary, the second group has a MORB-like signature which is more unusual during the Archean. Different scenarios will be discussed regards to the Archean geodynamics.

  5. Study on the genesis of Yishui banded iron formation (BIF) in the North China Craton: geochemical characteristics and tectonic environment

    Science.gov (United States)

    Moon, I.; Lee, I.; Yang, X.

    2015-12-01

    The Yishui BIFs are located in the Taishan Group, Shandong province of Eastern Block of North China Craton. The iron ore samples were collected from the mine pits. Major elements were analyzed by X-ray Fluoresence Spectromemter (XRF). Trace elements and REY (REE + Y) were analyzed by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Petrological, mineralogical and geochemical analyses of iron ores and their wall rock (amphibolite) were conducted to trace the genesis of Yishui BIF. Iron ores of Yishui BIF are mainly composed of SiO2 and Fe2O3T (SiO2+ Fe2O3T= 85.8 to 98.8 wt%) and consistent with major mineral components which are quartz and iron oxide such as magnetite and hematite. Low contents of TiO2 (0.01 to 0.09 wt%) , Al2O3 (0.42 to 1.18 wt%) and HFSE indicate no or little effect of detrital contamination. Iron ores have positive La, Eu, Gd, Er and Y anomalies with enriched HREE in PAAS normalized REY graph. The REY patterns of iron ores were used as a fingerprint to trace the source of iron and silica. Distinctive positive Eu anomalies (Eu/Eu*= 2.44-4.19), Y anomalies (Y/Y*=0.97 - 4.19), slightly negative Ce anomalies (Ce/Ce*= 0.87-0.97) and enriched HREE ((La/Yb)SN= 0.17-0.32) indicate that mixture of seawater and high-temperature hydrothermal fluid (>250 ◦C). Depositional environment in North China Craton implies that Yishui BIFs were formed at Neoarchean and associated arc-related tectonic setting. All these data suggest that Yishui BIFs belong to typical Algoma-type BIF.

  6. Delineation of seismic source zones based on seismicity parameters and probabilistic evaluation of seismic hazard using logic tree approach

    Indian Academy of Sciences (India)

    K S Vipin; T G Sitharam

    2013-06-01

    The delineation of seismic source zones plays an important role in the evaluation of seismic hazard. In most of the studies the seismic source delineation is done based on geological features. In the present study, an attempt has been made to delineate seismic source zones in the study area (south India) based on the seismicity parameters. Seismicity parameters and the maximum probable earthquake for these source zones were evaluated and were used in the hazard evaluation. The probabilistic evaluation of seismic hazard for south India was carried out using a logic tree approach. Two different types of seismic sources, linear and areal, were considered in the present study to model the seismic sources in the region more precisely. In order to properly account for the attenuation characteristics of the region, three different attenuation relations were used with different weightage factors. Seismic hazard evaluation was done for the probability of exceedance (PE) of 10% and 2% in 50 years. The spatial variation of rock level peak horizontal acceleration (PHA) and spectral acceleration (Sa) values corresponding to return periods of 475 and 2500 years for the entire study area are presented in this work. The peak ground acceleration (PGA) values at ground surface level were estimated based on different NEHRP site classes by considering local site effects.

  7. Cursory seismic drift assessment for buildings in moderate seismicity regions

    Institute of Scientific and Technical Information of China (English)

    Zhu Yong; R.K.L. Su; Zhou Fulin

    2007-01-01

    This paper outlines a methodology to assess the seismic drift of reinforced concrete buildings with limited structural and geotechnical information. Based on the latest and the most advanced research on predicting potential near-field and far field earthquakes affecting Hong Kong, the engineering response spectra for both rock and soil sites are derived. A new step-by-step procedure for displacement-based seismic hazard assessment of building structures is proposed to determine the maximum inter-storey drift demand for reinforced concrete buildings. The primary information required for this assessment is only the depth of the soft soil above bedrock and the height of the building. This procedure is further extended to assess the maximum chord rotation angle demand for the coupling beam of coupled shear wall or frame wall structures, which may be very critical when subjected to earthquake forces. An example is provided to illustrate calibration of the assessment procedure by using actual engineering structural models.

  8. Seismic damage and destructive potential of seismic events

    Directory of Open Access Journals (Sweden)

    S. M. Petrazzuoli

    1995-06-01

    Full Text Available This paper has been written within a research framework investigating the destructive potential of seismic events. The elastic response spectra seem insufficient to explain the behaviour of structures subject to large earthquakes in which they experience extensive plastic deformations. Recent works emphasise that there were many difficulties in the definition of a single pararneter linked to the destl-uctive potential of an earthquake. In this work a study on the effect of frequency content on structural damage has been carried out. The behaviour of two different elastoplastic oscillators has been analysed, considering several artificial earthquakes. The results obtained suggest a method for evaluating the destructive seismic potential of an earthquake through the response spectra ad the frequency content of the signal. and through the mechai~ical characteristics of the structures within the analysed area.

  9. Crustal Structure, Seismic Anisotropy and Deformations of the Ediacaran/Cambrian of the Małopolska Block in SE Poland Based on Data from Two Seismic Wide-Angle Experiments

    Science.gov (United States)

    Środa, Piotr

    2017-04-01

    The area of SE Poland represents a complex contact of tectonic units of different consolidation age—from the Precambrian East European Craton, through Palaeozoic West European Platform (including Małopolska Block) to Cenozoic Carpathians and Carpathian Foredeep. In order to investigate the anisotropic properties of the upper crust of the Małopolska Block and their relation to tectonic evolution of the area, two seismic datasets were used: seismic wide-angle off-line recordings from POLCRUST-01 deep seismic reflection profile and recordings from active deep seismic experiment CELEBRATION 2000. During acquisition of deep reflection seismic profile POLCRUST-01 in 2010, a 35-km-long line of 14 recorders (PA-14), oriented perpendicularly to the profile, was deployed to record the refractions from the upper crust (Pg) at wide range of azimuths. These data were used for an analysis of the azimuthal anisotropy of the MB with the modified delay-time inversion method. The results of modelling of the off-line refractions from the MB suggest 6% HTI anisotropy of the Cambrian/Ediacaran basement, with 130º azimuth of the fast velocity axis and mean Vp of 4.9 km/s. To compare this result with previous, independent information about anisotropy at larger depth, a subset of previously modelled data from CELEBRATION 2000 experiment, recorded in the MB area, was also analysed by inversion. The recordings of Pg phase at up to 120 km offsets were analysed using anisotropic delay-time inversion, providing information down to 12 km depth. The CELEBRATION 2000 model shows 9% HTI anisotropy with 126º orientation of the fast axis. Thus, local-scale anisotropy of this part of MB confirms the large-scale anisotropy suggested by previous studies based on data from a broader area and larger depth interval. The azimuthal anisotropy (i.e. HTI symmetry of the medium) is interpreted as a result of strong compressional deformation during the accretion of terranes to the EEC margin, leading to

  10. Reconstruction of a 2D seismic wavefield by seismic gradiometry

    Science.gov (United States)

    Maeda, Takuto; Nishida, Kiwamu; Takagi, Ryota; Obara, Kazushige

    2016-12-01

    We reconstructed a 2D seismic wavefield and obtained its propagation properties by using the seismic gradiometry method together with dense observations of the Hi-net seismograph network in Japan. The seismic gradiometry method estimates the wave amplitude and its spatial derivative coefficients at any location from a discrete station record by using a Taylor series approximation. From the spatial derivatives in horizontal directions, the properties of a propagating wave packet, including the arrival direction, slowness, geometrical spreading, and radiation pattern can be obtained. In addition, by using spatial derivatives together with free-surface boundary conditions, the 2D vector elastic wavefield can be decomposed into divergence and rotation components. First, as a feasibility test, we performed an analysis with a synthetic seismogram dataset computed by a numerical simulation for a realistic 3D medium and the actual Hi-net station layout. We confirmed that the wave amplitude and its spatial derivatives were very well-reproduced for period bands longer than 25 s. Applications to a real large earthquake showed that the amplitude and phase of the wavefield were well reconstructed, along with slowness vector. The slowness of the reconstructed wavefield showed a clear contrast between body and surface waves and regional non-great-circle-path wave propagation, possibly owing to scattering. Slowness vectors together with divergence and rotation decomposition are expected to be useful for determining constituents of observed wavefields in inhomogeneous media.

  11. Seismic Isolation Working Meeting Gap Analysis Report

    Energy Technology Data Exchange (ETDEWEB)

    Coleman, Justin [Idaho National Lab. (INL), Idaho Falls, ID (United States); Sabharwall, Piyush [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2014-09-01

    The ultimate goal in nuclear facility and nuclear power plant operations is operating safety during normal operations and maintaining core cooling capabilities during off-normal events including external hazards. Understanding the impact external hazards, such as flooding and earthquakes, have on nuclear facilities and NPPs is critical to deciding how to manage these hazards to expectable levels of risk. From a seismic risk perspective the goal is to manage seismic risk. Seismic risk is determined by convolving the seismic hazard with seismic fragilities (capacity of systems, structures, and components (SSCs)). There are large uncertainties associated with evolving nature of the seismic hazard curves. Additionally there are requirements within DOE and potential requirements within NRC to reconsider updated seismic hazard curves every 10 years. Therefore opportunity exists for engineered solutions to manage this seismic uncertainty. One engineered solution is seismic isolation. Current seismic isolation (SI) designs (used in commercial industry) reduce horizontal earthquake loads and protect critical infrastructure from the potentially destructive effects of large earthquakes. The benefit of SI application in the nuclear industry is being recognized and SI systems have been proposed, in the American Society of Civil Engineers (ASCE) 4 standard, to be released in 2014, for Light Water Reactors (LWR) facilities using commercially available technology. However, there is a lack of industry application to the nuclear industry and uncertainty with implementing the procedures outlined in ASCE-4. Opportunity exists to determine barriers associated with implementation of current ASCE-4 standard language.

  12. Discussion about the relationship between seismic belt and seismic statistical zone

    Institute of Scientific and Technical Information of China (English)

    潘华; 金严; 胡聿贤

    2003-01-01

    This paper makes a summary of status of delimitation of seismic zones and belts of China firstly in aspects of studying history, purpose, usage, delimiting principles, various presenting forms and main specialties. Then the viewpoints are emphasized, making geographical divisions by seismicity is just the most important purpose of delimiting seismic belts and the concept of seismic belt is also quite different from that of seismic statistical zone used in CPSHA method. The concept of seismic statistical zone and its history of evolvement are introduced too. Large differences between these two concepts exist separately in their statistical property, actual meaning, gradation, required scale, and property of refusing to overlap each other, aim and usage of delimitation. But in current engineering practice, these two concepts are confused. On the one hand, it causes no fit theory for delimiting seismic statistical zone in PSHA to be set up; on the other hand, researches about delimitation of seismic belts with purposes of seismicity zoning and studying on structural environment, mechanism of earthquake generating also pause to go ahead. Major conclusions are given in the end of this paper, that seismic statistical zone bases on the result of seismic belt delimiting, it only arises in and can be used in the especial PSHA method of China with considering spatially and temporally inhomogeneous seismic activities, and its concept should be clearly differentiated from the concept of seismic belt.

  13. Seismic techniques in coal mining

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharyya, A.K.; Belleza, G.V.

    1983-01-01

    The aim of this study is to investigate the peripheral fracture zones in coal pillars left for support in underground mines. The fracture zones are caused by the redistribution of stresses in strata resulting from the process of excavation and blasting if it is used. The extent and degree of these fracture zones, in turn, have a direct influence on the ability of pillars to provide stable support to the overlying strata. Seismic methods such as refraction, uphole, and collinear techniques outlined in previous reports are being used to investigate the extent and degree of the peripheral fracture zones. Some of the work that has been carried out and is described in this report, relates to the study of peripheral fracture zones in coal pillars using seismic techniques.

  14. Statistical Physics Approaches to Seismicity

    CERN Document Server

    Sornette, D

    2008-01-01

    This entry in the Encyclopedia of Complexity and Systems Science, Springer present a summary of some of the concepts and calculational tools that have been developed in attempts to apply statistical physics approaches to seismology. We summarize the leading theoretical physical models of the space-time organization of earthquakes. We present a general discussion and several examples of the new metrics proposed by statistical physicists, underlining their strengths and weaknesses. The entry concludes by briefly outlining future directions. The presentation is organized as follows. I Glossary II Definition and Importance of the Subject III Introduction IV Concepts and Calculational Tools IV.1 Renormalization, Scaling and the Role of Small Earthquakes in Models of Triggered Seismicity IV.2 Universality IV.3 Intermittent Periodicity and Chaos IV.4 Turbulence IV.5 Self-Organized Criticality V Competing mechanisms and models V.1 Roots of complexity in seismicity: dynamics or heterogeneity? V.2 Critical earthquakes ...

  15. Tube-wave seismic imaging

    Science.gov (United States)

    Korneev, Valeri A [LaFayette, CA

    2009-05-05

    The detailed analysis of cross well seismic data for a gas reservoir in Texas revealed two newly detected seismic wave effects, recorded approximately 2000 feet above the reservoir. A tube-wave (150) is initiated in a source well (110) by a source (111), travels in the source well (110), is coupled to a geological feature (140), propagates (151) through the geological feature (140), is coupled back to a tube-wave (152) at a receiver well (120), and is and received by receiver(s) (121) in either the same (110) or a different receiving well (120). The tube-wave has been shown to be extremely sensitive to changes in reservoir characteristics. Tube-waves appear to couple most effectively to reservoirs where the well casing is perforated, allowing direct fluid contact from the interior of a well case to the reservoir.

  16. DISPLACEMENT BASED SEISMIC DESIGN CRITERIA

    Energy Technology Data Exchange (ETDEWEB)

    HOFMAYER,C.H.

    1999-03-29

    The USNRC has initiated a project to determine if any of the likely revisions to traditional earthquake engineering practice are relevant to seismic design of the specialized structures, systems and components of nuclear power plants and of such significance to suggest that a change in design practice might be warranted. As part of the initial phase of this study, a literature survey was conducted on the recent changes in seismic design codes/standards, on-going activities of code-writing organizations/communities, and published documents on displacement-based design methods. This paper provides a summary of recent changes in building codes and on-going activities for future codes. It also discusses some technical issues for further consideration.

  17. Displacement Based Seismic Design Criteria

    Energy Technology Data Exchange (ETDEWEB)

    Costello, J.F.; Hofmayer, C.; Park, Y.J.

    1999-03-29

    The USNRC has initiated a project to determine if any of the likely revisions to traditional earthquake engineering practice are relevant to seismic design of the specialized structures, systems and components of nuclear power plants and of such significance to suggest that a change in design practice might be warranted. As part of the initial phase of this study, a literature survey was conducted on the recent changes in seismic design codes/standards, on-going activities of code-writing organizations/communities, and published documents on displacement-based design methods. This paper provides a summary of recent changes in building codes and on-going activities for future codes. It also discusses some technical issues for further consideration.

  18. An economical educational seismic system

    Science.gov (United States)

    Lehman, J. D.

    1980-01-01

    There is a considerable interest in seismology from the nonprofessional or amateur standpoint. The operation of a seismic system can be satisfying and educational, especially when you have built and operated the system yourself. A long-period indoor-type sensor and recording system that works extremely well has been developed in the James Madison University Physics Deparment. The system can be built quite economically, and any educational institution that cannot commit themselves to a professional installation need not be without first-hand seismic information. The system design approach has been selected by college students working a project or senior thesis, several elementary and secondary science teachers, as well as the more ambitious tinkerer or hobbyist at home 

  19. PdS and SdP Receiver Functions Image of the Lithosphere underneath the Southern African Regions

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Thybo, Hans; Levander, A

    2009-01-01

    One of the unique spots in our Earth is the Kaapvaal craton; it preserves a rich record of the early earth and is underlain by unusually thick, ~ 200 km deep, chemically depleted lithospheric mantle of early Archean age. The internal structure of this unusual upper mantle, termed the tectosphere...... of a significant difference in anisotropy between the craton and the surrounding tectonic belts. The evidence for this variation arises from the good azimuthal coverage, which provides an obvious polarity reversal of signals versus back azimuth coinciding spatially with the Kaapvaal boundaries. To confirm...

  20. Electrical Conductivity Model of the Mantle Lithosphere of the Slave Craton (NW Canada) and its tectonic interpretation in the context of Geochemical Results

    Science.gov (United States)

    Lezaeta, P.; Chave, A.; Evans, R.; Jones, A. G.; Ferguson, I.

    2002-12-01

    The Slave Craton, northwestern Canada, contains the oldest known rocks on Earth, with exposed outcrop over an area of about 600x400 km2. The discovery of economic diamondiferous kimberlite pipes during the early 1990s motivated extensive research in the region. Over the last six years, four types of deep-probing magnetotelluric (MT) surveys were conducted within the framework of diverse geoscientific programs, aimed at determining the regional-scale electrical structures of the craton. Two of the surveys involved novel acquisition; one through frozen lake ice along ice roads during winter, and the second deploying ocean-bottom instrumentation from float planes during summer. The latter surveys required one year of recording between summers, thus allowing long period transfer functions that lead to mantle penetration depths of over 300 km. Two-dimensional modeling of the MT data from along the winter road showed the existence of a high conductivity zone at depths of 80-120 km beneath the central Slave craton. This anomalous region is spatially coincident with an ultradepleted harzburgitic layer in the upper mantle that was interpreted by others to be related to a subducted slab emplaced during the mid-Archean. A 3-D electrical conductivity model of the Slave lithosphere has been obtained, by trial and error, to fit the magnetic transfer and MT response functions from the lake experiments. This 3-D model traces the central Slave conductor as a NE-SW oriented mantle structure. Its NE-SW orientation coincides with that of a late fold belt system, with the first phase of craton-wide plutonism at ca 2630-2590 Ma, three-part subdivision of the craton based on SKS results, and with a G10 (garnet) geochemical mantle boundaries. All of these highlight a NE-SW structural grain to the lithospheric mantle of the craton, in sharp contrast to the N-S grain of the crust. Constraints on the depth range and lateral extension of the electrical conductive structure are obtained

  1. Seismic hazard studies in Egypt

    Directory of Open Access Journals (Sweden)

    Abuo El-Ela A. Mohamed

    2012-12-01

    Full Text Available The study of earthquake activity and seismic hazard assessment of Egypt is very important due to the great and rapid spreading of large investments in national projects, especially the nuclear power plant that will be held in the northern part of Egypt. Although Egypt is characterized by low seismicity, it has experienced occurring of damaging earthquake effect through its history. The seismotectonic sitting of Egypt suggests that large earthquakes are possible particularly along the Gulf of Aqaba–Dead Sea transform, the Subduction zone along the Hellenic and Cyprean Arcs, and the Northern Red Sea triple junction point. In addition some inland significant sources at Aswan, Dahshour, and Cairo-Suez District should be considered. The seismic hazard for Egypt is calculated utilizing a probabilistic approach (for a grid of 0.5° × 0.5° within a logic-tree framework. Alternative seismogenic models and ground motion scaling relationships are selected to account for the epistemic uncertainty. Seismic hazard values on rock were calculated to create contour maps for four ground motion spectral periods and for different return periods. In addition, the uniform hazard spectra for rock sites for different 25 periods, and the probabilistic hazard curves for Cairo, and Alexandria cities are graphed. The peak ground acceleration (PGA values were found close to the Gulf of Aqaba and it was about 220 gal for 475 year return period. While the lowest (PGA values were detected in the western part of the western desert and it is less than 25 gal.

  2. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    Energy Technology Data Exchange (ETDEWEB)

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2003-10-01

    In this report we will show the fundamental concepts of two different methods to compute seismic energy absorption. The first methods gives and absolute value of Q and is based on computation with minimum phase operators. The second method gives a relative energy loss compared to a background trend. This method is a rapid, qualitative indicator of anomalous absorption and can be combined with other attributes such as band limited acoustic impedance to indicate areas of likely gas saturation.

  3. Research on the effect estimation of seismic safety evaluation

    Institute of Scientific and Technical Information of China (English)

    邹其嘉; 陶裕禄

    2004-01-01

    Seismic safety evaluation is a basic work for determining the seismic resistance requirements of major construction projects. The effect, especially the economic effect of the seismic safety evaluation has been generally concerned. The paper gives a model for estimating the effect of seismic safety evaluation and calculates roughly the economic effect of seismic safety evaluation with some examples.

  4. Major, trace and platinum group element (PGE) geochemistry of Archean Iron Ore Group and Proterozoic Malangtoli metavolcanic rocks of Singhbhum Craton, Eastern India: Inferences on mantle melting and sulphur saturation history

    Digital Repository Service at National Institute of Oceanography (India)

    Singh, M.R.; Manikyamba, C.; Ray, J.; Ganguly, S.; Santosh, M.; Saha, A.; Rambabu, S.; Sawant, S.S.

    The geological and metallogenic history of the Singhbhum Craton of eastern India is marked by several episodes of volcanism, plutonism, sedimentation and mineralization spanning from Paleoarchean to Mesoproterozoic in a dynamic tectonic milieu...

  5. Seismicity of Afghanistan and vicinity

    Science.gov (United States)

    Dewey, James W.

    2006-01-01

    This publication describes the seismicity of Afghanistan and vicinity and is intended for use in seismic hazard studies of that nation. Included are digital files with information on earthquakes that have been recorded in Afghanistan and vicinity through mid-December 2004. Chapter A provides an overview of the seismicity and tectonics of Afghanistan and defines the earthquake parameters included in the 'Summary Catalog' and the 'Summary of Macroseismic Effects.' Chapter B summarizes compilation of the 'Master Catalog' and 'Sub-Threshold Catalog' and documents their formats. The 'Summary Catalog' itself is presented as a comma-delimited ASCII file, the 'Summary of Macroseismic Effects' is presented as an html file, and the 'Master Catalog' and 'Sub-Threshold Catalog' are presented as flat ASCII files. Finally, this report includes as separate plates a digital image of a map of epicenters of earthquakes occurring since 1964 (Plate 1) and a representation of areas of damage or strong shaking from selected past earthquakes in Afghanistan and vicinity (Plate 2).

  6. Seismic risk mapping for Germany

    Science.gov (United States)

    Tyagunov, S.; Grünthal, G.; Wahlström, R.; Stempniewski, L.; Zschau, J.

    2006-06-01

    The aim of this study is to assess and map the seismic risk for Germany, restricted to the expected losses of damage to residential buildings. There are several earthquake prone regions in the country which have produced Mw magnitudes above 6 and up to 6.7 corresponding to observed ground shaking intensity up to VIII-IX (EMS-98). Combined with the fact that some of the earthquake prone areas are densely populated and highly industrialized and where therefore the hazard coincides with high concentration of exposed assets, the damaging implications from earthquakes must be taken seriously. In this study a methodology is presented and pursued to calculate the seismic risk from (1) intensity based probabilistic seismic hazard, (2) vulnerability composition models, which are based on the distribution of residential buildings of various structural types in representative communities and (3) the distribution of assets in terms of replacement costs for residential buildings. The estimates of the risk are treated as primary economic losses due to structural damage to residential buildings. The obtained results are presented as maps of the damage and risk distributions. For a probability level of 90% non-exceedence in 50 years (corresponding to a mean return period of 475 years) the mean damage ratio is up to 20% and the risk up to hundreds of millions of euro in the most endangered communities. The developed models have been calibrated with observed data from several damaging earthquakes in Germany and the nearby area in the past 30 years.

  7. Building a Smartphone Seismic Network

    Science.gov (United States)

    Kong, Q.; Allen, R. M.

    2013-12-01

    We are exploring to build a new type of seismic network by using the smartphones. The accelerometers in smartphones can be used to record earthquakes, the GPS unit can give an accurate location, and the built-in communication unit makes the communication easier for this network. In the future, these smartphones may work as a supplement network to the current traditional network for scientific research and real-time applications. In order to build this network, we developed an application for android phones and server to record the acceleration in real time. These records can be sent back to a server in real time, and analyzed at the server. We evaluated the performance of the smartphone as a seismic recording instrument by comparing them with high quality accelerometer while located on controlled shake tables for a variety of tests, and also the noise floor test. Based on the daily human activity data recorded by the volunteers and the shake table tests data, we also developed algorithm for the smartphones to detect earthquakes from daily human activities. These all form the basis of setting up a new prototype smartphone seismic network in the near future.

  8. Seismic microzonation of Bangalore, India

    Indian Academy of Sciences (India)

    P Anbazhagan; T G Sitharam

    2008-11-01

    In the present study, an attempt has been made to evaluate the seismic hazard considering local site effects by carrying out detailed geotechnical and geophysical site characterization in Bangalore, India to develop microzonation maps. An area of 220 km2, encompassing Bangalore Mahanagara Palike (BMP) has been chosen as the study area. Seismic hazard analysis and microzonation of Bangalore are addressed in three parts: in the first part, estimation of seismic hazard is done using seismotectonic and geological information. Second part deals with site characterization using geotechnical and shallow geophysical techniques. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis (using the program SHAKE 2000) using both standard penetration test (SPT) data and shear wave velocity data from multichannel analysis of surface wave (MASW) survey. Further, field experiments using microtremor studies have also been carried out for evaluation of predominant frequency of the soil columns. The same has been assessed using 1-D ground response analysis and compared with microtremor results. Further, the Seed and Idriss simplified approach has been adopted to evaluate the soil liquefaction susceptibility and liquefaction resistance assessment. Microzonation maps have been prepared with a scale of 1:20,000. The detailed methodology, along with experimental details, collated data, results and maps are presented in this paper.

  9. Importance of direct and indirect triggered seismicity

    CERN Document Server

    Helmstetter, A; Helmstetter, Agnes; Sornette, Didier

    2003-01-01

    Using the simple ETAS branching model of seismicity, which assumes that each earthquake can trigger other earthquakes, we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as in the overall level of seismicity in the presence of a constant external seismicity source. We show that, in this model, the proportion of triggered seismicity is equal to the proportion of secondary plus later-generation aftershocks, and is given by the average number of triggered events per earthquake. Based on these results and on the observation that a large fraction of seismicity are triggered earthquakes, we conclude that similarly a large fraction of aftershocks occurring a few hours or days after a mainshock are triggered indirectly by the mainshock.

  10. Seismic activity at the western Pyrenean edge

    Science.gov (United States)

    Ruiz, M.; Gallart, J.; Díaz, J.; Olivera, C.; Pedreira, D.; López, C.; González-Cortina, J. M.; Pulgar, J. A.

    2006-01-01

    The present-day seismicity at the westernmost part of the Pyrenean domain reported from permanent networks is of low to moderate magnitude. However, it is poorly constrained due to the scarce station coverage of the area. We present new seismic data collected from a temporary network deployed there for 17 months that provides an enhanced image of the seismic activity and its tectonic implications. Our results delineate the westward continuity of the E-W Pyrenean band of seismicity, through the Variscan Basque Massifs along the Leiza Fault, ending up at the Hendaya Fault. This seismicity belt is distributed on a crustal scale, dipping northward to almost 30 km depth. Other relevant seismic events located in the area can be related to the central segment of the Pamplona fault, and to different E-W thrust structures.

  11. The crustal structure of the eastern Fennoscandian Shield and central part of the East-European platform based on seismic, regional geophysic and geological data

    Science.gov (United States)

    Mints, M. V.; Berzin, R. G.; Babayants, P. S.; Konilov, A. N.; Suleimanov, A. K.; Zamozhniaya, N. G.; Zlobin, V. L.

    2003-04-01

    The 1-EU and 4B CDP transects worked out during 1998-2002 years by "Spetsgeophyzica", together with previously developed CDP profiles, have crossed most of the main tectonic units of the eastern Fennoscandian Shield and central part of the East-European platform. They provide seismic images of the Early Precambrian crust and upper mantle from the surface to about 80 km depth (25 s). The Neoarchaean granite-greenstone complexes of the Karelia craton along the 4B profile form a series of the tectonic slices descending eastward, some of which can be traced to the Moho. The Palaeoproterozoic structures presented by two main types: (1) volcano-sedimentary (VS) and (2) granulite-gneiss (GN) belts. The Pechenga-Varzuga VS belt has been identified as overthrust-underthrust southward-dipping package. Tectonic slices formed by the Palaeoproterozoic VS belts alternating with slices of the Neoarchaean granite-gneisses form the imbricated crustal unit that extends along the eastern margin of the Neoarchaean Karelia craton. The slices dip steeply northeastward flattening and partially juxtaposing at 20 km depth at the 1-EU cross-section. This level, which can be understood as the surface of main detachment, ascends westward. An imbrication and related thickening of the crust was caused by displacement of crustal slices in western and southwestern directions because of the Palaeoproterozoic collision event. The Palaeoproterozoic Onega unit comprising VS assemblages originated in a setting of the rifted passive margin forms the northwestward displaced thrust nappe complex. It is considered initially belonging to the southern edge of the Svecofennian passive margin. The Lapland GN belt has been transected by the Polar and EGGI profiles. Both cross-sections demonstrated that it constitutes thick composite crustal-scale tectonic slice. According to geophysical data, the continuation of the Lapland GN belt beneath the platform cover of the East European Craton forms an extended arch

  12. Contrasting geochemical and Sm-Nd isotopic compositions of Archean metasediments from the Kongling high-grade terrain of the Yangtze craton: Evidence for cratonic evolution and redistribution of REE during crustal anatexis

    Science.gov (United States)

    Gao, Shan; Ling, Wenli; Qiu, Yumin; Lian, Zhou; Hartmann, Gerald; Simon, Klaus

    1999-07-01

    Twenty-three clastic metasediments from the Kongling high-grade terrain of the Yangtze craton, South China were analyzed for major, trace and rare earth elements and Sm-Nd isotopic ratios. Associated dioritic-tonalitic-trondhjemitic (DTT) and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance. The results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical, geochemical and Sm-Nd isotopic compositions. Group A is characterized by having no to slight negative Eu anomalies (Eu/Eu∗ = 0.82-1.07), being high in Cr (191-396 ppm) and Ni (68-137 ppm), and low in Th (3.3-7.8 ppm) and REE (ΣREE = 99-156 ppm). These characteristics are similar to those of metasediments from Archean greenstone belts. In addition, the Group A metasediments have the value of the Chemical Index of Alteration (CIW) close to felsic gneisses. Their Sm-Nd isotopic, REE and trace element compositions can be interpreted by mixtures of the DTT gneisses and amphibolites. Dating of detrital zircons from 2 Group A samples by SHRIMP reveals a major concordant age group of 2.87-3.0 Ga, which is identical to the age of the trondhjemitic gneiss. These results strongly suggest that Group A was principally the first-cycle erosion product of the local Kongling DTT gneiss and amphibolite. Moreover, the higher than amphibolite Cr content and slight Eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3.0-3.3 Ga in age also played a role. Group B is characterized by the presence of graphite and shows a more evolved composition similar to post-Archean shales with a prominent negative Eu anomaly (Eu/Eu∗ = 0.48-0.77) and high CIW. On paired Cr/Th vs La/Co and Co/Th plots, Group B samples conform to a two-end member mixing line of the Kongling granitic gneiss and amphibolite. However, data on Nd model age and CIW suggest that the granite component should

  13. Seismic imaging of sandbox experiments – laboratory hardware setup and first reflection seismic sections

    OpenAIRE

    Kukowski, N.; Oncken, O.; M.-L. Buddensiek; C. M. Krawczyk

    2012-01-01

    With the study and technical development introduced here, we combine analogue sandbox simulation techniques with seismic physical modelling of sandbox models. For that purpose, we designed and developed a new mini-seismic facility for laboratory use, comprising a seismic tank, a PC-driven control unit, a positioning system, and piezo-electric transducers used here the first time in an array mode. To assess the possibilities and limits of seismic imaging of small-scale structures in sandbox mo...

  14. Seismic imaging of sandbox experiments – laboratory hardware setup and first reflection seismic sections

    OpenAIRE

    C. M. Krawczyk; Buddensiek, M.-L.; Oncken, O.; Kukowski, N.

    2013-01-01

    With the study and technical development introduced here, we combine analogue sandbox simulation techniques with seismic physical modelling of sandbox models. For that purpose, we designed and developed a new mini-seismic facility for laboratory use, comprising a seismic tank, a PC-driven control unit, a positioning system, and piezoelectric transducers used here for the first time in an array mode. To assess the possibilities and limits of seismic imaging of small-scale str...

  15. A Review of Seismicity in 2010

    Institute of Scientific and Technical Information of China (English)

    Ji Ping; Li Gang; Liu Jie; Ni Sidao

    2011-01-01

    @@ 1 SURVEY OF GLOBE SEISMICITY IN 2010 A total of 28 strong earthquakes with Ms ≥ 7.0 occurred in 2010 throughout the world according to the China Seismic Network (Table 1).The strongest was the Chile earthquake measuring Ms8.8 on February 27, 2010 (Fig.1).There was an apparent increase in frequency and the energy release of earthquakes in 2010, compared with seismicity in 2009.

  16. LANL seismic screening method for existing buildings

    Energy Technology Data Exchange (ETDEWEB)

    Dickson, S.L.; Feller, K.C.; Fritz de la Orta, G.O. [and others

    1997-01-01

    The purpose of the Los Alamos National Laboratory (LANL) Seismic Screening Method is to provide a comprehensive, rational, and inexpensive method for evaluating the relative seismic integrity of a large building inventory using substantial life-safety as the minimum goal. The substantial life-safety goal is deemed to be satisfied if the extent of structural damage or nonstructural component damage does not pose a significant risk to human life. The screening is limited to Performance Category (PC) -0, -1, and -2 buildings and structures. Because of their higher performance objectives, PC-3 and PC-4 buildings automatically fail the LANL Seismic Screening Method and will be subject to a more detailed seismic analysis. The Laboratory has also designated that PC-0, PC-1, and PC-2 unreinforced masonry bearing wall and masonry infill shear wall buildings fail the LANL Seismic Screening Method because of their historically poor seismic performance or complex behavior. These building types are also recommended for a more detailed seismic analysis. The results of the LANL Seismic Screening Method are expressed in terms of separate scores for potential configuration or physical hazards (Phase One) and calculated capacity/demand ratios (Phase Two). This two-phase method allows the user to quickly identify buildings that have adequate seismic characteristics and structural capacity and screen them out from further evaluation. The resulting scores also provide a ranking of those buildings found to be inadequate. Thus, buildings not passing the screening can be rationally prioritized for further evaluation. For the purpose of complying with Executive Order 12941, the buildings failing the LANL Seismic Screening Method are deemed to have seismic deficiencies, and cost estimates for mitigation must be prepared. Mitigation techniques and cost-estimate guidelines are not included in the LANL Seismic Screening Method.

  17. Using Composites in Seismic Retrofit Applications

    Science.gov (United States)

    2007-11-02

    composite shells/wraps/ jackets for the seismic retrofit of concrete columns, a number of these could potentially be used, and these are briefly discussed...Use of Concrete and Steel Jackets for Seismic Retrofit For reinforced concrete columns with these substandard reinforcement details, retrofit systems...an overview of the variations possible for the application of FRP composite jackets for purposes of seismic retrofit of columns. Wherever possible

  18. New Methodology for Rapid Seismic Risk Assessment

    Science.gov (United States)

    Melikyan, A. E.; Balassanian, S. Y.

    2002-05-01

    Seismic risk is growing worldwide and is, increasingly, a problem of developing countries. Along with growing urbanization future earthquakes will have more disastrous social and economic consequences. Seismic risk assessment and reduction are important goals for each country located in seismically active zone. For Armenia these goals are of primary importance because the results of studies carried out by Armenian NSSP for assessment of the losses caused by various types of disasters in Armenia had shown that earthquakes are the most disastrous hazard for Armenia. The strategy for seismic risk reduction in 1999 was adopted by the Government of Armenia as a high priority state program. The world experience demonstrates that for efficient response the rapid assessment of seismic losses is necessary. There are several state-of-the-art approaches for seismic risk assessment (Radius, Hazus, etc.). All of them required large amount of various input data, which is impossible to collect in many developing countries, in particular in Armenia. Taking into account this very serious problem existing for developing countries, as well as rapid seismic risk assessment need immediately after strong earthquake the author undertake the attempt to contribute into a new approach for rapid seismic risk assessment under the supervision of Prof. S. Balassanian. The analysis of numerous factors influencing seismic risk in Armenia shows that the following elements contribute most significantly to the possible losses: seismic hazard; density of population; vulnerability of structures. Proposed approach for rapid seismic risk assessment based on these three factors has been tested for several seismic events. These tests have shown that such approach might represent from 80 to 90 percent of real losses.

  19. Causality between expansion of seismic cloud and maximum magnitude of induced seismicity in geothermal field

    Science.gov (United States)

    Mukuhira, Yusuke; Asanuma, Hiroshi; Ito, Takatoshi; Häring, Markus

    2016-04-01

    Occurrence of induced seismicity with large magnitude is critical environmental issues associated with fluid injection for shale gas/oil extraction, waste water disposal, carbon capture and storage, and engineered geothermal systems (EGS). Studies for prediction of the hazardous seismicity and risk assessment of induced seismicity has been activated recently. Many of these studies are based on the seismological statistics and these models use the information of the occurrence time and event magnitude. We have originally developed physics based model named "possible seismic moment model" to evaluate seismic activity and assess seismic moment which can be ready to release. This model is totally based on microseismic information of occurrence time, hypocenter location and magnitude (seismic moment). This model assumes existence of representative parameter having physical meaning that release-able seismic moment per rock volume (seismic moment density) at given field. Seismic moment density is to be estimated from microseismic distribution and their seismic moment. In addition to this, stimulated rock volume is also inferred by progress of microseismic cloud at given time and this quantity can be interpreted as the rock volume which can release seismic energy due to weakening effect of normal stress by injected fluid. Product of these two parameters (equation (1)) provide possible seismic moment which can be released from current stimulated zone as a model output. Difference between output of this model and observed cumulative seismic moment corresponds the seismic moment which will be released in future, based on current stimulation conditions. This value can be translated into possible maximum magnitude of induced seismicity in future. As this way, possible seismic moment can be used to have feedback to hydraulic stimulation operation in real time as an index which can be interpreted easily and intuitively. Possible seismic moment is defined as equation (1), where D

  20. DOBRE-2000: Deep Reflection Seismic, Gravimetric and Surface Structural Controls Across a Devonian Failed Rift in the Southeastern Europe

    Science.gov (United States)

    Roy-Chowdhury, K.; Bayer, U.; Gajewski, D.; Huebscher, C.; Rabbel, W.; Saintot, A.; Starostenko, V. I.; Stephenson, R.; Stovba, S. M.; Tolkunov, A.; Thybo, H.

    2001-12-01

    Situated between the Ukrainian Shield and the Voronezh Masif, the Pripyat-Dniepr-Donets Basin (PDD) is a crustal-scale geodynamic feature associated with the Late Devonian rifting of the East European Craton. The Donbas Foldbelt (DF), comprising the eastern part of the PDD, includes pre- & syn-rift deposits below a large thickness of post-rift successions. Later, DF has been inverted (elevated, eroded, deformed). With 20+ km of sediments, it has a large economic potential, but its tectonic history - and the cause for its isolated evolution - is not well understood. Recently, 130+ km multi-channel reflection seismic profiling data has been acquired across the southern part of the DF in the framework of an international industry-academic collaboration. Coincident gravity data has been collected along the profile too, and extensive structural studies have been carried out to understand the spatio-temporal distribution of the stress-regime in the area. The high-resolution seismic images reveal an extensive stair-step like fragmentation of the basement including faults with upto 2km offset. The typical size of these "steps" are influenced by the ambient conditions at the time of their formation. Combined use of the different datasets is expected to shed light on several intriguing features associated with DF. The presence/extent of salt, causing localization and/or partition of strain both laterally and vertically, may be studied by using its seismic and gravitational reponses simultaneously. The interaction between the lower crust and the upper mantle may also be studied in the same manner, which should result in a lithological interpretation at depth favoring in turn one of the causative mechanisms.

  1. Infrasound Generation from the HH Seismic Hammer.

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Kyle Richard

    2014-10-01

    The HH Seismic hammer is a large, "weight-drop" source for active source seismic experiments. This system provides a repetitive source that can be stacked for subsurface imaging and exploration studies. Although the seismic hammer was designed for seismological studies it was surmised that it might produce energy in the infrasonic frequency range due to the ground motion generated by the 13 metric ton drop mass. This study demonstrates that the seismic hammer generates a consistent acoustic source that could be used for in-situ sensor characterization, array evaluation and surface-air coupling studies for source characterization.

  2. Issues on the seismic performance of embankments

    DEFF Research Database (Denmark)

    Zania, Varvara; Tsompanakis, Y.; Psarropoulos, P.N.

    2011-01-01

    Seismic vulnerability of embankments with reinforcement at their base is strongly related to the slip displacements, which may accumulate along the interface between soil and geosynthetic. The inertial accelerations within the embankment, due to the propagation of seismic waves and the subsequent...... performed. The stability of the soil mass was estimated in terms of seismic slip deformations along low-shear-strength interfaces, while the response of the embankment is assessed through the acceleration time histories at the top surface of the soil. This investigation presents also the effect of the most......’t be neglected during the seismic design of embankments....

  3. Infrasound Generation from the HH Seismic Hammer.

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Kyle Richard

    2014-10-01

    The HH Seismic hammer is a large, "weight-drop" source for active source seismic experiments. This system provides a repetitive source that can be stacked for subsurface imaging and exploration studies. Although the seismic hammer was designed for seismological studies it was surmised that it might produce energy in the infrasonic frequency range due to the ground motion generated by the 13 metric ton drop mass. This study demonstrates that the seismic hammer generates a consistent acoustic source that could be used for in-situ sensor characterization, array evaluation and surface-air coupling studies for source characterization.

  4. A Review of Seismicity in 2004

    Institute of Scientific and Technical Information of China (English)

    Li Gang; Liu Jie; Yu Surong

    2005-01-01

    @@ 1. SURVEY OF GLOBE SEISMICITY IN 2004 A total of 19 strong earthquakes with Ms≥7.0 occurred in the world according to the Chinese Seismic Station Network in 2004 (Table 1 ). The strongest earthquake was the Sumatra earthquake with Ms 8.7 near the northwest coast of Sumatra on December 26 ( Fig. 1 ). Global seismicity maintains the same patterns from recent years, being distributed mainly on the western part of the circum-Pacific seismic zone. Remarkable macroseismic activities were seen in the India-Australian plate and in the Japan region. The macroseismic activities of Ms≥7.0 in 2004 were as follows:

  5. Seismic displacement of gravity retaining walls

    Directory of Open Access Journals (Sweden)

    Kamal Mohamed Hafez Ismail Ibrahim

    2015-08-01

    Full Text Available Seismic displacement of gravity walls had been studied using conventional static methods for controlled displacement design. In this study plain strain numerical analysis is performed using Plaxis dynamic program where prescribed displacement is applied at the bottom boundary of the soil to simulate the applied seismic load. Constrained absorbent side boundaries are introduced to prevent any wave reflection. The studied soil is chosen dense granular sand and modeled as elasto-plastic material according to Mohr–Column criteria while the gravity wall is assumed elastic. By comparing the resulted seismic wall displacements calculated by numerical analysis for six historical ground motions with that calculated by the pseudo-static method, it is found that numerical seismic displacements are either equal to or greater than corresponding pseudo-static values. Permissible seismic wall displacement calculated by AASHTO can be used for empirical estimation of seismic displacement. It is also found that seismic wall displacement is directly proportional with the positive angle of inclination of the back surface of the wall, soil flexibility and with the earthquake maximum ground acceleration. Seismic wall sliding is dominant and rotation is negligible for rigid walls when the ratio between the wall height and the foundation width is less than 1.4, while for greater ratios the wall becomes more flexible and rotation (rocking increases till the ratio reaches 1.8 where overturning is susceptible to take place. Cumulative seismic wall rotation increases with dynamic time and tends to be constant at the end of earthquake.

  6. Probabilistic Seismic Hazard Analysis for Yemen

    Directory of Open Access Journals (Sweden)

    Rakesh Mohindra

    2012-01-01

    Full Text Available A stochastic-event probabilistic seismic hazard model, which can be used further for estimates of seismic loss and seismic risk analysis, has been developed for the territory of Yemen. An updated composite earthquake catalogue has been compiled using the databases from two basic sources and several research publications. The spatial distribution of earthquakes from the catalogue was used to define and characterize the regional earthquake source zones for Yemen. To capture all possible scenarios in the seismic hazard model, a stochastic event set has been created consisting of 15,986 events generated from 1,583 fault segments in the delineated seismic source zones. Distribution of horizontal peak ground acceleration (PGA was calculated for all stochastic events considering epistemic uncertainty in ground-motion modeling using three suitable ground motion-prediction relationships, which were applied with equal weight. The probabilistic seismic hazard maps were created showing PGA and MSK seismic intensity at 10% and 50% probability of exceedance in 50 years, considering local soil site conditions. The resulting PGA for 10% probability of exceedance in 50 years (return period 475 years ranges from 0.2 g to 0.3 g in western Yemen and generally is less than 0.05 g across central and eastern Yemen. The largest contributors to Yemen’s seismic hazard are the events from the West Arabian Shield seismic zone.

  7. The 1.33-1.30 Ga Yanliao large igneous province in the North China Craton: Implications for reconstruction of the Nuna (Columbia) supercontinent, and specifically with the North Australian Craton

    Science.gov (United States)

    Zhang, Shuan-Hong; Zhao, Yue; Li, Xian-Hua; Ernst, Richard E.; Yang, Zhen-Yu

    2017-05-01

    The Yanliao rift zone in the northern North China Craton (NCC) is the location of the standard section for late Paleoproterozoic-Mesoproterozoic stratigraphy in China and is associated with the emplacement of large volumes of diabase sills. Detailed field investigations show that the sills are distributed over a region that is >600 km long and >200 km wide, with areal extent > 1.2 ×105 km2 and cumulative thickness of the sills in any one area ranging from 50 m to >1800 m. High-resolution secondary ion mass spectrometry (SIMS) baddeleyite dating shows that emplacement of these sills occurred between about 1330 and 1305 Ma with a peak age of 1323 Ma. Emplacement of these diabase sills was accompanied by pre-magmatic uplift that started at about 1.35-1.34 Ga as indicated by the disconformity between the Changlongshan and Xiamaling formations and absence of sedimentation after the Xiamaling Formation in some areas. All the diabase sills exhibit similar geochemical features of tholeiitic compositions with intraplate characteristics. Given a relatively short duration of emplacement at 1.33-1.30 Ga, along with the large areal extent and volume, as well as intraplate character, this magmatic province constitutes a large igneous province (LIP). This Yanliao LIP and the accompanying pre-magmatic uplift were related either to a mantle plume and/or continental rifting during breakup of the NCC from the Nuna (Columbia) supercontinent. Paleomagnetic, ash bed and LIP data and other geological constraints suggest that the NCC had a close connection with Siberia, Laurentia, Baltica, North Australia and India crustal blocks. In particular, the most direct age match between the 1.33-1.30 Ga Yanliao LIP and the 1.33-1.30 Ga Derim Derim-Galiwinku LIP of the North Australian Craton (NAC), as well as the similarities between the late Paleoproterozoic-Mesoproterozoic stratigraphic units of the Yanliao rift in the NCC with the southeastern McArthur Basin in the NAC, indicate that the

  8. Sensitivity of Seismic Interferometry and Conventional Reflection Seismics at a Landfil to Processing and Survey Errors

    NARCIS (Netherlands)

    Konstantaki, L.A.; Draganov, D.S.; Heimovaara, T.J.; Ghose, R.

    2013-01-01

    Understanding how sensitive the seismic method is to errors that can occur during a seismic survey or during the processing of the seismic data is of high importance for any exploration geophysical project. Our aim is to image the subsurface of a landfill, which is typically a heterogeneous system

  9. Detailed seismic modeling of induced seismicity at the Groningen gas field

    NARCIS (Netherlands)

    Paap, B.F.; Steeghs, T.P.H.; Kraaijpoel, D.A.

    2016-01-01

    We present the results of a detailed seismic modeling study of induced seismicity observed at the Groningen gas field, situated in the North-eastern part of the Netherlands. Seismic simulations are valuable to support the interpretation of observed earthquake waveforms recordings and to increase the

  10. Combined teleseismic imaging of the structure of southern African cratons using P-receiver functions and P-and S-finite-frequency tomography

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Thybo, Hans; Levander, Alan;

    2011-01-01

    bands (1, 0.5 and 0.25 Hz for P and 0.1, 0.05 and 0.02 Hz for S) to obtain 3-D P- and S-wave perturbation models for the upper mantle. Crustal corrections are based on the RF models. Tests showed that our dataset is able to resolve structure of 3°x3° up to 400 km depth. The high-velocity cratonic roots...... extend to 300-350 km depth. Lower velocities are detected below the Bushveld complex and the mobile belts. The model also suggests a stratified structure, since we found a low velocity zone (LVZ) at about 170 km depth in the cratonic areas. SdP RFs and surface-wave tomography are in progress and should...

  11. Identification of 3.5 Ga detrital zircons from Yangtze craton in south China and the implication for Archean crust evolution

    Institute of Scientific and Technical Information of China (English)

    LIU Xiaoming; GAO Shan; LING Wenli; YUAN Honglin; HU Zhaochu

    2006-01-01

    The LA-ICP-MS U-Pb dating of hundreds of detrital zircon grains from the Sinian sandstones of Liantuo formation and tillites of Nantuo formation at Sanxia area in Yichang identified 3319-3508 Ma zircon grains. Their 207pb/206pb and 206pb/238U ages show excellent agreement (concordia degree 99 %-100 % ). Their CL images exhibit well-developed oscillatory zoning and the Th/U ratios are within 0. 46-0. 76, implying that they are igneous zircons which formed during middle-early Archean. These zircons are the oldest ones discovered in Yangtze craton until now. However, the detrital zircons with ages older than 3.3 Ga in the metamorphic rocks of Kongling group were not found by further investigation, which suggests the presence of crust older than high-grade metamorphic Kongling terrain in Yangtze craton.

  12. High Resolution Seismic Imaging of the Brawley Seismic Fault Zone

    Science.gov (United States)

    Goldman, M.; Catchings, R. D.; Rymer, M. J.; Lohman, R. B.; McGuire, J. J.; Sickler, R. R.; Criley, C.; Rosa, C.

    2011-12-01

    In March 2010, we acquired a series of high-resolution P-wave seismic reflection and refraction data sets across faults in the Brawley seismic zone (BSZ) within the Salton Sea Geothermal Field (SSGF). Our objectives were to determine the dip, possible structural complexities, and seismic velocities within the BSZ. One dataset was 3.4 km long trending east-west, and consisted of 334 shots recorded by a 2.4 km spread of 40 hz geophones placed every 10 meters. The spread was initially laid out from the first station at the eastern end of the profile to roughly 2/3 into the profile. After about half the shots, the spread was shifted from roughly 1/3 into the profile to the last station at the western end of the profile. P-waves were generated by Betsy-Seisgun 'shots' spaced every 10 meters. Initial analysis of first breaks indicate near-surface velocities of ~500-600 meters/sec, and deeper velocities of around 2000 meters/sec. Preliminary investigation of shot gathers indicate a prominent fault that extends to the ground surface. This fault is on a projection of the Kalin fault from about 40 m to the south, and broke the surface down to the west with an approximately north-south strike during a local swarm of earthquakes in 2005 and also slipped at the surface in association with the 2010 El Mayor-Cucapah earthquake in Baja California. The dataset is part of the combined Obsidian Creep data set, and provides the most detailed, publicly available subsurface images of fault structures in the BSZ and SSGF.

  13. Investigations on Local Seismic Phases and Modeling of Seismic Signals

    Science.gov (United States)

    1993-10-31

    Brocher, T. M., 1987. Coincident seismic reflection/refraction studies of the continental lithosphere: a global review, Rev. Geophys., 25, 723-742...36.39 Laza 300889 42.105 -07.516 13. 3.7 3.9 35.37 Nazare 310389 39.601 -09.493 25 ? 3.7 3.5 33.35 Camero 2009 87 42.138 - 02.476 05. 3.5 3.6 34.35 Aldea ...used might be accurate enough to describe the global waveforms recorded. NEAR SOURCE SITE EFFECTS EXPECTED AT YUCCA FLAT The map of Paleozoic basement

  14. Electrical conductivity images across the Namibian passive margin: Implications for tectonic processes along the Kaoko Belt, the western Kongo Craton and the Walvis Ridge

    Science.gov (United States)

    Weckmann, Ute; Meqbel, Naser; Kapinos, Gerhard; Jegen-Kulcsar, Marion; Ritter, Oliver

    2014-05-01

    The Special Priority Programme SAMPLE of the German Science Foundation DFG is focussed on investigating processes related to the breakup of supercontinent Gondwana and the post breakup evolution of the passive continental margins of Africa and South America. Within this framework an amphibian magnetotelluric (MT) experiment was conducted at the Southern African passive continental margin, starting at the Walvis Ridge in the Atlantic Ocean and crossing onshore the entire Kaoko Belt and the western boundary of the Kongo Craton in Northern Namibia. High-quality MT data at 167 onshore and xx offshore sites show a strong variability within short distances and indicate complex subsurface structures in parts of the Kaoko Belt and along some of the major thrust and fault zones. To identify the main conductivity features and resolve their properties in more spatial detail we started our modelling procedure with 2D inversion for a sub-set of the data where the 3D effects are less dominant along the amphibian profile. However, to account for 3D effects in the MT data and to assess robustness of conductivity anomalies revealed in the 2D model we used the entire data set for the 3D inversion using ModEM. 2D and 3D inversion models show zones of high electrical conductivity that correlate with surface expressions of prominent faults such as the Purros Mylonite Zone and the Three Palm Mylonite Zone of the Kaoko Belt. Outcropping Etendeka flood basalts in the Western Kaoko Zones are imaged by 10-15km deep reaching zones of high resistivity. Additionally, the inversion models reveal a spatial correlation of resistive zones with the cratonic Northern Platform; however, the geologically defined onset of the Kongo Craton appears as an area of high conductivity. Compared with other craton boundaries in Southern Africa this is very untypical.

  15. Petrological and Sr-Nd-Os isotopic constraints on the origin of the Fanshan ultrapotassic complex from the North China Craton

    Science.gov (United States)

    Niu, Xiaolu; Chen, Bin; Liu, Ankun; Suzuki, K.; Ma, Xu

    2012-09-01

    The Fanshan ultramafic-syenitic complex is located on the northern margin of North China Craton, with zircon U-Pb ages of 220 Ma. It is a concentrically zoned complex, with syenite in the core, surrounded by ultramafic rocks (clinopyroxenite, glimmerite) and garnet-clinopyroxene syenite, respectively, towards the rim. Diopside, biotite, orthoclase, melanite, magnetite and apatite are the major minerals, with subordinate sphene and calcite. Mineralogy, petrology and geochemical studies point to the formation of the complex through fractional crystallization and accumulation from a SiO2-undersaturated ultrapotassic alkaline-peralkaline parent magma that is characterized by high CaO, Fe2O3, K2O and fluid compositions (P2O5, CO2, H2O, F), and by high temperature and high oxygen fugacity. Rocks from the complex are highly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE; e.g., Rb, Ba, Sr), depleted in high field strength elements (HFSE; e.g., Nb, Ta, Ti), and show relatively homogeneous Sr-Nd isotopic compositions with initial 87Sr/86Sr = 0.70513-0.70597 and ɛNd(t) = - 5.8 to - 5.3. The data suggest that the Fanshan complex originated from a phlogopite-clinopyroxenite-rich lithosphere mantle source that had previously been metasomatized by melts from carbonated oceanic crust above a subduction zone. Highly radiogenic Os isotope compositions (initial 187Os/188Os = 0.299-2.449) suggest that the parent magma to the Fanshan complex has been contaminated by Precambrian mafic crustal rocks during magma emplacement in crustal levels. The occurrence of the Fanshan complex, together with many other ultramafic/alkaline plutons of similar ages, on the northern margin of the North China Craton suggests that the northern margin of the craton entered into a large-scale extensional regime in late Triassic after the final amalgamation between Mongolian microcontinent and the craton.

  16. Chemical deposits associated to metavolcanosedimentary sequences of the central portion of the São Francisco craton the state of Bahia, Brazil: a review

    OpenAIRE

    Carvalho, Ilson Guimarães

    2000-01-01

    p. 279-284 Supracrustal suites of metavolcanosedimentary rocks (SC) occur in the central portion of the São Francisco Craton in the State of Bahia. They were primarily formed by calc- alkaline to perialkaline volcanic flows and tuffs, clastic and chemical sediments. The latter are referred to the banded iron (BIF), iron-manganese (BIMF) and manganese (BMP) formations, iron-poor magnesian-rich carbonate formation (IPMRCF), and minor metacherts. BIF and IPMRCF are present in all the reported...

  17. Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements, REE geochemistry and Sr-Nd-O isotope systematics of ultramafic dykes

    Indian Academy of Sciences (India)

    Abhijit Roy; A Sarkar; S Jeyakumar; S K Aggrawal; M Ebihara; H Satoh

    2004-12-01

    Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma, Sri ∼0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; ( HREE)N ∼ 2-3 times chondrite, (Gd/Yb)N∼1). The Nd(t) values vary from +1.23 to −3.27 whereas 18O values vary from +3.16‰ to +5.29‰ (average +3.97‰ ± 0.75‰) which is lighter than the average mantle value. Isotopic, trace and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised by the fluid (±silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted, variable Nd, low Sri(0.702) and low 18O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the granitic crust which possibly originated due to the same thermal pulse.

  18. Multi-phase tectonic structures in the collision zone of the Kolyma-Omolon microcontinent and the eastern margin of the North Asian craton, Northeastern Russia

    OpenAIRE

    Prokopiev, A. V.; Oxman, V. S.

    2009-01-01

    The sequence of formation of structures is established in the zone of junction of the eastern margin of the North Asian craton and the northeastern flank of the Kolyma-Omolon microcontinent, in the area of bend of the Kolyma structural loop. Detailed structural studies revealed two phases in the formation of Mesozoic structures – an early thrust phase and a late strike-slip phase. Structures formed during each of the phases are described. Thrust structures are represented...

  19. Sequence stratigraphy of the Upper Cambrian (Furongian; Jiangshanian and Sunwaptan) Tunnel City Group, Upper Mississippi Valley: Transgressing assumptions of cratonic flooding

    Science.gov (United States)

    Eoff, Jennifer D.

    2014-01-01

    New data from detailed measured sections permit comprehensive analysis of the sequence framework of the Furongian (Upper Cambrian; Jiangshanian and Sunwaptan stages) Tunnel City Group (Lone Rock Formation and Mazomanie Formation) of Wisconsin and Minnesota. The sequence-stratigraphic architecture of the lower part of the Sunwaptan Stage at the base of the Tunnel City Group, at the contact between the Wonewoc Formation and Lone Rock Formation, records the first part of complex polyphase flooding (Sauk III) of the Laurentian craton, at a scale smaller than most events recorded by global sea-level curves. Flat-pebble conglomerate and glauconite document transgressive ravinement and development of a condensed section when creation of accommodation exceeded its consumption by sedimentation. Thinly-bedded, fossiliferous sandstone represents the most distal setting during earliest highstand. Subsequent deposition of sandstone characterized by hummocky or trough cross-stratification records progradational pulses of shallower, storm- and wave-dominated environments across the craton before final flooding of Sauk III commenced with carbonate deposition during the middle part of the Sunwaptan Stage. Comparison of early Sunwaptan flooding of the inner Laurentian craton to published interpretations from other parts of North America suggests that Sauk III was not a single, long-term accommodation event as previously proposed.

  20. SHRIMP zircon U-Pb ages for the Paleoproterozoic metamorphic-magmatic events in the southeast margin of the North China Craton

    Institute of Scientific and Technical Information of China (English)

    GUO SuShu; LI ShuGuang

    2009-01-01

    A garnet-pyroxene bearing amphibolite as a xenolith hosted by the Mesozoic igneous rocks from Xuzhou-Suzhou area was dated by zircon SHRIMP U-Pb method, which yields a metamorphic age of Archean metamorphic complex named Wuhe group in the Bengbu uplift give a metamorphic U-Pb age Bengbu uplift give a magma crystallization U-Pb age of 2054 ± 22 Ma. Both the Xuzhou-Suzhou area and Bengbu uplift are located in the southeastern margin of the North China Craton. Therefore, these ages indicate that there is a Paleoproterozoic tectonic zone in the southeastern margin of the North China Craton, and its metamorphic and magmatic ages are consistent with those of the other three Paleoproterozoic tectonic zones in the North China Craton. In view of the large scale sinistral strike-slip movement occurred at the Mesozoic along the Tan-Lu fault zone, the position of the eastern Shandong area, which is a south section of the Paleoproterozoic Jiao-Liao-Ji Belt, was correlated to Xuzhou-Suzhou-Bengbu area prior to movement of the Tan-Lu fault zone. This suggests that the Xuzhou-Suzhou-Bengbu Paleoproterozoic tectonic zone might be a southwest extension of the Paleoproterozoic Jiao-Liao-Ji Belt.

  1. Eclogite xenoliths from Orapa: Ocean crust recycling, mantle metasomatism and carbon cycling at the western Zimbabwe craton margin

    Science.gov (United States)

    Aulbach, S.; Jacob, D. E.; Cartigny, P.; Stern, R. A.; Simonetti, S. S.; Wörner, G.; Viljoen, K. S.

    2017-09-01

    Major- and trace-element compositions of garnet and clinopyroxene, as well as 87Sr/86Sr in clinopyroxene and δ18O in garnet in eclogite and pyroxenite xenoliths from Orapa, at the western margin of the Zimbabwe craton (central Botswana), were investigated in order to trace their origin and evolution in the mantle lithosphere. Two groups of eclogites are distinguished with respect to 87Sr/86Sr: One with moderate ratios (0.7026-0.7046) and another with 87Sr/86Sr >0.7048 to 0.7091. In the former group, heavy δ18O attests to low-temperature alteration on the ocean floor, while 87Sr/86Sr correlates with indices of low-pressure igneous processes (Eu/Eu∗, Mg#, Sr/Y). This suggests relatively undisturbed long-term ingrowth of 87Sr at near-igneous Rb/Sr after metamorphism, despite the exposed craton margin setting. The high-87Sr/86Sr group has mainly mantle-like δ18O and is suggested to have interacted with a small-volume melt derived from an aged phlogopite-rich metasome. The overlap of diamondiferous and graphite-bearing eclogites and pyroxenites over a pressure interval of ∼3.2 to 4.9 GPa is interpreted as reflecting a mantle parcel beneath Orapa that has moved out of the diamond stability field, due to a change in geotherm and/or decompression. Diamondiferous eclogites record lower median 87Sr/86Sr (0.7039) than graphite-bearing samples (0.7064) and carbon-free samples (0.7051), suggesting that interaction with the - possibly oxidising - metasome-derived melt caused carbon removal in some eclogites, while catalysing the conversion of diamond to graphite in others. This highlights the role of small-volume melts in modulating the lithospheric carbon cycle. Compared to diamondiferous eclogites, eclogitic inclusions in diamonds are restricted to high FeO and low SiO2, CaO and Na2O contents, they record higher equilibrium temperatures and garnets have mostly mantle-like O isotopic composition. We suggest that this signature was imparted by a sublithospheric melt with

  2. Gold deposits of the northern margin of the North China craton: Multiple late Paleozoic-Mesozoic mineralizing events

    Science.gov (United States)

    Hart, C.J.R.; Goldfarb, R.J.; Qiu, Y.; Snee, L.; Miller, L.D.; Miller, M.L.

    2002-01-01

    The northern margin of the North China craton is well-endowed with lode gold deposits hosting a resource of approximately 900 tonnes (t) of gold. The ???1,500-km-long region is characterized by east-trending blocks of metamorphosed Archean and Proterozoic strata that were episodically uplifted during Variscan, Indosinian, and Yanshanian deformational and magmatic events. At least 12 gold deposits from the Daqinshan, Yan-Liao (includes the Zhangjiakou, Yanshan, and Chifeng gold districts), and Changbaishan gold provinces contain resources of 20-100 t Au each. Most deposits are hosted in uplifted blocks of Precambrian metamorphic rocks, although felsic Paleozoic and Mesozoic plutons are typically proximal and host ???30% of the deposits. The lodes are characterized by sulfide-poor quartz veins in brittle structures with low base metal values and high Au:Ag ratios. Although phyllic alteration is most common, intensive alkali feldspar metasomatism characterizes the Wulashan, Dongping, and Zhongshangou deposits, but is apparently coeval with Variscan alkalic magmatism only at Wulashan. Stepwise 40Ar-39Ar geochronology on 16 samples from gangue and alteration phases, combined with unpublished SHRIMP U-Pb dates on associated granitoids, suggest that gold mineralizing events occured during Variscan, Indosinian, and Yanshanian orogenies at circa 350, 250, 200, 180, 150, and 129 Ma. However, widespread Permo-Triassic (???250 Ma) and Early Jurassic (???180 Ma) thermal events caused variable resetting of most of the white mica and K-feldspar argon spectra, as well as previously reported K-Ar determinations. Compiled and new stable isotope and fluid inclusion data show that most ??18O values for ore-stage veins range from 8 to 14???, indicating a fluid in equilibrium with the Precambrian metamorphic basement rocks; ??D values from fluid inclysions range widely from -64 to -154???, which is indicative of a local meteoric component in some veins; and highly variable ??34S data

  3. Radioelemental, petrological and geochemical characterization of the Bundelkhand craton, central India: implication in the Archaean geodynamic evolution

    Science.gov (United States)

    Ray, Labani; Nagaraju, P.; Singh, S. P.; Ravi, G.; Roy, Sukanta

    2016-06-01

    We have carried out radioelemental (232Th, 238U, 40K), petrological and geochemical analyses on granitoids and gneisses covering major rock formations of the Bundelkhand craton, central India. Our data reveal that above characteristics are distinct among granitoids (i.e. pink, biotite and grey granitoids) and gneisses (i.e. potassic and sodic types). Pink granitoid is K-feldspar-rich and meta-aluminous to per-aluminous in character. Biotite granitoid is meta-aluminous in character. Grey granitoid is rich in Na-feldspar and mafic minerals, granodiorite to diorite in composition and meta-aluminous in character. Among these granitoids, radioelements (Th, U, K) are highest in pink granitoid (45.0 ± 21.7 ppm, 7.2 ± 3.4 ppm, 4.2 ± 0.4 %), intermediate in biotite granitoid (44.5 ± 28.2 ppm, 5.4 ± 2.8 ppm, 3.4 ± 0.7 %) and lowest in grey granitoid (17.7 ± 4.3 ppm, 4.4 ± 0.6 ppm, 3.0 ± 0.4 %). Among gneisses, potassic-type gneisses have higher radioelements (11.8 ± 5.3 ppm, 3.1 ± 1.2 ppm, 2.0 ± 0.5 %) than the sodic-type gneisses (5.6 ± 2.8 ppm, 1.3 ± 0.5 ppm, 1.4 ± 0.7 %). Moreover, the pink granitoid and the biotite granitoid have higher Th/U (6 and 8, respectively) compared to the grey granitoid (Th/U: 4), implying enrichment of Th in pink and biotite granitoids relative to grey granitoid. K/U among pink, biotite and grey granitoids shows little variation (0.6 × 104, 0.6 × 104, 0.7 × 104, respectively), indicating relatively similar increase in K and U. Therefore, mineralogical and petrological data along with radioelemental ratios suggest that radioelemental variations in these lithounits are mainly related to abundances of the radioactive minerals that have formed by the fractionation of LILE from different magma sources. Based on present data, the craton can be divided into three distinct zones that can be correlated with its evolution in time and space. The central part, where gneisses are associated with metavolcanics of greenstone belt, is

  4. Petrogenesis of the middle Jurassic appinite and coeval granitoids in the Eastern Hebei area of North China Craton

    Science.gov (United States)

    Fan, Wenbo; Jiang, Neng; Xu, Xiyang; Hu, Jun; Zong, Keqing

    2017-05-01

    An integrated study of zircon U-Pb ages and Hf-O isotopic compositions, whole rock elemental and Sr-Nd isotope geochemistry was conducted on three lithologically diverse middle Jurassic plutons from the Eastern Hebei area of the North China Craton (NCC), in order to reveal both their petrogenesis and possible tectonic affinity. The three plutons have consistent magmatic zircon U-Pb ages from 167 ± 1 Ma to 173 ± 1 Ma. The Nianziyu pluton has typical characteristics of appinite with low SiO2 (43.7-52.6%), high Ca, Mg, Fe and H2O contents. It possesses subduction-related trace element patterns, enriched Nd-Hf isotopic signatures as well as elevated zircon δ18O values (6.2-7.2‰), arguing for an enriched mantle source metasomatized by fluids related to subduction. The Shuihutong monzogranites have high silica (SiO2 = 75.4-75.9%) and alkali contents, low Ca contents and striking negative Ba, Sr and Eu anomalies. Samples from the pluton have more evolved Nd-Hf isotopic values and are considered to be most likely derived from anatexis of ancient lower continental crust. Hybridization between mantle- and ancient lower crust-derived magmas is proposed for the mafic microgranular enclave-bearing Baijiadian granitoids, which are characterized by variable εNd (t) and εHf(t) values. Integrated with the regional geologic history, we suggest that the formation of the three middle Jurassic plutons were related to the subduction of the Paleo-Pacific ocean plate beneath the NCC. Their petrogenetic differences reflect complex magmatic processes in subduction settings involving melting of multiple sources, possible partly facilitated by fluid metasomatism and water-rich magma injection, accompanied with various degrees of magma mixing. The appearance of middle Jurassic appinitic rocks leads us to propose that the NCC destruction and lithosphere thinning were facilitated and controlled by the weakening of the lithospheric mantle after hydration because of the subduction of the

  5. Spectral characteristics of banded iron formations in Singhbhum craton, eastern India: Implications for hematite deposits on Mars

    Directory of Open Access Journals (Sweden)

    Mahima Singh

    2016-11-01

    Full Text Available Banded iron formations (BIFs are major rock units having hematite layers intermittent with silica rich layers and formed by sedimentary processes during late Archean to mid Proterozoic time. In terrestrial environment, hematite deposits are mainly found associated with banded iron formations. The BIFs in Lake Superior (Canada and Carajas (Brazil have been studied by planetary scientists to trace the evolution of hematite deposits on Mars. Hematite deposits are extensively identified in Meridiani region on Mars. Many hypotheses have been proposed to decipher the mechanism for the formation of these deposits. On the basis of geomorphological and mineralogical studies, aqueous environment of deposition is found to be the most supportive mechanism for its secondary iron rich deposits. In the present study, we examined the spectral characteristics of banded iron formations of Joda and Daitari located in Singhbhum craton in eastern India to check its potentiality as an analog to the aqueous/marine environment on Mars. The prominent banding feature of banded iron formations is in the range of few millimeters to few centimeters in thickness. Fe rich bands are darker (gray in color compared to the light reddish jaspilitic chert bands. Thin quartz veins (<4 mm are occasionally observed in the hand-specimens of banded iron formations. Spectral investigations have been conducted in VIS/NIR region of electromagnetic spectrum in the laboratory conditions. Optimum absorption bands identified include 0.65, 0.86, 1.4 and 1.9 μm, in which 0.56 and 0.86 μm absorption bands are due to ferric iron and 1.4 and 1.9 μm bands are due to OH/H2O. To validate the mineralogical results obtained from VIS/NIR spectral radiometry, laser Raman and Fourier transform infrared spectroscopic techniques were utilized and the results were found to be similar. Goethite-hematite association in banded iron formation in Singhbhum craton suggests dehydration activity, which has

  6. Spectral characteristics of banded iron formations in Singhbhum craton, eastern India:Implications for hematite deposits on Mars

    Institute of Scientific and Technical Information of China (English)

    Mahima Singh; Jayant Singhal; K. Arun Prasad; V.J. Rajesh; Dwijesh Ray; Priyadarshi Sahoo

    2016-01-01

    Banded iron formations (BIFs) are major rock units having hematite layers intermittent with silica rich layers and formed by sedimentary processes during late Archean to mid Proterozoic time. In terrestrial environment, hematite deposits are mainly found associated with banded iron formations. The BIFs in Lake Superior (Canada) and Carajas (Brazil) have been studied by planetary scientists to trace the evo-lution of hematite deposits on Mars. Hematite deposits are extensively identified in Meridiani region on Mars. Many hypotheses have been proposed to decipher the mechanism for the formation of these deposits. On the basis of geomorphological and mineralogical studies, aqueous environment of deposi-tion is found to be the most supportive mechanism for its secondary iron rich deposits. In the present study, we examined the spectral characteristics of banded iron formations of Joda and Daitari located in Singhbhum craton in eastern India to check its potentiality as an analog to the aqueous/marine envi-ronment on Mars. The prominent banding feature of banded iron formations is in the range of few millimeters to few centimeters in thickness. Fe rich bands are darker (gray) in color compared to the light reddish jaspilitic chert bands. Thin quartz veins (<4 mm) are occasionally observed in the hand-specimens of banded iron formations. Spectral investigations have been conducted in VIS/NIR region of electromagnetic spectrum in the laboratory conditions. Optimum absorption bands identified include 0.65, 0.86, 1.4 and 1.9 mm, in which 0.56 and 0.86 mm absorption bands are due to ferric iron and 1.4 and 1.9 mm bands are due to OH/H2O. To validate the mineralogical results obtained from VIS/NIR spectral radiometry, laser Raman and Fourier transform infrared spectroscopic techniques were utilized and the results were found to be similar. Goethite-hematite association in banded iron formation in Singhbhum craton suggests dehydration activity, which has altered the primary

  7. Seismic monitoring of torrential and fluvial processes

    Science.gov (United States)

    Burtin, Arnaud; Hovius, Niels; Turowski, Jens M.

    2016-04-01

    In seismology, the signal is usually analysed for earthquake data, but earthquakes represent less than 1 % of continuous recording. The remaining data are considered as seismic noise and were for a long time ignored. Over the past decades, the analysis of seismic noise has constantly increased in popularity, and this has led to the development of new approaches and applications in geophysics. The study of continuous seismic records is now open to other disciplines, like geomorphology. The motion of mass at the Earth's surface generates seismic waves that are recorded by nearby seismometers and can be used to monitor mass transfer throughout the landscape. Surface processes vary in nature, mechanism, magnitude, space and time, and this variability can be observed in the seismic signals. This contribution gives an overview of the development and current opportunities for the seismic monitoring of geomorphic processes. We first describe the common principles of seismic signal monitoring and introduce time-frequency analysis for the purpose of identification and differentiation of surface processes. Second, we present techniques to detect, locate and quantify geomorphic events. Third, we review the diverse layout of seismic arrays and highlight their advantages and limitations for specific processes, like slope or channel activity. Finally, we illustrate all these characteristics with the analysis of seismic data acquired in a small debris-flow catchment where geomorphic events show interactions and feedbacks. Further developments must aim to fully understand the richness of the continuous seismic signals, to better quantify the geomorphic activity and to improve the performance of warning systems. Seismic monitoring may ultimately allow the continuous survey of erosion and transfer of sediments in the landscape on the scales of external forcing.

  8. Seismic monitoring at The Geysers

    Energy Technology Data Exchange (ETDEWEB)

    Majer, E.L.; Romero, A.; Vasco, D.; Kirkpatrick, A.; Peterson, J.E. [Lawrence Berkeley Lab., CA (United States); Zucca, J.J.; Hutchings, L.J.; Kasameyer, P.W. [Lawrence Livermore National Lab., CA (United States)

    1993-04-01

    During the last several years Lawrence Berkeley Laboratory (LBL) and Lawrence Livermore National Laboratory (LLNL) have been working with industry partners at The Geysers geothermal field to evaluate and develop methods for applying the results of microearthquake (MEQ) monitoring. It is a well know fact that seismicity at The Geysers is a common occurrence, however, there have been many studies and papers written on the origin and significance of the seismicity. The attitude toward MEQ data ranges from being nothing more than an curious artifact of the production activities, to being a critical tool in evaluating the reservoir performance. The purpose of the work undertaken b y LBL and LLNL is to evaluate the utility, as well as the methods and procedures used in of MEQ monitoring, recommend the most cost effective implementation of the methods, and if possible link physical processes and parameters to the generation of MEQ activity. To address the objectives above the MEQ work can be categorized into two types of studies. The first type is the direct analysis of the spatial and temporal distribution of MEQ activity and studying the nature of the source function relative to the physical or chemical processes causing the seismicity. The second broad area of study is imaging the reservoir/geothermal areas with the energy created by the MEQ activity and inferring the physical and/or chemical properties within the zone of imaging. The two types of studies have obvious overlap, and for a complete evaluation and development require high quality data from arrays of multicomponent stations. Much of the effort to date at The Geysers by both DOE and the producers has concentrated establishing a high quality data base. It is only within the last several years that this data base is being fully evaluated for the proper and cost effective use of MEQ activity. Presented here are the results to date of DOE`s effort in the acquisition and analysis of the MEQ data.

  9. The Italian National Seismic Network

    Science.gov (United States)

    Michelini, Alberto

    2016-04-01

    The Italian National Seismic Network is composed by about 400 stations, mainly broadband, installed in the Country and in the surrounding regions. About 110 stations feature also collocated strong motion instruments. The Centro Nazionale Terremoti, (National Earthquake Center), CNT, has installed and operates most of these stations, although a considerable number of stations contributing to the INGV surveillance has been installed and is maintained by other INGV sections (Napoli, Catania, Bologna, Milano) or even other Italian or European Institutions. The important technological upgrades carried out in the last years has allowed for significant improvements of the seismic monitoring of Italy and of the Euro-Mediterranean Countries. The adopted data transmission systems include satellite, wireless connections and wired lines. The Seedlink protocol has been adopted for data transmission. INGV is a primary node of EIDA (European Integrated Data Archive) for archiving and distributing, continuous, quality checked data. The data acquisition system was designed to accomplish, in near-real-time, automatic earthquake detection and hypocenter and magnitude determination (moment tensors, shake maps, etc.). Database archiving of all parametric results are closely linked to the existing procedures of the INGV seismic monitoring environment. Overall, the Italian earthquake surveillance service provides, in quasi real-time, hypocenter parameters which are then revised routinely by the analysts of the Bollettino Sismico Nazionale. The results are published on the web page http://cnt.rm.ingv.it/ and are publicly available to both the scientific community and the the general public. This presentation will describe the various activities and resulting products of the Centro Nazionale Terremoti. spanning from data acquisition to archiving, distribution and specialised products.

  10. PARAMETERS OF KAMCHATKA SEISMICITY IN 2008

    Directory of Open Access Journals (Sweden)

    Vadim A. Saltykov

    2015-09-01

    Full Text Available The paper describes seismicity of Kamchatka for the period of 2008 and presents 2D distribution of background seismicity parameters calculated from data published in the Regional Catalogue of Kamchatka Earthquakes. Parameters under study are total released seismic energy, seismic activity A10, slope of recurrence graph γ, parameters of RTL, ΔS and Z-function methods, and clustering of earthquakes. Estimations of seismicity are obtained for a region bordered by latitude 50.5–56.5N, longitude 156E–167E, with depths to 300 km. Earthquakes of energy classes not less than 8.5 as per the Fedotov’s classification are considered. The total seismic energy released in 2008 is estimated. According to a function of annual seismic energy distribution, an amount of seismic energy released in 2008 was close to the median level (Fig. 1. Over 2/3 of the total amount of seismic energy released in 2008 resulted from three largest earthquakes (МW ≥ 5.9. About 5 percent of the total number of seismic events are comprised of grouped earthquakes, i.e. aftershocks and swarms. A schematic map of the largest earthquakes (МW ≥ 5.9 and grouped seismic events which occurred in 2008 is given in Fig. 2; their parameters are listed in Table 1. Grouped earthquakes are excluded from the catalogue. A map showing epicenters of independent earthquakes is given in Fig. 3. The slope of recurrence graph γ and seismic activity A10 is based on the Gutenberg-Richter law stating the fundamental property of seismic process. The recurrence graph slope is calculated from continuous exponential distribution of earthquakes by energy classes. Using γ is conditioned by observations that in some cases the slope of the recurrence graph decreases prior to a large earthquake. Activity A10 is calculated from the number of earthquakes N and recurrence graph slope γ. Average slopes of recurrence graph γ and seismic activity A10 for the area under study in 2008 are calculated; our

  11. The GEOSCOPE broadband seismic observatory

    Science.gov (United States)

    Douet, Vincent; Vallée, Martin; Zigone, Dimitri; Bonaimé, Sébastien; Stutzmann, Eléonore; Maggi, Alessia; Pardo, Constanza; Bernard, Armelle; Leroy, Nicolas; Pesqueira, Frédéric; Lévêque, Jean-Jacques; Thoré, Jean-Yves; Bes de Berc, Maxime; Sayadi, Jihane

    2016-04-01

    The GEOSCOPE observatory has provided continuous broadband data to the scientific community for the past 34 years. The 31 operational GEOSCOPE stations are installed in 17 countries, across all continents and on islands throughout the oceans. They are equipped with three component very broadband seismometers (STS1, T240 or STS2) and 24 or 26 bit digitizers (Q330HR). Seismometers are installed with warpless base plates, which decrease long period noise on horizontal components by up to 15dB. All stations send data in real time to the IPGP data center, which transmits them automatically to other data centers (FDSN/IRIS-DMC and RESIF) and tsunami warning centers. In 2016, three stations are expected to be installed or re-installed: in Western China (WUS station), in Saint Pierre and Miquelon Island (off the East coast of Canada) and in Walis and Futuna (SouthWest Pacific Ocean). The waveform data are technically validated by IPGP (25 stations) or EOST (6 stations) in order to check their continuity and integrity. Scientific data validation is also performed by analyzing seismic noise level of the continuous data and by comparing real and synthetic earthquake waveforms (body waves). After these validations, data are archived by the IPGP data center in Paris. They are made available to the international scientific community through different interfaces (see details on http://geoscope.ipgp.fr). Data are duplicated at the FDSN/IRIS-DMC data center and a similar duplication at the French national data center RESIF will be operational in 2016. The GEOSCOPE broadband seismic observatory also provides near-real time information on global moderate-to-large seismicity (above magnitude 5.5-6) through the automated application of the SCARDEC method (Vallée et al., 2011). By using global data from the FDSN - in particular from GEOSCOPE and IRIS/USGS stations -, earthquake source parameters (depth, moment magnitude, focal mechanism, source time function) are determined about 45

  12. Pre-Seismic Electromagnetic Effects

    Institute of Scientific and Technical Information of China (English)

    Guo Yahong

    2007-01-01

    Along with intense rock strain and rock bursting processes at the late stage of earthquake preparation, mechanical-electrical energy conversion appears in the seismogenic region and its nearby rock formations, which correspondingly stimulate certain electromagnetic effects. The paper mainly analyzes the pre-seismic electromagnetic effect of the ionosphere and proposes a method of monitoring VLF radio waves over the additional ionized region and so on. It is deemed that the method is of significance for short and imminent term prediction of strong earthquakes.

  13. Uncertainty analysis in seismic tomography

    Science.gov (United States)

    Owoc, Bartosz; Majdański, Mariusz

    2017-04-01

    Velocity field from seismic travel time tomography depends on several factors like regularization, inversion path, model parameterization etc. The result also strongly depends on an initial velocity model and precision of travel times picking. In this research we test dependence on starting model in layered tomography and compare it with effect of picking precision. Moreover, in our analysis for manual travel times picking the uncertainty distribution is asymmetric. This effect is shifting the results toward faster velocities. For calculation we are using JIVE3D travel time tomographic code. We used data from geo-engineering and industrial scale investigations, which were collected by our team from IG PAS.

  14. A Preliminary Study on Seismicity and Stages of Seismic Energy Accumulation in Seismotectonic Regions of Tianshan

    Institute of Scientific and Technical Information of China (English)

    Li Yingzhen; Shen Jun; Wang Haitao

    2006-01-01

    Using seismic parameters, the characteristics of the seismic activity in various seismotectonic regions of Tianshan were studied in this paper. These regions are going through different stages of seismic energy accumulation. Current seismic risk levels of these areas were analyzed synthetically by the tectonic movement rates, as well as the characteristics of the seismic activity and the recurrence intervals of strong earthquakes. We preliminarily studied the characteristics of seismic activity in different seismic energy accumulating stages. The result shows that the characteristics of the seismic activity in various seismotectonic regions of the Tianshan area are influenced, not only by the regional tectonic movement, but also by the energy accumulating stage of various seismic tectonics. In the intense tectonic movement areas, it is important to estimate its stage of energy accumulating in order to predict the upper limit of the potential earthquake magnitude. In the less intense tectonic movement areas, the estimating of the stage of energy accumulation will help us recognize the dangerous level of the potential strong earthquake. The study shows that the seismotectonic regions in southern Tianshan have reached the mid-stage and late-stage of energy accumulation, with a higher seismic activity and thus a higher seismic dangerous level than those in the northern and middle Tianshan. The earthquake risk of southern Tianshan is up to Ms7.0, while that of the middle Tianshan is up to Ms6.0 and that of northern Tianshan is only around Ms5.0 ~ 6.0.

  15. Time-lapse seismic within reservoir engineering

    NARCIS (Netherlands)

    Oldenziel, T.

    2003-01-01

    Time-lapse 3D seismic is a fairly new technology allowing dynamic reservoir characterisation in a true volumetric sense. By investigating the differences between multiple seismic surveys, valuable information about changes in the oil/gas reservoir state can be captured. Its interpretation involves d

  16. Seismic design of reactors in NUCEF

    Energy Technology Data Exchange (ETDEWEB)

    Kurosaki, Akira [Mitsui Shipbuilding and Engineering Co. Ltd., Tokyo (Japan); Kuchiya, Masao; Yasuda, Naomitsu; Kitanaka, Tsutomu; Ogawa, Kazuhiko; Sakuraba, Koichi; Izawa, Naoki; Takeshita, Isao

    1997-03-01

    Basic concept and calculation method for the seismic design of the main equipment of the reactors in NUCEF (Nuclear Fuel Cycle Safety Engineering Research Facility) are described with actual calculation examples. The present paper is published to help the seismic design of the equipment and application of the authorization for the design and constructing of facilities. (author)

  17. Time-lapse seismic within reservoir engineering

    NARCIS (Netherlands)

    Oldenziel, T.

    2003-01-01

    Time-lapse 3D seismic is a fairly new technology allowing dynamic reservoir characterisation in a true volumetric sense. By investigating the differences between multiple seismic surveys, valuable information about changes in the oil/gas reservoir state can be captured. Its interpretation involves d

  18. Making Waves: Seismic Waves Activities and Demonstrations

    Science.gov (United States)

    Braile, S. J.; Braile, L. W.

    2011-12-01

    The nature and propagation of seismic waves are fundamental concepts necessary for understanding the exploration of Earth's interior structure and properties, plate tectonics, earthquakes, and seismic hazards. Investigating seismic waves is also an engaging approach to learning basic principles of the physics of waves and wave propagation. Several effective educational activities and demonstrations are available for teaching about seismic waves, including the stretching of a spring to demonstrate elasticity; slinky wave propagation activities for compressional, shear, Rayleigh and Love waves; the human wave activity to demonstrate P- and S- waves in solids and liquids; waves in water in a simple wave tank; seismic wave computer animations; simple shake table demonstrations of model building responses to seismic waves to illustrate earthquake damage to structures; processing and analysis of seismograms using free and easy to use software; and seismic wave simulation software for viewing wave propagation in a spherical Earth. The use of multiple methods for teaching about seismic waves is useful because it provides reinforcement of the fundamental concepts, is adaptable to variable classroom situations and diverse learning styles, and allows one or more methods to be used for authentic assessment. The methods described here have been used effectively with a broad range of audiences, including K-12 students and teachers, undergraduate students in introductory geosciences courses, and geosciences majors.

  19. Time-lapse seismic within reservoir engineering

    NARCIS (Netherlands)

    Oldenziel, T.

    2003-01-01

    Time-lapse 3D seismic is a fairly new technology allowing dynamic reservoir characterisation in a true volumetric sense. By investigating the differences between multiple seismic surveys, valuable information about changes in the oil/gas reservoir state can be captured. Its interpretation involves

  20. 7 CFR 1792.104 - Seismic acknowledgments.

    Science.gov (United States)

    2010-01-01

    ... registered architect or engineer responsible for the building design stating that seismic provisions pursuant to § 1792.103 of this subpart will be used in the design of the building. (a) For projects in which... include the identification and date of the model code or standard that is used in the seismic design...

  1. Global Seismic Hazard Assessment Program - GSHAP legacy

    Directory of Open Access Journals (Sweden)

    Laurentiu Danciu

    2015-04-01

    Full Text Available Global Seismic Hazard Assessment Program - or simply GSHAP, when launched, almost two decades ago, aimed at establishing a common framework to evaluate the seismic hazard over geographical large-scales, i.e. countries, regions, continents and finally the globe. Its main product, the global seismic hazard map was a milestone, unique at that time and for a decade have served as the main reference worldwide. Today, for most of the Earth’s seismically active regions such Europe, Northern and Southern America, Central and South-East Asia, Japan, Australia, New Zealand, the GSHAP seismic hazard map is outdated. The rapid increase of the new data, advance on the earthquake process knowledge, technological progress, both hardware and software, contributed all in updates of the seismic hazard models. We present herein, a short retrospective overview of the achievements as well as the pitfalls of the GSHAP. Further, we describe the next generation of seismic hazard models, as elaborated within the Global Earthquake Model, regional programs: the 2013 European Seismic Hazard Model, the 2014 Earthquake Model for Middle East, and the 2015 Earthquake Model of Central Asia. Later, the main characteristics of these regional models are summarized and the new datasets fully harmonized across national borders are illustrated for the first time after the GSHAP completion.

  2. Permanent downhole seismic sensors in flowing wells

    NARCIS (Netherlands)

    Jaques, P.; Ong, H.; Jupe, A.; Brown, I.; Jansenns, M.

    2003-01-01

    It is generally accepted that the 'Oilfield of the Future' will incorporate distributed permanent downhole seismic sensors in flowing wells. However the effectiveness of these sensors will be limited by the extent to which seismic signals can be discriminated, or de-coupled, from flow induced

  3. Robust seismic images amplitude recovery using curvelets

    NARCIS (Netherlands)

    Moghaddam, Peyman P.; Herrmann, Felix J.; Stolk, C.C.

    2007-01-01

    In this paper, we recover the amplitude of a seismic image by approximating the normal (demigration-migration) operator. In this approximation, we make use of the property that curvelets remain invariant under the action of the normal operator. We propose a seismic amplitude recovery method that

  4. Seismic surveying for coal mine planning

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, B. [CMTE/CSIRO Exploration and Mining, Kenmore, Qld. (Australia)

    2002-07-01

    More and more coal in Australia is extracted by underground mining methods especially by longwall mining. These methods can be particularly sensitive to relatively small-scale structural discontinuities and variations in roof and floor rock character. Traditionally, information on these features has been obtained through drilling. However, this is an expensive process and its relevance is limited to the immediate neighbourhood of the boreholes. Seismic surveying, especially by 3D seismic, is an alternative tool for geological structure delineation. It is one of the most effective geophysical methods available for identification of geological structures such as faults, folds, washouts, seam splits and thickness changes which are normally associated with potential mining hazards. Seismic data even can be used for stratigraphic identification. The information extracted from seismic data can be integrated into mine planning and design. In this paper, computer aided interpretation techniques for maximising the information from seismic data are demonstrated and the ability of seismic reflection methods to resolve localised geological features illustrated. Both synthetic and real seismic data obtained in recent 2D and 3D seismic surveys from Australian coal mines are used. 7 refs., 9 figs.

  5. Seismic Design Guidelines For Port Structures

    DEFF Research Database (Denmark)

    Burcharth, H. F.; Bernal, Alberto; Blazquez, Rafael

    -balance approach, in which structures are designed to resist a prescribed level of seismic force specified as a fraction of gravity. These methodologies have contributed to the acceptable seismic performance of port structures, particularly when the earthquake motions are more or less within the prescribed design...