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Sample records for evolucao crustal da

  1. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd

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    Sato, Kei

    1998-07-01

    Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga ({approx} 0.5% in volume), 3.1 - 2.9 Ga ({approx}16%), 2.7 - 2.6 ({approx} 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining {approx} 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still preserved within tectonic provinces of different ages. The remainder represents continental crust reworked in younger tectono-thermal events. In particular crustal reworking was predominating over juvenile accretion during Meso-Neoproterozoic. The Transbrasiliano Lineament is a megasuture, active in the Neoproterozoic, which separates a large northwestern mass, including the Amazonian and Sao Luis Cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the Sao Francisco and Rio de La Plata are the largest. The crustal evolutions of these two large continental masses are considered individually, and can be resumed following form: I - Old Archean rocks (>3.4 Ga) are found only within the south-eastern part (Gaviao Block

  2. Geochronology and crustal evolution of the deposit area Cu-Au Gameleira, Carajas mineral province, Para state, Brazil; Geocronologia e evolucao crustal da area do deposito de Cu-Au Gameleira, provincia mineral de Carajas (Para), Brasil

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    Galarza, Marco Antonio; Macambira, Moacir Jose Buenano [Para Univ. (UFPA), Belem (Brazil). Centro de Geociencias. Lab. de Geologia Isotopica (Para-Iso)

    2002-12-15

    The Gameleira Cu-Au deposit is hosted by rocks of the Igarape Pojuca Group, Itacaiunas Supergroup, Carajas Mineral Province, southeastern Amazonian Craton. This group is represented mainly by mafic metavolcanic rocks (MVN), amphibolite, biotite schist, banded iron formation and/or hydrothermalite and cut by intrusive mafic rocks (IMR) as well as by deformed Itacaiunas granites of Archean age (2.56 Ga) and Pojuca and Gameleira granites of Proterozoic age (1.87 and 1.58 Ga). Zircon crystals from a saprolite (2615 {+-} 10 Ma and 2683 {+-} 7 Ma) and from an IMR sample (2705 {+-} 2 Ma) are coeval with those from gabbros of the neighboring Aguas Claras deposit. Pb-Pb dating of whole rock samples and chalcopyrite from the MVR indicated ages of 2245 {+-} 29 Ma and 2419 {+-} 12 Ma, respectively, while leached chalcopyrite yielded ages of 2217 {+-} 19 Ma and 2180 {+-} 84 Ma. These ages are interpreted as due to partial resetting provoked by the Proterozoic granitic intrusions or by tectonic reactivation along the Carajas and Cinzento strike slip systems or alternatively, as due to total resetting provoked by the last one. The T{sub DM} ages between 3.12 and 3.33 Ga for the MVR and IMR, and the initial epsilon{sub Nd} (t) values of -0.89 to -3.26 suggest continental contribution from older crustal material and possibly magma generation in a continental rift or active continental margin environment. (author)

  3. Análise de incertezas e inversão conjunta para aprimoramento da modelagem crustal

    OpenAIRE

    Moreira, Lucas Paes

    2013-01-01

    O objetivo deste trabalho é apresentar duas novas metodologias para aprimorar a modelagem crustal usando inversão conjunta de múltiplos dados geofísicos. O primeiro método proposto é a análise das incertezas da inversão conjunta da função do receptor e dispersão de ondas superficiais. Inversões conjuntas destes dois grupos de dados estão se tornando populares devido à capacidade de reduzir a não-unicidade em modelos de velocidades de ondas sísmicas. No entanto, as incertezas dos modelos calib...

  4. Geology, petrology and U-Pb geochronology of Serra da Rajada Granitic Pluton: implications about ediacaran magmatic evolution in NE portion of the Rio Piranhas-Serido Domain (NE of Borborema Province); Geologia, petrologia e geocronologia U-Pb do Pluton Granitico Serra da Rajada: implicacoes sobre a evolucao magmatica ediacarana na porcao do Dominio Rio Piranhas-Serido (NE da Provincia Borborema)

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    Costa, Alan Pereira da; Dantas, Alexandre Ranier, E-mail: alan.costa@cprm.gov.br, E-mail: alexandre.dantas@cprm.gov.br [Servico Geologico do Brasil (CPRM), Natal, RN (Brazil). Nucleo de Apoio de Natal/Superintendencia Regional de Recife; Nascimento, Marcos Antonio Leite do; Galindo, Antonio Carlos, E-mail: marcos@geologia.ufrn.br, E-mail: galindo@geologia.ufrn.br [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Departamento de Geologia

    2015-12-15

    The Ediacaran plutonic activity, related to the Brazilian/Pan-African orogeny, is one of the most important geological features in the Borborema Province, formed by batholiths, stocks and dikes. The Serra da Rajada Granitic Pluton (SRGP), located in the central portion of the Rio Piranhas-Serido Domain, is an example of these bodies. This site is the target of cartographic, petrographic, lithochemical and geochronological studies. Its rocks are described as monzogranites consisting of K-feldspar, plagioclase (oligoclase-An{sub 23-24%}), quartz and biotite (main mafic), having as accessory minerals opaque, titanite, allanite, apatite and zircon. Chlorite, white mica and carbonate are alteration minerals. Lithochemical data from 15 samples show quite evolved rocks (SiO{sub 2} , 69% to 75%), rich in alkalis (Na{sub 2}O + K{sub 2}O ≥ 8.0%), depleted in MgO (≤ 0.45%), CaO (≤ 1.42%) and TiO{sub 2} (≤ 0.36%), and displaying moderate levels of Fe{sub 2}O{sub 3} t (2.16 to 3.53%). These rocks present a transitional nature between metaluminous and peraluminous (predominance of the latter) and have subalkaline/monzonitic affinity (high-K Calc-alkaline). Harker diagrams represent negative correlations in Fe{sub 2}O{sub 3}t, MgO and CaO, indicating fractionation of mafic and plagioclase. The REE spectrum show enrichment of light in relation to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in Eu (Eu/ Eu* = 0.70 to 10.13) suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows correlating the SRGP rocks with those described as Equigranular high-K Calc-alkaline Suite. The U-Pb geochronology and Sm-Nd isotope dating indicate that the biotite monzogranite have a crystallization age of 557 ± 13 Ma and TDM model age of 2.36 Ga, respectively, and ε{sub Nd} value of - 20.10 for the crystallization age, allowing to infer a crustal source for the magma generated in the Paleoproterozoic age. (author)

  5. Evolucao da Odontología na Ultima Decada

    OpenAIRE

    Perales, Segundo L.

    2014-01-01

    El efecto de las fuerzas ortodóncicas ú ortopédicas (mas allá de los dientes y procesos alveolares), siempre ha sido sujeto a muchas controversias, en parte debido a la semántica, también a las técnicas usadas para registrar los cambios observados y medidos. En los últimos años ha alcanzado popularidad la Ortopedia Funcional de los Maxilares debido al intercambio de conocimientos y experiencias con las diferentes técnicas de la Escuela Ortodóncica, dando como resultado una mayor investigación...

  6. Reassessment of the geologic evolution of selected precambrian terranes in Brazil, based on new SHRIMP U-Pb data, part 3: Borborema, Southern Mantiqueira and Rio Negro-Juruena provinces; Reavaliacao da evolucao geologica em terrenos pre-cambrianos brasileiros com base em novos dados U-Pb SHRIMP, parte 3: Provincias Borborema, Mantiqueira Meridional e Rio Negro-Juruena

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    Silva, Luiz Carlos da; Pimentel, Marcio [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: luizcarlos@aneel.gov.br; Scandolara, Jaime; Ramgrab, Gilberto [Centro de Pesquisas e Recursos Minerais, Brasilia, DF (Brazil); Wildner, Wilson; Sander, Andrea [Centro de Pesquisas e Recursos Minerais, Porto Alegre, RS (Brazil); Angelim, Luiz Alberto de Aquino [Centro de Pesquisas e Recursos Minerais, Recife, PE (Brazil); Vasconcelos, Antonio Maurilio [Centro de Pesquisas e Recursos Minerais, Fortaleza, CE (Brazil); Rizzoto, Gilmar; Quadros, Marcio Luiz do Espirito Santo [Centro de Pesquisas e Recursos Minerais, Porto Veolho, RO (Brazil); Armstrong, Richard [Australian National Univ., Canberra (Australia). Research School of Earth Sciences; Rosa, Ana Lucia Zucatti da [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas

    2002-12-15

    This paper discusses new SHRIMP U-Pb data for 17 key-exposures (mostly granites and ortho gneisses) from the Borborema, Southern Mantiqueira (Pelotas Orogen) and Rio Negro-Juruena provinces. In the Borborema Province (Ceara state) two samples from the Cruzeta Complex TTG ortho gneisses, ascribed to the Paleoproterozoic basement, were studied. One revealed Paleoarchean crystallization minimum age of ca. 3270 Ma. Accordingly, the gneiss is interpreted as the oldest continental crustal remnant already recognised in Ceara. The other sample, from the Saboeiro-Aiuaba Granite gave a crystallization age of ca. 625 Ma, suggesting the correlation of this syn-orogenic pluton with the Brasiliano II orogenic system (climax at 630 Ma). In the Paraiba state the granodioritic gneiss pluton ascribed to the Mesoproterozoic Sume Complex showed a crystallization age of ca. 640 Ma, also indicating that its evolution is associated with the Brasiliano II orogenic system. In the Pernambuco state one widespread ortho gneissic unit within the Pernambuco-Alagoas Massif (Belem do Sao Francisco Complex), mapped as a component of the Meso proterozoic Cariris Velho Orogen, yielded a crystallization age of ca. 2079 Ma and metamorphic overprinting at ca. 655 Ma (1{sigma}), without evidence of a Mesoproterozoic (Cariris Velhos) reworking. In the southern part of the province, near the northern margin of the Sao Francisco Craton, the Santa Maria da Boa Vista (S-type) orthogneiss yielded a crystallisation age of ca. 3070 Ma. In the southern Mantiqueira Province/Pelotas Orogen a foliated granitic pluton (mylonitic) from the Florianopolis Batholith showed Paleoproterozoic protolithic age of ca. 2175 Ma and imprecise Brasiliano age on reprecipitated overgrowths. Both results match previous ages obtained on the orthogneisses protoliths from the Aguas Mornas complex, the main exposure of reworked basement within the batholith. The large, zoned calc-alkaline pluton of the Maruim Suite, confirmed its

  7. Crustal permeability

    Science.gov (United States)

    Gleeson, Tom; Ingebritsen, Steven E.

    2016-01-01

    Permeability is the primary control on fluid flow in the Earth’s crust and is key to a surprisingly wide range of geological processes, because it controls the advection of heat and solutes and the generation of anomalous pore pressures.  The practical importance of permeability – and the potential for large, dynamic changes in permeability – is highlighted by ongoing issues associated with hydraulic fracturing for hydrocarbon production (“fracking”), enhanced geothermal systems, and geologic carbon sequestration.  Although there are thousands of research papers on crustal permeability, this is the first book-length treatment.  This book bridges the historical dichotomy between the hydrogeologic perspective of permeability as a static material property and the perspective of other Earth scientists who have long recognized permeability as a dynamic parameter that changes in response to tectonism, fluid production, and geochemical reactions. 

  8. Reassessment of the geologic evolution of selected precambrian terranes in Brazil, based on new SHRIMP U-Pb data, part 1: central-eastern border of Sao Francisco Craton in Bahia state, Brazil; Reavaliacao da evolucao geologica em terrenos pre-cambrianos brasileiros com base em novos dados U-Pb SHRIMP, parte 1: limite centro-oriental do Craton Sao Francisco na Bahia

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    Silva, Luiz Carlos da; Pimentel, Marcio; Jost, Hardy [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: luizcarlos@aneel.gov.br; Delgado, Inacio Medeiros; Arcanjo, Joao Batista; Melo, Roberto Campello de; Teixeira, Leo R.; Cardoso Filho, Joao Moraes; Pereira, Luiz Henrique Monteiro [Companhia de Pesquisas de Recursos Minerais (CPRM), Salvador, BA (Brazil); Armstrong, Richard [Australian National Univ., Canberra (Australia). Research School of Earth Sciences

    2002-12-15

    the Eastern Bahia Belt collision. The isotopic signature and the metamorphic assemblage are suggestive of recrystallization in very deep crustal levels, under high P and T conditions. A similar metamorphic regime is recorded in the western Jequie Block (sample LC 61), so far interpreted as a craton area which has been stable since the Archean. Accordingly, the Eastern Bahia Belt was characterized as the deep roots of a collisional orogeny, with discrete newly accreted magmas between ca. 2200? and ca. 2090 Ma - herein ascribed to the Western Bahia Orogeny which was formerly referred to as the Itabuna, Salvador-Curaca and Salvador-Esplanada belts. (author)

  9. Geological evolution of the center-southern portion of the Guyana shield based on the geochemical, geochronological and isotopic studies of paleoproterozoic granitoids from southeastern Roraima, Brazil; Evolucao geologica da porcao centro-sul do escudo das Guianas com base no estudo geoquimico, geocronologico e isotopico dos granitoides paleoproterozoicos do sudeste de Roraima, Brasil

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    Almeida, Marcelo Esteves

    2006-07-01

    Granite. On the other hand, xenoliths of Martins Pereira and biotite bearing enclaves are founded in the younger, undeformed, and SiO{sub 2}-rich Igarape Azul Granite (1.89 Ga). This last and the high-K calc-alkaline Caroebe Granite (1.90-1.89 Ga, Agua Branca Suite), including coeval volcanic rocks (1.89 Ga, Jatapu volcanics) and charnockitoids (1.89 Ga, e.g. Santa Maria Enderbite), crop out in the southern UAD. This sub domain is characterized only by local and slight NE-SW ductile-brittle dextral shear zones. A-type granites such as Moderna (ca. 1.81 Ga) and Mapuera (ca. 1.87 Ga) granites, cross cut both areas of UAD. The geological mapping also identified three main types of metalotects in this region. Gold mineralization is observed in Martins Pereira-Serra Dourada granitoids (northern UAD); alluvial columbitetantalite is related to Igarape Azul granitoids (southern UAD); and amethyst is associated to pegmatites from Moderna A-type granites. The Nd-Pb isotope data suggest that all granitoids of UAD were generated by reworking of older and previous crustal sources (sialic Rhyacian-Archean and/or juvenile Transamazonian origin) and mantle input is not probably a viable model. Although the dominant process may be subduction in the early stage of NUAD evolution, post-collisional magmatism may be a significant process in the production of new continental crust in the southern UAD. It is possible that, following oceanic closure in the Anaua arc system (2.03 Ga) and subsequent collisional orogeny (1.97-1.94 Ga?), under plated mantle melts (basalt liquids) were trapped below preexisting lower crustal rocks of various compositions (e.g. granulite, metatonalites, amphibolite). The basalt liquids and subsequently melted lower crust could produced the immense volumes of granite (and volcanics) observed at 1.90-1.87 Ga. This geological picture is similar to the Tapajos Domain (TD) in the southern Amazonian Craton and suggest that both belong to the same province (Ventuari

  10. Reassessment of the geologic evolution of selected precambrian terranes in Brazil, based on SHRIMP U-Pb data, part 2: mineiro and Aracuai orogens and Southern Sao Francisco craton; Reavaliacao da evolucao geologica em terrenos pre-cambrianos brasileiros com base em novos dados U-Pb SHRIMP, parte 2: orogeno Aracuai, cinturao mineiro e craton Sao Francisco Meridional

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Luiz Carlos da; Pimentel, Marcio [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: luizcarlos@aneel.gov.br; Leite, Carlos Augusto; Vieira, Valter Salino; Silva, Marcio Antonio da; Paes, Vinicius Jose de Castro; Cardoso Filho, Joao Moraes [Companhia de Pesquisas de Recursos Minerais (CPRM), Belo Horizonte, MG (Brazil); Armstrong, Richard [Australian National Univ., Canberra (Australia). Research School of Earth Sciences; Noce, Carlos Mauricio; Pedrosa-Soares, Antonio Carlos [Minas Gerais Univ., Belo Horizonte (Brazil). Inst. de Geociencias. Centro de Pesquisa Manuel Teixeira da Costa; Carneiro, Mauricio Antonio [Ouro Preto Univ., MG (Brazil). Dept. de Geologia

    2002-12-15

    Aracuai Orogen, the Caparao charnockitic granulite, revealed magmatic crystallization age of ca. 2195 Ma. Zircons from an amphibolite of the Pocrane Complex, also a basement inlier within the Aracuai Orogen, yielded an age of ca. 1500 Ma. Both inliers furnished well-constrained neo proterozoic metamorphic overprint at ca. 590 Ma. The sub alkaline gneissic granite from the Salto da Divisa Suite yielded a magmatic crystallization age of ca. 870 Ma, close to U-Pb ages of the continental rift magmatism found in the African counterpart of the Aracuai Orogen. Four gneissic granites from the Aracuai Orogen (three of them previously interpreted as part of the Archean/Paleoproterozoic basement) were dated in the range of ca. 560-570 Ma, and were correlated to the {gamma}2{sub 2} syn-collisional magmatism. Borders of some zircon grains from the older (ca. 570 Ma) dated unit (Nanuque Granite) yielded ages around 500 Ma, similar to U-Pb ages obtained from titanite, monazite and zircon in other localities from the Aracuai Orogen. This youngest ages could be related to heating effects caused by melting of country rocks and ascent of magmas formed during the collapse of the orogen. (author)

  11. Tectonic-stratigraphic evolution of Cumuruxatiba Basin - Brazil; Evolucao tectono-estratigrafica da Bacia de Cumuruxatiba

    Energy Technology Data Exchange (ETDEWEB)

    Lobato, Gustavo; Fernandes, Flavio L.; Silva, Eric Zagotto; Ferreira Neto, Walter Dias [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia (COPPE). Lab. de Modelagem Multidisciplinar de Bacias Sedimentares; Ribeiro, Juliana [Agencia Nacional do Petroleo, Gas Natural e Biocombustiveis (ANP), Brasilia, DF (Brazil)

    2008-07-01

    In recent years, the exploratory interest on Cumuruxatiba Basin has been inconstant, with modest discoveries of oil. Aiming to deepen the geological knowledge of the basin and in order to attract the interest of oil companies, the ANP (National Agency of Petroleum, Natural Gas and Biofuels) signed contract with COPPE/UFRJ for carrying out an analysis basin project. The project was developed by the Basin Analysis Multidisciplinary Modeling Laboratory (Lab2M/UFRJ) in the period 2006/2007, and was with the main objective outline the main structural and seismo-stratigraphic features of the basin, and in an integrated and multidisciplinary way, build a model of its sedimentation and tectono-stratigraphic evolution. This paper presents the results of the regional seismic mapping, aided by well and potential methods data. The stratigraphic succession the basin has been divided into genetic units (UN-B, UN-C e UN-D) corresponding to second order depositional sequences, they are: UN-B, corresponding by a rift and sag-rift siliciclastic deposits, plus the Aptian evaporitic deposits; UN-C, characterized by carbonatic deposits, and shelf related sediments; and UN-D, corresponding by a final transgressive (siliciclastic) - regressive (mix) cycle, between Cenomanian and actual days. (author)

  12. In situ isotopic analyses of U and Pb in zircon by remotely operated SHRIMP II, and Hf by LA-ICP-MS: an example of dating and genetic evolution of zircon by {sup 176}Hf/{sup 177}Hf from the Ita Quarry in the Atuba Complex, SE, Brazil; Analises in situ de U e Pb em zircao por SRIMP II por controle remoto e de Hf por LA-ICP-MS: um exemplo de datacao e da evolucao genetica de zircao atraves da razao {sup 176}Hf/{sup 177} em amostra da Pedreira Ita no Complexo Atuba, SE, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Sato, K.; Siga Junior, Oswaldo; McReath, Ian; Sproesser, Walter; Basei, Miguel Angelo Stipp [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Centro de Pesquisas Geocronologicas], e-mail: keisato@usp.br, e-mail: osigajr@usp.br, e-mail: ianmcr@usp.br, e-mail: wmspres@usp.br, e-mail: baseimas@usp.br; Silva, Josiane Aline da [Universidade de Sao Paulo (USP), SP (Brazil). Programa de Pos-graduacao em Geoquimica e Geotectonica; Dunyi, Liu [Institute of Geology, Beijing (China); Iizuka, Takafumi; Rino, Shuji; Hirata, Takafumi [Tokyo Institute of Technology, Tokyo (Japan)

    2009-10-15

    Remotely-operated SHRIMP dating of zircon is an interesting alternative for dating of zircon crystals. Although it does not represent any technical progress of the geochronological method using the U-Pb system in zircon it is a very useful and cheap facility. The procedure was first used for mass spectrometric analyses involving two international laboratories in Sao Paulo, Brazil and Beijing, China. It was applied to samples of three gneiss-migmatitic rocks from the Ita quarry in the Atuba Complex (located between the Luis Alves and the Apiai Domain) to test previous controversial hypotheses about its evolution. The presence of important archaean and paleo proterozoic components in the complex is confirmed by analyses of zircon found in probably neo proterozoic leucosomes. Diorite intrusion also occurred during the neo proterozoic, associated with the 0.6Ga continental collisions involved in the assembly of Gondwana. The determination of Hf isotope ratios by LA-ICP/MS represents a new option for checking the relative importance of mantle ({epsilon}{sub Hf} > 0) and crustal contributions (({epsilon}{sub Hf} < 0) during the growth of the zircon crystals. While the archaean component in the complex was derived from the mantle ({epsilon}{sub Hf} + 1.5 to + 8.7) the paleo proterozoic component had a crustal contribution ({epsilon}{sub Hf} - 9.1 to -10.1). (author)

  13. Lunar Crustal Stratigraphy

    Science.gov (United States)

    McCallum, I. S.; O'Brien, H. E.

    1996-03-01

    Intense bombardment during the first 600 Ma of lunar history has rendered the task of reconstructing the stratigraphy of the lunar crust especially difficult. On a planetary scale, the distribution of lithologies around multi-ringed basins coupled with orbital geochemical data reveal that the lunar crust is heterogeneous both laterally and vertically. Ejecta from the large multi-ringed basins is exclusively of crustal origin since twenty five years of lunar sample study have failed to identify any unequivocal mantle samples. Given the most recent determination of crustal thickness, this implies an upper limit to the depth of excavation of around 60 km. In the younger multi-ringed basins (Orientale and Imbrium), the occurrence of anorthosites in inner rings is consistent with an anorthositic upper crust (Al2O3 = 26-28 wt.%). On the other hand, basin impact melts, most notably the low-K Fra Mauro (LKFM) composition associated with the Imbrium and Serenitatis basins, are distinctly more mafic with a composition corresponding to norite (Al2O3 ~ 20 wt.%). Cratering models suggest that such melts are generated at the lower to middle crustal depths (30 to 60 km). The paucity of unequivocal deep-seated crystalline plutonic rocks is also consistent with cratering models which suggest that unmelted rock fragments in ejecta blankets are most likely derived from the upper part of the crust. Consequently, the possibility exists that no crystalline lunar samples from deeper that ~30 km are present in the returned sample collection.

  14. Tectonic-stratigraphic evolution of Espirito Santo Basin - Brazil; Evolucao tectono-estratigrafica da Bacia do Espirito Santo

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Eric Zagotto; Fernandes, Flavio L.; Lobato, Gustavo; Ferreira Neto, Walter Dias [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia (COPPE). Lab. de Modelagem de Bacias (LAB2M); Petersohn, Eliane [Agencia Nacional do Petroleo, Gas Natural e Biocombustiveis (ANP), Brasilia, DF (Brazil)

    2008-07-01

    This paper documents the analysis of seismic data of the Espirito Santo basin obtained during the project realized through partnership between COPPE/UFRJ/Lab2M with the Agencia Nacional do Petroleo, Gas Natural e Biocombustiveis (ANP) during 2006 and 2007. The major objective of the seismic data interpretation in the project was to define the main structural and stratigraphic features in order to build a sedimentation model and a tectonic-stratigraphic evolution model of the Espirito Santo basin. Thus, the sedimentary package has been divided into eight genetic units (UN), grouped into five third order stratigraphic sequences, namely: UN-B, represented by siliciclastics rocks of the rift stage and evaporitic sag-rift stage, deposited during the Aptian; UN-C, which represents the carbonatic rocks deposited in a marine environment, and siliciclastics rocks located in the proximal portions during the Albian; and UN-D, represented by sediments, composed mainly by pelites, deposited in between the Cenomanian and Recent, and includes the Eocene volcanic event, which one changed the sedimentation pattern of the basin. (author)

  15. Mortalidade perinatal no municipio de Salvador, Bahia: evolucao de 2000 a 2009

    Directory of Open Access Journals (Sweden)

    Elsa Jacinto

    2013-10-01

    Full Text Available OBJETIVO Analisar a evolução da mortalidade perinatal quanto à dimensão do problema e sua extensão. MÉTODOS Estudo descritivo de tendência temporal com 10.994 óbitos perinatais, de mães residentes em Salvador, BA, com idade gestacional ≥ 22 semanas, idade do recém-nascido até seis dias e 500 g ou mais de peso ao nascer, registrados de 2000 a 2009. Utilizaram-se dados do Sistema de Informações de Nascidos Vivos e do Sistema de Informações sobre Mortalidade do sitio eletrônico do Datasus/Ministério da Saúde. Calcularam-se taxas de mortalidade perinatal e fetal/1.000 nascimentos e neonatal precoce/1.000 nascidos vivos. Aplicaram-se: teste Qui-quadrado de Pearson para diferenças em proporções, teste de sequências ( runs , cálculo de médias móveis e coeficiente de determinação linear (R 2 para análise de tendência. Utilizou-se a classificação de Wigglesworth para causas de morte. RESULTADOS A taxa de mortalidade perinatal mostrou tendência decrescente, sendo reduzida em 42,0% no período (de 33,1 (2000 para 19,2 (2009, com maior contribuição da taxa neonatal precoce (-56,3%. A mortalidade fetal representou grande proporção (61,9% da taxa de mortalidade perinatal em 2009. A classificação dos óbitos apontou como causas mais frequentes de óbito perinatal: asfixia intraparto (8,8/1.000, imaturidade (7,1/1.000 e malformações congênitas (1,3/1.000. CONCLUSÕES Mesmo em declínio, a taxa de mortalidade perinatal continua elevada e o predomínio recente da mortalidade fetal indica mudança no perfil de causas e impacto nas ações de prevenção. A consulta pré-natal de qualidade com controle de riscos e melhoria da assistência ao parto pode reduzir a ocorrência de causas evitáveis.

  16. Evolucao dos precos relativos de grupos alimentares entre 1939 e 2010, em Sao Paulo, SP

    Directory of Open Access Journals (Sweden)

    Tania Yuka Yuba

    2013-06-01

    Full Text Available OBJETIVO: Analisar a evolução dos preços relativos dos grupos de produtos alimentares e sua influência nas políticas públicas para uma alimentação saudável. MÉTODOS: Foram analisados dados do município de São Paulo de 1939 a 2010, a partir da aplicação de métodos de cálculo de números-índices. Foram utilizados dados do banco de preços e estruturas de ponderação da Fundação Instituto de Pesquisas Econômicas (1939 a 1988 e do Instituto Brasileiro de Geografia e Estatística (1989 a 2010. O banco de preços foi organizado, sua consistência foi testada e os preços foram deflacionados pelo Índice de Preços ao Consumidor. Os dados relativos a preços deflacionados foram calculados e agregados por categorias e grupos alimentares da pirâmide alimentar adaptada. Os índices de preços de cada grupo foram construídos aplicando a fórmula de Laspeyres modificada. O índice geral de preços da alimentação foi comparado com índices de cada grupo alimentar e respectiva categoria: alimentos in natura; alimentos industrializados; bebidas; carnes, leguminosas, leite e ovos; cereais e tubérculos; e refeições fora do domicílio. RESULTADOS: Os grupos alimentares de gorduras, óleos, condimentos, açúcares e alimentos processados (alimentos industrializados apresentaram tendência de redução de preços em termos relativos. O índice dos alimentos in natura, como frutas e verduras, apresentaram tendência de elevação de preços. Outros grupos alimentares, como cereais, farinhas e massas, carnes, leite e ovos, apresentaram estabilidade de preços relativos ao longo do tempo. CONCLUSÕES: A evolução dos preços relativos dos alimentos no município de São Paulo mostra tendência desfavorável à manutenção da alimentação saudável em nível domiciliar em longo prazo.

  17. Crustal thickness controlled by plate tectonics

    DEFF Research Database (Denmark)

    Artemieva, Irina M.; Meissner, Rolf

    2012-01-01

    /gabbro–eclogite phase transition in crustal evolution and the links between lithosphere recycling, mafic magmatism, and crustal underplating. We advocate that plate tectonics processes, togetherwith basalt/gabbro–eclogite transition, limit crustal thickness worldwide by providing effective mechanisms of crustal...

  18. Evolution of the PI - Productivity Index; Evolucao do IP - Indice de Produtividade

    Energy Technology Data Exchange (ETDEWEB)

    Feitosa, Gilvan Soares [Petroleo Brasileiro S.A. (PETROBRAS), Rio de Janeiro, RJ (Brazil)

    2012-07-01

    The productivity index (PI), the most direct and widely used measure of a well productivity, is defined as the ratio of oil-well rate to the associated pressure drawdown - from average reservoir pressure to bottom hole-flowing-well pressure. It is known that the actual value of PI can only be attained at pseudosteady-state condition, which requires a lot of time (days, or even months), what is not practical for most well tests. For this reason, PI is often obtained from short transient flow test, which gives usually an overestimate of the actual PI. How larger than the actual value is the transient PI? This paper investigates the PI evolution, from the earlier transient well's production period up to the pseudosteady-state flow establishment, under single-phase flow, and later on, as pressure drops below saturation pressure and then oil and gas flow through the reservoir to the well. For analysis of PI during the transient period is defined a dimensionless PI (IP{sub D}), as the ratio of the time-dependent transient PI (IP{sub t}), to the constant pseudosteady-state PI (IP{sub pss}). For transient radial flow, IP{sub D} is developed as a function of dimensionless time, t{sub DA}, and depends on the stabilized drainage area, the Dietz shape factor, the skin factor and the well radius. It is shown that transient PI (IP{sub t}) is always greater than the actual PI (IP{sub pss}) and decreases monotonically with time. At the infinite-acting end IPt reaches the smallest value, which is the closest to the actual pseudosteady-state PI, in the range of 1 to 60% higher, for a broad range of shape factors. The more eccentric the well in the drainage area the more IP{sub t} departs from the actual PI. It is presented a couple of reservoir-limit well test field-cases, where the well was produced long enough until a pseudosteady-state flow was established. Its results, among others, illustrate and substantiate the main theoretical developments of this work. (author)

  19. Crustal Ages of the Ocean Floor - Poster

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Crustal Ages of the Ocean Floor Poster was created at NGDC using the Crustal Ages of the Ocean Floor database draped digitally over a relief of the ocean floor...

  20. Crustal structure beneath Eastern Greenland

    DEFF Research Database (Denmark)

    Reiche, Sönke; Thybo, H.; Kaip, G.

    2011-01-01

    The conjugate Atlantic passive margins of western Norway and eastern Greenland are characterized by the presence of coast-parallel mountain ranges with peak elevations of more than 3.5 km close to Scoresby Sund in Eastern Greenland. Knowledge about crustal thickness and composition below these mo...

  1. Crustal structure of Central Sicily

    Science.gov (United States)

    Giustiniani, Michela; Tinivella, Umberta; Nicolich, Rinaldo

    2018-01-01

    We processed crustal seismic profile SIRIPRO, acquired across Central Sicily. To improve the seismic image we utilized the wave equation datuming technique, a process of upward or downward continuation of the wave-field between two arbitrarily shaped surfaces. Wave equation datuming was applied to move shots and receivers to a given datum plane, removing time shifts related to topography and to near-surface velocity variations. The datuming procedure largely contributed to attenuate ground roll, enhance higher frequencies, increase resolution and improve the signal/noise ratio. Processed data allow recognizing geometries of crust structures differentiating seismic facies and offering a direct image of ongoing tectonic setting within variable lithologies characterizing the crust of Central Sicily. Migrated sections underline distinctive features of Hyblean Plateau foreland and above all a crustal thinning towards the Caltanissetta trough, to the contact with a likely deep Permo-Triassic rifted basin or rather a zone of a continent to oceanic transition. Inhomogeneity and fragmentation of Sicily crust, with a distinct separation of Central Sicily basin from western and eastern blocks, appear to have guided the tectonic transport inside the Caltanissetta crustal scale syncline and the accumulation of allochthonous terrains with south and north-verging thrusts. Major tectonic stack operated on the construction of a wide anticline of the Maghrebian chain in northern Sicily. Sequential south-verging imbrications of deep elements forming the anticline core denote a crust wedge indenting foreland structures. Deformation processes involved multiple detachment planes down to decoupling levels located near crust/mantle transition, supporting a presence of high-density lenses beneath the chain, interrelated to a southwards push of Tyrrhenian mantle and asthenosphere.

  2. South Atlantic pale oceanography and evolution during the Albian; Paleoceanografia e a evolucao do Atlantico Sul no Albiano

    Energy Technology Data Exchange (ETDEWEB)

    Azevedo, Ricardo Latge Milward de [PETROBRAS, Rio de Janeiro, RJ (Brazil). Diretoria de Exploracao e Producao]. E-mail: ricardolatge@petrobras.com.

    2004-11-01

    A vast array of geochemical, geophysical, sedimentological and paleontological data, together with modern environmental analogues in the Red Sea, support the view that the South Atlantic maintained its bi partitioned condition from latest Aptian to the middle Albian. The lineament comprising the Florianopolis High and Sao Paulo Dorsal formed an effective barrier to sea-water circulation between the Southern South Atlantic (SSA) and Central South Atlantic (CSA) until late Albian times. During that time, the latter communicated mainly with the North Atlantic, which in turn was connected to the Tethys Sea. The CSA was then entirely located within an arid climatic belt, and subject to a negative hydric balance, whereas an estuarine circulation pattern prevailed in the SSA. The comparison of carbon and oxygen stable isotope results from limestones in various parts of the world demonstrates that the CSA waters were warmer than those of the Malvinas in the South, and the Tethyan Sea to the North. The CSA sedimentary evolution was coeval with profound paleoceanographic changes. These were mainly induced by global tectonic phenomena related to the dynamics of oceanic crustal accretion, culminating with the definitive interconnection of the Tethyan and Indian oceanic waters by the end-Albian. Halokynetic movements and orbital variations brought about oscillations in accommodation space, which permitted the stacking of tens of shallowing-upward cycles with varied magnitudes. (author)

  3. Crustal Deformation In Northeastern Italy.

    Science.gov (United States)

    Zerbini, S.; Romagnoli, C.; Richter, B.; Lago, L.; Domenichini, F.; Simon, D.

    Four permanent GPS stations have been installed in northeastern Italy starting mid 1996. Three stations: Bologna, Medicina and Porto Corsini are located in the south- eastern Po Plain, while the fourth one was set up in the Trieste harbor. The network was installed to monitor vertical crustal movements at tide gauge sites and in sub- siding areas of the Po Plain. At Medicina, since October 1996, it is also operative a superconducting gravimeter periodically controlled by means of absolute gravity mea- surements. The stations, which are distributed around the northern edge of the Adria plate, provide information on vertical and horizontal displacements related to crustal deformation. The temporal behavior of the Adria plate, in response to the convergence of the surrounding regions, has been presumably more complex than a simple horizon- tal displacement and, most likely, involved flexural bending processes. The GPS and the continuous gravity data have been analyzed and interpreted to estimate vertical and horizontal rates at the four sites. The presence of relevant seasonal signals has been identified in the series of station coordinates as well as in the gravity data. These fluc- tuations, if not accounted for, may corrupt the high precision estimate of the long-term trends.

  4. Science Academies Refresher Course on Crustal Strength ...

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 22; Issue 3. Science Academies Refresher Course on Crustal Strength Rheology and Seismicity (CSRS-2017). Information and Announcements Volume 22 Issue 3 March 2017 pp 328-328 ...

  5. Evolution of possibilities of solar energy in building in Porto Alegre (Brazil); Evolucao da desiposbilidade de energia solar na edificaco em porto alegre, RS. Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Mascaro, J. J.; Favero, R. C.; Saugo, A.

    2004-07-01

    The urban form is studied as resultant of the effective urban legislation in each part of the city, and as the definer of the landscape as well as the urban ambience. The case of the humid subtropical city is the central subject of this work, for being a region in which the climate requires insolation in the winter (passive solar heating), as much for construction as for urban enclosure. Requirement this that cannot be supplied by compact urban forms, proposed by the most current literature that worries about problems of urban transportation, for considering them as being the most efficient energetically. Although advantages are recognized in this proposal, the simple transposition of the adopted solutions in the cold and tempered climates, and in paradigmatic cities, is questioned, exactly because they supply the requirements of its place of implantation, the culture and the local landscape. (Author)

  6. Modeling of development and projection of the accumulated recoverable oil volume: methodology and application; Modelagem da evolucao e projecao de volume de oleo recuperavel acumulado: metodologia e aplicacao

    Energy Technology Data Exchange (ETDEWEB)

    Melo, Luciana Cavalcanti de; Ferreira Filho, Virgilio Jose Martins; Rocha, Vinicius Brito [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia (COPPE)

    2004-07-01

    A relevant problem that petroleum companies deal is the estimate of the future levels of reserves The objective of the reserve forecasting is pursued through the construction of mathematical models. Considering that the exploration process is an informed and controlled process, in order to reach the exploration targets, the exploration process is lead inside of a sequence of decisions based on the reached results. Such decisions are taken surrounded by an uncertain environment added to the random nature of the process. Another important assumption that must be taken into consideration is the dependency of the exploration on the conditions, or structure, of the discovered resources and the final potential. The modeling starts with the establishment of a general problem, when the models are being constructed, based on suppositions associated to the main concepts, and ends with the attainment of specific solutions, when the best description, or model, is selected through the estimate of the respective parameters and of the measurement adjustments. The result of this approach reflects the essence of the exploration process and how it is reflected in the incorporation of reserves and history of field discoveries. A case study is used for validation of the models and the estimates. (author)

  7. Crustal Structure of the Khartoum Basin, Sudan

    Science.gov (United States)

    El Tahir, Nada; Nyblade, Andrew; Julià, Jordi; Durrheim, Raymond

    2017-04-01

    The Khartoum basin is one of several Mesozoic rift basins in Sudan associated with the Central Africa Rift System. Little is known about the deep crustal structure of this basin, and this limited knowledge hampers the development of a more detailed understanding of its origin and evolution. Constraints on crustal structure in Sudan are only available through regional gravity studies and continental-scale tomography models, but these studies have poor resolution in the Khartoum basin. Here, we investigate the crustal structure of the northern part of the Khartoum basin beneath 3 permanent seismic stations in Khartoum, Sudan through the H-k stacking of receiver functions and the joint inversion of receiver functions and Rayleigh-wave group velocities. Our H-k-stacking results indicate that crustal thickness beneath the Khartoum basin ranges between 33 and 37 km, with an average of 35 km and that crustal Vp/Vs ratio ranges from 1.74 to 1.81, with an average of 1.78. These results are consistent with 1D velocity models developed from the joint inversion of receiver functions and Rayleigh-wave group velocities, which display similar estimates for crustal thickness and an average shear-wave velocity of 3.7 km/s for the basin's crust. Our results provide the first seismic estimate of Moho depth for a basin in Sudan and, when compared to average crustal thickness for the unrifted Proterozoic crust in eastern Africa, reveal that at most a few kilometers of crustal thinning has occurred beneath the Khartoum basin.

  8. Microbial life in ridge flank crustal fluids.

    Science.gov (United States)

    Huber, Julie A; Johnson, H Paul; Butterfield, David A; Baross, John A

    2006-01-01

    To determine the microbial community diversity within old oceanic crust, a novel sampling strategy was used to collect crustal fluids at Baby Bare Seamount, a 3.5 Ma old outcrop located in the north-east Pacific Ocean on the eastern flank of the Juan de Fuca Ridge. Stainless steel probes were driven directly into the igneous ocean crust to obtain samples of ridge flank crustal fluids. Genetic signatures and enrichment cultures of microorganisms demonstrate that these crustal fluids host a microbial community composed of species indigenous to the subseafloor, including anaerobic thermophiles, and species from other deep-sea habitats, such as seawater and sediments. Evidence using molecular techniques indicates the presence of a relatively small but active microbial population, dominated by bacteria. The microbial community diversity found in the crustal fluids may indicate habitat variability in old oceanic crust, with inputs of nutrients from seawater, sediment pore-water fluids and possibly hydrothermal sources. This report further supports the presence of an indigenous microbial community in ridge flank crustal fluids and advances our understanding of the potential physiological and phylogenetic diversity of this community.

  9. Trace element differences between Archean, Proterozoic and Phanerozoic crustal components: Implications for crustal growth processes

    Science.gov (United States)

    Tarney, J.; Wyborn, L. E. A.; Sheraton, J. W.; Wyborn, D.

    1988-01-01

    Critical to models for continental crust growth and recycling are the processes through which crustal growth takes place. In particular, it is important to know whether these processes have changed fundamentally with time in response to the earth's thermal evolution, and whether the crustal compositions generated are compatible with crustal remobilization, crustal recycling, or represent primary additions. There are some significant and consistent differences in the major and trace element compositions of crustal components with time which have important implications for crustal growth processes. These will be illustrated with reference to Archean rocks from a number of shield areas, Proterozoic granitoids from Australia and elsewhere, Palaeozoic granitoids from Australia and Scotland, and Mesozoic - recent granitoids from present continental margin belts. Surprisingly some rather simple and consistent patterns energy using this technique. There are then significant differences in compositions of granitoid crustal additions throughout geological time, with a particular type of granitoid apparently dominating a particular time period. This implies that the tectonic processes giving rise to granite generation have changed in response to the earth's thermal evolution.

  10. Nd isotopes and crustal growth rate

    Science.gov (United States)

    Albarede, F.

    1988-01-01

    Sm/Nd isotopic constraints on crustal growth is discussed. In order to constrain Sm/Nd fractionation between continental crust and depleted mantle, an extensive data base of isotopic measurements (assumed to be adequately representative of continental crust) was compiled. The results imply that the evolution of depleted mantles was roughly linear, with no major discontinuities over the course of geologic time. This is different from other determinations of depleting mantle evolution, which show nonlinear behavior. The Sm/Nd evolution lines for continental crust and depleted mantle intersect between 3.8 to 4.0 Ga, which may indicate that the onset of continental growth was later than 4.5 Ga. A mathematical model is described, the results of which imply that time integrated crustal additions from the mantle are about 1.8 to 2.5 cu km/a, whereas crustal subtractions by sediment recycling are about 0.6 to 1.5 cu km/a. This results in a net time integrated crustal growth rate of about 1 cu km/a, which is similar to present day rates determined, for example, by Reymer and Schubert.

  11. Crustal structure of the Khartoum Basin, Sudan

    CSIR Research Space (South Africa)

    El Tahir, N

    2013-05-01

    Full Text Available The crustal structure of the northern part of the Khartoum Basin has been investigated using data from 3 permanent seismic stations within 40 km of Khartoum and two modeling methods, H–k stacking of receiver functions and a joint inversion...

  12. Reports on crustal movements and deformations. [bibliography

    Science.gov (United States)

    Cohen, S. C.; Peck, T.

    1983-01-01

    This Catalog of Reports on Crustal Movements and Deformation is a structured bibliography of scientific papers on the movements of the Earth crust. The catalog summarizes by various subjects papers containing data on the movement of the Earth's surface due to tectonic processes. In preparing the catalog we have included studies of tectonic plate motions, spreading and convergence, microplate rotation, regional crustal deformation strain accumulation and deformations associated with the earthquake cycle, and fault motion. We have also included several papers dealing with models of tectonic plate motion and with crustal stress. Papers which discuss tectonic and geologic history but which do not present rates of movements or deformations and papers which are primarily theoretical analyses have been excluded from the catalog. An index of authors cross-referenced to their publications also appears in the catalog. The catalog covers articles appearing in reviewed technical journals during the years 1970-1981. Although there are citations from about twenty journals most of the items come from the following publications: Journal of Geophysical Research, Tectonophysics, Geological Society of America Bulletin of the Seismological Society of America, Nature, Science, Geophysical Journal of the Royal Astronomical Society, Earth and Planetary Science Letters, and Geology.

  13. Modes of continental extension in a crustal wedge

    KAUST Repository

    Wu, Guangliang

    2015-07-01

    © 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.

  14. A new model of crustal structure of Siberia

    DEFF Research Database (Denmark)

    Cherepanova, Yulia; Artemieva, Irina; Thybo, Hans

    2010-01-01

    , or tectonic similarities, or seismic data reported not along seismic reflection/refraction profiles but as interpolated contour maps are excluded from the new crustal database. Due to uneven quality of seismic data related both to data acquisition problems and interpretation limitations, a special attention......-dependence (we use tectono-thermal ages) of crustal parameters allows for distinguishing the effects of various tectonic processes on the crustal structure. The analysis provides the basis for studies of crustal evolution and geodynamic process in the region where the age of tectonic structures spans over ~4 Ga...

  15. Crustal structure of Bristol Bay Region, Alaska

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, A.K.; McLean, H.; Marlow, M.S.

    1985-04-01

    Bristol Bay lies along the northern side of the Alaska Peninsula and extends nearly 600 km southwest from the Nushagak lowlands on the Alaska mainland to near Unimak Island. The bay is underlain by a sediment-filled crustal downwarp known as the north Aleutian basin (formerly Bristol basin) that dips southeast toward the Alaska Peninsula and is filled with more than 6 km of strata, dominantly of Cenozoic age. The thickest parts of the basin lie just north of the Alaska Peninsula and, near Port Mollar, are in fault contact with older Mesozoic sedimentary rocks. These Mesozoic rocks form the southern structural boundary of the basin and extend as an accurate belt from at least Cook Inlet to Zhemchug Canyon (central Beringian margin). Offshore multichannel seismic-reflection, sonobuoy seismic-refraction, gravity, and magnetic data collected by the USGS in 1976 and 1982 indicate that the bedrock beneath the central and northern parts of the basin comprises layered, high-velocity, and highly magnetic rocks that are locally deformed. The deep bedrock horizons may be Mesozoic(.) sedimentary units that are underlain by igneous or metamorphic rocks and may correlate with similar rocks of mainland western Alaska and the Alaska Peninsula. Regional structural and geophysical trends for these deep horizons change from northeast-southwest to northwest-southeast beneath the inner Bering shelf and may indicate a major crustal suture along the northern basin edge.

  16. Crustal permeability: Introduction to the special issue

    Science.gov (United States)

    Ingebritsen, Steven E.; Gleeson, Tom

    2015-01-01

    The topic of crustal permeability is of broad interest in light of the controlling effect of permeability on diverse geologic processes and also timely in light of the practical challenges associated with emerging technologies such as hydraulic fracturing for oil and gas production (‘fracking’), enhanced geothermal systems, and geologic carbon sequestration. This special issue of Geofluids is also motivated by the historical dichotomy between the hydrogeologic concept of permeability as a static material property that exerts control on fluid flow and the perspective of economic geologists, geophysicists, and crustal petrologists who have long recognized permeability as a dynamic parameter that changes in response to tectonism, fluid production, and geochemical reactions. Issues associated with fracking, enhanced geothermal systems, and geologic carbon sequestration have already begun to promote a constructive dialog between the static and dynamic views of permeability, and here we have made a conscious effort to include both viewpoints. This special issue also focuses on the quantification of permeability, encompassing both direct measurement of permeability in the uppermost crust and inferential permeability estimates, mainly for the deeper crust.

  17. A relook into the crustal architecture of Laxmi Ridge, northeastern ...

    Indian Academy of Sciences (India)

    derived free-air gravity (FAG) data to derive the crustal structure of Laxmi Ridge and adjacent areas. 2D and 3D crustal modelling suggests that the high resolution FAG low associated with the ridge is due to underplating and that it is of ...

  18. Evaluation of mechanical strength and hydrate products evolution of calcium aluminate cement, for endodontic applications; Avaliacao da evolucao da resistencia mecanica e dos produtos de hidratacao de um cimento de aluminato de calcio, visando sua aplicacao em endodontia

    Energy Technology Data Exchange (ETDEWEB)

    Luz, A.P.; Borba, N.Z.; Pandolfelli, V.C., E-mail: anapaula.light@gmail.com, E-mail: vicpando@power.ufscar.br [Universidade Federal de Sao Carlos (UFSCar), SP (Brazil). Departamento de Engenharia de Materiais

    2011-07-01

    Mineral trioxide aggregate (MTA) is the most used retrograde filling cement in the endodontic area. Nevertheless, although its composition is similar to the conventional Portland cement, its high cost, long setting time and low mechanical strength have led to a continuous search for new alternative materials. Considering these aspects, the mechanical strength and crystalline phase evolution of a calcium aluminate cement (CAC), during its hydration process, have been evaluated in this work aiming to apply such material for endodontic treatments. Secar 71 cement samples were prepared and kept in contact with water or SBF (simulated body fluid) during 15 days at 37 deg C. Compressive strength, apparent porosity, X ray diffraction and thermogravimetric tests were carried out for the samples evaluation after 1, 3, 7 and 15 days. The main identified phases were CAH{sub 10}, C{sub 2}AH{sub 8}, C{sub 3}AH{sub 6} and AH{sub 3}. Moreover, when in the presence of SBF, some changes in the amount of the hydrates in the CAC samples were observed, which affected the mechanical behavior of the cement. (author)

  19. Evolution of the economic importance of the oil and gas industrial sector in Brazil: impacts on macroeconomic indicators; Evolucao da importancia economica da industria de petroleo e gas natural no Brasil: contribuicao a variaveis macroeconomicas

    Energy Technology Data Exchange (ETDEWEB)

    Canelas, Andre Luis de Souza

    2007-06-15

    This thesis analyzes the evolution of the macroeconomic importance of the oil and gas sector in Brazil, in the recent years, which is represented by its contribution to the macroeconomic indicators, which are: GDP, Investment, Foreign Direct Investment, Trade Balance, Tax Revenue, Jobs, Wages and Inflation. The results found indicate that the oil and gas sector has a relevant contribution to the values of the Brazilian GDP, total amount of investment, total amount of foreign direct investment, tax revenue, inflation and trade balance, whereas this sector has a less relevant impact for the creation of jobs and wages in Brazil. (author)

  20. Analysis of institutional evolution of regulatory activity in the Brazilian electric sector: 1920-1997; Analise da evolucao institucional da atividade de regulacao no setor eletrico brasileiro: 1920-1997

    Energy Technology Data Exchange (ETDEWEB)

    Tavares, Mauricio Lopes; Ferreira, Elnatan Chagas; Dias, Jose Antonio Siqueira [Universidade Estadual de Campinas (DEMIC/FEEC/UNICAMP), SP (Brazil). Fac. de Engenharia Eletrica e de Computacao. Dept. de Eletronica e Microeletronica], Email: siqueira@demic.fee.unicamp.br

    2006-07-01

    An analysis of the institutional evolution of the governmental organizations which were responsible for the regulation of the electrical energy sector in Brazil (before the establishment of the ANEEL) is presented . Taking into account the various levels of subordination and independence in their actuation, the different missions and powers given to these agencies regarding the inspection, controlling, planning and regulating the industry, are compared and discussed. The conducted analysis is essentially formal, based on the legal instruments which defined and established the creation of those agencies. (author)

  1. Tectonic-stratigraphic evolution of mini-basins and salt provinces of Espirito Santo Basin-Brazil; Analise da evolucao tectono sedimentar de mini-bacias e provincias de sal da Bacia do Espirito Santo

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira Neto, Walter Dias; Fernandes, Flavio Luis [Petroleum Geoscience Technology Ltda. (PGT), Rio de Janeiro, RJ (Brazil); Mohriak, Webster [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil); Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, RJ (Brazil)

    2008-07-01

    The Espirito Santo Basin integrates the group of basins along the eastern Brazilian continental margin. It is located between 18 deg and 21 deg S, encompassing an area of approximately 220,000 km{sup 2}, onshore and offshore the Espirito Santo State. Its geological limit with the Campos Basin to the south is defined by a Precambrian basement high (Vitoria Arch), and its northern limit with the Mucuri Basin is defined by a geopolitical limit. The study of salt tectonics processes in the Espirito Santo Basin allowed the deformational analysis and interpretation of the chronological evolution of the mini-basins developed between salt diapirs. We observe an intrinsic relationship between halokinesis and creation of subsidence troughs that may be important for trapping hydrocarbon reservoirs, and consequently form oil and gas accumulations in this portion of the basin. This geodynamics evolution of these structures is marked by a strong linkage between salt movement and coeval sedimentation in the interdomal basins, forming structures and stratigraphic traps that may constitute important aspects for the petroleum geology. (author)

  2. Detailed crustal thickness variations beneath the Illinois Basin area: Implications for crustal evolution of the midcontinent

    Science.gov (United States)

    Yang, Xiaotao; Pavlis, Gary L.; Hamburger, Michael W.; Marshak, Stephen; Gilbert, Hersh; Rupp, John; Larson, Timothy H.; Chen, Chen; Carpenter, N. Seth

    2017-08-01

    We present high-resolution imaging results of crustal and upper mantle velocity discontinuities across the Illinois Basin area using both common conversion point stacking and plane wave migration methods applied to P wave receiver functions from the EarthScope Ozark, Illinois, Indiana, and Kentucky experiment. The images reveal unusually thick crust (up to 62 km) throughout the central and southeastern Illinois Basin area. A significant Moho gradient underlies the NW trending Ste. Genevieve Fault Zone, which delineates the boundary between the Illinois Basin and Ozark Dome. Relatively thinner crust (Proterozoic convergent margin tectonics around 1.55-1.35 Ga; (3) by Late Precambrian magmatic underplating at the base of older crust, associated with the creation of the Eastern Granite-Rhyolite Province around 1.3 Ga; and (4) through crustal "relamination" during an episode of Proterozoic flat-slab subduction beneath the Illinois Basin, possibly associated with the Grenville Orogeny.

  3. Mapping crustal thinning beneath the Eastern Pyrenees

    Science.gov (United States)

    Diaz, Jordi; Chevrot, Sebastien; Verges, Jaume; Sylvander, Matthieu; Ruiz, Mario; Antonio-Vigil, Amanda

    2017-04-01

    The eastern termination of the Pyrenees is a complex region marked by two large tectonic events, the building of the Pyrenees during the Alpine orogeny and the Neogene extensional processes associated to the rotation of the Sardinia-Corsica block and the opening of the Valencia Trough. This complex tectonic history has left major imprints in crustal structures. Previous studies based on gravity data and active seismic profiles have documented a crustal thinning from 40-45 km about 80 km to the west of the Mediterranean coastline to less than 25 km beneath the eastern termination of the Pyrenees. To progress in the knowledge of the geometry of this transition, two passive seismic profiles have been acquired from mid 2015 to late 2016 within the OROGEN project, an academic-industrial collaboration between CNRS-Total-BRGM and CSIC. Up to 38 broad-band stations were deployed along two orthogonal lines, with an interstation spacing close to 10 km. First results of receiver function migration on the E-W profile suggest a smooth Moho thinning smoothly from 40 km beneath the western termination of the line to 23 km close to the coastline. The NNE-SSW profile shows a clearly defined Moho beneath Iberia, slightly deepening from 32 to 35 km northwards, a 28-30 km thick crust underneath the North Pyrenean Front Thrust and a complex geometry in the Axial Zone. Data from natural events located in the Gulf of Roses and near the intersecting point of the profiles have been recorded along the lines, hence allowing to produce wide angle reflection/refraction profiles providing additional constraints on the geometry of the crust/mantle boundary in the Eastern Pyrenees. These new results will be integrated with the available geophysical and geologic information for a more accurate geodynamical interpretation of the results. (Additional founding by the MISTERIOS project, CGL2013-48601-C2-1-R)

  4. Crustal structure of China from deep seismic sounding profiles

    Science.gov (United States)

    Li, S.; Mooney, W.D.

    1998-01-01

    More than 36,000 km of Deep Seismic Sounding (DSS) profiles have been collected in China since 1958. However, the results of these profiles are not well known in the West due to the language barrier. In this paper, we summarize the crustal structure of China with a new contour map of crustal thickness, nine representative crustal columns, and maps showing profile locations, average crustal velocity, and Pn velocity. The most remarkable aspect of the crustal structure of China is the well known 70+ km thickness of the crust of the Tibetan Plateau. The thick (45-70 km) crust of western China is separated from the thinner (30-45 km) crust of eastern China by the north-south trending seismic belt (105??E). The average crustal velocity of China ranges from 6.15 to 6.45 km/s, indicating a felsic-to-intermediate bulk crustal composition. Upper mantle (Pn) velocities are 8.0 ?? 0.2 km/s, equal to the global continental average. We interpret these results in terms of the most recent thermo-tectonic events that have modified the crust. In much of eastern China, Cenoxoic crustal extension has produced a thin crust with a low average crustal velocity, similar to western Europe and the Basin and Range Province, western USA. In western China, Mesozoic and Cenoxoic arc-continent and continent-continent collisions have led to crustal growth and thickening. Inferences on the process of crustal thickening are provided by the deep crustal velocity structure as determined by DSS profiles and other seismological studies. A high velocity (7.0-7.4 km/s) lower-crustal layer has been reported in western China only beneath the southernmost Tibetan Plateau. We identity this high-velocity layer as the cold lower crust of the subducting Indian plate. As the Indian crust is injected northward into the Tibetan lower crust, it heats and assimilates by partial melting, a process that results in a reduction in the seismic velocity of the lower crust in the central and northern Tibetan Plateau

  5. Evolution of crustal thickening in the central Andes, Bolivia

    Science.gov (United States)

    Eichelberger, Nathan; McQuarrie, Nadine; Ryan, Jamie; Karimi, Bobak; Beck, Susan; Zandt, George

    2015-09-01

    Paleoelevation histories from the central Andes in Bolivia have suggested that the geodynamic evolution of the region has been punctuated by periods of large-scale lithospheric removal that drive rapid increases in elevation at the surface. Here, we evaluate viable times and locations of material loss using a map-view reconstruction of the Bolivian orocline displacement field to forward-model predicted crustal thicknesses. Two volumetric models are presented that test assumed pre-deformation crustal thicknesses of 35 km and 40 km. Both models predict that modern crustal thicknesses were achieved first in the northern Eastern Cordillera (EC) by 30-20 Ma but remained below modern in the southern EC until ≤10 Ma. The Altiplano is predicted to have achieved modern crustal thickness after 10 Ma but only with a pre-deformation thickness of 50 km, including 10 km of sediment. At the final stage, the models predict 8-25% regional excess crustal volume compared to modern thickness, largely concentrated in the northern EC. The excess predicted volume from 20 to 0 Ma can be accounted for by: 1) crustal flow to the WC and/or Peru, 2) localized removal of the lower crust, or 3) a combination of the two. Only models with initial crustal thicknesses >35 km predict excess volumes sufficient to account for potential crustal thickness deficits in Peru and allow for lower crustal loss. However, both initial thickness models predict that modern crustal thicknesses were achieved over the same time periods that paleoelevation histories indicate the development of modern elevations. Localized removal of lower crust is only necessary in the northern EC where crustal thickness exceeds modern by 20 Ma, prior to paleoelevation estimates of modern elevations by 15 Ma. In the Altiplano, crustal thicknesses match modern values at 10 Ma and can only exceed modern values by 5 Ma, post-dating when modern elevations were thought to have been established. Collectively, these models predict that

  6. Seismically constrained two-dimensional crustal thermal structure of ...

    Indian Academy of Sciences (India)

    m2 for stable ... Keywords. Cambay basin; P-wave velocity; heat flow; heat generation; 2-D modelling; crustal thermal structure; Moho depth; Curie isotherm. ... major disadvantage of ignoring the effect of lateral variation in the heat production ...

  7. Crustal Structure beneath Mexico from Receiver Functions

    Science.gov (United States)

    Espindola, V.; Quintanar, L.; Espindola, J.

    2011-12-01

    The Servicio Sismológico Nacional (SSN) is Mexico's official organism in charge of the observation of seismicity in the country. Operated by the Universidad Nacional Autonoma de Mexico, it counts with 32 broadband stations deployed throughout the country. The coverage includes most of the geologic provinces of the territory, which vary widely in their geologic characteristics. The availability of records from teleseisms at those stations makes feasible to obtain sound and homogeneous estimates of the structure of the crust in the Mexican territory through the analysis of receiver functions (RF). In this work we present the results of the analysis of RF obtained from events registered from 1998 to 2009 in the 32 stations of the SSN. The RF technique, which uses converted phases at major velocity discontinuities, is a well established technique to infer the velocity contrasts and thickness of the underlying crust. Using this method we were able to infer the depth of the Moho, a major intracrustal discontinuity and in some cases the depth to the base of the subducting plate. We present maps of crustal thickness in Mexico, which varies between about 29 km in the Yucatan peninsula to more than 40 km in central Mexico. Poisson's coefficient varies between 0.19 and 0.30. The position of the descending slab shows a large variation in the subduction angle (from about 6° in the SE margin of the Pacific coast to about 60° in the NW ) as has been found from other techniques.

  8. Ionospheric precursors for crustal earthquakes in Italy

    Directory of Open Access Journals (Sweden)

    L. Perrone

    2010-04-01

    Full Text Available Crustal earthquakes with magnitude 6.0>M≥5.5 observed in Italy for the period 1979–2009 including the last one at L'Aquila on 6 April 2009 were considered to check if the earlier obtained relationships for ionospheric precursors for strong Japanese earthquakes are valid for the Italian moderate earthquakes. The ionospheric precursors are based on the observed variations of the sporadic E-layer parameters (h'Es, fbEs and foF2 at the ionospheric station Rome. Empirical dependencies for the seismo-ionospheric disturbances relating the earthquake magnitude and the epicenter distance are obtained and they have been shown to be similar to those obtained earlier for Japanese earthquakes. The dependences indicate the process of spreading the disturbance from the epicenter towards periphery during the earthquake preparation process. Large lead times for the precursor occurrence (up to 34 days for M=5.8–5.9 tells about a prolong preparation period. A possibility of using the obtained relationships for the earthquakes prediction is discussed.

  9. The Sub-Crustal Stress Field in the Taiwan Region

    Directory of Open Access Journals (Sweden)

    Robert Tenzer and Mehdi Eshagh

    2015-01-01

    Full Text Available We investigate the sub-crustal stress in the Taiwan region. A tectonic configuration in this region is dominated by a collision between the Philippine oceanic plate and the Eurasian continental margin. The horizontal components of the sub-crustal stress are computed based on the modified _ formulae in terms of the stress function with a subsequent numerical differentiation. This modification increases the (degree-dependent convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a spectral resolution, which is compatible with currently available global crustal models. Moreover, the solution to the Vening _ (VMM inverse isostasy problem is explicitly incorporated in the stress function definition. The sub-crustal stress is then computed for a variable Moho geometry, instead of assuming only a constant Moho depth. The regional results reveal that the Philippine plate subduction underneath the Eurasian continental margin generates the shear sub-crustal stress along the Ryukyu Trench. Some stress anomalies associated with this subduction are also detected along both sides of the Okinawa Trough. A tensional stress along this divergent tectonic plate boundary is attributed to a back-arc rifting. The sub-crustal stress, which is generated by a (reverse subduction of the Eurasian plate under the Philippine plate, propagates along both sides of the Luzon (volcanic Arc. This stress field has a prevailing compressional pattern.

  10. Crustal thickness investigation on three broadband stations in Northern Sumatra

    Science.gov (United States)

    Anggono, T.; Syuhada; Soedjatmiko, B.; Amran, A.

    2017-04-01

    We present a preliminary result of crustal thickness in Northern Sumatra from receiver function analysis and grid search. Total of 111 teleseismic events from three broadband stations (TPTI, KCSI, and BSI) of IA-Network were used to calculate the receiver functions. We identified direct P and S arrival from the receiver function. Converted phases Ps were relatively clear for all three broadband stations. Ps-P time was estimated about 2 - 3 s, 2 s, and 5 - 6 s for station TPTI, KCSI, and BSI, respectively. We applied H-k stacking method to obtain crustal thickness and Vp/Vs ratio beneath the three broadband stations. At station TPTI, we obtained the crustal thickness is about 19.54 ± 3.84 km, Vp/Vs ratio is about 1.73 ± 0.14. At station KCSI, the crustal thickness was estimated to be 37.07 ± 4.47 km, Vp/Vs ratio is about 1.84 ± 0.10. At station BSI, which is located to the north of these two stations, the crustal thickness was estimated to be 40.56 ± 2.26 km, Vp/Vs ratio is about 1.81 ± 0.05. These results show relatively large variation of crustal thickness in the Northern Sumatra.

  11. Plume-driven plumbing and crustal formation in Iceland

    Science.gov (United States)

    Allen, R.M.; Nolet, G.; Morgan, W.J.; Vogfjord, K.; Nettles, M.; Ekstrom, G.; Bergsson, B.H.; Erlendsson, P.; Foulger, G.R.; Jakobsdottir, S.; Julian, B.R.; Pritchard, M.; Ragnarsson, S.; Stefansson, R.

    2002-01-01

    Through combination of surface wave and body wave constraints we derive a three-dimensional (3-D) crustal S velocity model and Moho map for Iceland. It reveals a vast plumbing system feeding mantle plume melt into upper crustal magma chambers where crustal formation takes place. The method is based on the partitioned waveform inversion to which we add additional observations. Love waves from six local events recorded on the HOTSPOT-SIL networks are fitted, Sn travel times from the same events measured, previous observations of crustal thickness are added, and all three sets of constraints simultaneously inverted for our 3-D model. In the upper crust (0-15 km) an elongated low-velocity region extends along the length of the Northern, Eastern and Western Neovolcanic Zones. The lowest velocities (-7%) are found at 5-10 km below the two most active volcanic complexes: Hekla and Bardarbunga-Grimsvotn. In the lower crust (>15 km) the low-velocity region can be represented as a vertical cylinder beneath central Iceland. The low-velocity structure is interpreted as the thermal halo of pipe work which connects the region of melt generation in the uppermost mantle beneath central Iceland to active volcanoes along the neovolcanic zones. Crustal thickness in Iceland varies from 15-20 km beneath the Reykjanes Peninsula, Krafla and the extinct Snfellsnes rift zone, to 46 km beneath central Iceland. The average crustal thickness is 29 km. The variations in thickness can be explained in terms of the temporal variation in plume productivity over the last ~20 Myr, the Snfellsnes rift zone being active during a minimum in plume productivity. Variations in crustal thickness do not depart significantly from an isostatically predicted crustal thickness. The best fit linear isostatic relation implies an average density jump of 4% across the Moho. Rare earth element inversions of basalt compositions on Iceland suggest a melt thickness (i.e., crustal thickness) of 15-20 km, given passive

  12. Deep structure beneath Lake Ontario: Crustal-scale Grenville subdivisions

    Science.gov (United States)

    Forsyth, D. A.; Milkereit, B.; Zelt, Colin A.; White, D. J.; Easton, R. M.; Hutchinson, Deborah R.

    1994-01-01

    Lake Ontario marine seismic data reveal major Grenville crustal subdivisions beneath central and southern Lake Ontario separated by interpreted shear zones that extend to the lower crust. A shear zone bounded transition between the Elzevir and Frontenac terranes exposed north of Lake Ontario is linked to a seismically defined shear zone beneath central Lake Ontario by prominent aeromagnetic and gravity anomalies, easterly dipping wide-angle reflections, and fractures in Paleozoic strata. We suggest the central Lake Ontario zone represents crustal-scale deformation along an Elzevir–Frontenac boundary zone that extends from outcrop to the south shore of Lake Ontario.Seismic images from Lake Ontario and the exposed western Central Metasedimentary Belt are dominated by crustal-scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east-dipping linear reflections. The images show that zones analogous to the interpreted Grenville Front Tectonic Zone are also present within the Central Metasedimentary Belt and support models of northwest-directed crustal shortening for Grenvillian deep crustal deformation beneath most of southeastern Ontario.A Precambrian basement high, the Iroquoian high, is defined by a thinning of generally horizontal Paleozoic strata over a crestal area above the basement shear zone beneath central Lake Ontario. The Iroquoian high helps explain the peninsular extension into Lake Ontario forming Prince Edward County, the occurrence of Precambrian inlier outcrops in Prince Edward County, and Paleozoic fractures forming the Clarendon–Linden structure in New York.

  13. Deep Crustal Structure Northeastern Gulf of Mexico

    Science.gov (United States)

    Christeson, Gail; Eddy, Drew; van Avendonk, Harm; Norton, Ian; Karner, Garry; Johnson, Chris; Kneller, Erik; Snedden, John

    2013-04-01

    The Gulf of Mexico is a small ocean basin between the US and Mexico that opened up soon after the breakup of Pangea. Although the area has been heavily surveyed with seismic reflection profiles, the deep structure of the region is poorly understood because of lack of penetration beneath the thick sediments and salt. We present the results of two wide-angle seismic refraction profiles in the northeastern Gulf of Mexico that constrain seismic velocities and thicknesses of the sediments and crust from the continental shelf to deep ocean basin. Profile GUMBO 3 extends 523 km from offshore Alabama south-southwest via the De Soto Canyon to the central Gulf of Mexico, while GUMBO 4 extends 507 km from the northwestern Florida peninsula across the Florida Escarpment to the central Gulf of Mexico. On both profiles, ocean bottom seismometers were positioned at 12-km spacing, and recorded air gun shots at offsets >100 km. We use a tomographic inversion of first-arrival and secondary travel time picks from these data to build a layered velocity model (water, sediments, crystalline crust, mantle) along each profile. On GUMBO 3 and GUMBO 4 the thickness of crystalline crust from the continental shelf to the deep basin decreases from ~25 km to ~7 km (GUMBO 4) or ~8 km (GUMBO 3) over a horizontal distance of ~150 km. Velocities of 7-7.5 km/s are observed at the base of the crust along most of GUMBO 3, while velocities of 6.5-7 km/s are observed at similar depths along GUMBO 4. We suggest that higher lower crustal velocities, and thicker oceanic crust, on GUMBO 3 compared to GUMBO 4 may be explained by elevated syn-rift mantle temperatures in the vicinity of the De Soto Canyon and South Georgia Rift during rifting and continental breakup. We have integrated seismic refraction, seismic reflection, and well data to interpret sequence stratigraphic units along GUMBO 3 and GUMBO 4. We have constructed a geologic history of the late-Jurassic/early-Cretaceous, beginning first with Louann

  14. Combined crustal-geological cross-section of Ellesmere Island

    DEFF Research Database (Denmark)

    Stephenson, Randell Alexander; Schiffer, Christian; Oakey, Gordon

    Ellesmere Island, in Canada’s Arctic, consists of a series of ~SW-NE trending tectonic provinces, the crustal structure and geological expression of which represent a combination of interplate, accretionary orogenesis in the Palaeozoic and, most recently, intraplate deformation in the Cenozoic...... (Eurekan “Orogeny”). An almost complete absence of information about the crustal or lithosphere structure of Ellesmere Island has been addressed by the acquisition of teleseismic data between 2010 and 2012 on a passive seismological array called ELLITE (“Ellesmere Island Teleseismic Experiment......”). The ELLITE array consisted of seven broadband stations, deployed for two years on a 520 km long, N-S orientated profile and was logistically supported by the GSC (Canada) and SEIS-UK. Extracted Receiver Functions (RFs) and a resulting composite two-dimensional crustal scale cross-section of Ellesmere Island...

  15. Crustal structure and active tectonics in the Eastern Alps

    DEFF Research Database (Denmark)

    Brückl, E.; Behm, M.; Decker, K.

    2010-01-01

    and underthusting of AD mantle below PA from southwest to northeast. The Moho fragmentation correlates well with major upper crustal structures and is supported by gravity, seismic, and geodetic data. An analysis of crustal thickening suggests that active convergence is associated with continued thrusting...... and lateral extrusion in the central Eastern Alps and thickening of the Adriatic indenter under the Southern Alps. According to the velocity relations at the triple junction, PA moves relative to EU and AD along ENE and SE striking faults, mainly by strike slip. An eastward directed extensional component...

  16. Rheology of Melt-bearing Crustal Rocks

    Science.gov (United States)

    Rosenberg, C. L.; Medvedev, S.; Handy, M. R.

    2006-12-01

    A review and reinterpretation of previous experimental data on the deformation of melt-bearing crustal rocks (Rosenberg and Handy, 2005) revealed that the relationship of aggregate strength to melt fraction is non-linear, even if plotted on a linear ordinate and abscissa. At melt fractions, Φ 0.07, the dependence of aggregate strength on Φ is significantly greater than at Φ > 0.07. This melt fraction (Φ= 0.07) marks the transition from a significant increase in the proportion of melt-bearing grain boundaries up to this point to a minor increase thereafter. Therefore, we suggest that the increase of melt-interconnectivity causes the dramatic strength drop between the solidus and a melt fraction of 0.07. A second strength drop occurs at higher melt fractions and corresponds to the breakdown of the solid (crystal) framework, corresponding to the well-known "rheologically critical melt percentage" (RCMP; Arzi, 1978). Although the strength drop at the RCMP is about 4 orders of magnitude, the absolute value of this drop is small compared to the absolute strength of the unmelted aggregate, rendering the RCMP invisible in a linear aggregate strength vs. melt fraction diagram. Predicting the rheological properties and thresholds of melt-bearing crust on the basis of the results and interpretations above is very difficult, because the rheological data base was obtained from experiments performed at undrained conditions in the brittle field. These conditions are unlikely to represent the flow of partially melted crust. The measured strength of most of the experimentally deformed, partially-melted samples corresponds to their maximum differential stress, before the onset of brittle failure, not to their viscous strength during "ductile" (viscous) flow. To overcome these problems, we extrapolated a theoretically-derived flow law for partially melted granite deforming by diffusion-accommodated grain-boundary sliding (Paterson, 2001) and an experimentally-derived flow law for

  17. Study of te evolution of the GEANT4 electrons transport algorithm to applications in radiotherapy;Estudo da evolucao do algoritmo de transporte de eletrons do GEANT4 para aplicacoes em radioterapia

    Energy Technology Data Exchange (ETDEWEB)

    Malthez, Anna Luiza M.C.; Button, Vera L. da S.N. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Faculdade de Engenharia Eletrica e de Computacao. Dept. de Engenharia Biomedica; Rocha, Jose R. de O. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Centro de Engenharia Biomedica

    2009-07-01

    In this work a bibliographic review was made about the GEANT4 applicability in radiotherapy, and also a study of electrons transport algorithm in order to establish the key points for future works with GEANT4. In papers already published, the GEANT4 version 4.6.1 was considered appropriated for photons simulations in applications of clinic significance in radiotherapy (accuracy {approx} 2%), however to electrons was checked that versions older than 8.3 present problems related to electrons transport algorithm, as size step artifact. The GEANT4 algorithm revision, version 8.3, resulted in substantial improvements of some values calculated in simulations, especially the loss energy per step and the boundary vicinity simulation of electrons, beyond better results stability, compared to versions 8.2. We concluded that electrons transport parameters within the following ranges: dRoverRange<0.3, RangeFactor=0.02, GeomFactor=3 and skin=1 is possible to get results with 1% accuracy to cavities simulations, although occur differences between simulated and theoretical doses, indicating that others parameters and the dose shift should be better evaluated. (author)

  18. The evolution of the thermo solar brazilian industry and the prices of the kWh/m{sup 2}; Evolucao da Industria Brasileira de Sistemas Termossolares e os Precos do kWh/m{sup 2}

    Energy Technology Data Exchange (ETDEWEB)

    Fantinelli, Jane Tassinari; Pereira, Jose Tomaz Vieira [Universidade Estadual de Campinas (UNICAMP), Campinas, SP (Brazil). Faculdade de Engenharia Mecanica]. E-mail: janetassinari@terra.com.br; tomaz@unicamp.br; Pereira, Elizabeth Marques Duarte [Pontificia Univ. Catolica de Minas Gerais, Belo Horizonte, MG (Brazil). Centro Brasileiro de Desenvolvimento da Energia Solar Termica. GREEN Solar]. E-mail: elizabeth.pereira @green.pucminas.br

    2006-07-01

    This article shows the evolution of the brazilian industry in the development of thermo solar systems for water heating applied to sanitary purposes and the prices reached for systems with small water volumes. The performed research concentrated on the acting of the various agents such as manufacturers, government organizations and R and D institutions involved in the development, production and solar collectors costs reduction.

  19. Influence of Sn content on microstructural and mechanical properties of centrifugal cast Ti-Nb-Sn biomedical alloys; Efeitos da adicao de Sn na evolucao microestrutural e em propriedades mecanicas de ligas Ti-Nb-Sn biomedicas fundidas por centrifugacao

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, E.S.N.; Contieri, R.J.; Caram, R., E-mail: ederlopes@fem.unicamp.b [Universidade Estadual de Campinas (DEMA/FEM/UNICAMP), SP (Brazil). Fac. de Engenharia Mecanica. Dept. de Engenharia de Materiais; Moraes, P.E.L. [FATEC Artur Azevedo, Mogi Mirim, SP (Brazil); Costa, A.M.S. [Universidade de Sao Paulo (DEMAR/EEL/USP), Lorena, SP (Brazil). Escola de Engenharia. Dept. de Engenharia de Materiais

    2010-07-01

    The arc voltaic centrifugal casting is an interesting alternative in terms of economic and technological development in the production of components based on materials with high reactivity and high melting point, such as titanium alloys. In this work, Ti-30Nb (wt. %) with additions of Sn (2, 4, 6, 8 and 10 wt. %) were formed by casting process. Characterization of the samples included optical microscopy, scanning electron microscopy, X-ray diffraction, Vickers hardness and elastic modulus measures by acoustic techniques. It was observed that the microstructure of the samples investigated is composed by dendritic structures, with clear segregation of alloying elements. The Vickers hardness and the elastic modulus decreased with the addition of Sn. The results show that the mechanical behavior of Ti-Nb alloys can be controlled within certain limits, by adding Sn. (author)

  20. Crustal Gravitational Potential Energy Change and Subduction Earthquakes

    Science.gov (United States)

    Zhu, P. P.

    2017-05-01

    Crustal gravitational potential energy (GPE) change induced by earthquakes is an important subject in geophysics and seismology. For the past forty years the research on this subject stayed in the stage of qualitative estimate. In recent few years the 3D dynamic faulting theory provided a quantitative solution of this subject. The theory deduced a quantitative calculating formula for the crustal GPE change using the mathematic method of tensor analysis under the principal stresses system. This formula contains only the vertical principal stress, rupture area, slip, dip, and rake; it does not include the horizontal principal stresses. It is just involved in simple mathematical operations and does not hold complicated surface or volume integrals. Moreover, the hanging wall vertical moving (up or down) height has a very simple expression containing only slip, dip, and rake. The above results are significant to investigate crustal GPE change. Commonly, the vertical principal stress is related to the gravitational field, substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal GPE change. The alternative formula indicates that even with lack of in situ borehole measured stress data, scientists can still quantitatively calculate crustal GPE change. The 3D dynamic faulting theory can be used for research on continental fault earthquakes; it also can be applied to investigate subduction earthquakes between oceanic and continental plates. Subduction earthquakes hold three types: (a) crust only on the vertical up side of the rupture area; (b) crust and seawater both on the vertical up side of the rupture area; (c) crust only on the vertical up side of the partial rupture area, and crust and seawater both on the vertical up side of the remaining rupture area. For each type we provide its quantitative formula of the crustal GPE change. We also establish a simplified model (called

  1. Gravity Constraints On The Crustal Structure of Northern Tunisia

    Science.gov (United States)

    Jallouli, Chokri; Mickus, Kevin L.; Turki, Mohamed M.

    Bouguer gravity data were analyzed to determine the general crustal and upper mantle structure in northern Tunisia. Residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments. Residual gravity anomalies contain short wavelength anomalies superimposed on a long wavelength component that decreases in amplitude northward towards the Tunisian coastline. An edge enhancement analysis (e.g., enhanced analytic signals) of the short wavelength anomalies suggests a previously unknown east-west trending gravity anomaly south of 37°N with source depths between 3 and 7 km. Modeling of the regional, residual and Bouguer gravity anomalies indicate there are two possible solutions for the residual gravity decreasing in northern Tunisia: 1) thickening of Cenozoic and Mesozoic sediments north of a strike-slip faults or 2) a crustal and upper mantle low density zone interpreted to be crustal material of the remnant subducted African plate. The latter result is favored based on seismic tomographic images of the Mediterranean region which implies subducting material exists under the African coast, geologic interpretations suggesting the Tell Atlas may be a thrust wedge accreted by underplating of the African continental crust and seismic refraction models indicating a thinning of sediments in northern Tunisia. The east-west trending gravity anomalies south of 37°N corresponds to an important structural feature that could be either a strike slip/transform fault or the northern edge the African plate.

  2. Crustal growth at active continental margins: Numerical modeling

    NARCIS (Netherlands)

    Vogt, Katharina|info:eu-repo/dai/nl/370618947; Gerya, Taras; Castro, Antonio

    The dynamics and melt sources for crustal growth at active continental margins are analyzed by using a 2D coupled petrological–thermomechanical numerical model of an oceanic-continental subduction zone. This model includes spontaneous slab retreat and bending, dehydration of subducted crust, aqueous

  3. Gravity anomalies, crustal structure and rift tectonics at the Konkan ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 121; Issue 3. Gravity anomalies, crustal structure and rift tectonics at the Konkan and Kerala basins, western continental margin of India. Sheena V Dev M Radhakrishna Shyam Chand C Subrahmanyam. Volume 121 Issue 3 June 2012 pp 813-822 ...

  4. Crustal structure of the Eastern Alps and their foreland

    DEFF Research Database (Denmark)

    Grad, M.; Brückl, E.; Majdanski, M.

    2009-01-01

    The subject of this paper concerns the seismic modelling of the crustal structure in the transition zone from the Bohemian Massif, across the Molasse basin and the Eastern Alps to the Southern Alps, mainly on the territory of Austria. The CEL10/Alp04 profile crosses the triple point of the Europe...

  5. THE CRUSTAL STRUCTURE OF ELLESMERE ISLAND FROM RECEIVER FUNCTION MODELLING

    DEFF Research Database (Denmark)

    Schiffer, Christian; Stephenson, Randell Alexander; Oakey, Gordon

    Island is poorly investigated, which leads to large ambiguity and uncertainty of geological interpretations, especially on a crustal and lithospheric scale. To fill this information gap a seismological survey (ELLITE) was performed. A north-south oriented and ~520 km long array, consisting of 7 broadband...

  6. Using Crustal Fluids to Peer Into the Subseafloor Microbial Habitat

    Science.gov (United States)

    Huber, J. A.

    2008-12-01

    In hard rock seafloor environments, fluids emanating from the basement are one of the best windows into the subseafloor and its resident microbial community. These low-temperature crustal fluids are ubiquitous at both active hydrothermal systems and ridge flank environments. Over the last 15 years, studies of the microbial communities in crustal fluids from eruptive events, drill holes, ridge flanks, and hydrothermal seamounts have revealed a phylogenetically and physiologically diverse microbial community, representing a wide spectrum of thermal tolerances and metabolic strategies from both the subseafloor and the deep sea. In addition, emerging technologies in seafloor sampling capacity and microbial ecology are rapidly increasing our ability to study this difficult habitat. This presentation will provide an overview of what we have learned about the population structure, genomic repertoire, and physiological function of microbes in crustal fluids and what the future holds for subseafloor biosphere research. Data will be integrated with geochemical measurements in crustal environments to better define the subseafloor habitat and its resident microbial community.

  7. Crustal thickness of Turkey determined by receiver function

    Science.gov (United States)

    Tezel, Timur; Shibutani, Takuo; Kaypak, Bülent

    2013-10-01

    Two-hundred and sixty-seven teleseismic events with a moment magnitude greater than 5.5 which occurred between January 2005 and October 2010 were analyzed to determine the Moho depth variation beneath Turkey by using the Receiver Function (RF) technique. The RF technique was applied to 120 broadband seismic stations, which were already deployed in the area permanently by the Kandilli Observatory and Earthquake Research Institute (KOERI) and the Disaster and Emergency Management Presidency (AFAD). The RFs were stacked considering back-azimuth, slowness and waveform similarities to enhance the signal/noise ratio. The genetic algorithm (GA) was used to obtain both 1-D shear-wave speed model and the Moho depth beneath each seismic station. A data set consisting of 112 shear-speed models derived from RFs revealed the crustal structure of Turkey. For imaging, several 2-D profiles of depth-migrated RFs were constructed to delineate the fine crustal structure. The Moho discontinuity is clearly seen on all profiles and the mid-crustal velocity discontinuity within the crust is observed in some profiles. The depth of the Moho varies between 24 and 48 km. The thinnest crustal thickness is located on the coast of Western Turkey, and the deepest Moho boundary is observed in Eastern Turkey. The shear wave velocities vary between 4.0 km/s and 4.5 km/s in the uppermost mantle beneath Turkey.

  8. A proposed concept for a crustal dynamics information management network

    Science.gov (United States)

    Lohman, G. M.; Renfrow, J. T.

    1980-01-01

    The findings of a requirements and feasibility analysis of the present and potential producers, users, and repositories of space-derived geodetic information are summarized. A proposed concept is presented for a crustal dynamics information management network that would apply state of the art concepts of information management technology to meet the expanding needs of the producers, users, and archivists of this geodetic information.

  9. Seismic velocity and crustal thickness inversions: Moon and Mars

    Science.gov (United States)

    Drilleau, Melanie; Blanchette-Guertin, Jean-François; Kawamura, Taichi; Lognonné, Philippe; Wieczorek, Mark

    2017-04-01

    We present results from new inversions of seismic data arrival times acquired by the Apollo active and passive experiments. Markov chain Monte Carlo inversions are used to constrain (i) 1-D lunar crustal and upper mantle velocity models and (ii) 3-D lateral crustal thickness models under the Apollo stations and the artificial and natural impact sites. A full 3-D model of the lunar crustal thickness is then obtained using the GRAIL gravimetric data, anchored by the crustal thicknesses under each Apollo station and impact site. To avoid the use of any seismic reference model, a Bayesian inversion technique is implemented. The advantage of such an approach is to obtain robust probability density functions of interior structure parameters governed by uncertainties on the seismic data arrival times. 1-D seismic velocities are parameterized using C1-Bézier curves, which allow the exploration of both smoothly varying models and first-order discontinuities. The parameters of the inversion include the seismic velocities of P and S waves as a function of depth, the thickness of the crust under each Apollo station and impact epicentre. The forward problem consists in a ray tracing method enabling both the relocation of the natural impact epicenters, and the computation of time corrections associated to the surface topography and the crustal thickness variations under the stations and impact sites. The results show geology-related differences between the different sites, which are due to contrasts in megaregolith thickness and to shallow subsurface composition and structure. Some of the finer structural elements might be difficult to constrain and might fall within the uncertainties of the dataset. However, we use the more precise LROC-located epicentral locations for the lunar modules and Saturn-IV upper stage artificial impacts, reducing some of the uncertainties observed in past studies. In the framework of the NASA InSight/SEIS mission to Mars, the method developed in

  10. Crustal displacements in Greenland caused by ice mass variability

    DEFF Research Database (Denmark)

    Nielsen, Karina

    The climate of the Earth is changing. A consequence of this is observed at the polar regions such as Greenland, where the ice sheet is melting with an increasing rate. The unloading of ice causes the Earth to respond elastically in terms of uplift and an outward horizontal deformation of the crust....... This motion can be measured by permanent Global Positioning System (GPS) receivers. Hence, the rates of crustal displacement are an indirect measure of the occurring mass changes. Currently, 55 GPS sites are located around the margin of the Greenland ice sheet, continuously providing information about...... the state of the ice sheet. However, the Earth is also adjusting viscoelastically to variations in the late Pleistocene ice sheets i.e. glacial isostatic adjustment (GIA). Observed rates of crustal displacement therefor contain signals from both past and present ice mass variations. Hence, to interpret...

  11. Bimodal magmatism produced by progressively inhibited crustal assimilation.

    Science.gov (United States)

    Meade, F C; Troll, V R; Ellam, R M; Freda, C; Font, L; Donaldson, C H; Klonowska, I

    2014-06-20

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.

  12. Bimodal magmatism produced by progressively inhibited crustal assimilation

    Science.gov (United States)

    Meade, F. C.; Troll, V. R.; Ellam, R. M.; Freda, C.; Font, L.; Donaldson, C. H.; Klonowska, I.

    2014-06-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose ‘progressively inhibited crustal assimilation’ (PICA) as a major cause of bimodality in continental volcanism.

  13. Compositional stratigraphy of crustal material from near-infrared spectra

    Science.gov (United States)

    Pieters, Carle M.

    1987-01-01

    An Earth-based telescopic program to acquire near-infrared spectra of freshly exposed lunar material now contains data for 17 large impact craters with central peaks. Noritic, gabbroic, anorthositic and troctolitic rock types can be distinguished for areas within these large craters from characteristic absorptions in individual spectra of their walls and central peaks. Norites dominate the upper lunar crust while the deeper crustal zones also contain significant amounts of gabbros and anorthosites. Data for material associated with large craters indicate that not only is the lunar crust highly heterogeneous across the nearside, but that the compositional stratigraphy of the lunar crust is nonuniform. Crustal complexity should be expected for other planetary bodies, which should be studied using high spatial and spectral resolution data in and around large impact craters.

  14. Detailed Northern Anatolian Fault Zone crustal structure from receiver functions

    Science.gov (United States)

    Cornwell, D. G.; Kahraman, M.; Thompson, D. A.; Houseman, G. A.; Rost, S.; Turkelli, N.; Teoman, U.; Altuncu Poyraz, S.; Gülen, L.; Utkucu, M.

    2013-12-01

    We present high resolution images derived from receiver functions of the continental crust in Northern Turkey that is dissected by two fault strands of the Northern Anatolian Fault Zone (NAFZ). The NAFZ is a major continental strike-slip fault system that is comparable in length and slip rate to the San Andreas Fault Zone. Recent large earthquakes occurred towards the western end of the NAFZ in 1999 at Izmit (M7.5) and Düzce (M7.2). As part of the multi-disciplinary Faultlab project, we aim to develop a model of NAFZ crustal structure and locate deformation by constraining variations in seismic properties and anisotropy in the upper and lower crust. The crustal model will be an input to test deformation scenarios in order to match geodetic observations from different phases of the earthquake loading cycle. We calculated receiver functions from teleseismic earthquakes recorded by a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield. This Dense Array for North Anatolia (DANA) was deployed from May 2012 until September 2013 and we selected large events (Mw>5.5) from the high quality seismological dataset to analyze further. Receiver functions were calculated for different frequency bands then collected into regional stacks before being inverted for crustal S-wave velocity structure beneath the entire DANA array footprint. In addition, we applied common conversion point (CCP) migration using a regional velocity model to construct a migrated 3D volume of P-to-S converted and multiple energy in order to identify the major crustal features and layer boundaries. We also performed the CCP migration with transverse receiver functions in order to identify regions of anisotropy within the crustal layers. Our preliminary results show a heterogeneous crust above a flat Moho that is typically at a depth of 33 km. We do not observe a prominent step in the Moho beneath the surface

  15. The nature of crustal reflectivity at the southwest Iberian margin

    Science.gov (United States)

    Buffett, G. G.; Torne, M.; Carbonell, R.; Melchiorre, M.; Vergés, J.; Fernàndez, M.

    2017-11-01

    Reprocessing of multi-channel seismic reflection data acquired over the northern margin of the Gulf of Cádiz (SW Iberian margin) places new constraints on the upper crustal structure of the Guadalquivir-Portimão Bank. The data presented have been processed with optimized stacking and interval velocity models, a better approach to multiple attenuation, preserved amplitude information to derive the nature of seismic reflectivity, and accurate time-to-depth conversion after migration. The reprocessed data reveal a bright upper crustal reflector just underneath the Paleozoic basement that spatially coincides with the local positive free-air gravity high called the Gulf of Cádiz Gravity High. To investigate the nature of this reflector and to decipher whether it could be associated with pieces of mantle material emplaced at upper crustal levels, we calculated its reflection coefficient and compared it to a buried high-density ultramafic body (serpentinized peridotite) at the Gorringe Bank. Its reflection coefficient ratio with respect to the sea floor differs by only 4.6% with that calculated for the high-density ultramafic body of the Gorringe Bank, while it differs by 35.8% compared to a drilled Miocene limestone unconformity. This means that the Gulf of Cádiz reflector has a velocity and/or density contrast similar to the peridotite at the Gorringe Bank. However, considering the depth at which it is found (between 2.0 and 4.0 km) and the available geological information, it seems unlikely that the estimated shortening from the Oligocene to present is sufficient to emplace pieces of mantle material at these shallow levels. Therefore, and despite the similarity in its reflection coefficient with the peridotites of the Gorringe Bank, our preferred interpretation is that the upper crustal Gulf of Cádiz reflector represents the seismic response of high-density intracrustal magmatic intrusions that may partially contribute to the Gulf of Cádiz Gravity High.

  16. Crustal radial anisotropy beneath Cameroon from ambient noise tomography

    Science.gov (United States)

    Ojo, Adebayo Oluwaseun; Ni, Sidao; Li, Zhiwei

    2017-01-01

    To increase the understanding of crustal deformation and crustal flow patterns due to tectonic processes in Cameroon, we study the lateral variability of the crustal isotropic velocity and radial anisotropy estimated using Ambient Noise Tomography (ANT). Rayleigh and Love wave Noise Correlation Functions (NCFs) were retrieved from the cross-correlation of seismic ambient noise data recorded in Cameroon, and phase velocities at periods of 8 to 30 s were measured to perform surface wave tomography. Joint inversion of Rayleigh and Love wave data for isotropic velocity models could not fit the observed dispersions simultaneously. We attribute the Love-Rayleigh discrepancy to the presence of radial anisotropy in the crust and estimated its magnitude. Our 3-D radial anisotropic model reveals the spatial variation of strong to weak positive (Vsh > Vsv) and negative (Vsv > Vsh) radial anisotropy in the crust. We observe negative radial anisotropy in the upper crust that is associated mainly with the location of a previously reported mantle plume. The anisotropy could be attributed to the vertical alignment of fossil microcracks or metamorphic foliations due to the upwelling of plume material. A strong positive radial anisotropy is centered at the location of an inferred boundary between the Congo Craton and the Oubanguides Belt that might be related to the preferred orientation of crustal anisotropic minerals associated with shearing in this fault zone. The middle crust is characterized by a widespread negative radial anisotropy that is likely caused by the flow-induced alignment of anisotropic minerals that crystallized during magma intrusion. The magnitude of the radial anisotropy varies systematically from predominantly negative in the middle crust to positive in the lower crust. The imaged patterns of the isotropic velocity and radial anisotropy are consistent with previous studies and agree with regional tectonics.

  17. Crustal response to lithosphere evolution:examples from Eurasia

    OpenAIRE

    Artemieva, Irina; Thybo, Hans; Cherepanova, Yulia; Chemia, Zurab

    2012-01-01

    We present a new model for the structure of the crust in an area which stretches from the North Atlantic region in the west to the Verkhoyansk Ridge in the east and encompasses Greenland, Iceland, most of Europe, West Siberian basin, and the Siberian cratons. The model is based on critically assessed results from various seismic studies, including reflection and refraction profiles and receiver function studies. The region includes a nearly continuous age record for crustal evolution over ca....

  18. Stress-wave experiments on selected crustal rocks and minerals

    Science.gov (United States)

    Grady, D. E.

    1983-09-01

    Large amplitude compressive stress wave experiments on selected crustal rocks and minerals was performed. The materials studied included Vermont marble, Blair dolomite, Oakhall limestone, z-cut calcite and oil shale. In each case specific constitutive features were studied. Features include interrelation of plastic yielding and phase transformation, rate dependent plastic flow, dilatency under dynamic loading conditions, and energy dissipation at stress amplitudes below measured Hugoniot elastic limits. A new experimental method using inmaterial mutual inductance magnetic gauges is also described.

  19. History of crustal recycling recorded in transition zone diamonds

    Science.gov (United States)

    Pearson, D. G.; Stachel, T.; Palot, M.; Ickert, R. B.

    2015-12-01

    The Earth's transition zone (TZ) is a key region within the Earth that, from seismology, may be composed of a mixture of relatively primitive material together with the products of crustal recycling throughout the history of plate tectonics. The only samples of the TZ come in the form of inclusions in diamonds, that, for the most-part are retrogressed lower pressure equivalents of their precursor phases that formed at depth. Recent work by our group and others [1] on transition zone diamonds indicate that both peridotite and eclogitic paragenesis diamonds may record the products of crustal recycling. In-situ ion probe nitrogen and carbon isotopic measurements indicate the crystallisation of TZ diamonds from fluids bearing crustal signatures, of both oxidised and reduced forms. At the same time, majoritic garnets record extreme oxygen isotope compositions that track the interaction of oceanic crust with seawater at low temperature [2]. Such an origin is consistent with the few measured Sr-Nd isotope compositions of majorite garnet inclusions which resemble depleted MORB [3]. We have found considerably more enriched Sr isotope compositions (87Sr/86S ranging to > 0.8) in CaSiO3 inclusions that are from deep asthenosphere to TZ depths, supporting an origin that includes incorporation of recycled crustal sediment, in addition to the basaltic oceanic crust required to explain the phase equilibria [4]. Lastly, the discovery of hydrous ringwoodite in a diamond [5] containing more water than is soluble at the lower TZ adiabat indicates the possible role of recycling in transporting water as well as carbon into the TZ via a cool thermally unequilibrated slab. [1] Thomson et al (2014) CMP, 168, 1081. [2] Ickert et al (2015) Geochemical perspectives Letters, 1, 65-74. [3] Harte & Richardson (2011) Gondwana Research, 21, 236-235. [4] Walter et al. (2011) Science, 334, 54-57.[Pearson et al. (2014) Nature, 507, 221-224.

  20. Upper mantle and crustal structure of the East Greenland Caledonides

    DEFF Research Database (Denmark)

    Schiffer, Christian; Balling, N.; Jacobsen, B. H.

    Function study based on an average of 36 events per station reveals a clear eastward dipping high-velocity structure underneath the study area. The geophysical character, supported by synthetic modelling, is consistent with a 10 km thick subducted slab of eclogitized oceanic crust. This might be the key...... present selected results from on-going detailed studies of the crustal and upper mantle, including a Receiver Function inversion, seismic P-wave travel time tomography and gravity modelling....

  1. Erosion of the French Alpine foreland controlled by crustal thickening

    Science.gov (United States)

    Schwartz, Stéphane; Gautheron, Cécile; Audin, Laurence; Nomade, Jérôme; Dumont, Thierry; Barbarand, Jocelyn; Pinna-Jamme, Rosella; van der Beek, Peter

    2017-04-01

    In alpine-type collision belts, deformation of the foreland may occur as a result of forward propagation of thrusting and is generally associated with thin-skinned deformation mobilizing the sedimentary cover in fold-and-thrust belts. Locally, foreland deformation can involve crustal-scale thrusting and produce large-scale exhumation of crystalline basement resulting in significant relief generation. In this study, we investigate the burial and exhumation history of Tertiary flexural basins located in the western Alpine foreland, at the front of the Digne thrust-sheet (SE France), using low-temperature apatite fission-track (AFT) and (U-Th)/He (AHe) thermochronology. Based on the occurrence of partially to totally reset apatite grain ages, we document 3.3 to 4.0 km burial of these basins remnants between 12-6 Ma, related to thin-skinned thrust-sheet emplacement without major relief generation. The onset of exhumation is dated at 6 Ma and is linked to erosion associated with subsequent relief development. This evolution does not appear controlled by major climate changes (Messinian crisis) or by European slab breakoff. Rather, we propose that the erosional history of the Digne thrust-sheet corresponds to basement involvement in foreland deformation, leading to crustal thickening and the incipient formation of a new external crystalline massif. Our study highlights the control of deep-crustal tectonic processes on foreland relief development and its erosional response at mountain fronts.

  2. Plate tectonics and crustal deformation around the Japanese Islands

    Science.gov (United States)

    Hashimoto, Manabu; Jackson, David D.

    1993-01-01

    We analyze over a century of geodetic data to study crustal deformation and plate motion around the Japanese Islands, using the block-fault model for crustal deformation developed by Matsu'ura et al. (1986). We model the area including the Japanese Islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity. Geodetic data are used to obtain block motions and average slip rates of faults. This geodetic model predicts that the Pacific plate moves N deg 69 +/- 2 deg W at about 80 +/- 3 mm/yr relative to the Eurasian plate which is much lower than that predicted in geologic models. Substantial aseismic slip occurs on the subduction boundaries. The block containing the Izu Peninsula may be separated from the rigid part of the Philippine Sea plate. The faults on the coast of Japan Sea and the western part of the Median Tectonic Line have slip rates exceeding 4 mm/yr, while the Fossa Magna does not play an important role in the tectonics of the central Japan. The geodetic model requires the division of northeastern Japan, contrary to the hypothesis that northeastern Japan is a part of the North American plate. Owing to rapid convergence, the seismic risk in the Nankai trough may be larger than that of the Tokai gap.

  3. Crustal Signatures in Mantle Peridotites From Yakutian Kimberlites

    Science.gov (United States)

    Taylor, L. A.; Spetsius, Z.; Wiesli, R.; Anand, M.; Valley, J.

    2002-12-01

    Peridotites and eclogites are considered as the original hosts for diamonds in the mantle. However, it is now generally agreed that these "mantle" eclogites from kimberlites had their origin in the subduction of oceanic crust beneath the major cratons of the world. One of the first indications for such crustal protoliths was from studies of oxygen and carbon isotopes (e.g., Peter Deines and colleagues, Ian McGregor, as well as our group). Indeed, subsequent studies of such rocks have revealed several additional crustal signatures. A possible scenario involves the subduction of an ophiolite sequence, whereby the basaltic and lower mafic components were metamorphosed, devolatilized/partially melted, and otherwise transformed into eclogites. Being within the diamond-stability field, they later experience metasomatic diamond formation. Surprisingly, the closely associated diamondiferous peridotites are considered to be of original mantle origin. We pose the query: What became of the ultramafic portion at the bottom of the crustal sequence? Could this be the origin of at least some of the mantle peridotites? The restricted δ13C values for P-type (peridotitic) diamonds is commonly used as evidence for the mantle origin of peridotites. However, a compilation of δ13C data, published by Peter Deines and our group, for P-type diamonds, mainly from numerous south African pipes, also shows a significant number of values that are well below the mantle field (to -20 \\permil). Fresh, clean garnets were carefully selected from over a hundred peridotites collected from several Yakutian kimberlites. These were subjected to oxygen-isotope analyses by laser-fluorination at the University of Wisconsin. The majority of the δ18O values plot within the accepted mantle value of 5.5+/-0.4 \\permil (Mattey et al., 1994). However, a significant number (~20%) lies outside this window, both above and below. These values are interpreted to represent the effects of both high- and low

  4. Global Correlations of Mantle Structure with Crustal Tectonic Regions

    Science.gov (United States)

    Paulson, E.; Jordan, T. H.

    2011-12-01

    Tomographic models of Earth's mantle depend on a priori estimates of crustal elastic structure, but the model prior is usually independent of other structural information about the crust, such as geochronological age and tectonic history. Therefore, the correlation of mantle models with crustal structure can provide powerful insights about the relationship of mantle heterogeneity to lithospheric dynamics and continental evolution. In a meta-analysis of more than 20 whole-mantle tomographic models published by various research groups, we estimate the correlation between upper-mantle seismic structure and crustal tectonic structure by projecting the tomographic models onto the GTR1 global tectonic regionalization. The 5 x 5 degree GTR1 map comprises three continental regions based on generalized tectonic behavior during the Phanerozoic: S (Precambrian shields and platforms), P (Phanerozoic platforms), Q (Phanerozoic orogenic zones); as well as three oceanic regions based on crustal age: A (0-25 Ma), B (25-100 Ma), and C (>100 Ma). We computed shear-velocity perturbation profiles by averaging a tomographic model over each of the six tectonic regions. For each model, we assessed the statistical significance of the inter-regional variations at a fixed depth by computing the intra-regional variance and correlation length. The regionalized velocity profiles of the upper mantle are similar among all of the tomographic models that we analyzed. Within the oceanic regions, the models display a consistent increase of shear velocity with crustal age that remains statistically significant to a depth of 200 km. The oceanic shear-velocity variations are consistent with high-resolution models derived from anisotropic inversions of multi-phase waveform data in localized regions. The profiles for regions S and P show consistent and statistically significant cratonic signatures extending below 300 km depth. In particular, the shear velocity gradients of both regions are distinctly

  5. "Storms of crustal stress" and AE earthquake precursors

    Directory of Open Access Journals (Sweden)

    G. P. Gregori

    2010-02-01

    Full Text Available Acoustic emission (AE displays violent paroxysms preceding strong earthquakes, observed within some large area (several hundred kilometres wide around the epicentre. We call them "storms of crustal stress" or, briefly "crustal storms". A few case histories are discussed, all dealing with the Italian peninsula, and with the different behaviour shown by the AE records in the Cephalonia island (Greece, which is characterized by a different tectonic setting.

    AE is an effective tool for diagnosing the state of some wide slab of the Earth's crust, and for monitoring its evolution, by means of AE of different frequencies. The same effect ought to be detected being time-delayed, when referring to progressively lower frequencies. This results to be an effective check for validating the physical interpretation.

    Unlike a seismic event, which involves a much limited focal volume and therefore affects a restricted area on the Earth's surface, a "crustal storm" typically involves some large slab of lithosphere and crust. In general, it cannot be easily reckoned to any specific seismic event. An earthquake responds to strictly local rheological features of the crust, which are eventually activated, and become crucial, on the occasion of a "crustal storm". A "crustal storm" lasts typically few years, eventually involving several destructive earthquakes that hit at different times, at different sites, within that given lithospheric slab.

    Concerning the case histories that are here discussed, the lithospheric slab is identified with the Italian peninsula. During 1996–1997 a "crustal storm" was on, maybe elapsing until 2002 (we lack information for the period 1998–2001. Then, a quiet period occurred from 2002 until 26 May 2008, when a new "crustal storm" started, and by the end of 2009 it is still on. During the 1996–1997 "storm" two strong earthquakes occurred (Potenza and

  6. New geophysical models of Palmer Deep crustal structure

    Science.gov (United States)

    Yakymchuk, M. A.; Levashov, S. P.; Korchagin, I. N.; Bachmutov, V. G.; Solovyov, V. D.

    2009-04-01

    The 2004 (9th) and 2006 (11th) Ukrainian Antarctic expeditions acquired new geoelectrical data (‘short-impulse electromagnetic field formation' - FSPEF, and ‘vertical electric-resonance sounding' - VERS) along profiles across Drake Passage and along Bransfield Strait, Antarctic Peninsula, with the aim of studying the crustal structure of these features down to depths of >30 km. The sounding on this depth in Antarctic region was the first experience of deep modification of the VERS method using. Modelling experience of deep crustal structure by geophysical data with VERS method shows that there is a possibility to investigate the fluid regime, tectonic disturbances and crush zones in basement and local places of submarine volcanic activity too. This technology also gives a possibility to efficiently divide the cross-section on separate stratigraphic subsections in the sounding site and to determine its depth with high accuracy (Levashov et al., 2003; Levashov et al., 2007). Geophysical surveys enabled to yield new data set with information about Drake Passage and Palmer Deep inner crustal structure on broad continental margin of Antarctic Peninsula. Palmer Deep is located on continental (Pacific) shelf of the Antarctic Peninsula near Anvers Island and consists of three deep basins with depths from 1200м to 1500м. These basins were part of glacial outlet during glaciation's period (Rebesco et al., 1998). Geoelectrical models of Palmer Deep crustal structure along three profiles were built on the sounding data in separate points of continental shelf. Heterogeneity of Palmer Deep earth's crust obtained from VERS data modelling testified to processes of tectonic transformations of internal shelf structures. Tectonic factor explains some conformities of the most recent glaciomarine sediments and glacial streams forming during recent shelf-wide glaciations. New information about sediment distribution and inner crustal structure has an important value for searching

  7. Density heterogeneity of the North American upper mantle from satellite gravity and a regional crustal model

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2014-01-01

    We present a regional model for the density structure of the North American upper mantle. The residual mantle gravity anomalies are based on gravity data derived from the GOCE geopotential models with crustal correction to the gravity field being calculated from a regional crustal model. We analyze...... how uncertainties and errors in the crustal model propagate from crustal densities to mantle residual gravity anomalies and the density model of the upper mantle. Uncertainties in the residual upper (lithospheric) mantle gravity anomalies result from several sources: (i) uncertainties in the velocity......-density conversion and (ii) uncertainties in knowledge of the crustal structure (thickness and average Vp velocities of individual crustal layers, including the sedimentary cover). In this study, we address both sources of possible uncertainties by applying different conversions from velocity to density...

  8. Crustal motion in Indonesia from Global Positioning System measurements

    Science.gov (United States)

    Bock, Y.; Prawirodirdjo, L.; Genrich, J. F.; Stevens, C. W.; McCaffrey, R.; Subarya, C.; Puntodewo, S. S. O.; Calais, E.

    2003-08-01

    We present the crustal motion velocity field for the Indonesian archipelago based on Global Positioning System (GPS) field surveys conducted from 1991 to 1997, and 2001, totaling more than 150 sites, as well as on a reanalysis of global tracking data in the Scripps Orbit and Permanent Array Center archive from 1991 to 2001 in International Terrestrial Reference Frame 2000. We compute poles of rotation for the Australia, Eurasia, and Pacific plates based on our analysis of the global GPS data. We find that regional tectonics is dominated by the interaction of four discrete, rotating blocks spanning significant areas of the Sunda Shelf, the South Banda arc, the Bird's Head region of New Guinea, and East Sulawesi. The largest, the Sunda Shelf block (SSH), is estimated to be moving 6 ± 3 mm/yr SE relative to Eurasia. The South Banda block (SBB) rotates clockwise relative to both the SSH and Australia plate, resulting in 15 ± 8 mm/yr of motion across the Timor trough and 60 ± 3 mm/yr of shortening across the Flores Sea. Southern New Guinea forms part of the Australia plate from which the Bird's Head block (BHB) moves rapidly WSW, subducting beneath the Seram trough. The East Sulawesi block rotates clockwise about a nearby axis with respect to the Sunda Shelf, thereby transferring east-west shortening between the Pacific and Eurasia plates into north-south shortening across the North Sulawesi trench. Except for the Sunda Shelf, the crustal blocks are all experiencing significant internal deformation. In this respect, crustal motion in those regions does not fit the microplate tectonics model.

  9. Effect of Crustal Density Structures on GOCE Gravity Gradient Observables

    Directory of Open Access Journals (Sweden)

    Robert Tenzer Pavel Novák

    2013-01-01

    Full Text Available We investigate the gravity gradient components corrected for major known anomalous density structures within the Earth¡¦s crust. Heterogeneous mantle density structures are disregarded. The gravimetric forward modeling technique is utilized to compute the gravity gradients based on methods for a spherical harmonic analysis and synthesis of a gravity field. The Earth¡¦s gravity gradient components are generated using the global geopotential model GOCO-03s. The topographic and stripping gravity corrections due to the density contrasts of the ocean and ice are computed from the global topographic/bathymetric model DTM2006.0 (which also includes the ice-thickness dataset. The discrete data of sediments and crust layers taken from the CRUST2.0 global crustal model are then used to apply the additional stripping corrections for sediments and remaining anomalous crustal density structures. All computations are realized globally on a one arc-deg geographical grid at a mean satellite elevation of 255 km. The global map of the consolidated crust-stripped gravity gradients reveals distinctive features which are attributed to global tectonics, lithospheric plate configuration, lithosphere structure and mantle dynamics (e.g., glacial isostatic adjustment, mantle convection. The Moho signature, which is the most pronounced signal in these refined gravity gradients, is superimposed over a weaker gravity signal of the lithospheric mantle. An interpretational quality of the computed (refined gravity gradient components is mainly limited by a low accuracy and resolution of the CRUST2.0 sediment and crustal layer data and unmodeled mantle structures.

  10. MOLA Topography of the Crustal Dichotomy Boundary Zone, Mars

    Science.gov (United States)

    Frey, Herbert V.; E. H., Susan; H., James

    1998-01-01

    Mars Orbiter Laser Altimeter (MOLA) profiles frequently cross the crustal dichotomy boundary where the transition zone (TZ) between cratered highland terrain (CT) and lowland smooth plains (SP) is marked by mesas and knobby terrain. The detailed topographic character of the boundary zone is longitudinally variable, as is the geomorphology of the TZ. Some portions of the boundary are associated with an outer ring of the Utopia impact basin; MOLA topography is consistent with this. The regional character of the boundary topography is a 2-4 km step function from nearly flat SP to almost as flat CT. This rise has a regional slope of 1-2 degrees, 50-100 times that of the Cr and SP away from TZ, which suggests a significant change in crustal properties (thickness, composition or both) across the TZ. The overall topography is very similar to that at some passive continent-oceanic crustal margins on the Earth, with the seafloor allowed to adjust upward after removal of the overlying water. A possible temporal constraint on the CT/SP elevation difference comes from two MOLA profiles which pass through two large (150 km diameter) craters located at the boundary in Aeolis. The N and S rims of the more degraded crater are at the same elevation; north of the N rim the topography drops by greater than 2 km to the floor of the TZ. This crater predates the elevation offset between CT and TZ floor. The better preserved crater (Gale) has a N rim 2 km lower than its S rim, and appears to have been emplaced on a pre-existing regional slope of about I degree. Gale probably post- dates the elevation difference between CT and TZ floor. Based on the stratigraphy of the units in which these craters are found, the elevation difference appears to have been in place in the Mid to Late Noachian.

  11. Crustal structure beneath Portugal from teleseismic Rayleigh Wave Ellipticity

    Science.gov (United States)

    Attanayake, Januka; Ferreira, Ana M. G.; Berbellini, Andrea; Morelli, Andrea

    2017-08-01

    Up until now, Portugal lacked a countrywide shear velocity model sampling short length-scale crustal structure, which limits interpretations of seismicity and tectonics, and predictions of strong ground motion. In turn, such interpretations and predictions are important to help mitigate risk of destruction from future large on- and offshore earthquakes similar to those that Portugal has experienced in the past (e.g. the Mw 8.5-8.7 tsunamigenic event in 1755). In this study, we measured teleseismic Rayleigh Wave Ellipticity (RWE) from 33 permanent and temporary seismic stations in Portugal with wave periods between 15 s and 60 s, and inverted it for 1-D models of shear wave velocity (Vs) structure beneath each station using a fully non-linear Monte Carlo method. Because RWE is strongly sensitive to the uppermost few kilometres of the crust, both RWE measurements and Vs models are spatially correlated with surface geology in Portugal. For instance, we find that sedimentary basins produced by rifting that had begun in the Mesozoic such as the Lusitanian Basin (LB) and the Lower Tagus-Sado Basin (LTSB) are characterised by higher RWE (lower Vs). Interestingly, we observe similar RWE (and Vs) values in the interior of the Central Iberian Zone (CIZ), which is a metamorphic belt of Paleozoic age. Together with reduced crustal thickness previously estimated for the same parts of the CIZ, this suggests that the CIZ might have experienced an episode of extension possibly simultaneous to Mesozoic rifting. The Galicia-Tras-os-Montes-Zone (GTMZ) that has undergone polyphased deformation since the Paleozoic is characterised by the lowest RWE (highest Vs) in Portugal. Ossa Morena Zone and the South Portuguese Zone exhibit intermediate Vs values when compared to that of basins and the GTMZ. Our crustal Vs model can be used to provide new insights into the tectonics, seismicity and strong ground motion in Portugal.

  12. Testing Predictions of Continental Insulation using Oceanic Crustal Thicknesses

    Science.gov (United States)

    Hoggard, Mark; Shorttle, Oliver; White, Nicky

    2016-04-01

    The thermal blanketing effect of continental crust has been predicted to lead to elevated temperatures within the upper mantle beneath supercontinents. Initial break-up is associated with increased magmatism and the generation of flood basalts. Continued rifting and sea-floor spreading lead to a steady reduction of this thermal anomaly. Recently, evidence in support of this behaviour has come from the major element geochemistry of mid-ocean ridge basalts, which suggest excess rifting temperatures of ˜ 150 °C that decay over ˜ 100 Ma. We have collated a global inventory of ˜ 1000 seismic reflection profiles and ˜ 500 wide-angle refraction experiments from the oceanic realm. Data are predominantly located along passive margins, but there are also multiple surveys in the centres of the major oceanic basins. Oceanic crustal thickness has been mapped, taking care to avoid areas of secondary magmatic thickening near seamounts or later thinning such as across transform faults. These crustal thicknesses are a proxy for mantle potential temperature at the time of melt formation beneath a mid-ocean ridge system, allowing us to quantify the amplitude and duration of thermal anomalies generated beneath supercontinents. The Jurassic break-up of the Central Atlantic and the Cretaceous rifting that formed the South Atlantic Ocean are both associated with excess temperatures of ˜ 50 °C that have e-folding times of ˜ 50 Ma. In addition to this background trend, excess temperatures reach > 150 °C around the region of the Rio Grande Rise, associated with the present-day Tristan hotspot. The e-folding time of this more local event is ˜ 10 Ma, which mirrors results obtained for the North Atlantic Ocean south of Iceland. In contrast, crustal thicknesses from the Pacific Ocean reveal approximately constant potential temperature through time. This observation is in agreement with predictions, as the western Pacific was formed by rifting of an oceanic plate. In summary

  13. Quantifying precambrian crustal extraction: The root is the answer

    Science.gov (United States)

    Abbott, D.; Sparks, D.; Herzberg, C.; Mooney, W.; Nikishin, A.; Zhang, Y.-S.

    2000-01-01

    We use two different methods to estimate the total amount of continental crust that was extracted by the end of the Archean and the Proterozoic. The first method uses the sum of the seismic thickness of the crust, the eroded thickness of the crust, and the trapped melt within the lithospheric root to estimate the total crustal volume. This summation method yields an average equivalent thickness of Archean crust of 49 ?? 6 km and an average equivalent thickness of Proterozoic crust of 48 ?? 9 km. Between 7 and 9% of this crust never reached the surface, but remained within the continental root as congealed, iron-rich komatiitic melt. The second method uses experimental models of melting, mantle xenolith compositions, and corrected lithospheric thickness to estimate the amount of crust extracted through time. This melt column method reveals that the average equivalent thickness of Archean crust was 65 ?? 6 km. and the average equivalent thickness of Early Proterozoic crust was 60 ?? 7 km. It is likely that some of this crust remained trapped within the lithospheric root. The discrepancy between the two estimates is attributed to uncertainties in estimates of the amount of trapped, congealed melt, overall crustal erosion, and crustal recycling. Overall, we find that between 29 and 45% of continental crust was extracted by the end of the Archean, most likely by 2.7 Ga. Between 51 and 79% of continental crust was extracted by the end of the Early Proterozoic, most likely by 1.8-2.0 Ga. Our results are most consistent with geochemical models that call upon moderate amounts of recycling of early extracted continental crust coupled with continuing crustal growth (e.g. McLennan, S.M., Taylor, S.R., 1982. Geochemical constraints on the growth of the continental crust. Journal of Geology, 90, 347-361; Veizer, J., Jansen, S.L., 1985. Basement and sedimentary recycling - 2: time dimension to global tectonics. Journal of Geology 93(6), 625-643). Trapped, congealed, iron

  14. New Crustal Stress Map of the Mediterranean and Central Europe

    OpenAIRE

    Heidbach, Oliver; Custodio, Susana; Kingdon, Andrew; Mariucci, Maria Teresa; Montone, Paola; Müller, Birgit; Pierdominicini, Simona; RAJABI, Mojtaba; Reinecker, John; Reiter, Karsten; Tingay, Mark; Williams, John; Ziegler, Moritz

    2016-01-01

    The World Stress Map (WSM) Project was initiated in 1986 under the auspices of the International Lithosphere Program in order to compile globally the information on the contemporary crustal stress state. For the 30th anniversary the WSM database has been updated and increased the number of data records from 21,750 to 42,410 worldwide. For the Mediterranean and Central European stress map the number of data records has increased from 3877 to 8192. The data come from a wide range of stress indi...

  15. Crustal structure variations along the Lesser Antilles Arc

    Science.gov (United States)

    Schlaphorst, D.; Kendall, J. M.; Melekhova, E.; Blundy, J.; Baptie, B.; Latchman, J. L.

    2013-12-01

    Continental crust is predominantly formed along subduction zones. Therefore, an investigation of the crustal and mantle structure variation of these areas is crucial for understanding the growth of continental crust. This work deals with the seismological characteristics along the Lesser Antilles Arc, an island arc system built by the relatively slow subduction (~2cm/yr) of the North and South American plates beneath the Caribbean plate. The amount of subducted sediments changes significantly from sediment-rich subduction in the South to sediment-poor subduction in the North. The abundance of broadband seismic stations on the Lesser Antilles islands enables a range of seismic methods to be used to study arc processes. Furthermore, the abundance of cumulate samples allows for a detailed petrological analysis, which can be related to the seismological patterns. We use data from three component broadband stations located on the individual islands along the arc. From the island of Grenada in the South to the Virgin Islands in the North significant variations in sediment load, petrology and volcanism are observed along the arc. In this work, we investigate crustal structure using receiver functions to determine Moho depth and Vp/Vs ratio. The ratio gives an idea about the material of the subsurface as well as its water and its melt contents. The receiver functions are computed using the extended-time multitaper frequency domain cross-correlation receiver-function (ETMTRF) by Helffrich (2006). This method has the advantage of resistance to noise, which is helpful since most of the data around the arc will have been collected by stations close to the ocean, thus containing a large amount of noise. Our results show clear variations in these measurements. There are also regions where the Moho is not very sharp due to a low velocity contrast. The real data results were then compared to synthetic receiver functions from subsurface models. We compute a range of synthetic

  16. A reverse energy cascade for crustal magma transport

    Science.gov (United States)

    Karlstrom, Leif; Paterson, Scott R.; Jellinek, A. Mark

    2017-08-01

    Direct constraints on the ascent, storage and eruption of mantle melts come primarily from exhumed, long-frozen intrusions. These structures, relics of a dynamic magma transport network, encode how Earth's crust grows and differentiates over time. Furthermore, they connect mantle melting to an evolving distribution of surface volcanism. Disentangling magma transport processes from the plutonic record is consequently a seminal but unsolved problem. Here we use field data analyses, scaling theory and numerical simulations to show that the size distribution of intrusions preserved as plutonic complexes in the North American Cordillera suggests a transition in the mechanical response of crustal rocks to protracted episodes of magmatism. Intrusion sizes larger than about 100 m follow a power-law scaling expected if energy delivered from the mantle to open very thin dykes and sills is transferred to intrusions of increasing size. Merging, assimilation and mixing of small intrusions into larger ones occurs until irreversible deformation and solidification dissipate available energy. Mantle magma supply over tens to hundreds of thousands of years will trigger this regime, a type of reverse energy cascade, depending on the influx rate and efficiency of crustal heating by intrusions. Identifying regimes of magma transport provides a framework for inferring subsurface magmatic processes from surface patterns of volcanism, information preservation in the plutonic record, and related effects including climate.

  17. Crustal velocities from geodetic very long baseline interferometry

    Science.gov (United States)

    Fallon, F. W.; Dillinger, W. H.

    1992-05-01

    VLBI observations from the International Radio Interferometric Surveying and Crustal Dynamics Projects programs taken over a span of 5-8 yr (through August 1990) are used to derive relative velocities of 16 sites on the North American, Eurasian, Pacific, and African plates. The data reduction scheme simultaneously estimates earth orientation parameters and nutation for each session, local atmosphere and clock correction terms, source positions, and initial site positions, as well as the site velocities. Instead of an a priori geophysical crustal model, a minimal set of geometric constraints is used to obtain the velocities. Two alternative constraint formulations - setting the secular motion of the pole and mean length of day to fixed values, and fixing the net rotation of the sites - are considered. They are shown to be equivalent in that they yield equivalent velocity sets with allowance for translation and rotation. The resulting velocities have formal standard errors typically less than 0.2 cm/yr, and most velocities are significantly different from zero.

  18. A view into crustal evolution at mantle depths

    Science.gov (United States)

    Kooijman, Ellen; Smit, Matthijs A.; Ratschbacher, Lothar; Kylander-Clark, Andrew R. C.

    2017-05-01

    Crustal foundering is an important mechanism in the differentiation and recycling of continental crust. Nevertheless, little is known about the dynamics of the lower crust, the temporal scale of foundering and its role in the dynamics of active margins and orogens. This particularly applies to active settings where the lower crust is typically still buried and direct access is not possible. Crustal xenoliths derived from mantle depth in the Pamir provide a unique exception to this. The rocks are well-preserved and comprise a diverse set of lithologies, many of which re-equilibrated at high-pressure conditions before being erupted in their ultrapotassic host lavas. In this study, we explore the petrological and chronological record of eclogite and felsic granulite xenoliths. We utilized accessory minerals - zircon, monazite and rutile - for coupled in-situ trace-element analysis and U-(Th-)Pb chronology by laser-ablation (split-stream) inductively coupled plasma mass spectrometry. Each integrated analysis was done on single mineral zones and was performed in-situ in thin section to maintain textural context and the ability to interpret the data in this framework. Rutile thermo-chronology exclusively reflects eruption (11.17 ± 0.06Ma), which demonstrates the reliability of the U-Pb rutile thermo-chronometer and its ability to date magmatic processes. Conversely, zircon and monazite reveal a series of discrete age clusters between 55-11 Ma, with the youngest being identical to the age of eruption. Matching age populations between samples, despite a lack of overlapping ages for different chronometers within samples, exhibit the effectiveness of our multi-mineral approach. The REE systematics and age data for zircon and monazite, and Ti-in-zircon data together track the history of the rocks at a million-year resolution. The data reveal that the rocks resided at 30-40 km depth along a stable continental geotherm at 720-750 °C until 24-20 Ma, and were subsequently

  19. Crustal structure and rift tectonics across the Cauvery–Palar basin, eastern continental margin of India based on seismic and potential field modelling

    Digital Repository Service at National Institute of Oceanography (India)

    Twinkle, D.; Rao, G.S.; Radhakrishna, M.; Murthy, K.S.R.

    Cauvery–Palar basin. The 2D gravity and magnetic crustal models indicate several crustal blocks separated by major structures or faults, and the rift-related volcanic intrusive rocks that characterize the basin. The crustal models further reveal...

  20. Quantifying Crustal Thickness in Continental Collisional Belts: Global Perspective and a Geologic Application.

    Science.gov (United States)

    Hu, Fangyang; Ducea, Mihai N; Liu, Shuwen; Chapman, James B

    2017-08-01

    We present compiled geochemical data of young (mostly Pliocene-present) intermediate magmatic rocks from continental collisional belts and correlations between their whole-rock Sr/Y and La/Yb ratios and modern crustal thickness. These correlations, which are similar to those obtained from subduction-related magmatic arcs, confirm that geochemistry can be used to track changes of crustal thickness changes in ancient collisional belts. Using these results, we investigate temporal variations of crustal thickness in the Qinling Orogenic Belt in mainland China. Our results suggest that crustal thickness remained constant in the North Qinling Belt (~45-55 km) during the Triassic to Jurassic but fluctuates in the South Qinling Belt, corresponding to independently determined tectonic changes. In the South Qinling Belt, crustal thickening began at ~240 Ma and culminated with 60-70-km-thick crust at ~215 Ma. Then crustal thickness decreased to ~45 km at ~200 Ma and remained the same to the present. We propose that coupled use of Sr/Y and La/Yb is a feasible method for reconstructing crustal thickness through time in continental collisional belts. The combination of the empirical relationship in this study with that from subduction-related arcs can provide the crustal thickness evolution of an orogen from oceanic subduction to continental collision.

  1. Crustal and upper mantle structure of Siberia from teleseismic receiver functions

    DEFF Research Database (Denmark)

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

    2015-01-01

    . The current results of RF analysis of the crustal and mantle structure will help to build a model for tectonic and geodynamic evolution of different provinces of Siberia. We compare our results to the recent detailed models of crustal structure in the area and with seismic models for similar geodynamic...

  2. Satellite gravity anomalies and crustal features of the Central Indian Ocean Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, D.G.; Krishna, K.S.; Neprochnov, Y.P.; Grinko, B.N.

    Satellite free-air gravity anomaly contour map at 5 mGal interval, seismic reflection and bathymetric data lead to the identification of deformed crustal structure of the Central Indian Ocean Basin. Twenty-three NE-SW trending deformed crustal...

  3. Modeling Crustal Thickness Variations Beneath the East Pacific Rise: Mantle Diapirs or Plate Kinematics?

    Science.gov (United States)

    George, S. A.; Toomey, D. R.

    2003-12-01

    Geophysical studies along the East Pacific Rise between the Siqueiros and Clipperton fracture zones reveal along- and cross-axis variations in crustal thickness whose origins are poorly understood. By one view, variations in crustal thickness are the result of three-dimensional upwelling of the mantle associated with a melt-rich diapir centered at 9° 50'N. Alternatively, it has been proposed that the migration of the 9° 03'N overlapping spreading center (OSC) alters the thickness of crust by increasing the amount of time that a crustal unit resides near the spreading axis. In this case, crustal thickness variations arise from plate kinematics, and not from three-dimensional variations in mantle upwelling. We report on a modeling study designed to explore how the evolution of OSCs may alter the thickness of newly-formed crust. OSC propagation is modeled using the kinematic algorithm developed by Wilson [1990], modified to track parcels of crust through time. Given an OSC's kinematic history and two-dimensional descriptions of the melt flux out of the mantle (i.e. invariant along the rise), we predict relative variations in crustal thickness. Our modeling assumes that underplating increases the thickness of the crust and/or Moho transition zone as long as a crustal unit resides over the source of mantle-derived melt. Results suggest two general kinematic mechanisms whereby variations in crustal thickness can occur: those due to an offset between the mantle-level magmatic system and the spreading axis, and those due to any relative reduction in the velocity of a crustal unit as it moves off axis. Offset-induced crustal thickness variations are manifest as long-wavelength ( ˜50 km), low-amplitude cross-axis asymmetries. Local slowing of crustal units as they move off axis -- in direct association with the OSC and its overlap basins -- results in relatively short-wavelength ( ˜10 km), high-amplitude variations in crustal thickness. Using a kinematic history

  4. Crustal stress pattern in China and its adjacent areas

    Science.gov (United States)

    Hu, Xingping; Zang, Arno; Heidbach, Oliver; Cui, Xiaofeng; Xie, Furen; Chen, Jiawei

    2017-11-01

    During the update of the World Stress Map (WSM) database, we integrated the China stress database by strictly using the internationally developed quality ranking scheme for each individual stress data record. This effort resulted in a comprehensive and reliable dataset for the crustal stress of China and its adjacent areas with almost double the amount of data records from the WSM database release 2008, i.e., a total of 8228 data records with reliable A-C qualities in the region of 45-155° East and 0-60° North. We use this dataset for an analysis of the stress pattern for the orientation of maximum compressive horizontal stress (SHmax). In contrast to earlier findings that suggested that the mean SHmax orientation would be aligned with the direction of plate motion, we clearly see from our results that the plate boundary forces, as well as topography and faulting, are important control factors for the overall stress pattern. Furthermore, the smoothing results indicate that the SHmax orientation in China rotates clockwise from the west to the east, which results in a fan-shaped crustal stress pattern for the continental scale. The plate boundary forces around China, which are the Indian-Eurasian plate collision in the west and the Pacific plate subduction and the push from the Philippine plate in the east, can still be seen as the key driving processes and the first-order controls for the crustal stress pattern. The South-North seismic zone can be seen as the separation zone for the western and eastern plate boundary forces. Topographic variation and faulting activity, however, provide second-order changes, and lead to local variations and different inhomogeneity scales for the stress pattern. Due to differences in these factors, Northeast China and the central part of the Tibetan plateau have notably homogeneous stress patterns, while the South-North seismic zone, the Hindu Kush-Pamir region, and the Taiwan region have extremely inhomogeneous stress patterns

  5. A global estimate of the Earth's magnetic crustal thickness

    Science.gov (United States)

    Vervelidou, Foteini; Thébault, Erwan

    2014-05-01

    The Earth's lithosphere is considered to be magnetic only down to the Curie isotherm. Therefore the Curie isotherm can, in principle, be estimated by analysis of magnetic data. Here, we propose such an analysis in the spectral domain by means of a newly introduced regional spatial power spectrum. This spectrum is based on the Revised Spherical Cap Harmonic Analysis (R-SCHA) formalism (Thébault et al., 2006). We briefly discuss its properties and its relationship with the Spherical Harmonic spatial power spectrum. This relationship allows us to adapt any theoretical expression of the lithospheric field power spectrum expressed in Spherical Harmonic degrees to the regional formulation. We compared previously published statistical expressions (Jackson, 1994 ; Voorhies et al., 2002) to the recent lithospheric field models derived from the CHAMP and airborne measurements and we finally developed a new statistical form for the power spectrum of the Earth's magnetic lithosphere that we think provides more consistent results. This expression depends on the mean magnetization, the mean crustal thickness and a power law value that describes the amount of spatial correlation of the sources. In this study, we make a combine use of the R-SCHA surface power spectrum and this statistical form. We conduct a series of regional spectral analyses for the entire Earth. For each region, we estimate the R-SCHA surface power spectrum of the NGDC-720 Spherical Harmonic model (Maus, 2010). We then fit each of these observational spectra to the statistical expression of the power spectrum of the Earth's lithosphere. By doing so, we estimate the large wavelengths of the magnetic crustal thickness on a global scale that are not accessible directly from the magnetic measurements due to the masking core field. We then discuss these results and compare them to the results we obtained by conducting a similar spectral analysis, but this time in the cartesian coordinates, by means of a published

  6. Combined Gravimetric-Seismic Crustal Model for Antarctica

    Science.gov (United States)

    Baranov, Alexey; Tenzer, Robert; Bagherbandi, Mohammad

    2017-09-01

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24

  7. Lower Crustal and Moho Reflections Beneath Mount St. Helens

    Science.gov (United States)

    Levander, A.; Kiser, E.; Zelt, C. A.; Creager, K.; Ulberg, C. W.; Schmandt, B.; Hansen, S. M.; Abers, G. A.

    2016-12-01

    The multi-disciplinary project iMUSH (imaging Magma Under St. Helens) was designed to illuminate the magmatic system beneath Mount St Helens (MSH) from the subducting Juan de Fuca slab to the surface using seismic, magnetotelluric, and petrologic data. The iMUSH active source experiment consisted of 23 large shots and 6000 seismograph locations. Included in the active-source seismic experiment were 2 dense linear profiles striking NW-SE and NE-SW, each with over 1000 receivers ( 150 m spacing) and 8 shots. Using the 1D average velocity model around MSH determined from travel-time analysis (Kiser et al., 2016, Geology), we have common-midpoint stacked STA/LTA envelope functions from all of the data along the NW-SE profile. A number of bright reflection events in the CMP section show remarkably good correspondence with abrupt velocity changes that were imaged in the 2D travel-time analysis in the mid to lower crust and at the Moho: Reflections appear at 20-25 km depth at the tops of two lower crustal high velocity (Vp > 7.5 km/s) bodies. One of these high velocity bodies is directly beneath MSH. The other is 40 km SE of MSH, under the Indian Heaven volcanic field, a basaltic field last active 9 ka. We have interpreted the high velocity bodies as cumulates from Quaternary or Tertiary volcanism. Separating the two high Vp bodies is a lower velocity column (Vp ≤ 6.5 km/s) dipping to the SE from the midcrust to the Moho. In the CMP section, the Moho reflection is bright under the region of low velocity and dims beneath both of the high velocity lower crustal bodies. Seismicity associated with the 1980 eruption extended from the summit to 20 km depth, stopping just above the bright reflection at the top of the MSH high Vp body. Deep long period events under MSH, often associated with motion of magmatic fluids, cluster at 20-30 km depth along the southeastern edge of the same reflection. This leads us to suggest that lower crustal magmas migrate along the southeastern

  8. Combined Gravimetric-Seismic Crustal Model for Antarctica

    Science.gov (United States)

    Baranov, Alexey; Tenzer, Robert; Bagherbandi, Mohammad

    2018-01-01

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24

  9. Dislocation model for aseismic crustal deformation at Hollister, California

    Science.gov (United States)

    Matsuura, Mitsuhiro; Jackson, David D.; Cheng, Abe

    1986-01-01

    A model of crustal deformation during the interseismic phase is developed and applied (using the improved Bayesian inversion algorithm described by Jackson and Matsu'ura, 1985) to trilateration data for the USGS Hollister (CA) network. In the model, rigid blocks in motion relative to each other experience friction only in a brittle upper zone, while their ductile lower zones slide freely; the Hollister model comprises five blocks and nine rectangular fault patches. The data and results are presented in tables, graphs, and maps and characterized in detail. The model predicts steady block motion on time scales between 10 yr and 1 Myr, with net motion across the San Andreas/Calaveras fault system 38 + or - 3 mm/yr and brittle/ductile transition depths ranging from 0.4 to 11 km. Two San Andreas segments with higher probabilities of moderate-to-large earthquakes are identified.

  10. Moho depth and crustal composition in Southern Africa

    DEFF Research Database (Denmark)

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

    2013-01-01

    heterogeneous crustal structure with short wavelength variations in thickness (H), Vp/Vs-ratio (composition), and Moho sharpness, which defines ~20 blocks that do not everywhere coincide with surface tectonic features. In the Zimbabwe Craton, the Tokwe block has H = 35–38 km and Vp/Vs = 1.74–1.79 whereas......-existing lower crust, which is further supported by a very sharp Moho transition. The exposed cross-section in the Vredefort impact crater is non-representative of cratonic crust due to shallowMoho (34 km) and high Vp/Vs ~ 1.80 attributed to shock metamorphism. High Vp/Vs = 1.76 is typical of the Witwatersrand...

  11. Kinematics of the Sierra Nevada and Oregon Crustal Blocks

    Science.gov (United States)

    Vollick, J. J.; McCaffrey, R.; Sella, G.

    2004-12-01

    Northern California contains the intersection of the NW moving Sierra Nevada block and the clockwise rotating Oregon block. Adding to the tectonic complexity of the region are the interactions of the Pacific plate, Basin and Range, California Coast Ranges, Mendocino fracture zone, San Andreas fault and the Juan de Fuca plate. Our research focuses on how the interactions of these features influence the motions of the Oregon and Sierra Nevada blocks. We processed Global Positioning System (GPS) data collected during the 1998 and 1999 National Geodetic Survey High Accuracy Reference Network (HARN) surveys and by us in 2003. Our preliminary analysis of the velocity field indicates that the Oregon crustal block is rotating clockwise relative to the Sierra Nevada block around a pole approximately west of the Mendocino Triple Junction. Our future work involves finding a more exact location of the relative pole rotation between the blocks, the degree of rotation, and how this motion is being taken up.

  12. Variations and controls on crustal thermal regimes in Southeastern Australia

    Science.gov (United States)

    Mather, Ben; McLaren, Sandra; Taylor, David; Roy, Sukanta; Moresi, Louis

    2018-01-01

    The surface heat flow field in Australia has for many years been poorly constrained compared to continental regions elsewhere. 182 recent heat flow determinations and 66 new heat production measurements for Southeastern Australia significantly increase our understanding of local and regional lithospheric thermal regimes and allow for detailed thermal modelling. The new data give a mean surface heat flow for Victoria of 71 ± 15 mW m- 2 which fits within the 61-77 mW m- 2 range reported for Phanerozoic-aged crust globally. These data reveal three new thermally and compositionally distinct heat flow sub-provinces within the previously defined Eastern Heat Flow Province: the Delamerian heat flow sub-province (average surface heat flow 60 ± 9 mW m- 2); the Lachlan heat flow sub-province (average surface heat flow 74 ± 13 mW m- 2); and the Newer Volcanics heat flow sub-province (average surface heat flow 72 ± 16 mW m- 2) which includes extreme values that locally exceed 100 mW m- 2. Inversions of reduced heat flow and crustal differentiation find that the Delamerian sub-province has experienced significant crustal reworking compared to the Lachlan and Newer Volcanics sub-provinces. The latter has experienced volcanism within the last 8 Ma and the degree of variability observed in surface heat flow points (up to 8 mW m- 2 per kilometre laterally) cannot be replicated with steady-state thermal models through this sub-province. In the absence of a strong palaeoclimate signal, aquifer disturbances, or highly enriched granites, we suggest that this high variability arises from localised transient perturbations to the upper crust associated with recent intraplate volcanism. This is supported by a strong spatial correlation of high surface heat flow and known eruption points within the Newer Volcanics heat flow sub-province.

  13. Current knowledge on the crustal properties of Italy

    Directory of Open Access Journals (Sweden)

    C. Morelli

    1994-06-01

    Full Text Available The recent advances in experimental petrography together with the information derived from the super-deep drilling projects have provided additional constraints for the interpretation of refraction and reflection seismic data. These constraints can also be used in the interpretation of magnetic and gravity data to resolve nonuniqueness. In this study, we re-interpret the magnetic and gravity data of the Italian peninsula and neighbouring areas. In view of the constraints mentioned above, it is now possible to find an agreement between the seismic and gravity models of the Central Alps. By taking into account the overall crustal thickness, we have recognized the existence of three types of Moho: 1 European which extends to the north and west of the peninsula and in the Corsican-Sardinian block. Its margin was the foreland in the Alpine Orogeny and it was the ramp on which European and Adriatic mantle and crustal slices were overthrusted. This additional load caused bending and deepening and the Moho which now lies beneath the Adriatic plate reaching a maximum depth of approximately 75 km. 2 Adriatic (or African which lies beneath the Po plain, the Apennines and the Adriatic Sea. The average depth of the Moho is about 30-35 km below the Po plain and the Adriatic Sea and it increases toward the Alps and the Tyrrhenian Sea (acting as foreland along this margin. The maximum depth (50 km is reached in Calabria. 3 Pery-Tyrrhenian. This is an oceanic or thinned continental crust type of Moho. It borders the oceanic Moho of the Tyrrhenian Sea and it acquires a transitional character in the Ligurian and Provençal basins (<15 km thickness while further thickening occurs toward the East where the Adriatic plate is overthrusted. In addition, the interpretation of the heat flow data appears to confirm the origin of this Moho and its geodynamic allocation.

  14. Crustal block movements from Holocene shorelines: Rhodes Island (Greece)

    Science.gov (United States)

    Pirazzoli, P. A.; Montaggioni, L. F.; Saliège, J. F.; Segonzac, G.; Thommeret, Y.; Vergnaud-Grazzini, C.

    1989-12-01

    Signs of up to eight stepped Holocene shorelines, which have been reported in a previous study on the east coast of Rhodes Island, have been reinvestigated in detail on the basis of a new geomorphological survey, identification and petrological analysis of many new samples of exposed marine organic crusts and over 30 radiocarbon datings. Confirmation was obtained of the view that the island can be charactered by considering small crustal blocks up to a dozen kilometres long with each block being affected by a specific tectonic history, and a general trend towards an uplift increasing from south to north. Two successive phases of submergence-emergence have been revealed by petrogenetic sequences in many samples, which give evidence of the occurrence of positive and negative vertical movements. This implies possible rejuvenation effects of the later submergence phase on the apparent age of pre-existing algal crusts, and those have been taken into account and estimated. The most likely sequence of vertical crustal movements to have occurred has been specified for each block and a time range has been ascribed to each former shoreline. Independent up and down movements, increasing in amplitude from south to north, appear in most blocks. There is a recurrent periodicity varying from a few hundred to one or at most two thousand years. The largest vertical displacement observed during the late Holocene—a sudden uplift movement of about 3.8 m in the northernmost part of the island—is likely to be linked with the earthquake which destroyed the Colossus in 222 B.C.

  15. Effect of Varying Crustal Thickness on CHAMP Geopotential Data

    Science.gov (United States)

    Taylor, P. T.; Kis, K. I.; vonFrese, R. R. B.; Korhonen, J. V.; Wittmann, G.; Kim, H. R.; Potts, L. V.

    2003-01-01

    To determine the effect of crustal thickness variation on satellite-altitude geopotential anomalies we compared two regions of Europe with vastly different values, Central/Southern Finland and the Pannonian Basin. Crustal thickness exceeds 62 km in Finland and is less than 26 km in the Pannonian Basin. Heat-flow maps indicate that the thinner and more active crust of the Pannonian Basin has a value nearly three times that of the Finnish Svecofennian Province. Ground based gravity mapping in Hungary shows that the free-air gravity anomalies across the Pannonian Basin are near 0 to +20 mGal with shorter wavelength anomalies from +40 to less than +60 mGal and some 0 to greater than -20 mGal. Larger anomalies are detected in the mountainous areas. The minor value anomalies can indicate the isostatic equilibrium for Hungary (the central part of the Pannonian Basin). Gravity data over Finland are complicated by de-glaciation. CHAMP gravity data (400 km) indicates a west-east positive gradient of greater than 4 mGal across Central/Southern Finland and an ovoid positive anomaly (approximately 4 mGal) quasi-coincidental with the magnetic anomaly traversing the Pannonian Basin. CHAMP magnetic data (425 km) reveal elongated semicircular negative anomalies for both regions with South-Central Finland having larger amplitude (less than -6 nT) than that over the Pannonian Basin, Hungary (less than -5 nT). In both regions subducted oceanic lithosphere has been proposed as the anomalous body.

  16. 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

  17. Sensing the earth crustal deformation with nano-strain resolution fiber-optic sensors.

    Science.gov (United States)

    Liu, Qingwen; He, Zuyuan; Tokunaga, Tomochika

    2015-06-01

    Crustal deformation measurement with a high resolution on the order of nano-strains in static to low frequency region is required for geophysical research. Optical fiber sensors are very attractive in this research field due to their unique advantages including high resolution, small size and easy deployment. In this paper, a fiber optic strain sensor with nano-strain-resolution and large measurement range for sensing the earth crustal deformation is reported. With this sensor the tide induced crustal deformation and the seismic wave were successfully recorded in field experiments.

  18. Crustal and deep seismicity in Italy (30 years after

    Directory of Open Access Journals (Sweden)

    G. Selvaggi

    1997-06-01

    Full Text Available The first modern studies of seismicity in Italy date back to the late 60's and early 70's. Although with a sparse seismic network available and only a few telemetered short-period stations, significant studies were carried out that outlined the main features of Italian seismicity (see, e.g., Boschi et al., 1969. Among these studies, one of the most important achievements was the reconnaissance of a Wadati-Benioff zone in Southern Tyrrhenian, described for the first time in detail in the papers of Caputo et al.(1970, 1973. Today, after three decades of more and more detailed seismological monitoring of the Italian region and tens of thousands earthquakes located since then, the knowledge of the earthquake generation processes in our country is much improved, although some of the conclusions reached in these early papers still hold. These improvements were made possible by the efforts of many institutions and seismologists who have been working hard to bring seismological research in Italy to standards of absolute quality, under the pivoting role of the Istituto Nazionale di Geofisica (ING. From the relocation of about 30000 crustal earthquakes and detailed studies on intermediate and deep shocks carried out in the last few years, we show that seismic release in peninsular Italy is only weakly related to the Africa-Eurasia convergence, but rather is best explained by the existence of two separate subduction/collision arcs (Northern Apennines and Southern Apennines-Calabria-Sicily. The width of the deforming belt running along peninsular Italy is 30 to 60 km, it is broader in the north than in the south, and the two arcs are separated by a region of more distributed deformation and stress rotations in the Central Apennines. Along the belt, the reconnaissance of regions of continuous and weak release of seismic energy, adjacent to fault areas which are currently «locked» (and therefore are the best candidates for future earthquakes is another

  19. The crystal's view of upper-crustal magma reservoirs

    Science.gov (United States)

    Cooper, K. M.; Kent, A. J.; Huber, C.; Stelten, M. E.; Rubin, A. E.; Schrecengost, K.

    2015-12-01

    Upper-crustal magma reservoirs are important sites of magma mixing, crustal refining, and magma storage. Crystals residing in these reservoirs have been shown to represent valuable archives of the chemical and physical evolution of reservoirs, and the time scales of this evolution. This presentation addresses the question of "What do crystals "see" and record about processes within the upper crust? And how is that view similar or different between plutonic and volcanic records?" Three general observations emerge from study of the ages of crystals, combined with crystal-scale geochemical data: 1) Patterns of isotopic and trace-element data over time in zircon crystals from a given magmatic system (e.g., Yellowstone, WY, and Taupo Volcanic Zone, New Zealand) can show systematic changes in the degree of heterogeneity, consistent with extraction of melts from a long-lived (up to 100s of kyr), heterogeneous crystal mush and in some cases continued crystallization and homogenization of the magma during a short period (eruption. 2) Thermal histories of magma storage derived from crystal records also show that the vast majority of time recorded by major phases was spent in storage as a crystal mush, perhaps at near-solidus conditions. 3) Comparison of ages of accessory phases in both plutonic blocks and host magmas that brought them to the surface do not show a consistent relationship between the two. In some cases, zircons from plutonic blocks have age spectra much older than zircon in the host magma. In other cases, host and plutonic block zircons have similar age spectra and chemical characteristics, suggesting a closer genetic connection between the two. These observations suggest that crystals in plutonic bodies, if examined at similar spatial and temporal scales to those in volcanic rocks, would show records that are highly heterogeneous in chemistry and age on the scale of a pluton or a lobe of a pluton, but that local regions of limited chemical and age variability

  20. Fluvial archives, a valuable record of vertical crustal deformation

    Science.gov (United States)

    Demoulin, A.; Mather, A.; Whittaker, A.

    2017-06-01

    The study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms, but also for identifying the nature of crustal deformation and its history. In recent decades, geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens. Here, we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions (the effects of horizontal deformation are not addressed). Channel long profiles have received considerable attention in the literature, and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives, before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady-state characteristics. Then, we review the literature dealing with the transient response of rivers to tectonic perturbation, through the production of knickpoints propagating through the drainage network. Inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories. Finally, we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes. As well as the erosional imprint of tectonic forcing, sedimentary deposits, such as fluvial terrace staircases, are also considered as a classical component of tectonic geomorphology. We show that these studies have recently benefited from rapid advances in dating techniques, allowing more reliable reconstruction of incision histories and estimation of incision rates. The combination of progress in the understanding of transient river profiles and larger, more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace

  1. A numerical model for dynamic crustal-scale fluid flow

    Science.gov (United States)

    Sachau, Till; Bons, Paul; Gomez-Rivas, Enrique; Koehn, Daniel

    2015-04-01

    Fluid flow in the crust is often envisaged and modeled as continuous, yet minimal flow, which occurs over large geological times. This is a suitable approximation for flow as long as it is solely controlled by the matrix permeability of rocks, which in turn is controlled by viscous compaction of the pore space. However, strong evidence (hydrothermal veins and ore deposits) exists that a significant part of fluid flow in the crust occurs strongly localized in both space and time, controlled by the opening and sealing of hydrofractures. We developed, tested and applied a novel computer code, which considers this dynamic behavior and couples it with steady, Darcian flow controlled by the matrix permeability. In this dual-porosity model, fractures open depending on the fluid pressure relative to the solid pressure. Fractures form when matrix permeability is insufficient to accommodate fluid flow resulting from compaction, decompression (Staude et al. 2009) or metamorphic dehydration reactions (Weisheit et al. 2013). Open fractures can close when the contained fluid either seeps into the matrix or escapes by fracture propagation: mobile hydrofractures (Bons, 2001). In the model, closing and sealing of fractures is controlled by a time-dependent viscous law, which is based on the effective stress and on either Newtonian or non-Newtonian viscosity. Our simulations indicate that the bulk of crustal fluid flow in the middle to lower upper crust is intermittent, highly self-organized, and occurs as mobile hydrofractures. This is due to the low matrix porosity and permeability, combined with a low matrix viscosity and, hence, fast sealing of fractures. Stable fracture networks, generated by fluid overpressure, are restricted to the uppermost crust. Semi-stable fracture networks can develop in an intermediate zone, if a critical overpressure is reached. Flow rates in mobile hydrofractures exceed those in the matrix porosity and fracture networks by orders of magnitude

  2. Crustal Velocity Model of the Altai-Sayan Region

    Science.gov (United States)

    Behrend, M. J.; Mackey, K. G.

    2016-12-01

    We have developed a crustal velocity model for the the region encompassed by the Altai-Sayan Seismic Network of South-Central Russia (45o-55o N. X 79o-98o E.). Geographically, the study area includes the Altai and Sayan Mountain Ranges, Western Mongolia, Eastern Kazakhstan, and Northwest China. To develop our model we used phase arrival data from approximately 175 larger earthquakes recorded by the Altai-Sayan Seismic Network between 1977 and 1981 and reported in the bulletin Materialy po Seismichnosti Sibiri. To develop our model, we divided the region into 1o N-S x 2o E-W cells. Events within each cell, plus a small surrounding area, were relocated multiple times using a grid-search routine, in effort to determine the best fitting Pg and Sg velocities. Pg and Sg phase arrivals are generally from the 100-1000 km range and represent secondary arriving phases. These arrivals are dominant in this region and we consider the time picks and phase identifications to be reliable. Velocities tested range from 5.650 to 6.350 km/s for Pg and from 3.310 to 3.710 km/s for Sg. The best fitting velocities for each cell were then assigned to the geographic coordinates of the cell's center point. The standard Jeffreys-Bullen model was used for Pn velocities. The best fitting Pg and Sg velocities are those that minimize the average event residuals in a cell. High residual arrivals were omitted from the location process. In our model, Pg velocities range from 5.975-6.325 km/s, while Sg velocities range from 3.510-3.630 km/s, though the higher velocity extremes are constrained by one event and are not statistically significant. The average Pg velocity of the study area was, 6.147 km/s, and average Sg, 3.576 km/s. Geologically, these velocities are associated with the Central Asiatic Foldbelt and are consistent with regional crustal velocities along the southern edge of the Siberian Craton to the East as determined by previous studies.

  3. Constraints on the Venusian crustal thickness variations in the isostatic stagnant lid approximation

    National Research Council Canada - National Science Library

    Orth, C. P; Solomatov, V. S

    2012-01-01

    .... Here we assume that the remaining discrepancy between the observed and model geoid is due to crustal thickness variations and that the crust, the lithosphere and the mantle are in a state of double...

  4. The influence of crustal radioactivity on mantle convection and lithospheric thickness on Mars

    National Research Council Canada - National Science Library

    Kiefer, Walter S

    2016-01-01

    ... . In an important new paper, Plesa et al. (2016, doi: 10.1002/2016JE005126 ) have assessed how these variations in crustal thickness and heat flow affect the spatial pattern of convection in the Martian mantle...

  5. Displaced terranes and crustal evolution of the Levant and the eastern Mediterranean

    Science.gov (United States)

    Ben-Avraham, Zvi; Ginzburg, Avihu

    1990-08-01

    Geophysical data from the Levant and the eastern Mediterranean suggest that this area can be divided into distinct crustal units of different origins. For example, a marked difference in crustal structure and structural style exists in the Levant between Samaria and Judea, south of the Carmel structure, and the Galilee and Lebanon, north of it. On the other hand, several microcontinental fragments such as Cyprus, and the Eratosthenes and Anaximander Seamounts are embedded within the oceanic crust of the eastern Mediterranean. The present location of these units has resulted from complex tectonic processes which were active during the mid Paleozoic-Mesozoic evolution of this area. During this period several crustal units were accreted to the northern margin of Africa while others were detached away from it. The crustal evolution of the eastern Mediterranean and the Levant is intimately linked with the closure of the Paleo-Tethys, the formation of the Neo-Tethys, and its subsequent closure.

  6. Particle-in-Cell Simulations of Plasma Interaction with Lunar Crustal Magnetic Anomalies

    Science.gov (United States)

    Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.

    2012-03-01

    We present results from a kinetic plasma simulation on the interaction of ambient plasma with lunar crustal magnetic anomalies. We discuss implications of this work for physical phenomena at the Moon, such as lunar swirls and proton implantation.

  7. A New System for Understanding Mid-crustal Sheeted Complexes in a Tilted Crustal Section, Joshua Tree National Park, California

    Science.gov (United States)

    Ianno, A. J.; Paterson, S. R.

    2011-12-01

    The western portion of Joshua Tree National Park exposes a tilted crustal section through continental arc crust from 0-30 km. A significant portion of the middle crust is represented by Mesozoic, tabular, intrusive, igneous bodies ranging from 0.1 to 100 m in thickness. While these igneous bodies range in composition (gabbro to peraluminous granites), texture (equigranular to porphyritic), and grain size (very fine to coarse), patterns emerge between different regions of "sheeted complexes" that may be related to their emplacement and geochemical history. No consistent method of describing and comparing sheeted complexes exists in the literature, so we have developed a method of classifying sheeted complexes at Joshua Tree NP, which may be broadly applicable to all sheeted bodies. We classify these sheeted complexes using the terms homogeneous/heterogeneous and focused/defocused. A homogeneous sheeted complex generally contains magmas within a 10 wt% SiO2 range, although we are still testing the validity of this number. A focused sheeted complex has adjacent sheets or close spacing between sheets and Jurassic to Cretaceous sheeted complexes in western Joshua Tree NP. At Keys View, we observe a heterogeneous, spatially focused sheeted complex with 0.1-2 m thick sheets recording pressures indicating 15-22 km depth from top to bottom. Compositions range from gabbro to peraluminous granite, although tonalites-granodiorites and two-mica garnet granites are volumetrically dominant. A zone of elongate plutons (in map view) lying structurally above this could potentially be considered as a very thickly sheeted, homogeneous, focused sheeted complex and is composed of granodiorites, granites, and two-mica garnet granites. A more thickly sheeted (2-10 m), homogeneous, focused, sheeted granite complex with pressures indicating a depth of approximately 12 km is found along the northern edge of the park. The number of sheets decreases and the average thickness increases as this

  8. Global Mapping of Oceanic and Continental Shelf Crustal Thickness and Ocean-Continent Transition Structure

    Science.gov (United States)

    Kusznir, Nick; Alvey, Andy; Roberts, Alan

    2017-04-01

    The 3D mapping of crustal thickness for continental shelves and oceanic crust, and the determination of ocean-continent transition (OCT) structure and continent-ocean boundary (COB) location, represents a substantial challenge. Geophysical inversion of satellite derived free-air gravity anomaly data incorporating a lithosphere thermal anomaly correction (Chappell & Kusznir, 2008) now provides a useful and reliable methodology for mapping crustal thickness in the marine domain. Using this we have produced the first comprehensive maps of global crustal thickness for oceanic and continental shelf regions. Maps of crustal thickness and continental lithosphere thinning factor from gravity inversion may be used to determine the distribution of oceanic lithosphere, micro-continents and oceanic plateaux including for the inaccessible polar regions (e.g. Arctic Ocean, Alvey et al.,2008). The gravity inversion method provides a prediction of continent-ocean boundary location which is independent of ocean magnetic anomaly and isochron interpretation. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we can improve the determination of pre-breakup rifted margin conjugacy and sea-floor spreading trajectory during ocean basin formation. By restoring crustal thickness & continental lithosphere thinning to their initial post-breakup configuration we show the geometry and segmentation of the rifted continental margins at their time of breakup, together with the location of highly-stretched failed breakup basins and rifted micro-continents. For detailed analysis to constrain OCT structure, margin type (i.e. magma poor, "normal" or magma rich) and COB location, a suite of quantitative analytical methods may be used which include: (i) Crustal cross-sections showing Moho depth and crustal basement thickness from gravity inversion. (ii) Residual depth anomaly (RDA) analysis which is used to investigate OCT

  9. Decrease in oceanic crustal thickness since the breakup of Pangaea

    Science.gov (United States)

    van Avendonk, Harm J. A.; Davis, Joshua K.; Harding, Jennifer L.; Lawver, Lawrence A.

    2017-01-01

    Earth's mantle has cooled by 6-11 °C every 100 million years since the Archaean, 2.5 billion years ago. In more recent times, the surface heat loss that led to this temperature drop may have been enhanced by plate-tectonic processes, such as continental breakup, the continuous creation of oceanic lithosphere at mid-ocean ridges and subduction at deep-sea trenches. Here we use a compilation of marine seismic refraction data from ocean basins globally to analyse changes in the thickness of oceanic crust over time. We find that oceanic crust formed in the mid-Jurassic, about 170 million years ago, is 1.7 km thicker on average than crust produced along the present-day mid-ocean ridge system. If a higher mantle temperature is the cause of thicker Jurassic ocean crust, the upper mantle may have cooled by 15-20 °C per 100 million years over this time period. The difference between this and the long-term mantle cooling rate indeed suggests that modern plate tectonics coincide with greater mantle heat loss. We also find that the increase of ocean crustal thickness with plate age is stronger in the Indian and Atlantic oceans compared with the Pacific Ocean. This observation supports the idea that upper mantle temperature in the Jurassic was higher in the wake of the fragmented supercontinent Pangaea due to the effect of continental insulation.

  10. Anomalous crustal movements before great Wenchuan earthquake observed by GPS

    Directory of Open Access Journals (Sweden)

    Gu Guohua

    2011-05-01

    Full Text Available Studies of GPS data carried out before and after the great Wenchuan earthquake of Ms8.0 on May 12, 2008 show that anomalous crustal movements occurred before the earthquake. Data from 4 pre-earthquake observation sessions at a dense network of stations show that there were prominent broad-ranged long- and mid-term anomalies in horizontal displacements and strain and in vertical displacements. Data from the fewer-numbered reference stations of continuous GPS observations since 1999 in West and South China showed short-term preseismic anomalies in horizontal displacements. The detection of co-seismic horizontal displacements at these stations supports the existence of the pre-earthquake anomalies. Results of single-epoch solutions of data from continuous-observation stations near the epicenter also show large imminent anomalies in vertical displacements. Although the Wenchuan earthquake was not predicted, these results give a strong indication that GPS should be the main observation technique for long-term, mid-term, short-term and imminent earthquake predictions.

  11. Maps of North American crustal stability and geothermal potential

    Energy Technology Data Exchange (ETDEWEB)

    Fairbridge, R.W.

    1977-01-01

    A three-year program of analysis of crustal movements in North America was planned with the objective of preparing a series of 1 = 5 million scale maps depicting relative stability/instability. The part of the proposal completed during the first year is described; much of this first year's work was preparatory. Three time scales were considered for the data analysis: 1 - 10/sup 2/ yr., 10/sup 4/ yr., and 10/sup 8/ yr. Significant differences in sign and rate were suspected between short and long-term motions and these are now confirmed. The first part of the program is now complete. It consisted of two principal activities: (a) data collection for the short and mid-term scales on a U.S.-wide basis, excluding Alaska and Hawaii (all of this material has been reduced to compatible computer language and is stored on tape ready for further study, analysis and final cartography); (b) map and data analysis of the long-term scale with a completed draft map, applied specifically to the Mid-West and eastern U.S.

  12. Present three-dimensional crustal deformation in Hainan Island

    Directory of Open Access Journals (Sweden)

    Hu Yaxuan

    2014-05-01

    Full Text Available Hainan Island, located at the southeast edge of the Eurasian Plate, is affected by the motion of multiple plates, with its northeast edge mainly dilatating and its western margin presently compressing. By analyzing the GPS rates during 1999 – 2007 in Hainan and its adjacent region, we determined horizontal movement rates of 3. 0–21. 1 mm/a at the west of 104°E, evidently affected by the Indian Plate extrusion. Their directions are SE-SN-SW from east to west and are separated by the main fault. The principal strains have the same characteristics. The stations east of 104°E move mainly in the SEE direction. The eastward rates are 2. 1–8. 5 mm/a and northward rates are 0. 4–2. 7 mm/a. The GPS rates during 2009–2013 show that stations at the edge of the island move SEE relative to the Eurasian Plate, with rates relative to the mean benchmark, indicating that there are small relative movements between stations, whereas QION station, located in the middle, moves in the NW direction at a greater rate. Vertical differential movement is apparent in the northeast zone of the island. Upwelling of mantle plume material possibly influences the local stress. Three-dimensional GPS rates indicate that, at present, inherited crustal movement is dominant in Hainan.

  13. Lifetime and size of shallow magma bodies controlled by crustal-scale magmatism

    OpenAIRE

    Karakas, Ozge; Degruyter, Wim; Bachmann, Olivier; Dufek, Josef

    2017-01-01

    Magmatic processes on Earth govern the mass, energy and chemical transfer between the mantle, crust and atmosphere. To understand magma storage conditions in the crust that ultimately control volcanic activity and growth of continents, an evaluation of the mass and heat budget of the entire crustal column during magmatic episodes is essential. Here we use a numerical model to constrain the physical conditions under which both lower and upper crustal magma bodies form. We find that over long d...

  14. Estimating gravity changes caused by crustal strain: application to the Tibetan Plateau

    Science.gov (United States)

    Yin, Zhi; Xu, Caijun

    2017-08-01

    Temporal gravimetry is an efficient tool for monitoring mass transfers, but distinguishing the contribution of each process to the measured signals is challenging. Few effective methods have been developed to estimate the changes in gravity caused by crustal strain for large-scale geophysical problems. To fill this research gap, we proposed a formula that describes a negative linear correlation between changes in gravity and crustal dilatational strain. Surface observations of gravity changes and dilatational strains were simulated using PSGRN/PSCMP, which is a numerical code used to calculate the surface response to fault dislocations, and the accuracy of the formula was quantitatively verified. Four parameters are required for this formula: the crustal dilatational strain, the crustal density, the Moho depth, and a coefficient that characterizes the degree of crust-mantle coupling. To illustrate the application of this new method to a natural case study, including specifying the values of the necessary parameters, the crustal strain-caused gravity changes (CSGCs) were calculated at 1° × 1° grid nodes over the Tibetan Plateau (TP). The CSGC model shows that most of the crust of the TP is undergoing extension, which generates negative gravity signals. The magnitude of the Tibetan CSGC model is approximately 0.2 μGal yr-1, which is similar to the results obtained from numerical modelling of the crustal tectonics of the Taiwanese Orogen. To evaluate the reliability of the Tibetan CSGC model, the uncertainties in the crustal dilatational strain, crustal density, Moho depth, and crust-mantle coupling factor were evaluated and then used to estimate the CSGC uncertainty by applying the error propagation law. The CSGC model was used to analyse the mass transfers of the TP. The results suggest that a significant mass accumulation process may be occurring beneath the crust of the northern TP.

  15. Use of MAGSAT anomaly data for crustal structure and mineral resources in the US midcontinent

    Science.gov (United States)

    Carmichael, R. S.

    1983-01-01

    Magnetic field data acquired by NASA's MAGSAT satellite is used to construct a long-wavelength magnetic anomaly map for the U.S. midcontinent. This aids in interpretation of gross crustal geology (structure, lithologic composition, resource potential) of the region. Magnetic properties of minerals and rocks are investigated and assessed, to help in evaluation and modelling of crustal magnetization sources and depth to the Curie-temperature isotherm.

  16. Seismic evidence for widespread western-US deep-crustal deformation caused by extension

    Science.gov (United States)

    Moschetti, M.P.; Ritzwoller, M.H.; Lin, F.; Yang, Y.

    2010-01-01

    Laboratory experiments have established that many of the materials comprising the Earth are strongly anisotropic in terms of seismic-wave speeds. Observations of azimuthal and radial anisotropy in the upper mantle are attributed to the lattice-preferred orientation of olivine caused by the shear strains associated with deformation, and provide some of the most direct evidence for deformation and flow within the Earths interior. Although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes, large-scale observations have been limited to regions of particularly thick crust. Here we show that observations from ambient noise tomography in the western United States reveal strong deep (middle to lower)-crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the Cenozoic Era (since 65 Myr ago). The coincidence of crustal radial anisotropy with the extensional provinces of the western United States suggests that the radial anisotropy results from the lattice-preferred orientation of anisotropic crustal minerals caused by extensional deformation. These observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension. ?? 2010 Macmillan Publishers Limited. All rights reserved.

  17. Crustal strain-dependent serpentinisation in the Porcupine Basin, offshore Ireland

    Science.gov (United States)

    Prada, Manel; Watremez, Louise; Chen, Chen; O'Reilly, Brian M.; Minshull, Timothy A.; Reston, Tim J.; Shannon, Patrick M.; Klaeschen, Dirk; Wagner, Gerlind; Gaw, Viola

    2017-09-01

    Mantle hydration (serpentinisation) at magma-poor rifted margins is thought to play a key role in controlling the kinematics of low-angle faults and thus, hyperextension and crustal breakup. However, because geophysical data principally provide observations of the final structure of a margin, little is known about the evolution of serpentinisation and how this governs tectonics during hyperextension. Here we present new observational evidence on how crustal strain-dependent serpentinisation influences hyperextension from rifting to possible crustal breakup along the axis of the Porcupine Basin, offshore Ireland. We present three new P-wave seismic velocity models that show the seismic structure of the uppermost lithosphere and the geometry of the Moho across and along the basin axis. We use neighbouring seismic reflection lines to our tomographic models to estimate crustal stretching (βc) of ∼2.5 in the north at 52.5° N and >10 in the south at 51.7° N. These values suggest that no crustal embrittlement occurred in the northernmost region, and that rifting may have progressed to crustal breakup in the southern part of the study area. We observed a decrease in mantle velocities across the basin axis from east to west. These variations occur in a region where βc is within the range at which crustal embrittlement and serpentinisation are possible (βc 3-4). Across the basin axis, the lowest seismic velocity in the mantle spatially coincides with the maximum amount of crustal faulting, indicating fault-controlled mantle hydration. Mantle velocities also suggest that the degree of serpentinisation, together with the amount of crustal faulting, increases southwards along the basin axis. Seismic reflection lines show a major detachment fault surface that grows southwards along the basin axis and is only visible where the inferred degree of serpentinisation is >15%. This observation is consistent with laboratory measurements that show that at this degree of

  18. The crustal structure beneath the Netherlands from ambient seismic noise

    Science.gov (United States)

    Paulssen, Hanneke; Yudistira, Tedi; Trampert, Jeannot

    2017-04-01

    A 3-D shear velocity model of the crust beneath the Netherlands is determined from fundamental mode Rayleigh and Love wave group measurements derived from ambient seismic noise recordings. The data are obtained from a temporary array of broad-band seismometers in and around the Netherlands (the NARS-Netherlands project, 2008-2012) complemented with data from existing networks in the Netherlands, Belgium and Germany. Rayleigh and Love wave group velocity maps were constructed for the period range of 10 to 30 s. Lateral variations in the group velocity maps primarily reflect variations in sedimentary thickness across the Netherlands. The 2-psi Rayleigh wave and 4-psi Love wave fast directions of the group velocity maps are in agreement with the NW-SE direction of maximum compressive stress as well as with the NW-SE dominant direction of faulting in the Netherlands. The frequency dependence suggests that the azimuthal anisotropy is caused by lattice preferred orientation (LPO) of lower crustal minerals. A 3-D shear-velocity model is obtained by inversion of the group velocity maps using the Neighbourhood Algorithm. The results show a top layer that varies in thickness from 2 to 4 km with with a pattern that is similar to the base of the Rotliegend. A midcrustal discontinuity is found at a depth of about 13 km. The Moho appears to be relatively flat with an average depth of 33 km. Radial anisotropy is mainly positive (Vsh - Vsv > 0) for the lower crust. This can be an expression of LPO but also of horizontal layering or lamination. The top layer shows the largest variations in radial anisotropy with distinct areas of negative radial anisotropy that can be attributed to high-density near-vertical faulting in those regions.

  19. Crustal structure on the northeastern flank of the Kenya rift

    Science.gov (United States)

    Prodehl, C.; Jacob, A. W. B.; Thybo, H.; Dindi, E.; Stangl, R.

    1994-09-01

    The KRISP flank line E converges with the Kenya rift at an angle of about 45° and is approximately parallel to the older Anza graben to the north. The depth to the basement is almost zero along the entire onshore part of the profile with higher velocities at the southeastern end indicative of extensive Precambrian gabbroic intrusions in the upper crust. The Moho shallows steadily from about 35 km at the southeastern end of the profile to about 24 km under Lake Turkana. Even though the Moho rises fairly steadily, there is significant heterogeneity in the crust above it. This shows that the extension is unevenly distributed between the upper and the lower crust. The Moho is laminated and variably reflective. Compared to the KRISP cross-line D further south, the crust is unexpectedly thin and shows extension increasing in a northerly direction. This extension is probably not associated with the Anza and Kenya rifting but with the profile's position on the slope of the Kenya dome. The indications are that there is a relatively abrupt change to a 20-km Moho depth near the Lake Turkana Central shotpoint. This change to a mid-rift crustal thickness occurs not at the postulated margin at the southeastern shore of Lake Turkana but at least 50 km further to the northwest. We suggest that the position of this margin may need to be redefined. The P n velocity is quite high at 8.1 km/s. This may indicate either a cold upper mantle or anisotropy. An upper-mantle reflector has been identified between 15 and 20 km below the Moho. It dips gently away from the rift.

  20. Mechanism of crustal extension in the Laxmi Basin, Arabian Sea

    Directory of Open Access Journals (Sweden)

    Anju Pandey

    2015-11-01

    Full Text Available Continental rifting and magmatism has been extensively studied worldwide as it is believed that continental rifting, break up of continents and associated magmatism lead to genesis of new oceanic crust. However, various regions of the world show that these processes may lead to genesis of other types of crust than the oceanic crust. Laxmi Basin in the western continental margin of the India is one such region with an enigmatic crust. Due to its extreme strategic significance for the palaeogeographic reconstruction of continents during Cretaceous continental breakup of India, this basin has attracted various workers for more than two decades. However, still the issue of nature of crust in the basin remains controversial. In this contribution, in order to identify nature of crust, mechanism of continental extension in the Laxmi Basin has been studied for the first time through newly acquired seismic data from the basin. Here, we propose a plausible mechanism of crustal extension in the Laxmi Basin which eventually constrains the nature of crust of the Laxmi Basin. We have demonstrated that the crust in the Laxmi Basin can be categorised in two zones of stretched and transitional crust. In the stretched zone several fault bounded horst and graben structures are identified which preserve syn- and post-rift sediments along with different periods of hiatus in sedimentations as unconformities. These faults are identified as listric faults in the upper crust which sole out in the detachment faults. Detachment faults decouples the upper brittle and lower ductile crust. The transitional crust is identified as heavily intruded by sills and basaltic volcanic which were emplaced due to melting of subcontinental mantle (SCM after hyper-stretching of crust and serpentinisation of the SCM. Panikkar Ridge is proposed to be one such basaltic volcanic body derived from melting of lower part of the SCM.

  1. Moho, LAB and crustal velocities underneath central-eastern Greenland

    Science.gov (United States)

    Kraft, H. A.; Thybo, H.

    2014-12-01

    Major parts of Greenland are covered with up to 3.4 km of ice. Due to logistical challenges connected to the ice only very sparse geophysical information is available. We present here results of the TopoGreenland project, which forms the first regional seismic experiment conducted on the Greenlandic ice shield. Our objective is to gain detailed information about the lithospheric structure and to connect it with topographic features, the recent substantial uplift and the earlier history of rifting and break-up in the region. We focus on a 200 km x 600 km large area in central-eastern Greenland, where 22 broadband seismometers were installed between June 2009 and May 2012. 10 of those were operating on the ice cap, 12 on bedrock. 16 of the stations were installed along a 600 km long profile at 70°N, from Scorsbysund to the centre of the ice cap. The remaining 6 stations covered a 200 km wide area north of this profile. In addition data from 6 permanent and long-term stations from the GLISN network were integrated. Here we present models from P- and S- receiver function (PRF, SRF) calculations and Rayleigh wave tomography. The RF calculations were used to map Moho and LAB depths and to have well constrained input parameters for the tomography. From the Rayleigh wave tomography we then obtain models for crustal shear-velocities. The PRF for the stations on the ice cap show multiples with very high amplitudes from within the ice, why we decided to derive Moho and LAB depths for those stations from SRF. The results will be compared with a seismic refraction profile acquired in the same region and then linked to topographic features like the uplift of the mountain chain in East Greenland.

  2. INVESTIGATION OF CRUSTAL MOTION IN THE TIEN SHAN USING INSAR

    Energy Technology Data Exchange (ETDEWEB)

    Mellors, R J

    2011-02-25

    The northern Tien Shan of Central Asia is an area of active mid-continent deformation. Although far from a plate boundary, this region has experienced 5 earthquakes larger than magnitude 7 in the past century and includes one event that may as be as large as Mw 8.0. Previous studies based on GPS measurements indicate on the order of 23 mm/yr of shortening across the entire Tien Shan and up to 15 mm/year in the northern Tien Shan (Figure 1). The seismic moment release rate appears comparable with the geodetic measured slip, at least to first order, suggesting that geodetic rates can be considered a proxy for accumulation rates of stress for seismic hazard estimation. Interferometric synthetic aperture radar may provide a means to make detailed spatial measurements and hence in identifying block boundaries and assisting in seismic hazard. Therefore, we hoped to define block boundaries by direct measurement and by identifying and resolving earthquake slip. Due to political instability in Kyrgzystan, the existing seismic network has not performed as well as required to precisely determine earthquake hypocenters in remote areas and hence InSAR is highly useful. In this paper we present the result of three earthquake studies and show that InSAR is useful for refining locations of teleseismically located earthquakes. ALOS PALSAR data is used to investigate crustal motion in the Tien Shan mountains of Central Asia. As part of the work, considerable software development was undertaken to process PALSAR data. This software has been made freely available. Two damaging earthquakes have been imaged in the Tien Shan and the locations provided by ALOS InSAR have helped to refine seismological velocity models. A third earthquake south of Kyrgyzstan was also imaged. The use of InSAR data and especially L band is therefore very useful in providing groundtruth for earthquake locations.

  3. New Crustal Stress Map of the Mediterranean and Central Europe

    Science.gov (United States)

    Heidbach, Oliver; Custodio, Susana; Kingdon, Andrew; Mariucci, Maria Teresa; Montone, Paola; Müller, Birgit; Pierdominicini, Simona; Rajabi, Mojtaba; Reinecker, John; Reiter, Karsten; Tingay, Mark; Williams, John; Ziegler, Moritz

    2016-04-01

    The World Stress Map (WSM) Project was initiated in 1986 under the auspices of the International Lithosphere Program in order to compile globally the information on the contemporary crustal stress state. For the 30th anniversary the WSM database has been updated and increased the number of data records from 21,750 to 42,410 worldwide. For the Mediterranean and Central European stress map the number of data records has increased from 3877 to 8192. The data come from a wide range of stress indicators such as borehole data (e.g. hydraulic fracturing, drilling induced tensile fractures, borehole breakouts), earthquake focal mechanism solutions and stress inversions from these, engineering methods (overcoring, borehole slotter) and geological data (e.g. volcanic alignment, inversion of fault slip data). To guarantee the comparability of the different stress indicator the resulting data are quality-ranked using the WSM quality ranking scheme. The new data set has a better coverage and enables us to identifying the regional and local variability of the stress pattern. For the Mediterranean and Central Europe we analysed the wave-length of the stress pattern by determining the mean orientation of the maximum horizontal stress SHmax on a regular grid using an updated version of the hybrid approach of Heidbach et al. [2010]. The preliminary results show that the Africa-Eurasia plate convergence is a key control of the overall stress pattern. However, given the complex tectonic setting in particular due to the indentation/collision of the Adriatic micro block, the Alpine topography as well as forces that control the movement of the Anatolian and Aegean block, the stress pattern shows in these regions significant changes in the mean SHmax orientation as well as in the tectonic regime.

  4. Shallow Crustal Thermal Structures of Central Taiwan Foothills Region

    Directory of Open Access Journals (Sweden)

    Shao-Kai Wu

    2013-01-01

    Full Text Available Crustal thermal structures are closely related to metamorphism, rock rheology, exhumation processes, hydrocarbon maturation levels, frictional faulting and other processes. Drilling is the most direct way to access the temperature fields in the shallow crust. However, a regional drilling program for geological investigation is usually very expensive. Recently, a large-scale in-situ investigation program in the Western Foothills of Central Taiwan was carried out, providing a rare opportunity to conduct heat flow measurements in this region where there are debates as to whether previous measured heat flows are representative of the thermal state in this region. We successfully collected 28 geothermal gradients from these wells and converted them into heat flows. The new heat flow dataset is consistent with previous heat flows, which shows that the thermal structures of Central Taiwan are different from that of other subduction accretionary prisms. We then combine all the available heat flow information to analyze the frictional parameters of the Chelungpu fault zone that ruptured during the 1999, Chi-Chi, Taiwan, earthquake. The heat flow dataset gave consistent results compared with the frictional parameters derived from another independent study that used cores recovered from the Chelungpu fault zone at depth. This study also shows that it is suitable for using heat-flow data obtained from shallow subsurface to constrain thrusting faulting parameters, similar to what had been done for the strike-slip San Andreas Fault in California. Additional fieldworks are planned to study heat flows in other mountainous regions of Taiwan for more advanced geodynamic modeling efforts.

  5. Crustal anisotropy contribution under-evaluated under Tibet ?

    Science.gov (United States)

    Herquel, G.; Edme, P.

    2003-04-01

    Moho P-to-S converted phases may be used to determine the complete crustal component of anisotropy. Phases with a good signal-to-noise ratio and with sufficient azimuthal coverage are required to avoid misleading results. Previous results may be low estimates of this contribution in Tibet (0.15-0.3s) since some very large mantellic delays have been observed in other areas of the plateau. New measurements use data from stations with the largest mantellic delays δt observed in Tibet: at least 2 seconds (stations ST17, ST18 and ST19 from Indepth III and BUDO). As the data for station BUDO was good enough , we compare results obtained by original signals and by single receiver functions obtained in the frequency domain or by iterative deconvolution. The data were processed using waveform rotation-correlation, tangential energy minimization and particle motion analysis methods. The results are remarkably coherent concerning the fast polarization direction and the mean delay value using these different techniques. Using receiver function stacked data in different bins of backazimuth we obtained delay values in good agreement with the other techniques and hence the processing can be accelerated using this approach. At all 4 stations a mean value of delay of 0.15s is retrieved with an uncertainty of 0.05s: no single value exceed 0.3s. These new results are similar to the first estimations in Tibet and confirm the results obtained in other aeras (Ural Montains, New Zealand and Basin and Range). Finally, we observe also a good correlation with the fast polarization direction obtained by teleseismic shear wave analysis.

  6. On the rheology of crustal rocks containing low melt fractions

    Science.gov (United States)

    Rosenberg, C. L.; Handy, M. R.

    2003-04-01

    A review and reinterpretation of older experimental data on the deformation of partially-melted granite reveals a non-linear strength decrease with increasing melt fractions. This decrease is characterised by two sharp discontinuities, each reflecting a dramatic change of strength within a limited range of melt fractions. A first discontinuity is shown by all experiments at melt fractions between 0.0 and 0.1. The change of strength within this range of melt fractions is the largest over the entire melting range. The second discontinuity occurs at higher melt fractions (0.4 to 0.6) and corresponds to the well known rheologically critical melt percentage (RCMP). In contrast to recent interpretations, we infer that the experimental data do indicate the occurrence of the RCMP, for crystallising as well as for melting rocks. However, the magnitude of the stress drop at the RCMP is negligible compared to the stress drop at melt fractions RCMP, at melt fractions >= 0.4, as proposed by several experimentalists. We suggest that the attainment of a melt fraction of 0.03 to 0.08 will control the large-scale localisation of deformation into partially-melted crustal layers, irrespective of the attainment of the RCMP. If the RCMP is achieved, however, the large-scale deformational response of the crust may not be different than that of a crust containing a melt fraction of 0.1. Instead, the RCMP controls localisation of flow within magmatic bodies, where it effects the internal dynamics of magma chambers.

  7. Evaluating Crustal Contamination Effects on the Lithophile Trace Element Budget of Shergottites

    Science.gov (United States)

    Brandon, A. D.; Ferdous, J.; Peslier, A. H.

    2017-01-01

    The origin of the incompatible trace element (ITE) enriched compositions of shergottites has been a point of contention for decades [1-2]. Two scenarios have been proposed, the first is that enriched shergottite compositions reflect an ITE-enriched mantle source, whereas in the second, the ITE enrichment reflects crustal contamination of mantle-derived parent magmas. Evidence supporting the first scenario is that the ITE-enriched shergottite compositions are consistent with the outcomes of magma ocean crystallization [3], and that Os-Nd isotope relationships for shergottites cannot be explained by realistic crustal contamination models [4]. In contrast, Cl and S isotopes are consistent with shergottite magmas interacting with Mars crust [5,6], and ITE-enriched olivine-hosted melt inclusions and interstitial glass are found in depleted shergottite Yamato 980459 [7]. These findings indicate that some level of crustal interaction occurred but the question of whether ITE-enrichments in some bulk shergottites reflect crustal contamination remains open. Recently, a Mars crustal breccia meteorite has been found, NWA 7034 and its paired stones, that is our best analogue to an average of Mars ancient crust [8-10]. This allows for better constraints on crustal contamination of shergottite magmas. We modeled magma-crust mixing and assimilation-fractional crystallization (AFC) using ITE-depleted shergottite compositions and bulk NWA 7034 and its clasts as end-members. The results of these models indicate that crustal contamination can only explain the ITE-enriched compositions of some bulk shergottites under unusual circumstances. It is thus likely that the shergottite range of compositions reflects primarily mantle sources.

  8. Crustal-scale magmatism and its control on the longevity of magmatic systems

    Science.gov (United States)

    Karakas, Ozge; Degruyter, Wim; Bachmann, Olivier; Dufek, Josef

    2017-04-01

    Constraining the duration and evolution of crustal magma reservoirs is crucial to our understanding of the eruptive potential of magmatic systems, as well as the volcanic:plutonic ratios in the crust, but estimates of such parameters vary widely in the current literature. Although no consensus has been reached on the lifetime of magma reservoirs, recent studies have revealed about the presence, location, and melt fraction of multi-level (polybaric) storage zones in the crust. If magma accumulates at different crustal levels, it must redistribute significant enthalpy within the crustal column and therefore must influence the lifetime of magma plumbing systems. However, an evaluation of the mass and heat budget of the entire crustal column is lacking. Here, we use a two-dimensional thermal model to determine the thermal conditions under which both lower and upper crustal magma bodies form. We find that large lower crustal mush zones supply heat to the upper crust and reduce the amount of thermal energy necessary to form subvolcanic reservoirs. This indicates that the crust is thermally viable to sustain partially molten magma reservoirs over long timescales (>10^5-106 yr) for a range of magma fluxes (10^-4 to 10^-2 km^3/yr). Our results reconcile physical models of crustal magma evolution and field-based estimates of intrusion rates in numerous magmatic provinces (which include both volcanic and plutonic lithologies). We also show that young magmatic provinces ( 106 yr) can accumulate magma and build reservoirs capable of triggering supereruptions, even with intrusion rates as low as ≤10^-2 km^3/yr. Hence, the total duration of magmatism is critical in determining the size of the magma reservoirs, and should be combined with the magma intrusions rates to assess the capability of volcanic systems to form the largest eruptions on Earth.

  9. A unified analysis of crustal motion in Southern California, 1970-2004: The SCEC crustal motion map

    Science.gov (United States)

    Shen, Z.-K.; King, R. W.; Agnew, D. C.; Wang, M.; Herring, T. A.; Dong, D.; Fang, P.

    2011-11-01

    To determine crustal motions in and around southern California, we have processed and combined trilateration data collected from 1970 to 1992, VLBI data from 1979 to 1992, and GPS data from 1986 to 2004: a long temporal coverage required in part by the occurrence of several large earthquakes in this region. From a series of solutions for station positions, we have estimated interseismic velocities, coseismic displacements, and postseismic motions. Within the region from 31°N to 38°N. and east to 114°W, the final product includes estimated horizontal velocities for 1009 GPS, 190 trilateration, and 16 VLBI points, with ties between some of these used to stabilize the solution. All motions are relative to the Stable North American Reference Frame (SNARF) as realized through the velocities of 20 GPS stations. This provides a relatively dense set of horizontal velocity estimates, with well-tested errors, for the past quarter century over the plate boundary from 31°N to 36.5°N. These velocities agree well with those from the Plate Boundary Observatory, which apply to a later time period. We also estimated vertical velocities, 533 of which have errors below 2 mm/yr. Most of these velocities are less than 1 mm/yr, but they show 2-4 mm/yr subsidence in the Ventura and Los Angeles basins and in the Salton Trough. Our analysis also included estimates of coseismic and postseismic motions related to the 1992 Landers, 1994 Northridge, 1999 Hector Mine, and 2003 San Simeon earthquakes. Postseismic motions increase logarithmically over time with a time constant of about 10 days, and generally mimic the direction and relative amplitude of the coseismic offsets.

  10. Density heterogeneity of the upper mantle beneath Siberia from satellite gravity and a new regional crustal model

    DEFF Research Database (Denmark)

    Herceg, Matija; Thybo, Hans; Artemieva, Irina

    2013-01-01

    We present a new regional model for the density structure of the upper mantle below Siberia. The residual mantle gravity anomalies are based on gravity data derived from the GOCE gravity gradients and geopotential models, with crustal correction to the gravity field being calculated from a new...... on regional and global crustal models. We analyze how uncertainties and errors in the crustal model propagate from crustal densities to mantle residual gravity anomalies and the density model of the upper mantle. The new regional density model for the Siberian craton and the West Siberian Basin complements...

  11. New insights on the crustal thickness and its lateral variations beneath the Rif Cordillera

    Science.gov (United States)

    Gil de la Iglesia, A.; Diaz Cusi, J.; Gallart, J.; Carbonell, R.; Harnafi, M.; Levander, A.

    2014-12-01

    The Rif cordillera forms, together with the Betic ranges, one of the tightest orogenic arcs on Earth. This continental boundary zone is dominated now by the slow convergence between Nubia and Eurasia, but with clear evidences of extensional tectonics. One of the missing elements to constrain the complex geodynamics of the Gibraltar Arc System is the knowledge on crustal structure beneath northern Morocco. In the last decade a major effort has been done in this sense, from active and passive seismics. We compile here the recent results available from the Rif domains. Two 330 km long wide angle DSS profiles were recorded end of 2011 across the Rif in NS and EW transects within the Rifsis project, complemented by onshore recordings of the Gassis-WestMed marine profiles. At the same period, BB seismic arrays were deployed in the area within Topo-Iberia and Picasso projects, allowing receiver function analyses of crustal depths. The ray-tracing modeling of the Rifsis profiles reveal a large Moho step and an area of crustal thickening both in EW and NS directions, grossly coincident with the Bouguer gravity anomalies. The deployment logistics allowed that all the stations recorded all the shots, thus providing useful offline data. We will use here all available in-line and offline data to provide a map of the crustal thickness in northern Morocco. We combined two approaches: i) a hyperbolic time reduction applied to the seismic data, resulting in low-fold stacks in which the reflections from the Moho should appear as subhorizontal lines; ii) the arrival times of the observed PmP phases allow, assuming a mean crustal velocity, to assign a midpoint crustal thickness to each lecture. Although some uncertainties may be inherent to those approaches, a large crustal root, reaching more than 50 km, is well documented in the central part of the Rif Cordillera, close to the zone where the Alboran slab may still be attached to the lithosphere. We also compared these results with

  12. Evolution of the competitive environment of the Argentinean petroleum industry and strategical repositioning of the former Yacimientos Petroliferos Fiscales Sociedad del Estado - YPF; Evolucao do ambiente competitivo da industria de petroleo argentina e reposicionamento estrategico da ex-Yacimentos Petroliferos Fiscales Sociedad del Estado - YPF

    Energy Technology Data Exchange (ETDEWEB)

    Cavalcanti, Maria Alice F. Deschamps; Carneiro, Jorge Manoel T. [PETROBRAS, Rio de Janeiro, RJ (Brazil); Silva, Jorge Ferreira da [Pontificia Universidade Catolica, Rio de Janeiro, RJ (Brazil). Dept. de Administracao de Empresas

    1998-07-01

    This work analyses the evolution of Argentinean oil industry from 1988 until 1996, resulting from deregulation and YPF's privatization. The five competitive forces (Porter, 1980) evolved from low to medium level, making the competitive environment more hostile. YPF replied changing from a condition of low significance and/or incoherence on the major competitive methods ('stuck-in-the-middle strategy'), to a clear trend to Differentiation strategy (Porter, 1980). YPF's market-share fall from about 60% to 45, together with the improvement of profitability, which went from -6,3% (1988/90) to +11,4% (1994/96). (author)

  13. A historical analysis of the evolution of the program efficiency 'Low income households consumers of electrical energy' in the interior of Sao Paulo state; Uma analise historica da evolucao da eficiencia do programa 'Consumidor de baixa renda de energia eletrica' no interior do estado de Sao Paulo

    Energy Technology Data Exchange (ETDEWEB)

    Dias, Jose Antonio Siqueira [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Fac. de Engenharia Eletrica e de Computacao. Dept. de Eletronica e Microeletronica], e-mail: siqueira@demic.fee.unicamp.br; Tavares, Mauricio Lopes [Escola Superior de Agricultura Luiz de Queiroz (ESALQ/USP), Piracicaba, SP (Brazil). Dept. de Economia, Administracao e Sociologia], e-mail: mautavar@uol.com.br

    2004-07-01

    An analysis of the criteria used to select the beneficiaries of the federally-funded social program 'Consumidor de baixa renda de energia eletrica (Low Income Households Consumers of Electrical Energy)' in the State of Sao Paulo is presented. The study is based on statistical data obtained from the database of Companhia Paulista de Forca e Luz - CPFL, one of the most important electrical energy distributor in the mentioned region. The concept of 'low income household' is also discussed, based on studies presented by IBGE - Instituto Brasileiro de Geografia e Estatistica and by FIPE - Fundacao Instituto de Pesquisas Economicas, comparing the expected number of low income households with the actual number of consumers who receive the subsidy. (author)

  14. Crustal structure of the western Indian shield: Model based on regional gravity and magnetic data

    Directory of Open Access Journals (Sweden)

    Suman Kilaru

    2013-11-01

    This study probes the geometry of the different crustal units in terms of density and susceptibility variations in order to decipher the imprints of the major tectonic processes the region has undergone. In order to decipher the crustal geometry of the Gadra–Fatehpur profile, two NW–SE gravity and magnetic profile vertical sections (A–A′ in the south and B–B′ in the north are modelled on the basis of the constraints provided from previous seismic models. The crustal model of the Gadra–Fatehpur profile is composed of alluvium, Tertiary sediments, MIS, Marwar Supergroup, low-density layers (LDLs and the middle–lower crustal layers, with a distinct change in configuration from the southwest to northeast. The Moho dips from SW to NE, the MIS in the SW gives way to the thick pile of the Marwar Supergroup to the NE. The evolution of MIS has been suggested to have occurred as a consequence of delamination of the upper mantle. LDLs are incorporated in Gadra–Fatehpur model. In the SW, LDL (2550 kg/m3 lies below the MIS in the NE, another LDL (2604 kg/m3 is depicted below the mid-crustal layer.

  15. Contemporary crustal movement of southeastern Tibet: Constraints from dense GPS measurements

    Science.gov (United States)

    Pan, Yuanjin; Shen, Wen-Bin

    2017-03-01

    The ongoing collision between the Indian plate and the Eurasian plate brings up N-S crustal shortening and thickening of the Tibet Plateau, but its dynamic mechanisms remain controversial yet. As one of the most tectonically active regions of the world, South-Eastern Tibet (SET) has been greatly paid attention to by many geoscientists. Here we present the latest three-dimensional GPS velocity field to constrain the present-day tectonic process of SET, which may highlight the complex vertical crustal deformation. Improved data processing strategies are adopted to enhance the strain patterns throughout SET. The crustal uplifting and subsidence are dominated by regional deep tectonic dynamic processes. Results show that the Gongga Shan is uplifting with 1-1.5 mm/yr. Nevertheless, an anomalous crustal uplifting of ~8.7 mm/yr and negative horizontal dilation rates of 40-50 nstrain/yr throughout the Longmenshan structure reveal that this structure is caused by the intracontinental subduction of the Yangtze Craton. The Xianshuihe-Xiaojiang fault is a major active sinistral strike-slip fault which strikes essentially and consistently with the maximum shear strain rates. These observations suggest that the upper crustal deformation is closely related with the regulation and coupling of deep material.

  16. Crustal moment of inertia of glitching pulsars with the KDE0v1 Skyrme interaction

    Energy Technology Data Exchange (ETDEWEB)

    Madhuri, K.; Routray, T.R.; Pattnaik, S.P. [Sambalpur University, School of Physics, Jyotivihar (India); Basu, D.N. [Variable Energy Cyclotron Center, Kolkata (India)

    2017-07-15

    The mass, radius and crustal fraction of moment of inertia in neutron stars are calculated using β-equilibrated nuclear matter obtained from the Skyrme effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars are determined from the thermodynamic stability conditions using the KDE0v1 set. The neutron star masses obtained by solving the Tolman-Oppenheimer-Volkoff equations using neutron star matter obtained from this set are able to describe highly massive compact stars ∝ 2M {sub CircleDot}. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches. This fraction is highly dependent on the core-crust transition pressure and corresponding density. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a limit for the radius of the Vela pulsar, R ≥ 3.69 + 3.44M/M {sub CircleDot}. Present calculations suggest that the crustal fraction of the total moment of inertia can be ∝ 6.3% due to crustal entrainment caused by the Bragg reflection of unbound neutrons by lattice ions. (orig.)

  17. Qinghai-Tibet Plateau crustal thickness derived from EGM2008 and CRSUT2.0

    Directory of Open Access Journals (Sweden)

    Zhou Hao

    2014-11-01

    Full Text Available Qinghai-Tibet Plateau is the most complex region for crustal thickness inversion, while high-resolution earth gravity model (EGM makes it possible to obtain high precision gravity anomaly, which is a key parameter to depict the Earth’s inner structure in geodesy domain. On the basis of this principle, we calculated the Bouguer gravity anomalies in Qinghai-Tibet Plateau with EGM2008 and SRTM6. 0 by efficient high-degree spherical harmonic synthesis algorithm. In order to obtain the gravity anomaly caused by Moho density mutant, the noises caused by the topography was removed by wavelet details. Then, the crustal thickness was corrected on the basis of CRUST 2. 0 with the deep-large-scale single density interface formula. The inversion result indicates that the crustal thickness in Qinghai-Tibet Plateau is between 50 km and 75 km, which is in correspondence with the recent science research result. Compared with the 2 degree CRUST 2. 0 model, the spatial resolution of crustal thickness in our research can reach 40 arc minutes. In addition, there is a positive relationship between the inversed crustal thickness and topography, which can prove the effectiveness of Airy-Heiskanen isostatic model in gravity reduction.

  18. Lifetime and size of shallow magma bodies controlled by crustal-scale magmatism

    Science.gov (United States)

    Karakas, Ozge; Degruyter, Wim; Bachmann, Olivier; Dufek, Josef

    2017-06-01

    Magmatic processes on Earth govern the mass, energy and chemical transfer between the mantle, crust and atmosphere. To understand magma storage conditions in the crust that ultimately control volcanic activity and growth of continents, an evaluation of the mass and heat budget of the entire crustal column during magmatic episodes is essential. Here we use a numerical model to constrain the physical conditions under which both lower and upper crustal magma bodies form. We find that over long durations of intrusions (greater than 105 to 106 yr), extensive lower crustal mush zones develop, which modify the thermal budget of the upper crust and reduce the flux of magma required to sustain upper crustal magma reservoirs. Our results reconcile physical models of magma reservoir construction and field-based estimates of intrusion rates in numerous volcanic and plutonic localities. Young igneous provinces (less than a few hundred thousand years old) are unlikely to support large upper crustal reservoirs, whereas longer-lived systems (active for longer than 1 million years) can accumulate magma and build reservoirs capable of producing super-eruptions, even with intrusion rates smaller than 10-3 to 10-2 km3 yr-1. Hence, total duration of magmatism should be combined with the magma intrusion rates to assess the capability of volcanic systems to form the largest explosive eruptions on Earth.

  19. Crustal Structure around Ordos Terrain Derived from Ambient Noise Tomography

    Science.gov (United States)

    Liu, J.; Ning, J.; Tang, Y.; Chen, Y. J.

    2011-12-01

    We performed Rayleigh wave tomography around Ordos terrain by applying the ambient noise method to broadband seismic data. The data was recorded at 85 temporary stations of PKU array operated along Yinchuan-Jinan and 410 permanent stations of CEA network operated between Eastern margin of Tibetan plateau and Huabei basin. Receiver function technique was also applied to study Moho discontinuity in Southern Ordos by PKU array. We developed a new stacking technique to obtain high-quality dispersion curves of Rayleigh waves from cross correlation of seismic ambient noise. This technique is based on phase-matched filter and was implemented in a four-step iterative process: signal compression, stacking, signal extraction and signal decompression. We stack all the compressed Estimated Green Functions that have almost the same path to improve signal to noise ratio. Results show that this new stacking method is stable and can improve the quality of ambient noise inversion. The inversion results present in this study are consistent with tectonic nature in this region. S velocity at depths of 0-10 km beneath Huabei plain, Sichuan basin and Ordos terrain are obviously lower than those beneath Eastern margin of Tibetan plateau. That is probably due to the thick sediments in Huabei plain, Sichuan basin and Ordos block. S velocity beneath Lvliang-Taihang region keeps high in whole crust and this may relate to Cenozoic intrusion of mantle material here. Our results revealed that the crust is thick in the southern part of the Ordos terrain while it is a little thin in the northern part. This confirmed the result given by Chen et al. (2010) and explained the contradiction between the work of Chen's and former results. The contrasting crustal thickness of the Ordos terrain is also in accord with our Receiver Function results. Receiver functions revealed two interfaces at about 40 km and 60 km in southern part of the Ordos terrain, comparing with only one located at about 40 km depth

  20. A hemispherical dynamo model: Implications for the Martian crustal magnetization

    Science.gov (United States)

    Dietrich, W.; Wicht, J.; Christensen, U. R.

    2011-12-01

    In 1999 the Mars Global Surveyor detected a strong but very heterogeneous crustal magnetization mainly localized in the southern hemisphere. Their magnetization dichotomy may have either an external or an internal origin. In the first scenario, the Martian crust was fully magnetized by a dipolar dynamo induced in the Martian liquid core. After the core dynamo cessation, the crust was demagnetized by volcanoes, impacts or any other resurfacing event distributed not homogeneously over the surface. The internal origin, which is investigated here, relies on a per se hemispherical internal magnetric field. For this, we rely on that Mars never developed an inner core. The planets ancient dynamo was thus exclusively driven by secular cooling and radiogenic heating. Due to the small planetary size, the core mantle boundary (CMB) heat flux may be not as homogeneous, as in e.g. Earth. Mantle convection in smaller planets is thought to develope larger scales, maybe even a huge single-plume structure. Giant impacts might have played a crucial role in the thermal history of Mars, hence they are heating mainly one hemisphere. Giant plumes and major impact events would both cause a hemispherical CMB heat flux pattern. Therefore, we model the ancient Martian dynamo as rotating, convecting and conducting fluid heated by an internal heat source and contained in a spherical shell, where the CMB heat flux is perturbed by a sinusoidal anomaly. Compared to the classical columnar convection, we find a drastically different flow pattern. There meridional circulation seeking to equilibrate the heat difference between both hemispheres is diverted into two counterdirected cells of axisymmetric zonal flows (thermal winds) by the strong Coriolis force. Convective plumes are confined to the region of high heat flux in the vicinity of the southern pole. Core convection is thus dominated by equatorially antisymmetric and axisymmetric (EAA) modes. In the columnar regime, poloidal and toroidal

  1. A Reinvestigation of Crustal Thickness in the Tibetan Plateau Using Absolute Gravity, GPS and GRACE Data

    Directory of Open Access Journals (Sweden)

    Wenke Sun

    2011-01-01

    Full Text Available The geodetic evidence of the uplift and crustal thickness of the Tibetan Plateau has been presented for the first time (Sun et al. 2009 using gravity and GPS observations. In this paper, we reinvestigate this tectonic deformation in more detail using GRACE data and taking the GIA effect into account. We first summarize the previous gravity and GPS observations and a local gravity network in the Dali County. The comparison between the surface absolute gravity and space GRACE gravity measurements shows that they are harmonic, agree well. Finally, we assume that the residual gravity change reflects material transport accompanying vertical movements on the crustal bottom; the crustal thickening rate is inferred as 1.9 ¡_ 1.4 cm yr-1. As the crust thickens, the mass of a column of rock beneath the station decreases because mantle is displaced by crust, causing a reduction in gravity.

  2. Structural and Geologic Mapping of Southern Tellus Regio, Venus: Implications for Crustal Plateau Formation

    Science.gov (United States)

    Graupner, Melanie

    2013-03-01

    Crustal plateau formation on Venus is subject to animated debate, centered on plateau support and resulting surface deformation. Detailed mapping provides critical clues for plateau evolution. Southern Tellus Regio records broadly synchronous formation of contractional and extensional structures, accompanied by deposition of flood material. Short-wavelength folds occur across the entire plateau, the extent of which has previously been undocumented. Generally the early-formed structures record a high structural fluidity, marked by variable orientation of structures or juxtaposition of neighboring structural suites. This interpretation of the geologic history of the region indicates the necessity of an extremely high geothermal gradient and provides a means to evaluate the different crustal plateau hypotheses. The mantle downwelling, mantle upwelling, and pulsating continents hypotheses fail to accommodate the surface features recorded in this study. However, the lava pond hypothesis provides a suitable hypothesis of crustal plateau formation that accommodates structural elements recorded in this study.

  3. Fast crustal deformation computing method for multiple computations accelerated by a graphics processing unit cluster

    Science.gov (United States)

    Yamaguchi, Takuma; Ichimura, Tsuyoshi; Yagi, Yuji; Agata, Ryoichiro; Hori, Takane; Hori, Muneo

    2017-08-01

    As high-resolution observational data become more common, the demand for numerical simulations of crustal deformation using 3-D high-fidelity modelling is increasing. To increase the efficiency of performing numerical simulations with high computation costs, we developed a fast solver using heterogeneous computing, with graphics processing units (GPUs) and central processing units, and then used the solver in crustal deformation computations. The solver was based on an iterative solver and was devised so that a large proportion of the computation was calculated more quickly using GPUs. To confirm the utility of the proposed solver, we demonstrated a numerical simulation of the coseismic slip distribution estimation, which requires 360 000 crustal deformation computations with 82 196 106 degrees of freedom.

  4. On the precursors to the 2011 Tohoku earthquake: crustal movements and electromagnetic signatures

    Directory of Open Access Journals (Sweden)

    Makoto Kamiyama

    2016-03-01

    Full Text Available We compare the precursory behaviour of crustal movements with electromagnetic signatures for the 2011 off the Pacific Coast of Tohoku earthquake. First, we present the Global Positioning System (GPS data on the co-seismic variations and pre-seismic precursors (medium-term, short-term and imminent precursors. Then, we will review recently published results on electromagnetic precursors, including mainly short-term subionospheric very low frequency (VLF/LF propagation anomaly, ultralow frequency (ULF magnetic field depression and ULF/extremely low frequency (ELF atmospheric radiation. Finally, we examine the relationship between the crustal movements and electromagnetic phenomena. We conclude that at least short-term electromagnetic precursors are closely correlated in time with the corresponding crustal movements. This seems to provide evidence on the link between lithospheric and electromagnetic processes. Some discussions will be given on the possible mechanism of this link.

  5. Crustal imaging of the Northwest Himalaya and its foredeep region from teleseismic events

    Directory of Open Access Journals (Sweden)

    Sowrav Saikia

    2016-07-01

    Full Text Available Over 450 receiver functions from 8 broadband stations located in the Indo-Gangetic plain and Northwest Himalayan region are analyzed to examine the crustal properties across the contiguous region. We identified the P-to-S phase beneath each station and estimated the crustal thickness from time delay of this phase with respect to the direct P arrival. With the help of the slant stacking technique, we determined bulk crustal chemical properties and validated our estimate of crustal thickness. The Moho was encountered in the Indo-Gangetic plain at an average depth of 33 km and thickened towards the Northwest Himalaya with the Moho depth varying from 37 to 52 km. The thickest crust matched the highest topography, which is strong evidence of the occurrence of a crustal root of the mountain range. The time domain iterative linearized inversion technique is used to invert radial receiver functions to wave velocity structures for both tectonic regimes. From the forward modelling, we found mid-crustal low-velocity layers at different patches at a depth of 10–30 km in the Northwest Himalaya region. The presence of melts may be inferred in the mid crust with high values of Poisson ratio (σ ≥ 0.260 for the stations in the Northwest Himalaya. Towards south in the Indo-Gangetic alluvium plain, we estimated a medium to higher value of Poisson ratio (0.240 ≤ σ ≤ 0.290, but velocity modelling implies absence of an intracrustal low-velocity zone around the region.

  6. Crustal structure of north Peru from analysis of teleseismic receiver functions

    Science.gov (United States)

    Condori, Cristobal; França, George S.; Tavera, Hernando J.; Albuquerque, Diogo F.; Bishop, Brandon T.; Beck, Susan L.

    2017-07-01

    In this study, we present results from teleseismic receiver functions, in order to investigate the crustal thickness and Vp/Vs ratio beneath northern Peru. A total number of 981 receiver functions were analyzed, from data recorded by 28 broadband seismic stations from the Peruvian permanent seismic network, the regional temporary SisNort network and one CTBTO station. The Moho depth and average crustal Vp/Vs ratio were determined at each station using the H-k stacking technique to identify the arrival times of primary P to S conversion and crustal reverberations (PpPms, PpSs + PsPms). The results show that the Moho depth correlates well with the surface topography and varies significantly from west to east, showing a shallow depth of around 25 km near the coast, a maximum depth of 55-60 km beneath the Andean Cordillera, and a depth of 35-40 km further to the east in the Amazonian Basin. The bulk crustal Vp/Vs ratio ranges between 1.60 and 1.88 with the mean of 1.75. Higher values between 1.75 and 1.88 are found beneath the Eastern and Western Cordilleras, consistent with a mafic composition in the lower crust. In contrast values vary from 1.60 to 1.75 in the extreme flanks of the Eastern and Western Cordillera indicating a felsic composition. We find a positive relationship between crustal thickness, Vp/Vs ratio, the Bouguer anomaly, and topography. These results are consistent with previous studies in other parts of Peru (central and southern regions) and provide the first crustal thickness estimates for the high cordillera in northern Peru.

  7. Monitoring Vertical Crustal Deformation and Gravity Variations during Water Level Changes at the Three Gorges Reservoir

    Directory of Open Access Journals (Sweden)

    WANG Wei

    2017-06-01

    Full Text Available Monitoring vertical crustal deformation and gravity changes during water level changes at the Three Gorges reservoir is important for the safe operation of the Three Gorges Dam and for the monitoring and prevention of a regional geological disaster. In this study, we determined vertical crustal deformation and gravity changes during water level variations of the Three Gorges reservoir from direct calculations and actual measurements and a comprehensive solution. We used water areas extracted image data from the ZY-3 satellite and water level data to calculate gravity changes and vertical crustal deformation caused by every 5 m change in the water level due to storage and drainage of the Three Gorges reservoir from 145 m to 175 m. The vertical crustal deformation was up to 30 mm. The location of gravity change above 20 μ Gal(1 Gal=10-2 m/s2 was less than 2 km from the centerline of the Yangtze River. The CORS ES13 in Badong, near the reservoir, measured the vertical crustal deformation during water level changes. Because of the small number of CORS and gravity stations in the Three Gorges reservoir area, monitoring deformation and gravity related to changes in the Three Gorges reservoir water level cannot be closely followed. Using 26 CORS and some of the gravity stations in the Three Gorges area and based on loading deformation and the spherical harmonic analysis method, an integrated solution of vertical deformation and gravity variations during water level changes of the reservoir was determined, which is consistent with the actual CORS monitoring results. By comparison, we found that an integrated solution based on a CORS network can effectively enhance the capability of monitoring vertical crustal deformation and gravity changes during water level variations of the reservoir.

  8. Late-Archaean crustal growth in the Lewisian Complex of Northwest Scotland: Diachroneity in magmatic accretion and implications for models of crustal growth

    Science.gov (United States)

    Whitehouse, M. J.

    The Lewisian Complex of northwestern Scotland is an Archaean basement terrain that was reworked during the Proterozoic. Previous geochronological studies have established that the complex represents an entirely new crustal addition during late-Archaean times, and the difference between a Sm-Nd accretion date of 2920 + or - 50 Ma and a Pb/Pb metamorphic date of 2680 + or - 70 Ma was interpreted as indicating a crustal accretion-differentiation superevent (CADS) lasting 240 + or - 110 Ma. A combined Rb-Sr, Pb/Pb, and Sm-Nd isotopic study reported was applied to the Lewisian CADS to attempt to address the problem of whether this comprised a short regional scale magmatic accretion event followed approximately 200 Ma later by regional high-grade metamorphism, or a long period of episodic or semi-continuous magmatic accretion prior to high-grade metamorphism.

  9. Effects of crustal thickness on magmatic differentiation in subduction zone volcanism: A global study

    Science.gov (United States)

    Farner, Michael J.; Lee, Cin-Ty A.

    2017-07-01

    The majority of arc magmas are highly evolved due to differentiation within the lithosphere or crust. Some studies have suggested a relationship between crustal thickness and magmatic differentiation, but the exact nature of this relationship is unclear. Here, we examine the interplay of crustal thickness and magmatic differentiation using a global geochemical dataset compiled from active volcanic arcs and elevation as a proxy for crustal thickness. With increasing crustal thickness, average arc magma compositions become more silicic (andesitic) and enriched in incompatible elements, indicating that on average, arc magmas in thick crust are more evolved, which can be easily explained by the longer transit and cooling times of magmas traversing thick arc lithosphere and crust. As crustal thickness increases, arc magmas show higher degrees of iron depletion at a given MgO content, indicating that arc magmas saturate earlier in magnetite when traversing thick crust. This suggests that differentiation within thick crust occurs under more oxidizing conditions and that the origin of oxidation is due to intracrustal processes (contamination or recharge) or the role of thick crust in modulating melting degree in the mantle wedge. We also show that although arc magmas are on average more silicic in thick crust, the most silicic magmas (>70 wt.% SiO2) are paradoxically found in thin crust settings, where average compositions are low in silica (basaltic). We suggest that extreme residual magmas, such as those exceeding 70 wt.% SiO2, are preferentially extracted from shallow crustal magma bodies than from deep-seated magma bodies, the latter more commonly found in regions of thick crust. We suggest that this may be because the convective lifespan of crustal magma bodies is limited by conductive cooling through the overlying crustal lid and that magma bodies in thick crust cool more slowly than in thin crust. When the crust is thin, cooling is rapid, preventing residual magmas

  10. Magnetic crustal thickness in Greenland from CHAMP and Ørsted data

    DEFF Research Database (Denmark)

    Maule, Cathrine Fox; Purucker, Michael E.; Olsen, Nils

    2005-01-01

    The magnetic crustal thickness of Greenland and the surrounding area is determined by inversion of gridded values of the magnetic radial component as given by the IDEMM model, which is based on CHAMP and Ørsted data alone, and by the Comprehensive Model (CM4), which is based on satellite and obse......The magnetic crustal thickness of Greenland and the surrounding area is determined by inversion of gridded values of the magnetic radial component as given by the IDEMM model, which is based on CHAMP and Ørsted data alone, and by the Comprehensive Model (CM4), which is based on satellite...

  11. Crustal growth of the Izu-Ogasawara arc estimated from structural characteristics of Oligocene arc

    Science.gov (United States)

    Takahashi, N.; Yamashita, M.; Kodaira, S.; Miura, S.; Sato, T.; No, T.; Tatsumi, Y.

    2011-12-01

    Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out seismic surveys using a multichannel reflection system and ocean bottom seismographs, and we have clarified crustal structures of whole Izu-Ogasawara (Bonin)-Marina (IBM) arc since 2002. These refection images and velocity structures suggest that the crustal evolution in the intra-oceanic island arc accompanies with much interaction of materials between crust and mantle. Slow mantle velocity identified beneath the thick arc crusts suggests that dense crustal materials transformed into the mantle. On the other hand, high velocity lower crust can be seen around the bottom of the crust beneath the rifted region, and it suggests that underplating of mafic materials occurs there. Average crustal production rate of the entire arc is larger than expected one and approximately 200 km3/km/Ma. The production rate of basaltic magmas corresponds to that of oceanic ridge. Repeated crustal differentiation is indispensable to produce much light materials like continental materials, however, the real process cannot still be resolved yet. We, therefore, submitted drilling proposals to obtain in-situ middle crust with P-wave velocity of 6 km/s. In the growth history of the IBM arc, it is known by many papers that boninitic volcanisms preceded current bimodal volcanisms based on basaltic magmas. The current volcanisms accompanied with basaltic magmas have been occurred since Oligocene age, however, the tectonic differences to develop crustal architecture between Oligocene and present are not understood yet. We obtained new refraction/reflection data along an arc strike of N-S in fore-arc region. Then, we estimate crustal structure with severe change of the crustal thickness from refraction data, which are similar to that along the volcanic front. Interval for location of the thick arc crust along N-S is very similar to that along the volcanic front. The refection image indicates that the basement of the fore

  12. Crustal structure of western Hispaniola (Haiti) from a teleseismic receiver function study

    Science.gov (United States)

    Corbeau, J.; Rolandone, F.; Leroy, S.; Guerrier, K.; Keir, D.; Stuart, G.; Clouard, V.; Gallacher, R.; Ulysse, S.; Boisson, D.; Bien-aimé Momplaisir, R.; Saint Preux, F.; Prépetit, C.; Saurel, J.-M.; Mercier de Lépinay, B.; Meyer, B.

    2017-07-01

    Haiti, located at the northern Caribbean plate boundary, records a geological history of terrane accretion from Cretaceous island arc formations to the Eocene to Recent oblique collision with the Bahamas platform. Little is presently known about the underlying crustal structure of the island. We analyze P-waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in Haiti to determine the crustal structure of western Hispaniola. We compute teleseismic receiver functions using the Extended-Time Multi-Taper method and determine crustal thickness and bulk composition (Vp/Vs) using the H-k stacking method. Three distinctive and fault-bounded crustal domains, defined by their characteristic Moho depth distributions and bulk crustal Vp/Vs, are imaged across Haiti. We relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the Caribbean plate and are presently being deformed in a localized fold and thrust belt. In the northern domain, made up of volcanic arc facies, the crust has a thickness of 23 km and Vp/Vs of 1.75 ± 0.1 typical of average continental crust. The crust in the southern domain is part of the Caribbean Large Igneous Province (Caribbean LIP), and is 22 km thick with Vp/Vs of 1.80 ± 0.03 consistent with plume-related rocks of late Cretaceous age. Significantly thicker, the crust in central Haiti has values of Moho depths averaging 41 km and with Vp/Vs of 1.80 ± 0.05. We propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or LIP material. We produce a crustal profile along a N-S transect across Haiti accounting for the surface geology, shallow structural history, and new seismological constraints provided by variations of crustal thickness and bulk composition.

  13. Crustal Thickness and Structure in Southern Chile: Patagonia plate assembly structures and continental arc modifications

    Science.gov (United States)

    Rodriguez, E. E.; Russo, R. M.

    2016-12-01

    Crustal structure is the product of the processes that operated during a region's tectonic history. For Patagonia, these tectonic processes include its early Paleozoic assembly and accretion to the South America portion of Gondwana, Triassic rifting of Gondwana, and a long history as the upper plate during oceanic subduction since the Mesozoic. To assess the crustal structure and glean insight into how these tectonic processes affected the region, we combined data from two seismic networks, the Chile Ridge Subduction Project and Seismic Experiment of Aisen Chile - yielding a total of 77 broadband seismic stations - deployed from 2004 to 2007. The stations were concentrated 300 km inboard of the Chile trench, above structures unlikely to have been affected by ongoing Chile Ridge subduction. Events suitable for receiver function (RF) analyses (M > 5.9, of various backazimuths, epicentral distances of 30 - 90°) yielded 995 radial RFs, constructed using iterative time deconvolution (Ligorria and Ammon, 1999). We estimated crustal thicknesses and compressional to shear wave velocity ratios (Vp/Vs) using the H-k grid search method (Zhu and Kanamori, 2000); common conversion point (CCP) stacking (Zhu, et al., 2006) allowed imaging of crustal structure. Results limit crustal thicknesses to between 30 and 45 km. The crust varies smoothly from 30 km at the N margin of our study area ( 43°S) to a max depth of 45 km at 44.75°S, shallowing to 30 km at 49°S. On E-W CCP sections north of 46°S, the Moho dips westward, from a depth of 35 at 71°W to 45 km at its deepest near 72.75°W. Beneath the active Southern Volcanic Zone, which is bounded to the west by the Liquiñe-Ofqui fault, the Moho is ambiguous, producing unclear Ps phases possibly reflecting a lack of sharp impedance contrast or poor conversion efficiency at the base of the crust, perhaps due to deep-seated volcanic arc processes. The proximity of the Liquiñe-Ofqui strike-slip fault may also complicate the

  14. Vertical crustal movements in Southern California, 1974 to 1978

    Science.gov (United States)

    Burford, R.O.; Gilmore, Thomas D.

    1984-01-01

    An extensive resurvey of most of the first-order leveling network in southern California, known as the Southern California Releveling Program (SCRP), was carried out during the first 5 months of 1978. The primary scientific purpose of these measurements was to rapidly update the vertical control record throughout a recently uplifted region of southern California in order to more thoroughly document the vertical component of tectonic movement and to provide a reliable base for comparison with future levelings. Analyses of historic first-order leveling results have clearly demonstrated that a broad crustal upwarping, largely contained within a region consisting of the Transverse Ranges province and an area along the intervening section of the San Andreas fault system, had developed between about 1959 and 1974. Unfortunately, there is strong evidence that parts of the 1978 SCRP data are contaminated by the effects of intrasurvey tectonic deformation, limited surficial failures, and, less certainly, magnetically induced systematic error associated with the use of automatic levels. However, any distortions in leveling results caused by these or other factors are not so serious as to render the SCRP data useless. In fact, the bulk of these data can be accepted at face value, and most of the remaining data can be incorporated with some caution to augment the more reliable parts of the network. The evaluation of the 1978 leveling is based on a combination of circuit-misclosures, local timing of the field observations, analysis of profiles of apparent height changes derived from comparisons with previous levelings, and an analysis of the position and orientation of the various routes in relation to the regional structural grain and the gradients of differential vertical motion established by previous investigations. Comparisons of the 1978 SCRP results with the latest of the previous surveys along each route retained in the analysis show that all but about one-third of the

  15. Crustal evolution at mantle depths constrained from Pamir xenoliths

    Science.gov (United States)

    Kooijman, E.; Hacker, B. R.; Smit, M. A.; Kylander-Clark, A. R.; Ratschbacher, L.

    2012-12-01

    Lower crustal xenoliths erupted in the Pamir at ~11 Ma provide an exclusive opportunity to study the evolution of crust at mantle depths during a continent-continent collision. To investigate, and constrain the timing of, the petrologic processes that occurred during burial to the peak conditions (2.5-2.8 GPa, 1000-1100 °C; [1]), we performed chemical- and isotope analyses of accessory minerals in 10 xenoliths, ranging from eclogites to grt-ky-qtz granulites. In situ laser ablation split-stream ICPMS yielded 1) U-Pb ages, Ti concentrations and REE in zircon, 2) U/Th-Pb ages and REE in monazite, and 3) U-Pb ages and trace elements in rutile. In addition, garnet, and biotite and K-feldspar were dated using Lu-Hf and 40Ar/39Ar geochronology, respectively. Zircon and monazite U-(Th-)Pb ages are 101.9±1.8, 53.7±1.0, 39.1±0.8, 21.7±0.4, 18.2±0.5, 16.9±0.8, 15.1±0.3 (2σ) and 12.5-11.1 Ma; most samples showed several or all of these populations. The 53.7 Ma and older ages are xenocrystic or detrital. For younger ages, zircon and monazite in individual samples recorded different ages-although zircon in one rock and monazite in another can be the same age. The 39.1 Ma zircon and monazite mostly occur as inclusions in minerals of the garnet-bearing assemblage that represents the early, low-P stages of burial. Garnet Lu-Hf ages of 37.8±0.3 Ma support garnet growth at this time. Spinifex-like textures containing 21.7-11.1 Ma zircon and monazite record short-lived partial melting events during burial. Aligned kyanite near these patches indicates associated deformation. Zircons yielding ≤12.5 Ma exhibit increased Eu/Eu* and markedly decreased HREE concentrations, interpreted to record feldspar breakdown and omphacite growth during increasing pressure. Rutile U-Pb cooling ages are 10.8±0.3 Ma in all samples. This agrees with the weighted mean 40Ar/39Ar age of eight biotite, K-feldspar and whole rock separates of 11.00+0.16/-0.09 Ma. Rutile in eclogites provides Zr

  16. Evaluating Crustal Contamination Effects On The Lithophile Trace Element Budget Of Shergottites, NWA 856 As A Test Case

    Science.gov (United States)

    Brandon, A. D.; Ferdous, J.; Peslier, A. H.

    2017-01-01

    The issue of whether crustal contamination has affected the lithophile trace element budget of shergottites has been a point of contention for decades. The evaluation has focused on the enriched shergottite compositions as an outcome of crustal contamination of mantle-derived parent magmas or, alternatively, the compositions of these stones reflect an incompatible trace element (ITE) enriched mantle source.

  17. Seasonal crustal seismic velocity changes in Japan from noise-based monitoring

    Science.gov (United States)

    WANG, Q. Y.; Brenguier, F.; Campillo, M.; Lecointre, A.; Takeda, T.; Aoki, Y.; Longuevergne, L.

    2016-12-01

    The general framework of this work is to study how environmental seasonal perturbations impact the solid Earth in an active tectonic region. For this purpose we continuously monitor crustal seismic velocity changes using noise-based monitoring over the entire Japan. We perform a massive data analysis of the continuous seismic records of the very dense Hi-net short-period network (800 stations) from 2008 to 2012. When mapping seasonal velocity changes over the entire Japan we find large anomalies in the southern Kyushu island and in the Northern Hokkaido island. Transient seasonal crustal drops of seismic velocity in Kyushu are well explained by a model of pore pressure increase induced by heavy precipitation in summer during typhoon period. The other large seasonal anomaly located in Eastern Hokkaido (North Japan) shows both an effect of increased pore pressure during precipitation in summer (velocity decrease) and of closure of crustal cracks in winter (velocity increase) explained by both the effects of snow loading and pore pressure decrease by water drainage. The response of the crust in western Japan (Hokkaido and Honshu) is more enigmatic as it shows a very small sensitivity to both precipitation and snow loads effects. Finally, we show how better understanding these environmentally induced crustal perturbations improves our observations of tectonic-induced seismic property changes in the special case of the M9, 2011, Tohoku-Oki earthquake.

  18. Volcanoes: Where and Why? Crustal Evolution Education Project. Teacher's Guide [and] Student Investigation.

    Science.gov (United States)

    Stoever, Edward C., Jr.

    Crustal Evolution Education Project (CEEP) modules were designed to: (1) provide students with the methods and results of continuing investigations into the composition, history, and processes of the earth's crust and the application of this knowledge to man's activities and (2) to be used by teachers with little or no previous background in the…

  19. Electron impact ionization in the Martian atmosphere: Interplay between scattering and crustal magnetic field effects

    Science.gov (United States)

    Lillis, Robert J.; Fang, Xiaohua

    2015-07-01

    Precipitating electrons are typically the dominant source of energy input into Mars' nighttime upper atmosphere, with consequences for atmospheric and ionospheric structure, composition, chemistry, and electrodynamics. Mars' spatially heterogeneous crustal magnetic fields affect the fluxes of precipitating electrons, via both the magnetic mirror force and Gauss' law of conservation of magnetic flux. We use a kinetic electron transport model to examine ionization rate profiles that result from the combination of these magnetic effects and elastic and inelastic scattering by atmospheric neutrals. Specifically, we calculate ionization rates as a function of altitude, crustal magnetic field strength, and the initial energy and pitch angle of the precipitating electrons, covering the relevant ranges of these parameters. Several complex behaviors are exhibited, including bifurcating ionization peaks with distinct characteristics and energy-dependent and crustal field strength-dependent increases in ionization with decreasing pitch angle. Elucidating such behavior is important for understanding the effect of Mars' unique crustal fields on the Mars upper atmosphere and ionosphere, both to predict the consequences of measured electron precipitation and to enable, for the first time, downward coupling of global plasma models with thermosphere-ionosphere models.

  20. Oceanic crustal carbon cycle drives 26-million-year atmospheric carbon dioxide periodicities.

    Science.gov (United States)

    Müller, R Dietmar; Dutkiewicz, Adriana

    2018-02-01

    Atmospheric carbon dioxide (CO 2 ) data for the last 420 million years (My) show long-term fluctuations related to supercontinent cycles as well as shorter cycles at 26 to 32 My whose origin is unknown. Periodicities of 26 to 30 My occur in diverse geological phenomena including mass extinctions, flood basalt volcanism, ocean anoxic events, deposition of massive evaporites, sequence boundaries, and orogenic events and have previously been linked to an extraterrestrial mechanism. The vast oceanic crustal carbon reservoir is an alternative potential driving force of climate fluctuations at these time scales, with hydrothermal crustal carbon uptake occurring mostly in young crust with a strong dependence on ocean bottom water temperature. We combine a global plate model and oceanic paleo-age grids with estimates of paleo-ocean bottom water temperatures to track the evolution of the oceanic crustal carbon reservoir over the past 230 My. We show that seafloor spreading rates as well as the storage, subduction, and emission of oceanic crustal and mantle CO 2 fluctuate with a period of 26 My. A connection with seafloor spreading rates and equivalent cycles in subduction zone rollback suggests that these periodicities are driven by the dynamics of subduction zone migration. The oceanic crust-mantle carbon cycle is thus a previously overlooked mechanism that connects plate tectonic pulsing with fluctuations in atmospheric carbon and surface environments.

  1. Lithospheric Thickness Variations from Gravity and Topography in Areas of High Crustal Remanent Magnetization on Mars

    Science.gov (United States)

    Smrekar, S. E.; Raymond, C. A.

    2001-01-01

    Large regions of intense crustal re- manent magnetization were fortuitously discovered on Mars by the Mars Global Surveyor (MGS) spacecraft. Gravity and topography admittance studies are used to examine lithospheric structure in the areas of intense magnetization. Areas with positively magnetized crust appear to have thinner crust and elastic lithosphere than negatively magnetized crust. Additional information is contained in the original extended abstract.

  2. Tropics in Antarctica? Crustal Evaluation Education Project. Teacher's Guide [and] Student Investigation.

    Science.gov (United States)

    Stoever, Edward C., Jr.

    Crustal Evolution Education Project (CEEP) modules were designed to: (1) provide students with the methods and results of continuing investigations into the composition, history, and processes of the earth's crust and the application of this knowledge to man's activities and (2) to be used by teachers with little or no previous background in the…

  3. Reconstruction of the pre-breakup crustal thickness in Australia/Antarctica

    Science.gov (United States)

    Goncharov, A.

    2003-04-01

    Some 140 million years ago, Australia and Antarctica were parts of a single continent Gondwana. Before it broke into parts there was a process of extensive crustal extension. Thinning of the crust during this process was accompanied by deposition of vast amounts of sedimentary rocks along Australia’s Southern Margin, where the total sediment thickness locally (e.g., Ceduna Sub-basin) reaches 15 km. These sedimentary rocks may have been involved in oil and gas formation. Knowledge of the pre-breakup crustal thickness in Australia/Antarctica is important because it provides additional constraints for plate tectonic reconstructions of the two continents and ultimately leads to a more accurate assessment of the petroleum potential of Australia’s Southern Margin. Most reliable estimates of crustal thickness come from refraction seismic measurements which define the depth to the Moho boundary, where seismic velocity increases to 8 km/s or more. Such measurements were used in this research for Australia. Unlike Australia, Antarctica has poor coverage of seismic measurements of crustal thickness. For Antarctica, seismic measurements were supplemented by values predicted by the regression between seismically defined crustal thickness and upwardly continued gravity. Upward continuation emphasizes the effects of variations in crustal thickness in the total gravity signal. After compilation and computation of crustal thickness was completed, data points located on Australian continent were reconstructed to their pre-breakup position. The most up-to-date finite rotation parameters defining the movement of Australia relative to Antarctica were used in this process. To ensure that pre-breakup extension and thinning of the crust (during the 140 to 95 Ma time interval) were accounted for, points with crustal thickness values less than 30 km on both Australian and Antarctic margins were excluded from subsequent gridding. Crust thinner than 30 km was taken to have been affected

  4. Magmatic recharge buffers the isotopic compositions against crustal contamination in formation of continental flood basalts

    Science.gov (United States)

    Yu, Xun; Chen, Li-Hui; Zeng, Gang

    2017-07-01

    Isotopic compositions of continental flood basalts are essential to understand their genesis and to constrain the character of their mantle sources. Because of potential crustal contamination, it needs to be evaluated if and to which degree these basalts record original isotopic signals of their mantle sources and/or crustal signatures. This study examines the Sr, Nd, Hf, and Pb isotopic compositions of the late Cenozoic Xinchang-Shengzhou (XS) flood basalts, a small-scale continental flood basalt field in eastern China. The basalts show positive correlations between 87Sr/86Sr and 143Nd/144Nd, and negative correlations between 143Nd/144Nd and 176Hf/177Hf, which deviate from compositional arrays of crustal contamination and instead highlight variations in magmatic recharge intensity and mantle source compositions. The lava samples formed by high-volume magmatic recharge recorded signals of recycled sediments in the mantle source, which are characterized by moderate Ba/Th (91.9-106.5), excess 208Pb/204Pb relative to 206Pb/204Pb, and excess 176Hf/177Hf relative to 143Nd/144Nd. Thus, we propose that magmatic recharge buffers the original isotopic compositions of magmas against crustal contamination. Identifying and utilizing the isotope systematics of continental flood basalts generated by high volumes of magmatic recharge are thus crucial to trace their mantle sources.

  5. On the geographical distribution of induced time-varying crustal magnetic fields

    DEFF Research Database (Denmark)

    Thebault, E.; Hemant, K.; Hulot, G.

    2009-01-01

    of the Earth's crust. For spherical harmonic degrees 15-90, we estimate the root mean square of the crustal magnetic field secular variation to amount 0.06-0.12 nT/yr at the terrestrial surface between epochs 1960-2002.5. The geographical distribution of the signal shows absolute values reaching 0.65-1.30 n...

  6. A Unified Global Reference Frame of Vertical Crustal Movements by Satellite Laser Ranging

    Directory of Open Access Journals (Sweden)

    Xinhui Zhu

    2016-02-01

    Full Text Available Crustal movement is one of the main factors influencing the change of the Earth system, especially in its vertical direction, which affects people’s daily life through the frequent occurrence of earthquakes, geological disasters, and so on. In order to get a better study and application of the vertical crustal movement,as well as its changes, the foundation and prerequisite areto devise and establish its reference frame; especially, a unified global reference frame is required. Since SLR (satellite laser ranging is one of the most accurate space techniques for monitoring geocentric motion and can directly measure the ground station’s geocentric coordinates and velocities relative to the centre of the Earth’s mass, we proposed to take the vertical velocity of the SLR technique in the ITRF2008 framework as the reference frame of vertical crustal motion, which we defined as the SLR vertical reference frame (SVRF. The systematic bias between other velocity fields and the SVRF was resolved by using the GPS (Global Positioning System and VLBI (very long baseline interferometry velocity observations, and the unity of other velocity fields and SVRF was realized,as well. The results show that it is feasible and suitable to take the SVRF as a reference frame, which has both geophysical meanings and geodetic observations, so we recommend taking the SLR vertical velocity under ITRF2008 as the global reference frame of vertical crustal movement.

  7. Crustal rheology of the Himalaya and Southern Tibet inferred from magnetotelluric data

    Science.gov (United States)

    Unsworth, M. J.; Jones, A. G.; Wei, W.; Marquis, G.; Gokarn, S. G.; Spratt, J. E.; Bedrosian, Paul; Booker, John; Leshou, Chen; Clarke, Greg; Shenghui, Li; Chanhong, Lin; Ming, Deng; Sheng, Jin; Solon, Kurt; Handong, Tan; Ledo, Juanjo; Roberts, Brian

    2005-11-01

    The Cenozoic collision between the Indian and Asian continents formed the Tibetan plateau, beginning about 70million years ago. Since this time, at least 1,400km of convergence has been accommodated by a combination of underthrusting of Indian and Asian lithosphere, crustal shortening, horizontal extrusion and lithospheric delamination. Rocks exposed in the Himalaya show evidence of crustal melting and are thought to have been exhumed by rapid erosion and climatically forced crustal flow. Magnetotelluric data can be used to image subsurface electrical resistivity, a parameter sensitive to the presence of interconnected fluids in the host rock matrix, even at low volume fractions. Here we present magnetotelluric data from the Tibetan-Himalayan orogen from 77°E to 92°E, which show that low resistivity, interpreted as a partially molten layer, is present along at least 1,000km of the southern margin of the Tibetan plateau. The inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in Southern Tibet.

  8. Relaxation of compensated topography and the evolution of crustal plateaus on Venus

    Science.gov (United States)

    Nunes, Daniel Cahn; Phillips, Roger J.; Brown, C. David; Dombard, Andrew J.

    2004-01-01

    Crustal plateaus, dominant physiographic features on Venus, likely originate through dynamic mantle processes, although a debate exists on whether they formed by mantle upwellings or downwellings. Regardless of the mode of formation, several observations led to the hypothesis that viscous relaxation may be the driving force behind the apparent evolutionary sequence from a high-standing plateau to a low-standing plateau with elevated margins. We apply analytic and finite element models to test this hypothesis for isostatically compensated topography, as modeling of gravity data suggests that crustal plateaus are presently supported by crustal roots. Geotherm values combined with a surface temperature of 740 K preclude relaxation within 109 years, while geotherm values >=20 K km-1 can yield relaxation times of 108 years or less. Hence significant relaxation requires hot conditions in order to occur within the appropriate 1-Gyr timescale set by crustal plateau ages. We also show that a compensated plateau can either retain its shape as it relaxes or become more domical in appearance. Mantle temperatures plateau and produces domical relaxed profiles. Higher temperatures lead to a relatively inviscid mantle and relaxation that is largely insensitive to topographic wavelength, thus preserving the original topographic shape during relaxation. In either case, relaxation of compensated plateaus does not yield elevated rims. We propose that the state of compensation must be considered variable.

  9. New images of the crustal structure beneath eastern Tibet from a high-density seismic array

    Science.gov (United States)

    Liu, Zhen; Tian, Xiaobo; Gao, Rui; Wang, Gaochun; Wu, Zhenbo; Zhou, Beibei; Tan, Ping; Nie, Shitan; Yu, Guiping; Zhu, Gaohua; Xu, Xiao

    2017-12-01

    An east-west trending, high-density seismic array was deployed along the eastern margin of the Tibetan Plateau to investigate its eastward expansion. The 160 km long array spans the Ruoergai basin, Minjiang fault, Minshan Mountains, Tazang fault, and West Qinling. The array included 330 short-period seismographs spaced at 500 m intervals, which recorded teleseismic 3-component waveforms over a one month period. P-wave receiver functions calculated from 35 teleseismic events provided an image of crustal structure. The results show a massive thrust nappe structure around the Minshan Mountains and beneath the Minjiang fault. We suggest that this nappe formed after the closure of the Paleo-Tethyan ocean. The resultant Triassic thrusting contributed to partial uplift of the eastern Ruoergai basin and the Minshan Mountains in middle-to-late Miocene time. Receiver function images show that the Tazang fault is a crustal-scale rupture cutting across the Moho. The western Tazang fault appears as a nearly vertical strike-slip fault accommodating left lateral shear at the terminus of the eastern Kunlun fault. After clockwise rotation from an approximate east-west orientation to a nearly north-south orientation, the eastern Tazang fault became a west-dipping thrust fault, which caused crustal thickening beneath the Minshan Mountains and the West Qinling. Our results suggest that late Cenozoic uplift of the eastern margin of the plateau is produced by eastward overthrusting and crustal shortening, processes that absorbed slip along the Tazang and Kunlun faults.

  10. High resolution regional crustal models from irregularly distributed data: application to Asia and adjacent areas

    NARCIS (Netherlands)

    Stolk, W.; Kaban, M.K.; Beekman, F.; Tesauro, M.; Mooney, W.D.; Cloetingh, S.

    2013-01-01

    We propose a new methodology to obtain crustal models in areas where data is sparse and data spreading is heterogeneous. This new method involves both interpolating the depth to the Moho discontinuity between observations and estimating a velocity–depth curve for the crust at each interpolation

  11. Crustal thickness, discontinuity depth, and upper mantle structure beneath southern Africa: constraints from body wave conversions

    NARCIS (Netherlands)

    Stankiewicz, Jacek; Che, Sébastien; Hilst, R.D. van der; Wit, Maarten J. de

    2002-01-01

    The technique of receiver function analysis is applied to the study of crustal and upper mantle structures beneath the Kaapvaal craton in southern Africa and its surroundings. Seismic data were recorded by the seismic array of 82 sites deployed from April 1997 to April 1999 across southern Africa,

  12. A crustal thickness map of Africa derived from a global gravity field model using Euler deconvolution

    NARCIS (Netherlands)

    Tedla, G.E.; Meijde, M. van der; Nyblade, A.A.; Meer, F.D. van der

    2011-01-01

    We develop a new continental scale crustal model for Africa by modelling the free-air gravity anomaly EIGEN-GL04C, which was developed from 30 months of GRACE Level 1B data covering the period from 2003 February to 2005 July, and surface gravity data from seven different sources. From this gravity

  13. Global maps of the CRUST 2.0 crustal components stripped gravity disturbances

    NARCIS (Netherlands)

    Tenzer, R.; Hamayun, K.; Vajda, P.

    2009-01-01

    We use the CRUST 2.0 crustal model and the EGM08 geopotential model to compile global maps of the gravity disturbances corrected for the gravitational effects (attractions) of the topography and of the density contrasts of the oceans, sediments, ice, and the remaining crust down to the Moho

  14. The Crustal Thickness of the Philippine Sea Plate Derived from Gravity Data

    Directory of Open Access Journals (Sweden)

    Horng-Yuan Yen

    2015-01-01

    Full Text Available We constructed a new free-air gravity anomaly map of the Philippine Sea Plate (PSP using ship-tracked gravity data from the National Geophysical Data Center (NGDC. Our results show that the isogals trend correlates well with the tectonic structures in the PSP. After removing the gravity induced by sea water from the free-air gravity data, we obtained the regional Bouguer gravity anomaly, which is later used to compute the Moho geometry in the PSP by applying the Parker-Oldenburg iterative method. Our results indicate that in the southern part of the West Philippine Basin (WPB the crustal thickness is nearly homogeneous with a value of about 5 km, which implies that the WPB is quite stable. The low-amplitude and near-zero free-air gravity anomalies clearly indicate that the whole WPB, except at trenches and island arcs, is nearly in a state of isostatic equilibrium. The average crustal thickness of the Palau Kyushu Ridge (PKR is more than 10 km. In the eastern PSP the crustal thickness gradually increases eastward. Our results also imply that a relatively thin and low density mantle exists beneath the Parece Vela Basin (PVB as a consequence of back-arc spreading and serpentinized upwells of the thin crustal thickness.

  15. Existence of torsional surface waves in an earth's crustal layer lying ...

    Indian Academy of Sciences (India)

    This paper aims to study the dispersion of torsional surface waves in a crustal layer being sandwiched between a rigid boundary plane and a sandy mantle. In the mantle, rigidity and initial stress vary linearly while density remains constant. Dispersion relation has been deduced in a closed form by means of variable ...

  16. Crustal thickness mapping in Raipur–Katni area of Narmada–Son ...

    Indian Academy of Sciences (India)

    is seismically active and geologically complex with different geological formations. Magnetic data divides the area into two ... era (Ravi Shanker 1988). NSL is a sub-crustal fea- .... Figure 1. Map of the surface geology with various formations along with Narmada, Son and Ken Rivers (after Geological. Survey of India 1993).

  17. From the Surface Topography to the Upper Mantle, Seismic constraints on the Crustal structure Across Morocco

    Science.gov (United States)

    Carbonell, Ramon; Díaz, Jordi; Gallart, Josep; Gil, Alba; Ayarza, Puy; Palomeras, Immaculada; Levander, Alan; Marti, David; Harnafi, Mimoun

    2015-04-01

    The most characteristic topographic features of Morocco are the Atlas Mountains and the Rif Coordillera. These two orogenic belts are the response of different geodynamic processes acting at lithospheric scale caused by a unique driver, the collision between two tectonic plates. Both are located within the diffuse plate boundary zone separating Africa and Europe. The boundary zone is characterized by a relatively broad zone of deformation that includes Mountain chains in southern Iberia, the Betics and the Rif cordillera in Morocco. The zone delineates the arcuate arc system of Gribraltar. Within the last decade a large international effort have been devoted to the area mostly leaded by Spanish groups with the collaboration of international research teams (including scientist form Europe and USA). Key multi-seismic projects have been developed that aim to constrain the structure, composition and tectonic scenario from south of the Atlas to the Betics, across the Rif cordillera and the Alboran basin. The multidisciplinary research program includes: natural source (earthquakes) recording with temporal deployments of broad band (BB) instrumentation and, controlled source seismic acquisition experiments where, spatially dense recording of wide-angle seismic reflection shot gathers were acquired. The passive experiments consisted on: a transect from Merzouga across the Gibraltar arc and into the Iberian peninsula (untill south of Toledo); a nearly regular grid of BB which was achieve by multiple deployments of a number of BB. The controlled source datasets were able to constrain the crustal structure and provide seismic P-wave propagation velocity models from the coast across the Rif and the Atlas. Travel-time inversion of the controlled source seismic data across the Atlas constraints a crustal root to the south of the High Atlas, and reveals mantle wedge. A limited crustal imbrication also appears in the Middle Atlas. The crustal thickness, does not exceeded 40 km in

  18. Crustal Structure Beneath India and Tibet: New Constraints From Inversion of Receiver Functions

    Science.gov (United States)

    Singh, Arun; Ravi Kumar, M.; Mohanty, Debasis D.; Singh, Chandrani; Biswas, Rahul; Srinagesh, D.

    2017-10-01

    The Indian subcontinent comprises geological terranes of varied age and structural character. In this study, we provide new constraints to existing crustal models by inverting the P-to-s receiver functions (RFs) at 317 broadband seismic stations. Inversion results fill crucial gaps in existing velocity models (CRUST1.0 and SEAPS) by capturing regions which are less represented. The final model produced is much more heterogeneous and is able to capture the structural variations between closely spaced seismic stations. In comparison to the global models, major differences are seen for seismic stations located over various rift zones (e.g., Godavari, Narmada, and Cambay) and those close to the coastal regions where transition from oceanic to continental crust is expected to create drastic changes in the crustal configuration. Seismic images are produced along various profiles using 49,682 individual RFs recorded at 442 seismic stations. Lateral variations captured using migrated images across the Himalayan collisional front revealed the hitherto elusive southern extent of the Moho and intracrustal features south of the Main Central Thrust (MCT). Poisson's ratio and crustal thickness estimates obtained using H-k stacking technique and inversion of RFs are grossly similar lending credence to the robustness of inversions. An updated crustal thickness map produced using 1,525 individual data points from controlled source seismics and RFs reveals a (a) thickened crust (>55 km) at the boundary of Dharwar Craton and Southern Granulite Terrain, (b) clear difference in crustal thickness estimates between Eastern Dharwar Craton and Western Dharwar Craton, (c) thinner crust beneath Cambay Basin between southwest Deccan Volcanic Province and Delhi-Aravalli Fold Belt, (d) thinner crust (40 km) beneath paleorift zones like Narmada Son Lineament and Godavari Graben, and (f) very thick crust beneath central Tibet (>65 km) with maximum lateral variations along the Himalayan collision

  19. Reconstructing the Mid-Tertiary Southwestern North America Cordilleran Crust: Crustal Anisotropy

    Science.gov (United States)

    Porter, R. C.; Zandt, G.; McQuarrie, N.; Gilbert, H. J.; Hacker, B. R.

    2009-12-01

    The deployment of EarthScope USArray stations provides researchers with unprecedented quantities and coverage of publicly available seismic data that can be combined with other techniques to better understand the tectonic evolution of western North America. We utilize the receiver function method to map the crustal thickness and investigate the occurrence and orientation of lower crustal anisotropy for the southwestern U.S. Using the tectonic reconstruction of McQuarrie and Wernicke (2005), we then reconstruct the location and orientation of the anisotropy back to 36 Ma. We have completed the reconstruction for central and southern California, and found a dominant SW-NE oriented trend that we interpret as a fossilized fabric within underplated schists created from top-to-southwest sense of shear that existed along the length of coastal California during pre-transform, early-Tertiary subduction. Initial results from the Basin and Range show a generally consistent E-W anisotropy trend within the northern and central Basin and Range, orthogonal to modern faulting and mountain ranges. Within this area there is a correlation of generally stronger crustal anisotropy and thinner crust in the eastern Basin and Range. In the southern Basin and Range we observe more scatter in our anisotropy results, with a majority of stations exhibiting either a SW-NE or NNW-SSE orientation. Despite the variability in results, most anisotropy orientations appear to be orthogonal to nearby mountain ranges. These observations suggest that Tertiary extension in the Basin and Range is producing a lower crustal zone of anisotropy throughout the province. We are currently working to expand on these results by integrating elasticity tensors calculated from electron-backscatter diffraction measurements of samples of lower crustal rocks from the southwestern U.S.

  20. Three-dimensional seismic model of crustal structure in Southern Norway

    Science.gov (United States)

    Loidl, B.; Behm, M.; Thybo, H.; Stratford, W.

    2014-03-01

    New insights in crustal structure in southern Norway are given by combining stacking techniques and traveltime tomography of 3-D wide-angle reflection/refraction data. The Magnus Rex crustal scale wide-angle refraction/reflection data set in Southern Norway covers an area of 400 km × 430 km where 716 receivers on three profiles recorded seismic waves from 26 explosive sources. Previous data analysis focused on 2-D interpretation along the profiles. Here we extract additional P-wave velocity information by inverting inline and cross-line data simultaneously. We combine stacking routines, traveltime tomography, and interpolation algorithms to the high quality inline and cross-line data. A smooth 3-D crustal velocity model is inverted from traveltimes of diving Pg waves with similar results for two initial models. Initial models include a 1-D average model and an interpolated 3-D model based on robust, local 1-D velocity-depth functions derived from CMP-sorted and stacked records. The depth to Moho is determined from reflected waves (PmP) by traditional exploration seismology processing routines (CMP sorting, NMO correction, stacking, depth conversion). We find that this combination of stacking methods and traveltime tomography is well suited to exploit sparse 3-D wide-angle data. The results along the profiles are similar to the earlier 2-D models and the 3-D velocity model shows little lateral variation. The crust in SW Norway is generally 35-40 km thick and has relatively low average velocity, as it lacks the characteristic high-velocity lower crust, otherwise observed in the Baltic Shield. However, the Oslo Graben is characterized by high crustal velocities and a slightly elevated Moho. Our results suggest that this crustal structure continues towards the north along the strike of the graben.

  1. Evaluation of six NEHRP B/C crustal amplification models proposed for use in western North America

    Science.gov (United States)

    Boore, David; Campbell, Kenneth W.

    2016-01-01

    We evaluate six crustal amplification models based on National Earthquake Hazards Reduction Program (NEHRP) B/C crustal profiles proposed for use in western North America (WNA) and often used in other active crustal regions where crustal properties are unknown. One of the models is based on an interpolation of generic rock velocity profiles previously proposed for WNA and central and eastern North America (CENA), in conjunction with material densities based on an updated velocity–density relationship. A second model is based on the velocity profile used to develop amplification factors for the Next Generation Attenuation (NGA)‐West2 project. A third model is based on a near‐surface velocity profile developed from the NGA‐West2 site database. A fourth model is based on velocity and density profiles originally proposed for use in CENA but recently used to represent crustal properties in California. We propose two alternatives to this latter model that more closely represent WNA crustal properties. We adopt a value of site attenuation (κ0) for each model that is either recommended by the author of the model or proposed by us. Stochastic simulation is used to evaluate the Fourier amplification factors and their impact on response spectra associated with each model. Based on this evaluation, we conclude that among the available models evaluated in this study the NEHRP B/C amplification model of Boore (2016) best represents median crustal amplification in WNA, although the amplification models based on the crustal profiles of Kamai et al. (2013, 2016, unpublished manuscript, see Data and Resources) and Yenier and Atkinson (2015), the latter adjusted to WNA crustal properties, can be used to represent epistemic uncertainty.

  2. Sink or Swim? the Role of Intracrustal Differentiation in the Generation of Compositional Diversity and Crustal Delamination in the Archean

    Science.gov (United States)

    VanTongeren, J. A.; Herzberg, C. T.; Kaus, B.; Johnson, T. E.; Brown, M.

    2014-12-01

    Significant debate exists regarding the processes of crustal formation and stabilization in the Archean, with some researchers advocating for continuous subduction-like processes throughout earth history, and others advocating crustal recycling by lithospheric delamination or 'drip tectonics'. Much of the debate hinges on whether Archean mantle potential temperatures (Tp) were significantly hotter than the present day. The rock record of non-arc Archean primary magma compositions (Herzberg et al., 2010) has been used to infer higher ambient Tp (Tp = 1500-1650C) during the Archean, causing high melt fractions during decompression melting, and leading to extreme primary (oceanic) crustal thicknesses of 30-40 km (Herzberg and Rudnick, 2012). Such crustal thicknesses might inhibit subduction, in which case an alternative mechanism of crustal recycling would be required. In their recent paper, Johnson et al. (2014) showed that at Tp > 1500C, the lower portions of a thick homogenous Archean primary crust generated would be density unstable with respect to the ambient mantle. Additionally, they showed that given realistic rheological constraints, large-scale lower crustal delamination is a very efficient crustal recycling mechanism at Tp >1600C. The Archean crust, however, is likely to be internally differentiated. Here we present pMELTS and Perple_X modeling results on the intracrustal differentiation of Archean primary crust, resulting in the formation of TTG-like granitoids in the upper crust and a lower crust dominated by clinopyroxenite. Using the composition and density profiles generated by intracrustal differentiation, our geodynamic modeling extends the Tp over which efficient crustal delamination will occur to lower values, consistent with those likely throughout the Archean. Efficient crustal differentiation and delamination of dense mafic residues throughout the Archean may explain the apparent paucity of mafic lithologies relative to TTGs that characterize

  3. Crustal structure of the Siberian craton and the West Siberian basin: An appraisal of existing seismic data

    DEFF Research Database (Denmark)

    Cherepanova, Yulia; Artemieva, Irina M.; Thybo, Hans

    2013-01-01

    We present a digital model SibCrust of the crustal structure of the Siberian craton (SC) and the West Siberian basin (WSB), based on all seismic profiles published since 1960 and sampled with a nominal interval of 50 km. Data quality is assessed and quantitatively assigned to each profile based...... on acquisition and interpretation method and completeness of crustal model. The database represents major improvement in coverage and resolution and includes depth to Moho, thickness and average P-wave velocity of five crustal layers (sediments, and upper, middle, lower, and lowermost crust) and Pn velocity...

  4. Crustal Deformation Field Around Rift Zone In Southeastern Afar Derived From Jers-1/in-sar

    Science.gov (United States)

    Ozawa, T.; Nogi, Y.; Shibuya, K.

    Afar is one of the major active rift zones recognized on the ground and located around the triple junction of Arabia, Somalia and Nubian plates. Afar is one of the major rift zones recognized on the ground. The crustal deformation of Afar has been deduced from paleomagnetism, geology and seismology by many scientists. The current crustal deformation must be detected by geodetic measurements. Ruegg et al. (J. Geophys. Res., 1984) showed the crustal deformation across the Asal-Ghoubbet rift with rate of about 60 mm/yr extension derived from triangulation and trilateration. Walpersdorf et al. (J. Geodyn., 1999) show the opening between South Djibouti and Yemen with rate of 16 mm/yr by GPS surveys. Denser observations are required for detailed crustal deformation, however it is difficult to construct such observation network because of harsh environment. The geodetic application of remote sensing is useful in this region, and we apply JERS-1 SAR interferometry in southeastern Afar, which is one of the most active deformation area. In this study, we use six SAR scenes observed from 1996/5/20 to 1997/5/7, and generate five interferograms; these repeat cycles are 88 (2 pairs), 176, 264, 352 days. First, we generate the digital elevation model (DEM) from two 88 repeat cycle pairs applying the multiple pass SAR interferometry method by Kwok and Fahnestock (IEEE Trans. Geosci. Remote Sensing, 1996). Next, the topographic fringes of all pairs are removed using the DEM. The crustal deformation derived from SAR interferometry increases with expanding repeat cycle. Finally, the velocity field is estimated by fitting to linear trend for each pixel. The spreading rate of Asal-Ghoubbet rift derived from SAR interferometry is good agreement with that by Ruegg et al. (J. Geophys. Res., 1984). We can see the crustal deformation with the subsidence sense in the west of Asal-Ghoubbet rift. This suggests that the extension is distinguished in this area. The subsidence sense deformation

  5. An Inversion of Gravity and Topography for Mantle and Crustal Structure on Mars

    Science.gov (United States)

    Kiefer, Walter S.; Bills, Bruce G.; Nerem, R. Steven

    1996-01-01

    Analysis of the gravity and topography of Mars presently provides our primary quantitative constraints on the internal structure of Mars. We present an inversion of the long-wavelength (harmonic degree less than or equal to 10) gravity and topography of Mars for lateral variations of mantle temperature and crustal thickness. Our formulation incorporates both viscous mantle flow (which most prior studies have neglected) and isostatically compensated density anomalies in the crust and lithosphere. Our nominal model has a 150-km-thick high-viscosity surface layer over an isoviscous mantle, with a core radius of 1840 km. It predicts lateral temperature variations of up to a few hundred degrees Kelvin relative to the mean mantle temperature, with high temperature under Tharsis and to a lesser extent under Elysium and cool temperatures elsewhere. Surprisingly, the model predicts crustal thinning beneath Tharsis. If correct, this implies that thinning of the crust by mantle shear stresses dominates over thickening of the crust by volcanism. The major impact basins (Hellas, Argyre, Isidis, Chryse, and Utopia) are regions of crustal thinning, as expected. Utopia is also predicted to be a region of hot mantle, which is hard to reconcile with the surface geology. An alternative model for Utopia treats it as a mascon basin. The Utopia gravity anomaly is consistent with the presence of a 1.2 to 1.6 km thick layer of uncompensated basalt, in good agreement with geologic arguments about the amount of volcanic fill in this area. The mantle thermal structure is the dominant contributor to the observed geoid in our inversion. The mantle also dominates the topography at the longest wavelengths, but shorter wavelengths (harmonic degrees greater than or equal to 4) are dominated by the crustal structure. Because of the uncertainty about the appropriate numerical values for some of the model's input parameters, we have examined the sensitivity of the model results to the planetary

  6. Numerical model of crustal accretion and cooling rates of fast-spreading mid-ocean ridges

    Directory of Open Access Journals (Sweden)

    P. Machetel

    2013-10-01

    Full Text Available We designed a thermo-mechanical numerical model for fast-spreading mid-ocean ridge with variable viscosity, hydrothermal cooling, latent heat release, sheeted dyke layer, and variable melt intrusion possibilities. The model allows for modulating several accretion possibilities such as the "gabbro glacier" (G, the "sheeted sills" (S or the "mixed shallow and MTZ lenses" (M. These three crustal accretion modes have been explored assuming viscosity contrasts of 2 to 3 orders of magnitude between strong and weak phases and various hydrothermal cooling conditions depending on the cracking temperatures value. Mass conservation (stream-function, momentum (vorticity and temperature equations are solved in 2-D cartesian geometry using 2-D, alternate direction, implicit and semi-implicit finite-difference scheme. In a first step, an Eulerian approach is used solving iteratively the motion and temperature equations until reaching steady states. With this procedure, the temperature patterns and motions that are obtained for the various crustal intrusion modes and hydrothermal cooling hypotheses display significant differences near the mid-ocean ridge axis. In a second step, a Lagrangian approach is used, recording the thermal histories and cooling rates of tracers travelling from the ridge axis to their final emplacements in the crust far from the mid-ocean ridge axis. The results show that the tracer's thermal histories are depending on the temperature patterns and the crustal accretion modes near the mid-ocean ridge axis. The instantaneous cooling rates obtained from these thermal histories betray these discrepancies and might therefore be used to characterize the crustal accretion mode at the ridge axis. These deciphering effects are even more pronounced if we consider the average cooling rates occurring over a prescribed temperature range. Two situations were tested at 1275–1125 °C and 1050–850 °C. The first temperature range covers mainly the

  7. Recent crustal movement and great earthquakes in Qinghai-Tibet sub-plate

    Directory of Open Access Journals (Sweden)

    Guo Liangqian

    2011-08-01

    Full Text Available Crustal movement and incremental-movement data observed repeatedly at GPS stations during 1999–2009 were analyzed to study the effect of two earthquakes of Ms8.1 and Ms8.0 that occurred in 2001 and 2008, respectively, in Qinghai-Tibet sub-plate and its eastern margin. The result revealed certain anomalous pre-earthquake deformation and some large co-seismic changes. Prior to the 2008 Wenchuan Ms8.0 earthquake, the seismogenic Kunlunshan fault zone became a geographic boundary between different regional movements. At the time of the earthquake, there was an average cross-fault crustal shortening of −1.04 m and an average right-lateral strike slip of 0.76 m along the ruptured segment, as well as a strain-energy release of −62. 66 × 10.7.

  8. The use of satellite laser observations in studying the crustal movements

    Directory of Open Access Journals (Sweden)

    Gamal F. Attia

    2012-12-01

    Full Text Available The mutual tectonic displacements of the lithospheric blocks take place within the deep fracture dividing them into hundreds and thousands kilometers long. It is possible to suggest that the reason of the accumulation of considerable local shift deformations is the change of the velocity of the tectonic motion in some or other parts of fractures as a result of different physical, chemical and mechanical processes. Nowadays, the range precision of Satellite Laser Ranging (SLR technique reaches a few millimeters level. Therefore, the space geodesy technique becomes a very important tool in detecting and monitoring recent crustal movements. Regular repeated measurements of the baselines between some stations on different plates give the possibility to construct precise and detail models of crustal movements. In this paper, the length of four baselines between Helwan-SLR station and other four SLR stations are calculated using satellite geodetical technique.

  9. A COMPARISON OF TWO METHODS FADING MEMORY FILTER AND ADAPTIVE KALMAN FILTER IN MONITORING CRUSTAL MOVEMENT

    Directory of Open Access Journals (Sweden)

    Cahit Tağı ÇELİK

    2004-01-01

    Full Text Available Monitoring the Crustal Movement in Geodesy is performed by the deformation survey and analysis. If monitoring the crustal movements involves more than two epochs of survey campaign then from the plate tectonic theory, stations do not move randomly from one epoch to the other, therefore Kalman Filter may be suitable to use. However, if sudden movements happened in the crust in particular earthquake happened, the crust moves very fast in a very short period of time. When Kalman Filter used for monitoring these movements, from associated epoch, for a number of epochs the results may be biased. In the paper, comparison of two methods for elimination of the above mentioned biases have been performed. These methods are Fading Memory Filter and Adaptive Kalman Filter for an unknown bias.

  10. Geomorphology of the Martian Crustal Dichotomy Boundary: Implications for Age and Origin

    Science.gov (United States)

    Irwin, R. P.; Watters, T. R.

    2005-12-01

    The fairly abrupt decline in surface age, elevation, and crustal thickness from the southern highlands to the northern lowlands of Mars is termed the crustal dichotomy. The cause of northern crustal thinning remains among the major unresolved issues in Mars research. Most geophysical models have invoked degree-1 mantle convection, whereas others suggest plate tectonism or one or more giant impacts in the northern hemisphere. Other studies have focused on modifications to the highland/lowland dichotomy boundary, which may or may not be relevant to the issue of origin. These hypotheses include erosion, extensional faulting, lateral crustal flow, and flexure of an elastic lithosphere by loading of the lowlands. The geomorphology of the highland/lowland boundary region provides important controls for these geophysical models of early crustal development. Geologic observations suggest that the thin lowland crust and dichotomy boundary originated in the Early Noachian Epoch (>4 Ga). The slope within ancient cratered terrain along the boundary influenced post-Noachian fresh crater morphology, Late Noachian valley network planform, and the degradation of Middle to Late Noachian (~3.95-3.7 Ga) impact craters. For fresh (post-Noachian) craters emplaced on the dichotomy slope, the plane of the rim crest inclines subparallel to the exterior slope, although the interior cavity and central peak are oriented vertically, consistent with impacts on a precursor slope. Valleys converge down modern slopes, so the cratered dichotomy slope predates Late Noachian valley development. Degraded craters within the north-sloping cratered and dissected units have floors that are flat or slightly concave, so tilting did not occur after the crater floors were emplaced in Middle Noachian to Early Hesperian time. Most crater floors along the dichotomy boundary are not dissected, as one would expect from an erosional response to Late Noachian tilting, and the few craters with dissected floors have

  11. Espisodic detachment of Martian crustal magnetic fields leading to bulk atmospheric plasma escape

    Energy Technology Data Exchange (ETDEWEB)

    Brain, D A; Baker, A H; Briggs, J; Eastwood, J P; Halekas, J S; Phan, T

    2009-06-02

    We present an analysis of magnetic field and suprathermal electron measurements from the Mars Global Surveyor (MGS) spacecraft that reveals isolated magnetic structures filled with Martian atmospheric plasma located downstream from strong crustal magnetic fields with respect to the flowing solar wind. The structures are characterized by magnetic field enhancements and rotations characteristic of magnetic flux ropes, and characteristic ionospheric electron energy distributions with angular distributions distinct from surrounding regions. These observations indicate that significant amounts of atmosphere are intermittently being carried away from Mars by a bulk removal process: the top portions of crustal field loops are stretched through interaction with the solar wind and detach via magnetic reconnection. This process occurs frequently and may account for as much as 10% of the total present-day ion escape from Mars.

  12. Crustal architecture beneath the Tibet-Ordos transition zone, NE Tibet, and the implications for plateau expansion

    Science.gov (United States)

    Guo, Xiaoyu; Gao, Rui; Wang, Haiyan; Li, Wenhui; Keller, G. R.; Xu, Xiao; Li, Hongqiang; Encarnacion, John

    2015-12-01

    Most previous studies of the Tibetan Plateau have focused on the processes of crustal thickening and subsequent outward growth. However, lithospheric structure across the tectonic boundaries of the plateau has not yet been fully imaged, and therefore, how geological structures evolved in association with the lateral expansion of the margins remains unclear. Here together with interpretation of regional aeromagnetic anomalies, we employ a recently acquired 165 km long deep seismic reflection image that crosses the northeastern flank of the Tibetan Plateau. The resulting crustal "architecture" suggests that crustal shortening is a primary driver for plateau uplift of northeastern Tibet and that the Xiaoguan Shan to the east of the Liupan Shan belt marks the easternmost edge of the strata that has been affected by the northeastward growth of the plateau. In addition, decoupled crustal deformation owing to differential structural integrity has been accommodated during the subsequent northeastward growth of the plateau.

  13. Pulsating continents on Venus: An explanation for crustal plateaus and tessera terrains

    OpenAIRE

    Romeo Briones, Ignacio; Turcotte, Donald L.

    2008-01-01

    We propose that tessera terrains on Venus represent continental crust that does not participate in the periodic recycling of the lithosphere through global subduction events.We have studied the force balance on the boundary of a continental area that survives a global subduction event using an analytical model. In the proposed model, the ratio between the crustal and lithospheric mantle thicknesses controls the force balance. If the crust thickness is less than ∼2/5 of the lithosp...

  14. Crustal structure of the Agulhas Ridge (South Atlantic Ocean): Formation above a hotspot?

    Science.gov (United States)

    Jokat, Wilfried; Hagen, Claudia

    2017-10-01

    The southern South Atlantic Ocean contains several features believed to document the traces of hotspot volcanism during the early formation of the ocean basin, namely the Agulhas Ridge and the Cape Rise seamounts located in the southeast Atlantic between 36°S and 50°S. The Agulhas Ridge parallels the Agulhas-Falkland Fracture Zone, one of the major transform zones of the world. The morphology of the ridge changes dramatically from two parallel segments in the southwest, to the broad plateau-like Agulhas Ridge in the northeast. Because the crustal fabric of the ridge is unknown relating its evolution to hotspots in the southeast Atlantic is an open question. During the RV Polarstern cruise ANT-XXIII-5 seismic reflection and refraction data were collected along a 370 km long profile with 8 Ocean Bottom Stations to investigate its crustal fabric. The profile extends in NNE direction from the Agulhas Basin, 60 km south of the Agulhas Ridge, and continues into the Cape Basin crossing the southernmost of the Cape Rise seamounts. In the Cape Basin we found a crustal thickness of 5.5-7.5 km, and a velocity distribution typical for oceanic crust. The Cape Rise seamounts, however, show a higher velocity in comparison to the surrounding oceanic crust and the Agulhas Ridge. Underplated material is evident below the southernmost of the Cape Rise seamounts. It also has a 5-8% higher density compared to the Agulhas Plateau. The seismic velocities of the Agulhas Ridge are lower, the crustal thickness is approximately 14 km, and age dating of dredge samples from its top provides clear evidence of rejuvenated volcanism at around 26 Ma. Seismic data indicate that although the Cape Rise seamounts formed above a mantle thermal anomaly it had a limited areal extent, whereas the hotspot material that formed the Agulhas Ridge likely erupted along a fracture zone.

  15. Temperature and redox effect on mineral colonization in Juan de Fuca Ridge flank subsurface crustal fluids

    Directory of Open Access Journals (Sweden)

    Jean-Paul eBaquiran

    2016-03-01

    Full Text Available To examine microbe-mineral interactions in subsurface oceanic crust, we evaluated microbial colonization on crustal minerals that were incubated in borehole fluids for one year at the seafloor wellhead of a crustal borehole observatory (IODP Hole U1301A, Juan de Fuca Ridge flank as compared to an experiment that was not exposed to subsurface crustal fluids (at nearby IODP Hole U1301B. In comparison to previous studies at these same sites, this approach allowed assessment of the effects of temperature, fluid chemistry, and/or mineralogy on colonization patterns of different mineral substrates, and an opportunity to verify the approach of deploying colonization experiments at an observatory wellhead at the seafloor instead of within the borehole. The Hole U1301B deployment did not have biofilm growth, based on microscopy and DNA extraction, thereby confirming the integrity of the colonization design against bottom seawater intrusion. In contrast, the Hole U1301A deployment supported biofilms dominated by Epsilonproteobacteria (43.5% of 370 16S rRNA gene clone sequences and Gammaproteobacteria (29.3%. Sequence analysis revealed overlap in microbial communities between different minerals incubated at the Hole U1301A wellhead, indicating that mineralogy did not separate biofilm structure within the one-year colonization experiment. Differences in the Hole U1301A wellhead biofilm community composition relative to previous studies from within the borehole using similar mineral substrates suggest that temperature and the diffusion of dissolved oxygen through plastic components influenced the mineral colonization experiments positioned at the wellhead. This highlights the capacity of low abundance crustal fluid taxa to rapidly establish communities on diverse mineral substrates under changing environmental conditions such as from temperature and oxygen.

  16. Stochastic Stick - Slip Model Linking Crustal Shear Strength and Earthquake Interevent Times

    OpenAIRE

    Dionissios T. Hristopulos; V. Mouslopoulou

    2012-01-01

    The current understanding of the earthquake interevent times distribution (ITD) is incomplete. The Weibull distribution is often used to model the earthquake ITD. We link the earthquake ITD on single faults with the Earth's crustal shear strength distribution by means of a phenomenological stick - slip model. We obtain Weibull ITD for power-law stress accumulation, i.e., $\\sigma(t) = \\alpha t^{\\beta}$, where $\\beta >0$ for single faults or systems with homogeneous strength statistics. We show...

  17. Shallow and deep crustal control on differentiation of calc-alkaline and tholeiitic magma

    Science.gov (United States)

    Hora, John M.; Singer, Brad S.; Wörner, Gerhard; Beard, Brian L.; Jicha, Brian R.; Johnson, Clark M.

    2009-07-01

    The role of changing crustal interaction and plumbing geometry in modulating calc-alkaline vs. tholeiitic magma affinity is well illustrated by the influence of 70 km thick crust beneath Volcán Parinacota. Changes in petrologic affinity correlate with periods of cone-building, sector collapse, and rebuilding of the volcano over the last 52 ka, and are well explained by changes in magma recharge regime. With increasing recharge and magma output, lavas transition from low-Fe, strongly calc-alkaline, phenocryst-rich silicic compositions to medium-Fe, near-tholeiitic, mafic, and aphanitic characteristics. Strontium isotope data show that the change in magma regime did not affect all parts of the system simultaneously; these are characterized by distinctive 87Sr/ 86Sr ratios, which suggest an initially compartmentalized system. Relatively high ( 230Th/ 232Th) activity ratios of ~ 0.72 in early-erupted calc-alkaline lavas are consistent with interaction with high-U upper crust. Low ( 230Th/ 232Th) activity ratios of ~ 0.55 and up to 33% Th-excess in younger near-tholeiitic lavas correlate with steep REE patterns, indicating lower-crustal interaction. Thorium-excesses at the time of eruption approach the maximum that can be generated via small-degree garnet-residual melting in the lower crust or mantle and imply that transit time through the crustal column for the most tholeiitic magmas had to be short, on the order of secular equilibrium, suggesting stagnation times > 3 × 10 5 yr in the upper crust. In addition to more traditional explanations tied to magma source, expression of low-Fe 'calc-alkaline' (CA) vs. medium-Fe 'near-tholeiitic' (TH) magma series at the scale of individual volcanoes is likely to be modulated by transitions from compartmentalized, stagnant, assimilation-prone 'dirty' systems (CA) to 'clean' systems (TH) that are characterized by rapid magma throughput and minimal opportunity for upper-crustal contamination.

  18. The Crustal and Mantle Velocity Structure in Central Asia from 3D Travel Time Tomography

    Science.gov (United States)

    2010-09-01

    that the deformation in the shallow brittle crust occurs on a distributed network of faults, and some regions, such as the Tarim Basin , the Ordos and...Kunlun and the Tarim Basin (Molnar and Tapponnier, 1978). The Main Pamir Thrust has been interpreted to have accommodated about 300 km of crustal...southern Pamir, Kazakh shield, and the Tarim basin . High velocities delineate the subduction zones and active or fossil slabs. The Moho depth in the

  19. Crustal velocity structure of the Deccan Volcanic Province, Indian Peninsula, from observed surface wave dispersion

    Directory of Open Access Journals (Sweden)

    Gaddale Suresh

    2014-08-01

    Full Text Available Through inversion of fundamental mode group velocities of Love and Rayleigh waves, we study the crustal and subcrustal structure across the central Deccan Volcanic Province (DVP, which is one of the world’s largest terrestrial flood basalts. Our analysis is based on broadband seismograms recorded at seismological station Bhopal (BHPL in the central India from earthquakes located near west coast of India, with an average epicentral distance about 768 km. The recording station and epicentral zone are situated respectively on the northern and southern edges of DVP with wave paths across central DVP. The period of group velocity data ranges from 5 to 60 s for Rayleigh waves and 5 to 45 s for Love waves. Using the genetic algorithm, the observed data have been inverted to obtain the crust and subcrustal velocity structure along the wavepaths. Using this procedure, a similar velocity structure was also obtained earlier for the northwestern DVP, which is in the west of the present study region. Comparison of results show that the crustal thickness decreases westward from central DVP (39.6 km to northwestern DVP (37.8 km along with the decrease of thickness of upper crust; while the thickness of lower crust remains nearly same. From east to west S-wave velocity in the upper crust decreases by 2 to 3 per cent, while P-wave velocity in the whole crust and subcrust decreases by 3 to 6 per cent. The P- and S-wave velocities are positively correlated with crustal thickness and negatively correlated with earth’s heat flow. It appears that the elevated crustal and subcrustal temperature in the western side is the main factor for low velocities on this side.

  20. The diverse crustal structure and magmatic evolution of the Manihiki Plateau, central Pacific

    Science.gov (United States)

    Hochmuth, K.; Gohl, K.; Uenzelmann-Neben, G.; Werner, R.

    2014-07-01

    The Manihiki Plateau is a Large Igneous Province (LIP) in the central Pacific. It was emplaced as part of the "Super-LIP" Ontong Java Nui and experienced fragmentation into three sub-plateaus, possibly during the break-up of Ontong Java Nui. The Manihiki Plateau is presumably the centerpiece of this "Super-LIP" and its investigation can therefore decipher the break-up mechanisms as well as the evolution of the plateau after its initial emplacement. By analyzing two seismic refraction/wide-angle reflection profiles crossing the two largest sub-plateaus of the Manihiki Plateau, the High Plateau and the Western Plateaus, we give new insights into their crustal structure and magmatic evolution. The High Plateau shows a crustal structure of 20 km thickness and a seismic P wave velocity distribution, which is comparable to other LIPs. The High Plateau experienced a strong secondary volcanism, which can be seen in relicts of seamount chain volcanism. The Western Plateaus on the other hand show no extensive secondary volcanism and are mainly structured by fault systems and sedimentary basins. A constant decrease in Moho depth (9-17 km) is a further indicator of crustal stretching on the Western Plateaus. Those findings lead to the conclusion, that the two sub-plateaus of the Manihiki Plateau experienced a different magmatic and tectonic history. Whereas the High Plateau experienced a secondary volcanism, the Western Plateaus underwent crustal stretching during and after the break-up of Ontong Java Nui. This indicates, that the sub-plateaus of the Manihiki Plateau play an individual part in the break-up history of Ontong Java Nui.

  1. Influence of crustal fluids on growth and activity of marine deep biosphere microbial populations

    OpenAIRE

    Fichtel, Katja

    2014-01-01

    Like seawater, hydrothermal crustal fluids might support abundance, diversity and activity of microorganisms in marine sediments. The present work shows high numbers of metabolically active microorganisms in deep sediments overlying a midoceanic ridge. Sulfate diffusion from the bedrock fuels microbial sulfate reduction and anaerobic oxidation of methane. From crust-near layers non-sporeforming, sulfate-reducing Deltaproteobacteria were isolated, able to grow chemoheterotrophically, ferme...

  2. High resolution regional crustal models from irregularly distributed data: Application to Asia and adjacent areas

    OpenAIRE

    Stolk, W; Mikhail Kaban; F. Beekman; Magdala Tesauro; Mooney, W.D.; Cloetingh, S.

    2013-01-01

    We propose a new methodology to obtain crustal models in areas where data is sparse and data spreading is heterogeneous. This new method involves both interpolating the depth to the Moho discontinuity between observations and estimating a velocity–depth curve for the crust at each interpolation location. The Moho observations are interpolated using a remove–compute–restore technique, used in for instance geodesy. Observations are corrected first for Airy type isostasy. The residual observatio...

  3. A crustal model for a northeast-southwest profile through Ireland

    Science.gov (United States)

    Jacob, A. W. B.; Kaminski, W.; Murphy, T.; Phillips, W. E. A.; Prodehl, C.

    1985-03-01

    The Irish Caledonian Suture Seismic Project (ICSSP) consisting of a 250 km seismic refraction line was carried out in conjunction with, and as an extension of, the Caledonian Suture Seismic Project (CSSP) of the University of Durham. 51 seismic recording sites at 5 km intervals were deployed on the northwest flank of the Suture Zone in Ireland. Recordings were made from three shot points at the southwest of the line and from 31 shot points of the Durham programme in the North Irish Sea. A crustal model is presented which is based exclusively on a travel-time interpretation. The Pg velocities recorded in eastern Ireland rise quite rapidly with depth to 6.3-6.5 km/s but in the western part of the profile lower velocities between 6.0 and 6.3 km/s were recorded. Prominent energy in later arrivals can be correlated by two reflected phases from a mid-crustal boundary and the Moho. A low-velocity zone is present at the northeastern end of the line and a mid-crustal layer with an average velocity of about 6.4 km/s is separated from the lower crust, mean velocity 6.8 km/s, by a well established mid-crustal boundary zone of 1-2 km thickness at about 20 km depth. The Moho, around 32 km at its deepest, shallows towards the sea at both ends of the line. It is a sharp discontinuity under western Ireland but a transition zone of 3-4 km thickness in the east. An interpretation is given which takes into account (a) the geologic and tectonic history of Ireland and (b) data derived from the gravity and magnetic fields.

  4. Crustal modeling of the central part of the Northern Western Desert, Egypt using gravity data

    Science.gov (United States)

    Alrefaee, H. A.

    2017-05-01

    The Bouguer anomaly map of the central part of the Northern Western Desert, Egypt was used to construct six 2D gravity models to investigate the nature, physical properties and structures of the crust and upper mantle. The crustal models were constrained and constructed by integrating results from different geophysical techniques and available geological information. The depth to the basement surface, from eight wells existed across the study area, and the depth to the Conrad and Moho interfaces as well as physical properties of sediments, basement, crust and upper mantle from previous petrophysical and crustal studies were used to establish the gravity models. Euler deconvolution technique was carried on the Bouguer anomaly map to detect the subsurface fault trends. Edge detection techniques were calculated to outlines the boundaries of subsurface structural features. Basement structural map was interpreted to reveal the subsurface structural setting of the area. The crustal models reveals increasing of gravity field from the south to the north due to northward thinning of the crust. The models reveals also deformed and rugged basement surface with northward depth increasing from 1.6 km to 6 km. In contrast to the basement, the Conrad and Moho interfaces are nearly flat and get shallower northward where the depth to the Conrad or the thickness of the upper crust ranges from 18 km to 21 km while the depth to the Moho (crustal thickness) ranges from 31.5 km to 34 km. The crust beneath the study area is normal continental crust with obvious thinning toward the continental margin at the Mediterranean coast.

  5. Crustal architecture and geodynamics of North Queensland, Australia: Insights from deep seismic reflection profiling

    Science.gov (United States)

    Korsch, R. J.; Huston, D. L.; Henderson, R. A.; Blewett, R. S.; Withnall, I. W.; Fergusson, C. L.; Collins, W. J.; Saygin, E.; Kositcin, N.; Meixner, A. J.; Chopping, R.; Henson, P. A.; Champion, D. C.; Hutton, L. J.; Wormald, R.; Holzschuh, J.; Costelloe, R. D.

    2012-10-01

    A deep crustal seismic reflection and magnetotelluric survey, conducted in 2007, established the architecture and geodynamic framework of north Queensland, Australia. Results based on the interpretation of the deep seismic data include the discovery of a major, west-dipping, Paleoproterozoic (or older) crustal boundary, considered to be an ancient suture zone, separating relatively nonreflective, thick crust of the Mount Isa Province from thinner, two layered crust to the east. Farther to the east, a second major crustal boundary also dips west or southwest, offsetting the Moho and extending below it, and is interpreted as a fossil subduction zone. Across the region, the lower crust is mostly highly reflective and is subdivided into three mappable seismic provinces, but they have not been tracked to the surface. In the east, the Greenvale and Charters Towers Provinces, part of the Thomson Orogen, have been mapped on the surface as two discrete provinces, but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface, and also extend northwards to beneath the Hodgkinson Province, originally forming part of an extensive Neoproterozoic-Cambrian passive margin. Continuation of the Thomson Orogen at depth beneath the Hodgkinson and Broken River Provinces suggests that these provinces (which formed in an oceanic environment, possibly as an accretionary wedge at a convergent margin) have been thrust westwards onto the older continental passive margin. The Tasman Line, originally defined to represent the eastern limit of Precambrian rocks in Australia, has a complicated geometry in three dimensions, which is related to regional deformational events during the Paleozoic. Overall, the seismic data show evidence for a continental margin with a long history (Paleoproterozoic to early Mesozoic) but showing only limited outward growth by crustal accretion, because of a repeated history of overthrust shortening during repeated

  6. Regional Crustal Components of Martian Heat Flow from Mars Odyssey Gamma-Ray Spectrometry (GRS)

    Science.gov (United States)

    Hahn, B. C.; McLennan, S. M.

    2009-12-01

    Martian thermal state and evolution depend principally on the heat-producing element distributions in the planet’s crust and mantle, specifically the incompatible radiogenic isotopes of K, Th, and U. Normally these elements are preferentially sequestered into a planet’s crust during differentiation, and this is especially true for Mars, which possesses a thick and mostly ancient crust that is proportionally large with respect to the planet’s total volume. The Gamma-Ray Spectrometer (GRS) instrument on board the 2001 Mars Odyssey spacecraft can detect all three of these elements and has been used to map the K and Th abundances across nearly the entire Martian surface. It has been estimated that as much as 50% or more of the Martian planetary budget of heat producing elements has seen sequestered into the crust during planetary differentiation due to their incompatibility in igneous processes; a process that mostly took place very early in Martian geological history. As such, the crustal component of heat flow represents as much as half of the total planetary output of radiogenic heat. While GRS measurements can not constrain heat flow from mantle sources, previous work calculated the average crustal component of heat flow of 6.43 mW/m2 based on radiogenic elemental abundances. Orbital GRS data are of lower spatial resolution (5°x5° per pixel) than most other orbital remote sensing instruments and, accordingly, are best suited for global or large, regional-scale studies, rather than detailed, local analyses of geographically small features and landforms. Here we present detailed calculations for specific, areally-large, regions and geologic provinces on Mars, reporting the present-day crustal component of heat flow, the crustal heat flow at time of regional formation, and constraints of geothermal gradients from these measurements.

  7. Crustal structure of the SW Iberian passive margin: The westernmost remnant of the Ligurian Tethys?

    Science.gov (United States)

    Ramos, A.; Fernández, O.; Torne, M.; Sánchez de la Muela, A.; Muñoz, J. A.; Terrinha, P.; Manatschal, G.; Salas, M. C.

    2017-05-01

    At present, the SW Iberian margin is located along the convergent Iberia-Nubia plate boundary. In Mesozoic times, the margin was located at the triple junction of the Ligurian Tethys, Central Atlantic and Northern Atlantic. The characterization of its crustal structure has allowed us to propose a configuration for this triple junction and to determine the role that this transform margin played within the plate kinematic system. In this paper we present an integrated study based on the interpretation of a 2D regional multichannel seismic survey consisting of 58 profiles, tied with onshore geology and exploratory wells, and on gravimetric modeling performed over four NW-SE trending profiles. Integrated interpretation of MCS data combined with 2D gravity modeling reveals a complex pattern in the southward crustal thinning of SW Iberia and supports the possible presence of oceanic crust under the Gulf of Cadiz. The tapering of Iberian crust is characterized by steps with rapid changes in the thickness of the crust, and thinning to Based on gravimetric modeling results and the structures interpreted on reflection seismic profiles, 3 crustal domains reflecting progressive thinning have been defined for the SW Iberian margin. These domains trend roughly WSW-ENE, parallel to the main extensional fabric of the margin. Gravimetric modeling results are compatible with the presence of exhumed sub-continental mantle in the distal part of the margin. Integrated modeling also supports the fact that Cenozoic contraction is responsible for major uplift along the Guadalquivir Bank. Margin inversion and the pre-existing extensional crustal structure are responsible for the areal distribution and amplitude of the prominent positive gravity anomaly observed in the Gulf of Cadiz.

  8. A modified least-squares collocation method for the determination of crustal deformation: first results in the Swiss Alps

    OpenAIRE

    Egli, R.; Geiger, A.; Wiget, A.; Kahle, H.-G

    2017-01-01

    The calculation of recent crustal movements and the associated crustal deformation rely on a suitable interpolation of geodetic measurements with repetition cycles of years or decades and modern GPS permanent networks. A common interpolation methods is the least-square collocation (LSC). LSC requires some a priori assumptions about the characteristics of the velocity field, that is, stocasticity in Moritz's definition of LSC. We present a novel approach, called adaptative LSC (ALSC) to the in...

  9. Three-dimensional crustal deformations and strain field features constrained by dense GPS measurements in Northeastern Tibet

    Science.gov (United States)

    Zhang, Tengxu; Shen, Wen-Bin; Pan, Yuanjin

    2017-04-01

    The ongoing collision between the India plate and Eurasia plate brings N-S crustal shortening and thickening of the Tibetan Plateau. Here, using measurements from 40 Continuous Global Positioning System (CGPS) stations of the Crustal Movement Observation Network of China (CMONOC) we determine the latest three-dimensional crustal deformations in the NET region, and based on the Principal component analysis (PCA) technique we calculate and correct the common mode errors (CME). We also use GRACE observations to determine the deformations caused by surface pressure, non-tidal oceanic mass loading and hydrological loading. We find both GPS and GRACE observations show significant seasonal variation, and the observed seasonal vertical variation exhibits a good agreement with GRACE. The annual peak-to-peak amplitudes are between 3 and 40 mm/yr. The corrected vertical crustal deformation indicate that both the crustal uplift and subsidence are anisotropic in NET, and that the maximum uplift rate in the Longmen Shan fault reach 9.5mm/yr. We further use the horizontal velocity to calculate the strain rates throughout the NET. The result indicates that the shear band maintains feature consistent with the strike-slip fault along the Longmen Shan fault and Haiyuan fault. The crustal compression and extension can describe the uplifting and sinking of the crustal in a reasonable way. This study is supported by National 973 Project China (grant No. 2013CB733302) and NSFCs (grant Nos. 41174011, 41429401, 41210006, 41128003, 41021061); Guangxi Key Laboratory of Spatial Information and Geomatics (Grant No.1103108-12); Open Fund of Guangxi Key Laboratory of Spatial Information and Geomatics (Grant Nos. 15-140-07-32 and 14-045-24-17). Keywords: Continuous GPS observation; GRACE observation; principal component analysis; common mode error; crustal vertical deformation; strain rates

  10. Distinct crustal isostasy trends east and west of the Rocky Mountain Front

    Science.gov (United States)

    Schmandt, Brandon; Lin, Fan-Chi; Karlstrom, Karl E.

    2015-12-01

    Seismic structure beneath the contiguous U.S. was imaged with multimode receiver function stacking and inversion of Rayleigh wave dispersion and ellipticity measurements. Crust thickness and elevation are weakly correlated across the contiguous U.S., but the correlation is ~3-4 times greater for separate areas east and west of the Rocky Mountain Front (RMF). Greater lower crustal shear velocities east of the RMF, particularly in low-elevation areas with thick crust, are consistent with deep crustal density as the primary cause of the contrasting crust thickness versus elevation trends. Separate eastern and western trends are best fit by Airy isostasy models that assume lower crust to uppermost mantle density increases of 0.18 g/cm3 and 0.40 g/cm3, respectively. The former value is near the minimum that is plausible for felsic lower crust. Location of the transition at the RMF suggests that Laramide to post-Laramide processes reduced western U.S. lower crustal density.

  11. Crustal thickness estimates for Baja California, Sonora, and Sinaloa, Mexico, using disperse surface waves

    Science.gov (United States)

    López-Pineda, Leobardo; Rebollar, Cecilio J.; Quintanar, Luis

    2007-04-01

    Dispersed surface waves of regional events recorded at Network of Autonomously Recording Seismographs (NARS)-Baja and Red Sísmica de Banda Ancha (RESBAN) networks located over the Baja California Peninsula, Sonora, and Sinaloa, Mexico, were used to estimate shear wave elastic models and crustal thickness. We analyzed fundamental modes of surface waves with period between 10 and 40 s. Multiple filter analysis and the inversion method described by Herrmann and Ammon (2003) was used. Crustal thickness estimates for the Peninsular Ranges of Northern Baja California agree with those obtained by previous studies in the Peninsular Ranges of Northern Baja California. We analyzed dispersion of surface waves with northwest-southeast travel paths along the east and west sides of the Baja California Peninsula as well as a northwest-southeast travel path along the western sides of the Mexican states of Sonora and Sinaloa. It was found that the crustal structure east of the Baja California Peninsula is similar to the structure of Sonora and Sinaloa. The correlation between those two structures suggests dextral offset of the order of 275 ± 25 km if we consider Baja California Peninsula as a rigid body moving toward the northwest relative to the North America plate. This displacement between the structures is in agreement with the displacement determined by the dating of Miocene deposits located in San Felipe on the Baja California Peninsula (Pacific plate), and Isle Tiburon located west of Sonora (North America plate).

  12. Crustal structure of the NW Moroccan margin from deep seismic data (SISMAR Cruise)

    Science.gov (United States)

    Jaffal, Mohammed; Klingelhoefer, Frauke; Matias, Luis; Teixeira, Fernando; Amrhar, Mostafa

    2009-06-01

    During the SISMAR cruise (spring 2001), new deep seismic data were acquired on the Atlantic Moroccan margin. The purpose of the present work is to analyse and to interpret a part of the data consisting of four wide-angle seismic profiles (4, 5, 8 and 10) recorded offshore El Jadida. Lines 4 and 5, perpendicular to the margin, show a crustal thickness of 35 km under the western Moroccan Meseta which thins progressively seaward where it reaches a minimum thickness of 10 km. The calculated velocity models show that this crust consists of two crustal layers overlain by a sedimentary cover corresponding to the post-Paleozoic sediments, characterised by a low velocity. The detailed shallow structure is obtained primarily from multichannel seismic data. Half grabens are imaged and display deeper basins located at the foot of the continental slope where the sedimentary cover reaches a maximum thickness of 6 km. The sedimentary strata are disrupted by salt migration along faults and forming diapirs. The first crustal unit corresponds to the upper crust, with p-wave velocities ranging from 6 km/s at the top to 6.5 km/s at the base. The lower crust represented by the second unit is characterized by velocities increasing from 6.7 to 7.5 km/s at the base of the lower crust.

  13. Crustal thickness and Moho sharpness beneath the Midcontinent rift from receiver functions

    Directory of Open Access Journals (Sweden)

    Moikwathai Moidaki

    2013-02-01

    Full Text Available The Mesoproterozoic Midcontinent rift (MCR in the central US is an approximately 2000 km long, 100 km wide structure from Kansas to Michigan. During the 20-40 million years of rifting, a thick (up to 20 km layer of basaltic lava was deposited in the rift valleys. Quantifying the effects of the rifting and associated volcanic eruptions on the structure and composition of the crust and mantle beneath the MCR is important for the understanding of the evolution of continental lithosphere. In this study we measure the crustal thickness (H, and the sharpness of the Moho (R at about 24 portable and permanent stations in Iowa, Kansas, and South Dakota by stacking Pto- S converted waves (PmS and their multiples (PPmS and PSmS. Under the assumption that the crustal mean velocity in the study area is the same as the IASP91 earth model, we find a significantly thickened crust beneath the MCR of about 53 km. The crustal Vp/Vs ratios increases from about 1.80 off rift to as large as 1.95 within the rift, which corresponds to an increase of Poisson’s ratio from 0.28 to 0.32, suggesting a more mafic crust beneath the MCR. The R measurements are spatially variable and are relatively small in the vicinity of the MCR, indicating the disturbance of the original sharp Moho by the rifting and magmatic intrusion and volcanic eruption.

  14. Simulations of tremor-related creep reveal a weak crustal root of the San Andreas Fault

    Science.gov (United States)

    Shelly, David R.; Bradley, Andrew M.; Johnson, Kaj M.

    2013-01-01

    Deep aseismic roots of faults play a critical role in transferring tectonic loads to shallower, brittle crustal faults that rupture in large earthquakes. Yet, until the recent discovery of deep tremor and creep, direct inference of the physical properties of lower-crustal fault roots has remained elusive. Observations of tremor near Parkfield, CA provide the first evidence for present-day localized slip on the deep extension of the San Andreas Fault and triggered transient creep events. We develop numerical simulations of fault slip to show that the spatiotemporal evolution of triggered tremor near Parkfield is consistent with triggered fault creep governed by laboratory-derived friction laws between depths of 20–35 km on the fault. Simulated creep and observed tremor northwest of Parkfield nearly ceased for 20–30 days in response to small coseismic stress changes of order 104 Pa from the 2003 M6.5 San Simeon Earthquake. Simulated afterslip and observed tremor following the 2004 M6.0 Parkfield earthquake show a coseismically induced pulse of rapid creep and tremor lasting for 1 day followed by a longer 30 day period of sustained accelerated rates due to propagation of shallow afterslip into the lower crust. These creep responses require very low effective normal stress of ~1 MPa on the deep San Andreas Fault and near-neutral-stability frictional properties expected for gabbroic lower-crustal rock.

  15. Distinct crustal isostasy trends east and west of the Rocky Mountain Front

    KAUST Repository

    Schmandt, Brandon

    2015-12-14

    © 2015. American Geophysical Union. All Rights Reserved. Seismic structure beneath the contiguous U.S. was imaged with multimode receiver function stacking and inversion of Rayleigh wave dispersion and ellipticity measurements. Crust thickness and elevation are weakly correlated across the contiguous U.S., but the correlation is ∼3-4 times greater for separate areas east and west of the Rocky Mountain Front (RMF). Greater lower crustal shear velocities east of the RMF, particularly in low-elevation areas with thick crust, are consistent with deep crustal density as the primary cause of the contrasting crust thickness versus elevation trends. Separate eastern and western trends are best fit by Airy isostasy models that assume lower crust to uppermost mantle density increases of 0.18 g/cm3 and 0.40 g/cm3, respectively. The former value is near the minimum that is plausible for felsic lower crust. Location of the transition at the RMF suggests that Laramide to post-Laramide processes reduced western U.S. lower crustal density.

  16. Particle-in-cell simulations of the solar wind interaction with lunar crustal magnetic anomalies: Magnetic cusp regions

    Science.gov (United States)

    Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.

    2012-09-01

    As the solar wind is incident upon the lunar surface, it will occasionally encounter lunar crustal remanent magnetic fields. These magnetic fields are small-scale, highly non-dipolar, have strengths up to hundreds of nanotesla, and typically interact with the solar wind in a kinetic fashion. Simulations, theoretical analyses, and spacecraft observations have shown that crustal fields can reflect solar wind protons via a combination of magnetic and electrostatic reflection; however, analyses of surface properties have suggested that protons may still access the lunar surface in the cusp regions of crustal magnetic fields. In this first report from a planned series of studies, we use a 11/2-dimensional, electrostatic particle-in-cell code to model the self-consistent interaction between the solar wind, the cusp regions of lunar crustal remanent magnetic fields, and the lunar surface. We describe the self-consistent electrostatic environment within crustal cusp regions and discuss the implications of this work for the role that crustal fields may play regulating space weathering of the lunar surface via proton bombardment.

  17. The Crustal Structure of the North-South Earthquake Belt in China Revealed from Deep Seismic Soundings and Gravity Data

    Science.gov (United States)

    Zhao, Yang; Guo, Lianghui; Shi, Lei; Li, Yonghua

    2017-10-01

    The North-South earthquake belt (NSEB) is one of the major earthquake regions in China. The studies of crustal structure play a great role in understanding tectonic evolution and in evaluating earthquake hazards in this region. However, some fundamental crustal parameters, especially crustal interface structure, are not clear in this region. In this paper, we reconstructed the crustal interface structure around the NSEB based on both the deep seismic sounding (DSS) data and the gravity data. We firstly reconstructed the crustal structure of crystalline basement (interface G), interface between upper and lower crusts (interface C) and Moho in the study area by compiling the results of 38 DSS profiles published previously. Then, we forwardly calculated the gravity anomalies caused by the interfaces G and C, and then subtracted them from the complete Bouguer gravity anomalies, yielding the regional gravity anomalies mainly due to the Moho interface. We then utilized a lateral-variable density interface inversion technique with constraints of the DSS data to invert the regional anomalies for the Moho depth model in the study area. The reliability of our Moho depth model was evaluated by comparing with other Moho depth models derived from other gravity inversion technique and receiver function analysis. Based on our Moho depth model, we mapped the crustal apparent density distribution in the study area for better understanding the geodynamics around the NSEB.

  18. Crustal deformation in the Kumano Basin along the Nankai Trough inferred from repeated seafloor geodetic observations

    Science.gov (United States)

    Watanabe, T.; Tadokoro, K.; Sugimoto, S.; Okuda, T.; Muto, D.; Kimoto, A.; Miyata, K.; Kuno, M.

    2008-12-01

    At the Nankai Trough (NT), the Philippine Sea plate (PH) subducts beneath the southwest Japan at a rate of about 4-6 cm/yr, where great interplate earthquakes have repeatedly occurred every 100-200 years. A number of researchers have investigated crustal deformation caused by subduction of the PH based on geodetic measurements as represented by GPS observation. However it is difficult to infer the plate coupling strength in offshore areas, due to the poverty of offshore geodetic data. From a viewpoint of disaster mitigation, it is important to know the updip and downdip limit of the plate locking depth. For this issue, we have conducted observations of the seafloor crustal deformations around the NT using a GPS/Acoustic technique since 2004. In this system, we estimate the position of a surveying vessel by Kinematic GPS analysis and measure the distance between the vessel and the benchmark on the sea floor by Acoustic measurements. Next we determine the location of the benchmark. For the repeatability of observation, the location of benchmark is determined within a precision of 2-3 cm at horizontal components (Tadokoro et al., 2006). In the Kumano Basin, we have two seafloor benchmarks, which are located about 60 and 80 km away from the deformation front of the NT. The observations from 2005 to 2008 have illustrated that these benchmarks are moving at rates of about 5-6 cm/yr with velocity uncertainties of 1-3 cm/yr relative to the Amurian plate. In this study, in order to estimate interplate coupling at the NT, we calculated surface deformations accompanied with plate subduction in an elastic half-space and compared them with on- and offshore GPS velocities. Then, we investigated the effect of observation for the seafloor crustal deformations on slip resolution on the plate interface. We conclude that offshore crustal deformation data provide good constraints for the estimation of fault slips at the shallower part of the plate interface, especially at the depths

  19. Crustal structure and tectonic history of the Kermadec arc inferred from MANGO seismic refraction profiles

    Science.gov (United States)

    Bassett, D.; Kopp, H.; Sutherland, R.; Henrys, S.; Watts, A. B.; Timm, C.; Scherwath, M.; Grevemeyer, I.; de Ronde, C. E. J.

    2016-12-01

    We have analyzed three wide-angle seismic reflection and refraction profiles and applied spectral averaging techniques to regional grids of bathymetry and free-air gravity anomaly to place the first regional constraints on the crustal structure of the Kermadec arc. These observations are used to test contrasting tectonic models for an along-strike transition in margin structure, across which, 1) the remnant Lau-Colville and active Kermadec arc ridges narrow by >50%; 2) the backarc and forearc deepen by 1 km, and 3) the active volcanic arc is deflected west into the deepest known backarc basin. We use residual bathymetric anomalies to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the forearc with VP 6.5-7.3 km s-1 and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110±20 km) and strike ( 005° south of 25°S). South of the CKD the forearc is structurally homogeneous down-dip with VP 5.7-7.3 km s-1. Lower crustal velocities are similar to the northern Kermadec forearc, but there is no seismic or gravimetric evidence for an extinct arc ridge within the forearc. In the Havre Trough backarc, crustal thickness south of the CKD is 8-9 km, which is up-to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. The northern Kermadec/Tonga arc preserves a substrate of the Eocene arc, the southern Kermadec forearc preserves Mesozoic forearc rocks accreted at the Gondwana margin, and the central Kermadec arc may have fomed in the Kupe Abyssal Plain. The oldest arc related rocks recovered north and south of the CKD are 52 Ma and 16.7 Ma respectively, and plate tectonic reconstruction suggest the Eocene arc was originally conjoined with the Three Kings Ridge. The separation of these ridges during the early Oligocene likely formed the CKD. In contrast to previous interpretations, we

  20. Central Arctic Crustal Modeling Constrained by Potential Field data and recent ECS Seismic Data

    Science.gov (United States)

    Evangelatos, John; Oakey, Gordon; Saltus, Rick

    2017-04-01

    2-D gravity and magnetic models have been generated for several transects across the Alpha-Mendeleev ridge complex to study the regional variability of the crustal structure and identify large scale lateral changes. The geometry and density parameters for the models have been constrained using recently acquired seismic reflection and refraction data collected jointly by Canada and the United States as part of their collaborative Arctic ECS programs. A total of fifteen models have been generated perpendicular to the ridge complex, typically 50 to 150 km apart. A minimalist approach to modeling involved maintaining a simple, laterally continuous density structure for the crust while varying the model geometry to fit the observed gravity field. This approach is justified because low amplitude residual Bouguer anomalies suggest a relatively homogenous density structure within the ridge complex. These models have provided a new measure of the regional variability in crustal thickness. Typically, models with thinner crust correspond with deeper bathymetric depths of the ridge which is consistent with regional isostatic equilibrium. Complex "chaotic" magnetic anomalies are associated with the Alpha-Mendeleev ridge complex, which extends beneath the surrounding sedimentary basins. Pseudogravity inversion (magnetic potential) of the magnetic field provides a quantifiable areal extent of ˜1.3 x106 km2. Forward modeling confirms that the magnetic anomalies are not solely the result of magnetized bathymetric highs, but are caused to a great extent by mid- and lower crustal sources. The magnetization of the crust inferred from modeling is significantly higher than available lab measurements of onshore volcanic rocks. Although the 2-D models cannot uniquely identify whether the crustal protolith was continental or oceanic, there is a necessity for a significant content of high density and highly magnetic (ultramafic) material. Based on the crustal thickness estimates from our

  1. Uncommon evolution of probable central nervous system histoplasmosis: from leptomeningitis to posterior fossa granuloma. A case report with magnetic resonance images; Evolucao incomum de provavel histoplasmose de sistema nervoso central: de leptomeningite para granuloma da fossa posterior. Relato de caso com imagens por ressonancia magnetica

    Energy Technology Data Exchange (ETDEWEB)

    Carrilho, Paulo Eduardo Mestrinelli; Alves, Orival [Universidade Estadual do Oeste do Parana - UNIOESTE, Cascavel, PR (Brazil). Curso de Medicina. Disciplina de Neurologia e Neurocirurgia]. E-mail: carrilho@certto.com.br; Budant, Manfredo [UNITOM - Unidade de Diagnostico por Imagem, Cascavel, PR (Brazil). Centro de Tomografia; Bozo, Marlon K.; Meirelles, Noel [Universidade Estadual do Oeste do Parana - UNIOESTE, Cascavel, PR (Brazil). Curso de Medicina; Bueno, Alexandre Galvao [ANATOM - Instituto de Anatomia Patologica de Cascavel, PR (Brazil)

    2006-01-15

    We report a case of a young immunocompetent patient with probable central nervous system histoplasmosis with evolutive peculiar findings seen on magnetic resonance imaging. Leptomeningeal thickening was initially observed which subsequently became a posterior fossa granuloma. The diagnosis of fungal infection was only reached by histopathological study and the treatment was based on long term therapy with fluconazole wth good initial response. (author)

  2. Geologic evolution of the Paraiba do Sul complex, in the central part of the Ribeira belt, based on the geochemistry and U-Pb geochronology studies; Evolucao geologica do complexo Paraiba do Sul, no segmento central da faixa Ribeira, com base em estudos de geoquimica e geocronologia U-Pb

    Energy Technology Data Exchange (ETDEWEB)

    Valladares, Claudia Sayao

    1996-12-31

    Aiming the definition of the Complexo Paraiba do Sul evolution, the work presents a geochronological approach by the U-Pb method, considered appropriate to study polideformed terrains. The minerals used to the U-Pb dating (zircon, titanite and monazite) provides information about the ages of rock generation and the successive geological events the rocks were submitted. The U-Pb geochronological approach is pioneer in the investigated area and two questions referent to the Complexo Paraiba do Sul evolution in the central part of the Ribeira belt, were the aim of this approach. The first of them refers to the crystallization epoch and the gneisses metamorphism, interpreted here like orthogneisses, called Unidade Quirino of the Complexo Paraiba do Sul. The second refers to the metamorphism ages and meta sedimentary unit deformation. Looking for the contribution to the Complexo Paraiba do Sul evolution understanding, this work presents the data based on the geologic map of this area, comprising part of the Folha Volta Redonda (1:50.000), including petrographic, structural and microtectonic studies. It also presents and discusses the results of: 17 U-Pb analysis in zircon and titanite of the Complexo Paraiba do Sul orthogneisses collection; 24 geochemical analysis of major, minor, trace elements and ETR of the same collection; an U-Pb analysis in titanite of the Unidade Sao Joao, 5 U-Pb analysis in titanites and/or monazites of granites and granitoids; 12 geochemical analysis including major, minor and trace elements and ETR, in granites and sills of leucogranites. Finally, the data achieved were integrated with the objective to elaborate an evolutive view of the Complexo Paraiba do Sul 157 refs., 54 figs., 17 tabs.

  3. Micro-analysis by U-Pb method using LAM-ICPMS and its applications for the evolution of sedimentary basins: the example from Brasilia Belt; Micro-analise pelo metodo U-Pb usando LAM-CIPMS e suas aplicacoes para a evolucao de bacias sedimentares: o exemplo da faixa Brasilia

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Matteini, Massimo; Junges, Sergio Luiz; Giustina, Maria Emilia Schutesky Della; Dantas, Elton Luiz; Buhn, Bernhard, E-mail: marcio@unb.br [Universidade de Brasilia (UnB), DF (Brazil). Instituto de Geociencias; Rodrigues, Joseneusa Brilhante [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil)

    2015-07-01

    The U-Pb geochronological method using LAM-MC-ICPMS represents an important tool to investigate the geological evolution of sedimentary basins, as well as its geochronology, through the determination of upper limits for the depositional ages of detrital sedimentary rocks. The method has been applied in the Geochronology Laboratory of the Universidade de Brasilia, and in this study, a brief review of the provenance data for the sediments of the Neoproterozoic Brasilia Belt is presented and their significance for the evolution of the orogen is discussed. The results indicate that the Paranoa and Canastra Groups represent passive margin sequences formed along the western margin of the Sao Francisco-Congo continent. The Vazante Group presents similar provenance patterns, although Sm-Nd isotopic results suggest that its upper portions had contributions from younger (Neoproterozoic) sources, possibly from the Neoproterozoic Goias Magmatic Arc. On the other hand, metasediments of the Araxa and Ibia groups contain an important proportion of material derived from Neoproterozoic sources, demonstrating that they represent syn-orogenic basins. The provenance pattern of the Bambui Group is marked by an important Neoproterozoic component, showing that it constitutes a sedimentary sequence which is younger than 600 Ma, representing a foreland basin to the Brasilia Belt. (author)

  4. Mapping Antarctic Crustal Thickness using Gravity Inversion and Comparison with Seismic Estimates

    Science.gov (United States)

    Kusznir, Nick; Ferraccioli, Fausto; Jordan, Tom

    2017-04-01

    Using gravity anomaly inversion, we produce comprehensive regional maps of crustal thickness and oceanic lithosphere distribution for Antarctica and the Southern Ocean. Crustal thicknesses derived from gravity inversion are consistent with seismic estimates. We determine Moho depth, crustal basement thickness, continental lithosphere thinning (1-1/β) and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir 2008). The gravity anomaly contribution from ice thickness is included in the gravity inversion, as is the contribution from sediments which assumes a compaction controlled sediment density increase with depth. Data used in the gravity inversion are elevation and bathymetry, free-air gravity anomaly, the Bedmap 2 ice thickness and bedrock topography compilation south of 60 degrees south and relatively sparse constraints on sediment thickness. Ocean isochrons are used to define the cooling age of oceanic lithosphere. Crustal thicknesses from gravity inversion are compared with independent seismic estimates, which are still relatively sparse over Antarctica. Our gravity inversion study predicts thick crust (> 45 km) under interior East Antarctica, which is penetrated by narrow continental rifts featuring relatively thinner crust. The largest crustal thicknesses predicted from gravity inversion lie in the region of the Gamburtsev Subglacial Mountains, and are consistent with seismic estimates. The East Antarctic Rift System (EARS), a major Permian to Cretaceous age rift system, is imaged by our inversion and appears to extend from the continental margin at the Lambert Rift to the South Pole region, a distance of 2500 km. Offshore an extensive region of either thick oceanic crust or highly thinned continental crust lies adjacent to Oates Land and north Victoria Land, and also off West Antarctica around the Amundsen Ridges. Thin crust is

  5. Crustal thickness and composition beneath the High Lava Plains of Eastern Oregon from teleseismic receiver functions

    Science.gov (United States)

    Eagar, K. C.; Fouch, M. J.; James, D. E.; Carlson, R. W.

    2009-12-01

    The nature of the crust beneath the High Lava Plains of eastern Oregon is fundamental for understanding the origins of widespread Cenozoic volcanism in the region. Eruptions of flood basalts in the southern Cascadian back arc peaked ~17-15 Ma, and were followed by distributed bimodal volcanism along two perpendicular migrating tracks; the Snake River Plain and the High Lava Plains. The orientations of eruptive centers have led to several competing hypotheses about their cause, including a deep mantle plume, slab retreat and asthenospheric inflow, lithospheric delamination, and lithospheric extension. The goal of this project is to constrain the nature, geometry, and depth of the Moho across the High Lava Plains, which will shed light on questions regarding crustal influence on melt generation and differentiation and the degree of magmatic underplating. In this study, we analyze teleseismic receiver functions from 118 stations of the High Lava Plains temporary broadband array, 34 nearby EarthScope/USArray stations, and 5 other regional broadband stations to determine bulk crustal features of thickness (H) and Vp/Vs ratio (κ). Applying the H-κ stacking method, we search for the best-fitting solution of timing predictions for direct and multiple P-to-S conversions from the Moho interface. Converting Vp/Vs to Poisson ratio, which is dependent primarily upon rock composition, allows for comparison with other direct geological observations. Preliminary results show that the crust of the High Lava Plains is relatively thin (~31 km) with a very sharp gradient to thicker crust (~42 km) at the western edge of the Owyhee Plateau in southwestern Idaho. This gradient is co-located with the western margin of Precambrian North America and is in the vicinity of the Jordan Craters volcanic center. The sharp topography of the Moho might have been a factor in melt migration beneath this area. West of the High Lava Plains, the crust thickens to ~40 km into the Cascade volcanic arc

  6. 4-D crustal structure of the conterminous U.S.: Continental assembly, crustal growth, and deformation history from receiver functions, xenoliths, and structural mapping

    Science.gov (United States)

    Schulte-Pelkum, V.; Mahan, K. H.

    2015-12-01

    We investigate seismic and geological features related to the tectonic evolution of the crust on a continent-wide scale. We present continent-wide features using Transportable Array data receiver function analysis, followed by regional comparisons to tie to ground truth from xenolith studies and structural mapping. We stress that the Transportable Array, at ~75 km station spacing, only offers a collection of point measurements of the crust due to the lack of crossing raypaths. 7.x layers (lower crust with high seismic velocities) can be created during crustal growth processes such as magmatic or mechanical underplating and during crustal modification such as large-scale melting. We present receiver function results and a compilation of previous regional studies using refraction data or receiver functions from regional dense networks. 7.x layers appear predominantly in parts of the northern U.S. Cordillera and across the southeastern U.S. We compare the seismic results with a xenolith study in Montana that details incremental growth of the 7.x layer from the Archean on. Hydration of a granulitic lower crust can destroy the 7.x layer and has the potential to cause epirogenic uplift. We interpret the pattern seen across the Transportable Array in the light of this hypothesis. Ductile deformation of the deep crust generates shear fabrics that can be detected seismically. Receiver functions detect shear zones via contrasts in foliation to the surrounding material. We map foliation strikes and depths in the crust across the Transportable Array using azimuthal analysis of receiver functions. Strikes from receiver functions typically align with surface fault traces in tectonically active regions, with depths of the converters exceeding the brittle zone. We discuss continent-wide strikes mapped with receiver functions. Contrasting orientations of Proterozoic shear zones and pervasive surrounding foliations in basement exposures in Colorado are reflected in seismic results

  7. Interaction between a hotspot and a fracture zone: The crustal structure of Walvis Ridge at 6° E

    Science.gov (United States)

    Fromm, Tanja; Jokat, Wilfried; Behrmann, Jan H.

    2017-10-01

    The Walvis Ridge is one of the major hotspot trails in the South Atlantic and a classical example for volcanic island chains. Two models compete about the origin of the ridge: It is either the result of a deep mantle plume or active fracture zones above mantle inhomogeneities. Among other things crustal information is needed to constrain the models. Here, we provide such constraint with a 480 km long P-wave velocity model of the deep crustal structure of the eastern Walvis Ridge at 6° E. According to our data the Walvis Ridge stretches across the Florianopolis Fracture Zone into the Angola Basin. Here, we observe a basement high and thick basaltic layers covering the oceanic crust and the fracture zone. We found two crustal roots along the profile: one is located beneath the ridge crest, the other one beneath the northern basement high in the Angola Basin. The crustal thickness reaches 18 km and 12 km and the lower crustal velocities are 7.2 km/s and 7.4 km/s, respectively. The bathymetric expression of the ridge along the profile is less pronounced than closer to shore, which is mainly attributable to the absence of a thick layer of volcanic debris, rather than to reduced crustal thickness below the basement surface. Therefore, this part of the ridge was never or only briefly subaerially exposed. The crustal structure suggests that the ridge and the fracture zone formed independently of each other. The oceanic crust north of the fracture zone, which is buried underneath the basalt layer, is younger than the reconstructed age of hotspot volcanism of the Walvis Ridge. We interpret these structures north of the fracture zone to be at least partly a product of late stage volcanism.

  8. Constraints on the crustal structure beneath the Sinai subplate, SE Mediterranean, from analysis of local and regional travel times

    Directory of Open Access Journals (Sweden)

    Mohamed K. Salah

    2013-03-01

    Full Text Available The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift, the Dead Sea Transform fault, and the Red Sea rift. The upper and lower crustal structures of this tectonically active, rapidly developing region are yet poorly understood because of many limitations. For this reason, a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network (ENSN from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai. Because the velocity model used for routine earthquake location by ENSN is one-dimensional, the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures. Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west. The crustal Vp/Vs ratio is 1.74 from shallow (depth ≤ 10 km earthquakes and 1.76 from deeper (depth > 10 km crustal events. The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model (PREM, implying that the seismic stations are located above widely distributed, tectonically-induced low-velocity zones. These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures. The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities, which should be excluded from major future development projects and large constructions in central and southern Sinai.

  9. Continuous Spectrum of Crustal Structures and Spreading Processes from Volcanic Rifted Margins to Mid-Ocean Ridges

    Science.gov (United States)

    Karson, J. A.

    2016-12-01

    Structures generated by seafloor spreading in oceanic crust (and ophiolites) and thick oceanic crust of Iceland show a continuous spectrum of features that formed by similar mechanisms but at different scales. A high magma budget near the Iceland hotspot generates thick (40-25 km) mafic crust in a plate boundary zone about 50 km wide. The upper crust ( 10 km thick) is constructed by the subaxial subsidence and thickening of lavas fed by dense dike swarms over a hot, weak lower crust to produce structures analogous to seaward-dipping reflectors of volcanic rifted margins. Segmented rift zones propagate away from the hotspot creating migrating transform fault zones, microplate-like crustal blocks and rift-parallel strike-slip faults. These structures are decoupled from the underlying lower crustal gabbroic rocks that thin by along-axis flow that reduces the overall crustal thickness and smooths-out local crustal thickness variations. Spreading on mid-ocean ridges with high magma budgets have much thinner crust (10-5 km) generated at a much narrower (few km) plate boundary zone. Subaxial subsidence accommodates the thickening of the upper crust of inward-dipping lavas and outward-dipping dikes about 1-2 km thick over a hot weak lower crust. Along-axis (high-temperature ductile and magmatic) flow of lower crustal material may help account for the relatively uniform seismic thickness of oceanic crust worldwide. Spreading along even slow-spreading mid-ocean ridges near hotspots (e.g., the Reykjanes Ridge) probably have similar features that are transitional between these extremes. In all of these settings, upper crustal and lower crustal structures are decoupled near the plate boundary but eventually welded together as the crust ages and cools. Similar processes are likely to occur along volcanic rifted margins as spreading begins.

  10. Crustal structure of the Gulf of Aden southern margin: Evidence from receiver functions on Socotra Island (Yemen)

    Science.gov (United States)

    Ahmed, Abdulhakim; Leroy, Sylvie; Keir, Derek; Korostelev, Félicie; Khanbari, Khaled; Rolandone, Frédérique; Stuart, Graham; Obrebski, Mathias

    2014-12-01

    Breakup of continents in magma-poor setting occurs primarily by faulting and plate thinning. Spatial and temporal variations in these processes can be influenced by the pre-rift basement structure as well as by early syn-rift segmentation of the rift. In order to better understand crustal deformation and influence of pre-rift architecture on breakup we use receiver functions from teleseismic recordings from Socotra which is part of the subaerial Oligo-Miocene age southern margin of the Gulf of Aden. We determine variations in crustal thickness and elastic properties, from which we interpret the degree of extension related thinning and crustal composition. Our computed receiver functions show an average crustal thickness of ~ 28 km for central Socotra, which decreases westward along the margin to an average of ~ 21 km. In addition, the crust thins with proximity to the continent-ocean transition to ~ 16 km in the northwest. Assuming an initial pre-rift crustal thickness of 35 km (undeformed Arabian plate), we estimate a stretching factor in the range of ~ 2.1-2.4 beneath Socotra. Our results show considerable differences between the crustal structure of Socotra's eastern and western sides on either side of the Hadibo transfer zone; the east displays a clear intracrustal conversion phase and thick crust when compared with the western part. The majority of measurements across Socotra show Vp/Vs ratios of between 1.70 and 1.77 and are broadly consistent with the Vp/Vs values expected from the granitic and carbonate rock type exposed at the surface. Our results strongly suggest that intrusion of mafic rock is absent or minimal, providing evidence that mechanical thinning accommodated the majority of crustal extension. From our observations we interpret that the western part of Socotra corresponds to the necking zone of a classic magma-poor continental margin, while the eastern part corresponds to the proximal domain.

  11. Crustal seismic structure and depth distribution of earthquakes in the Archean Kuusamo region, Fennoscandian Shield

    Science.gov (United States)

    Uski, Marja; Tiira, Timo; Grad, Marek; Yliniemi, Jukka

    2012-01-01

    Two-dimensional crustal velocity models are derived from passive seismic observations for the Archean Karelian bedrock of north-eastern Finland. In addition, an updated Moho depth map is constructed by integrating the results of this study with previous data sets. The structural models image a typical three-layer Archean crust, with thickness varying between 40 and 52 km. P wave velocities within the 12-20 km thick upper crust range from 6.1 to 6.4 km/s. The relatively high velocities are related to layered mafic intrusive and volcanic rocks. The middle crust is a fairly homogeneous layer associated with velocities of 6.5-6.8 km/s. The boundary between middle and lower crust is located at depths between 28 and 38 km. The thickness of the lower crust increases from 5-15 km in the Archean part to 15-22 km in the Archean-Proterozoic transition zone. In the lower crust and uppermost mantle, P wave velocities vary between 6.9-7.3 km/s and 7.9-8.2 km/s. The average Vp/ Vs ratio increases from 1.71 in the upper crust to 1.76 in the lower crust. The crust attains its maximum thickness in the south-east, where the Archean crust is both over- and underthrust by the Proterozoic crust. A crustal depression bulging out from that zone to the N-NE towards Kuusamo is linked to a collision between major Archean blocks. Further north, crustal thickening under the Salla and Kittilä greenstone belts is tentatively associated with a NW-SE-oriented collision zone or major shear zone. Elevated Moho beneath the Pudasjärvi block is primarily explained with rift-related extension and crustal thinning at ˜2.4-2.1 Ga. The new crustal velocity models and synthetic waveform modelling are used to outline the thickness of the seismogenic layer beneath the temporary Kuusamo seismic network. Lack of seismic activity within the mafic high-velocity body in the uppermost 8 km of crust and relative abundance of mid-crustal, i.e., 14-30 km deep earthquakes are characteristic features of the Kuusamo

  12. Crustal seismic anisotropy and structure from textural and seismic investigations in the Cycladic region, Greece

    Science.gov (United States)

    Cossette, Élise; Schneider, David; Audet, Pascal; Grasemann, Bernhard

    2016-04-01

    studies, and reveal an intra-crustal discontinuity at depth varying from 3 to 11 km, mostly observed in the south-central Aegean. Harmonic decomposition of the receiver functions further indicates layering of both shallow and deep crustal anisotropy related to crustal structures. We model synthetic receiver functions based on constraints from the in situ rock properties that we measured using the EBSD technique. Our results indicate that the shallow upper crustal layer is characterized by metapelites with ~5% anisotropy, underlain by a 20 km thick and anisotropic layer of possible high-pressure rocks comprising blueschist and eclogite and/or restitic crust as a consequence of Miocene magmatism. Seismic anisotropy models require a sub-vertical axis of hexagonal symmetry in the upper crust (i.e. radial anisotropy), consistent with in situ rock data. Finally, a thinned crust is likely caused by back-arc extension associated with elevated sub-crustal temperatures, in agreement with thermal isostasy models of back arcs. This study demonstrates the importance of integrating rock textural data with seismic velocity profiles in the interpretation of crustal architecture.

  13. Coupled interactions between volatile activity and Fe oxidation state during arc crustal processes

    Science.gov (United States)

    Humphreys, Madeleine C.S.; Brooker, R; Fraser, D.C.; Burgisser, A; Mangan, Margaret T.; McCammon, C

    2015-01-01

    Arc magmas erupted at the Earth’s surface are commonly more oxidized than those produced at mid-ocean ridges. Possible explanations for this high oxidation state are that the transfer of fluids during the subduction process results in direct oxidation of the sub-arc mantle wedge, or that oxidation is caused by the effect of later crustal processes, including protracted fractionation and degassing of volatile-rich magmas. This study sets out to investigate the effect of disequilibrium crustal processes that may involve coupled changes in H2O content and Fe oxidation state, by examining the degassing and hydration of sulphur-free rhyolites. We show that experimentally hydrated melts record strong increases in Fe3+/∑Fe with increasing H2O concentration as a result of changes in water activity. This is relevant for the passage of H2O-undersaturated melts from the deep crust towards shallow crustal storage regions, and raises the possibility that vertical variations in fO2 might develop within arc crust. Conversely, degassing experiments produce an increase in Fe3+/∑Fe with decreasing H2O concentration. In this case the oxidation is explained by loss of H2 as well as H2O into bubbles during decompression, consistent with thermodynamic modelling, and is relevant for magmas undergoing shallow degassing en route to the surface. We discuss these results in the context of the possible controls on fO2 during the generation, storage and ascent of magmas in arc settings, in particular considering the timescales of equilibration relative to observation as this affects the quality of the petrological record of magmatic fO2.

  14. Mapping Curie temperature depth in the western United States with a fractal model for crustal magnetization

    Science.gov (United States)

    Bouligand, C.; Glen, J.M.G.; Blakely, R.J.

    2009-01-01

    We have revisited the problem of mapping depth to the Curie temperature isotherm from magnetic anomalies in an attempt to provide a measure of crustal temperatures in the western United States. Such methods are based on the estimation of the depth to the bottom of magnetic sources, which is assumed to correspond to the temperature at which rocks lose their spontaneous magnetization. In this study, we test and apply a method based on the spectral analysis of magnetic anomalies. Early spectral analysis methods assumed that crustal magnetization is a completely uncorrelated function of position. Our method incorporates a more realistic representation where magnetization has a fractal distribution defined by three independent parameters: the depths to the top and bottom of magnetic sources and a fractal parameter related to the geology. The predictions of this model are compatible with radial power spectra obtained from aeromagnetic data in the western United States. Model parameters are mapped by estimating their value within a sliding window swept over the study area. The method works well on synthetic data sets when one of the three parameters is specified in advance. The application of this method to western United States magnetic compilations, assuming a constant fractal parameter, allowed us to detect robust long-wavelength variations in the depth to the bottom of magnetic sources. Depending on the geologic and geophysical context, these features may result from variations in depth to the Curie temperature isotherm, depth to the mantle, depth to the base of volcanic rocks, or geologic settings that affect the value of the fractal parameter. Depth to the bottom of magnetic sources shows several features correlated with prominent heat flow anomalies. It also shows some features absent in the map of heat flow. Independent geophysical and geologic data sets are examined to determine their origin, thereby providing new insights on the thermal and geologic crustal

  15. Crustal structure of the North Iberian continental margin from seismic refraction/wide-angle reflection profiles

    Science.gov (United States)

    Ruiz, M.; Díaz, J.; Pedreira, D.; Gallart, J.; Pulgar, J. A.

    2017-10-01

    The structure and geodynamics of the southern margin of the Bay of Biscay have been investigated from a set of 11 multichannel seismic reflection profiles, recorded also at wide angle offsets in an onshore-offshore network of 24 OBS/OBH and 46 land sites. This contribution focuses on the analysis of the wide-angle reflection/refraction data along representative profiles. The results document strong lateral variations of the crustal structure along the margin and provide an extensive test of the crustal models previously proposed for the northern part of the Iberian Peninsula. Offshore, the crust has a typical continental structure in the eastern tip of the bay, which disappears smoothly towards the NW to reach crustal thickness close to 10 km at the edge of the studied area ( 45°N, 6°W). The analysis of the velocity-depth profiles, altogether with additional information provided by the multichannel seismic data and magnetic surveys, led to the conclusion that the crust in this part of the bay should be interpreted as transitional from continental to oceanic. Typical oceanic crust has not been imaged in the investigated area. Onshore, the new results are in good agreement with previous results and document the indentation of the Bay of Biscay crust into the Iberian crust, forcing its subduction to the North. The interpreted profiles show that the extent of the southward indentation is not uniform, with an Alpine root less developed in the central and western sector of the Basque-Cantabrian Basin. N-S to NE-SW transfer structures seem to control those variations in the indentation degree.

  16. Crustal structure beneath Beijing and its surrounding regions derived from gravity data

    Science.gov (United States)

    Jiang, Wenliang; Zhang, Jingfa; Lu, Xiaocui; Lu, Jing

    2011-06-01

    In this paper we use gravity data to study fine crustal structure and seismogenic environment beneath Beijing and its surrounding regions. Multi-scale wavelet analysis method is applied to separating gravity fields. Logarithmic power spectrum method is also used to calculate depth of gravity field source. The results show that the crustal structure is very complicated beneath Beijing and its surrounding areas. The crustal density exhibits laterally inhomogeneous. There are three large scale tectonic zones in North China, i.e., WNW-striking Zhangjiakou-Bohai tectonic zone (ZBTZ), NE-striking Taihang piedmont tectonic zone (TPTZ) and Cangxian tectonic zone (CTZ). ZBTZ and TPTZ intersect with each other beneath Beijing area and both of them cut through the lithosphere. The upper and middle crusts consist of many small-scale faults, uplifts and depressions. In the lower crust, these small-scale tectonic units disappear gradually, and they are replaced by large-scale tectonic units. In surrounding regions of Beijing, ZBTZ intersects with several other NE-striking tectonic units, such as Cangxian uplift, Jizhong depression and Shanxi Graben System (SGS). In west of Taihangshan uplift, gravity anomalies in upper and middle crusts are correlated with geological and topographic features on the surface. Compared with the crust, the structure is comparatively simple in uppermost mantle. Earthquakes mainly occurred in upper and middle crusts, especially in transitional regions between high gravity anomaly and low gravity anomaly. Occurrence of large earthquakes may be related to the upwelling of upper mantle and asthenosphere heat flow materials, such as Sanhe earthquake ( M S8.0) and Tangshan earthquake ( M S7.8).

  17. Late Cenozoic extension and crustal doming in the NE Chinese Pamir

    Science.gov (United States)

    Thiede, Rasmus C.; Sobel, Edward R.; Chen, Jie; Schoenbohm, Lindsay; Stockli, Daniel; Sudo, Masafumi; Strecker, Manfred

    2013-04-01

    The northward motion of the Pamir indenter with respect to Eurasia has resulted in coeval thrusting, strike-slip and normal faulting. The eastern Pamir is currently deformed by east-west oriented extension, accompanied by uplift and exhumation of the Kongur Shan (7719 m) and Muztagh Ata (7546 m) gneiss domes. Both domes are an integral part of the footwall of the Kongur Shan Extensional System (KES), a 250-km-long, north-south oriented graben. Why active normal faulting within the Pamir is primarily localized along the KES and not distributed more widely throughout the orogen, has remained unclear. In addition, relatively little is known about how deformation has evolved throughout the Cenozoic, despite refined estimates on present-day crustal deformation rates and microseismicity, which indicate where crustal deformation is presently being accommodated. To better constrain the spatiotemporal evolution of faulting along the KES, we present 39 new apatite fission-track, zircon U-Th-Sm/He, and 40Ar/39Ar cooling ages from a series of footwall transects along the KES graben shoulder. Combining this data with, present day topographic relief, 1D thermo-kinematic and exhumational modeling documents successive stages, rather than synchronous deformation and gneiss dome exhumation. While Kongur-Shan-exhumation started during the late Miocene, Muztagh Ata began earlier and has slowed down since the late Miocene. We present a new model, suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting Alai slab localizes extensional upper-plate deformation along the KES and decouples crustal motion between the Central/Western Pamir and Eastern Pamir/Tarim basin.

  18. Variation in Crustal Structure of the Lesser Caucasus Region from Teleseismic Receiver Functions

    Science.gov (United States)

    Lin, C. M.; Tseng, T. L.; Huang, B. S.; Legendre, C. P.; Karakhanian, A.

    2016-12-01

    The Caucasus, including the mountains of Greater and Lesser Caucasus, is formed by the continental collision between Arabia and Eurasia. The crustal thickness for this region was mostly constrained by joint analysis of receiver functions and surface waves. Although the thickest value of 52 km was reported under the Lesser Caucasus, the resolution of earlier studies were often limited by sparse array. Large gradient across Moho also makes the definition of Moho difficult. Moreover, higher value of the Vp/Vs ratio is commonly reported in the northeastern Turkey but no estimates had been made for the Caucasus. To further investigate the detail structure around the Lesser Caucasus, we constructed a new seismic network in Georgia and Armenia. We also include other broadband stations to enhance the coverage. The average interval in the Lesser Caucasus is roughly 30 km, much denser than any previous experiments. We selected P-waveforms from teleseismic earthquakes during the operation (January 2012 - June 2016) to calculate receiver functions and then estimate the crustal thickness (H) and Vp/Vs ratio (k) with the H-k stacking technique. Our preliminary results show that Moho depth increases from 40 km under the northeastern Turkey to 50 km beneath northern Georgia, no station with Moho deeper than 50 km under the Lesser Caucasus. The Vp/Vs ratios in the northeastern Anatolian plateau are around 1.8, which is slightly higher than the average of global continents but consistent with the previous estimates. Further to the east, some stations show anomalously higher Vp/Vs ratio in central & southern Armenia that may be associated with Holocene volcanism. In the future, we plan to join locally measured dispersion curves to invert the velocity model without velocity-depth trade-off. We expect to resolve the velocity variations of the crust beneath this region in small scale that may be tied to the continental collision and surface volcanism. Keywords: Caucasus, receiver

  19. Characteristics of Regional Crustal Deformation before 2016 Menyuan Ms6.4 Earthquake

    Science.gov (United States)

    Chen, Weitao; Gan, Weijun; Wang, Yuebing; Lian, Weiping

    2017-04-01

    On January 21, 2016,a strong earthquake with a magnitude of Ms 6.4 happened at Menyuan, Qinghai Province of China. In almost the same place, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. In this paper, we analyze the characteristics of regional crustal deformation before the 2016 Menyuan Ms6.4 earthquake by using the data from 10 continuous GPS stations and 74 campaign-mode GPS stations within 200 km of this event: (a) Based on the velocity field from over ten years GPS observations, a regional strain rate field is calculated. The results indicate that the crustal strain rate and seismic moment accumulation rate of the Qilian-Haiyuan active fault, which is the seismogenic tectonics of the event, are significantly higher than the surrounding regions.In a 20km×20km area around the seismogenic region, the maximum and minimum principal strain rates are 21.5 nanostrain/a (NW-SE extension) and -46.6 nanostrain/a (NE-SW compression), respectively, and the seismic moment accumulation rates is 17.4E15 N·m/a. The direction of principal compression is consistent with the focal mechanism of this event. (b) Based on theposition timeseries of the continuous GPS stations for a time-span of about 6 years before the event, we calculate the strain time series. The results show that the dilatation of the seismogenic region is continuously reduced with a "non-linear" trend since 2010, which means the seismogenic region has been in a state of compression. However, about 2-3 months before the event, both the dilatation and maximum shear strain shown significant inverse trends.These abnormal changes of crustal deformation may reflect the non-linear adjustment of the stress-strain accumulation of the seismogenic region, when the accumulation is approaching the critical value of rupture.

  20. 3-D crustal velocity structure of western Turkey: Constraints from full-waveform tomography

    Science.gov (United States)

    Çubuk-Sabuncu, Yeşim; Taymaz, Tuncay; Fichtner, Andreas

    2017-09-01

    The Sea of Marmara and western Turkey are characterized by intense seismicity and crustal deformation due to transition tectonics between the North Anatolian Fault Zone (NAFZ) and the extensional Aegean. Seismic imaging of the crust and uppermost mantle in W-NW Turkey is crucial to obtain a better understanding of its seismotectonics and geodynamics. So far, the Sea of Marmara and surroundings were considered in various active and passive seismic experiments providing significant information on crustal properties. Here, we further investigate the 3-D seismic velocity structure in this rapidly deforming region using non-linear full-waveform tomography based on the adjoint method. Our model is constrained by complete waveforms of 62 regional earthquakes (epicentral distance data uncertainties. Furthermore, quantitative resolution analyses yield 15 to 35 km horizontal resolution lengths in the shallow and deep crust beneath well-covered areas of W-NW Turkey. Our full-waveform tomography results indicate the presence of strong lateral and vertical velocity variations (2.55 ≤ VS ≤ 4.0 km/s) down to depths of ∼35 km. The seismic velocity distribution is characteristic of highly deformed and distributed crustal features along major fault zones (e.g. NAFZ and its branches), historic and recent regional volcanism (e.g. Kula volcanic province), and metamorphic core complex developments (e.g. Menderes and Kazdağ massifs). Radial anisotropy is very strong (around 20%) throughout the crust, further attesting to strong deformation and heterogeneity. Generally, our 3-D model is overall consistent with the active tectonics of western Turkey.

  1. Crustal structure of the Dabie orogenic belt (eastern China) inferred from gravity and magnetic data

    Science.gov (United States)

    Yang, Yu-shan; Li, Yuan-yuan

    2018-01-01

    In order to better characterize the crustal structure of the Dabie orogen and its tectonic history, we present a crustal structure along a 500 km long profile across the Dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data. Source depth estimations from the spectral analysis by continuous wavelet transform (CWT) provide better constraints for constructing the initial density model. The calculated gravity effects from the initial model show great discrepancy with the observed data, especially at the center of the profile. More practical factors are then incorporated into the gravity modeling. First, we add a high density body right beneath the high pressure metamorphic (HPM) and ultrahigh pressure metamorphic (UHPM) belt considering the exposed HPM and UHPM rocks in the mid of our profile. Then, the anomalous bodies A, B, and C inferred from the CWT-based spectral analysis results are fixed in the model geometry. In the final crustal density structure, two anomalous bodies B and C with high density and low magnetization could possibly be attributed to metasomatised mantle materials by SiO2-rich melt derived from the foundering subducted mafic lower crust. Under the extensional environment in the early Cretaceous, the upwelling metasomatised mantle was partially melted to produce the parental magma of the post-collisional mafic-ultramafic intrusive rocks. As for the low density body A with strong magnetization located in the lower crust right beneath the HP and UHP metamorphic belt, it is more likely to be composed of serpentinized mantle peridotite (SMP). This serpentinized mantle peridotite body (SMPB) represents the emplacement of mantle-derived peridotites in the crust, accompanying the exhumation of the UHP metamorphic rocks.

  2. Towards Crustal Structure of Java Island (Sunda Arc) from Ambient Seismic Noise Tomography

    Science.gov (United States)

    Widiyantoro, Sri; Zulhan, Zulfakriza; Martha, Agustya; Saygin, Erdinc; Cummins, Phil

    2015-04-01

    In our previous studies, P- and S-wave velocity structures beneath the Sunda Arc were successfully imaged using a global data set and a nested regional-global tomographic method was employed. To obtain more detailed P- and S-wave velocity structures beneath Java, in the central part of the Sunda Arc, we then used local data sets, i.e. newline from the MErapi AMphibious EXperiment (MERAMEX) and the Meteorological, Climatological and Geophysical Agency (MCGA), as well as employed a double-difference technique for tomographic imaging. The results of the imaging show e.g. that P- and S-wave velocities are significantly reduced in the uppermost mantle beneath central Java. In order to obtain detailed crustal structure information beneath Java, the Ambient Noise Tomography (ANT) method was used. The application of this method to the MERAMEX data has produced a good crustal model beneath central Java. We continue our experiment to image crustal structure of eastern Java. We have used seismic waveform data recorded by 22 MCGA stationary seismographic stations and 25 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms of cross-correlated noise between pairs of seismographic stations. Our preliminary results presented here indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly (as shown by our tomographic images). In future work we will install more seismographic stations in eastern Java as well as in western Java to conduct ANT imaging for the whole of Java Island. The expected result combined with the mantle velocity models resulting from our body wave tomography will allow for accurate location of earthquake hypocenters and determination of regional tectonic structures. Both of these are valuable for understanding seismic hazard in Java, the most densely populated

  3. Seismic Inversion for Hydrocarbon Exploration, Crustal Structure and Whole Earth Modeling

    Science.gov (United States)

    Sen, M. K.

    2005-05-01

    Seismic inversion employing travel time, amplitudes and full waveform attributes is a challenging task. In order to maintain accuracy and computational speed, it is important to make judicial choice of optimization methods, onstraints, a priori information, forward modeling operator and data. We have applied seismic inversion to a variety of applications including (1) full waveform inversion for estimating rock properties within a hydrocarbon reservoir, (2) joint inversion of seismic travel time and gravity data for delineating plate boundaries and crustal structure offshore Taiwan, (3) crustal velocity structure from waveform inversion of shear-couple PL waves, and (4) anisotropic structure of the core-mantle transition zone. Although all these applications make use of the same forward modeling algorithms and optimization routines, they are carefully designed to address the disparate scale and data types. For example, a semi-analytic approach for differential seismogram calculation is used for full waveform inversion in the first application while arc-parameter basis functions are used to represent the subsurface in the joint inversion of seismic and gravity data. Forward caculation is tailored to rapidly compute the response of the crustal structure for the shear coupled PL waves. To model anisotropic D" layer, we pre-compute the respose of the crust and the mantle layers (without D") for use in each iteration of the waveform inversion. In addition to deriving best fit models we also estimate parameter uncertainty and tradeoff between different parametes using Bayesian statistics. Such results are interpreted in terms of the physics of the problem being investigated.

  4. Solar wind interaction with the Martian upper atmosphere: Crustal field orientation, solar cycle, and seasonal variations

    Science.gov (United States)

    Dong, Chuanfei; Bougher, Stephen W.; Ma, Yingjuan; Toth, Gabor; Lee, Yuni; Nagy, Andrew F.; Tenishev, Valeriy; Pawlowski, Dave J.; Combi, Michael R.; Najib, Dalal

    2015-09-01

    A comprehensive study of the solar wind interaction with the Martian upper atmosphere is presented. Three global models: the 3-D Mars multifluid Block Adaptive Tree Solar-wind Roe Upwind Scheme MHD code (MF-MHD), the 3-D Mars Global Ionosphere Thermosphere Model (M-GITM), and the Mars exosphere Monte Carlo model Adaptive Mesh Particle Simulator (M-AMPS) were used in this study. These models are one-way coupled; i.e., the MF-MHD model uses the 3-D neutral inputs from M-GITM and the 3-D hot oxygen corona distribution from M-AMPS. By adopting this one-way coupling approach, the Martian upper atmosphere ion escape rates are investigated in detail with the combined variations of crustal field orientation, solar cycle, and Martian seasonal conditions. The calculated ion escape rates are compared with Mars Express observational data and show reasonable agreement. The variations in solar cycles and seasons can affect the ion loss by a factor of ˜3.3 and ˜1.3, respectively. The crustal magnetic field has a shielding effect to protect Mars from solar wind interaction, and this effect is the strongest for perihelion conditions, with the crustal field facing the Sun. Furthermore, the fraction of cold escaping heavy ionospheric molecular ions [(O2+ and/or O2+)/Total] are inversely proportional to the fraction of the escaping (ionospheric and corona) atomic ion [O+/Total], whereas O2+ and O2+ ion escape fractions show a positive linear correlation since both ion species are ionospheric ions that follow the same escaping path.

  5. Crustal seismic structure beneath Portugal and southern Galicia (Western Iberia) and the role of Variscan inheritance

    Science.gov (United States)

    Veludo, Idalina; Dias, Nuno A.; Fonseca, Paulo E.; Matias, Luís; Carrilho, Fernando; Haberland, Christian; Villaseñor, Antonio

    2017-10-01

    The crustal structure in Western Iberia, is the result of a complex geodynamic history. Most of the surface is covered by rocks dating to the Variscan orogeny, the coastal ranges dominated by Mesozoic structures and Mesocenozoic basins covering partially the mainland. In this study we present the results of a local earthquake tomographic study, performed to image in depth this complex crustal structure down to 24 km depth. The obtained tomograms present a good correlation with the surface geology, in general with higher Vp velocities in the north, and lower Vp velocities in the south. The heterogeneity observed on the surface geology of the Galicia-Tras-os-Montes Zone is well marked, being a relatively thin layer over the smoother structure of the Centro Iberia Zone CIZ. The CIZ crustal block confined between the Porto-Tomar-Ferreira do Alentejo and the Manteigas-Bragança faults having higher Vp values, enhancing the contrast to the Lusitanian Basin to the west. The Ossa-Morena Zone corresponds to the unit presenting the greater heterogeneity in both Vp and Vp/Vs models, showing also with a complex transition to the South Portuguese Zone and a relatively smooth transition to the Centro Iberian Zone. Unexpectedly, the South Portuguese Zone present an east-west velocity variation with no apparent correspondence with the surface geology. The transition to the coastal Mesocenozoic basins is clearly marked, the Lower Tagus Valley corresponding to a 4 km thick low velocity region. The relocation inland recorded seismicity in the period 2000-2014 allows cleansing some of the alignments and establish their correlation with some of the active structures in Portugal. The model features and seismicity pattern reveal the strong role played by the Variscan heritage.

  6. Crustal root beneath the Rif Cordillera as imaged from both active seismic data and teleseismic receiver functions.

    Science.gov (United States)

    Diaz, Jordi; Gil, Alba; Gallart, Josep; Carbonell, Ramon; Harnafi, Mimoun; Levander, Alan

    2015-04-01

    The Rif cordillera forms, together with the Betic ranges, one of the tightest orogenic arcs on Earth. This continental boundary zone is dominated now by the slow convergence between Nubia and Eurasia, but with clear evidences of extensional tectonics. One of the missing elements to constrain the complex geodynamics of the Gibraltar Arc System is the knowledge of the crustal architecture beneath northern Morocco. In the last decade a major effort has been done in this sense, from active and passive seismics. We compile here the recent results available from the Rif domains. Two 330 km long wide angle DSS profiles were recorded end of 2011 across the Rif in NS and EW transects within the Rifsis project, complemented by onshore recordings of the Gassis-WestMed marine profiles. At the same period, BB seismic arrays were deployed in the area within Topo-Iberia and Picasso projects, allowing receiver function analyses of crustal depths. The ray-tracing modeling of the Rifsis profiles reveal a large Moho step and an area of crustal thickening both in EW and NS directions, grossly coincident with the Bouguer gravity anomalies. The deployment logistics allowed that all the stations recorded all the shots, thus providing useful offline data. We will use here all available in-line and offline data to provide a map of the crustal thickness in northern Morocco. We combined two approaches: i) a hyperbolic time reduction applied to the seismic data, resulting in low-fold stacks in which the reflections from the Moho should appear as subhorizontal lines; ii) the arrival times of the observed PmP phases allow, assuming a mean crustal velocity, to assign a midpoint crustal thickness to each lecture. Although some uncertainties may be inherent to those approaches, a large crustal root, reaching more than 50 km, is well documented in the central part of the Rif Cordillera, close to the zone where the Alboran slab may still be attached to the lithosphere. We also compared these results

  7. Topography of the Betics: crustal thickening, dynamic topography and relief inheritance

    Science.gov (United States)

    Janowski, Marianne; Loget, Nicolas; Bellahsen, Nicolas; Husson, Laurent; Le Pourhiet, Laetitia; Meyer, Bertrand

    2017-04-01

    The main mechanism that explains high orogenic topographies is the isostatic adjustment due to crustal thickening. However in the Betic Cordillera (South Spain), the present-day elevation and crustal thickness are not correlated. That is at odds with the general premise of isostasy and requires reappraising the question of the driving mechanisms leading to the current topography. The Betics are located at the western edge of the alpine Mediterranean belt. Its Cenozoic orogenic building was disrupted by a major crustal thinning event induced by a slab rollback in the internal zones (Alboran domain) during Neogene. Topography was largely levelled and flooded by the sea during Neogene extension, and then has been folded since the Late Tortonian inversion. The present-day topography shows flat summits still preserved from fluvial regression in the internal zones (central and eastern Betics). These low-relief surfaces may be inherited from the Neogene planation toward sea-level as rocks cooling histories inferred from low-temperature thermochronology seem to point it out. Post-Tortonian shortening estimated thanks to a crustal-scale N-S cross-section in the eastern Betics (at the Sierra Nevada longitude) does not exceed few kilometers which is much lower than the shortening required by isostatic equilibrium, and is thus insufficient to explain the post-Tortonian topography building. We tested the hypothesis that mantle dynamics could in fact be an important mechanism that explains the topography of the Betics. We first computed the residual topography (i.e. the non-isostatic component of the elevation) using the most recent published Moho mapping of the area. In the western Betics, our results show important negative residual topography (down to -3 km) possibly associated with the west-Alboran slab suction. In the eastern Betics however, positive residual topography is important (up to +3 km) and can be explained by the dynamic mantle support of the topography, possibly

  8. Crustal motion measurements from the POLENET Antarctic Network: comparisons with glacial isostatic adjustment models

    Science.gov (United States)

    Wilson, T. J.; Konfal, S. A.; Bevis, M. G.; Spada, G.; Melini, D.; Barletta, V. R.; Kendrick, E. C.; Saddler, D.; Smalley, R., Jr.; Dalziel, I. W. D.; Willis, M. J.

    2016-12-01

    Crustal motions measured by GPS provide a unique proxy record of ice mass change, due to the elastic and viscoelastic response of the earth to removal of ice loads. The ANET/POLENET array of bedrock GPS sites spans much of the Antarctic interior, encompassing regions where glacial isostatic adjustment (GIA) models predict large crustal displacements due to LGM ice loss and including coastal West Antarctica where major modern ice mass loss is documented. To isolate the long-term GIA component of measured crustal motions, we computed and removed elastic displacements due to recent ice mass change. We used the annually resolved ice mass balance data from Martín-Español et al. (2016) derived from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003-2013. The Regional Elastic Rebound Calculator (REAR) [Melini et al., 2015] was used to compute elastic vertical and horizontal surface displacements. Uplift due to elastic rebound is substantial in West Antarctica, very minimal in East Antarctica, and variable across the Weddell Embayment. The ANET GPS-derived crustal motion patterns ascribed to non-elastic GIA are spatially complex and differ significantly in magnitude from model predictions. We present a systematic comparison of measured and predicted velocities within different sectors of Antarctica, in order to examine spatial patterns relative to modern ice mass changes, ice history model uncertainties, and lateral variations in earth properties. In the Weddell Embayment region most vertical velocities are lower than uplift predicted by GIA models. Several sites in the southernmost Transantarctic Mountains and the Whitmore Mountains, where small ice mass increase occurs, have vertical uplift significantly exceeding GIA model predictions. There is an intriguing spatial correlation of these fast-moving sites with a low-velocity anomaly in the upper mantle documented by analysis of teleseismic Rayleigh waves by

  9. InSAR observations and models of crustal deformation due to a glacial surge in Iceland

    Science.gov (United States)

    Auriac, A.; Sigmundsson, F.; Hooper, A.; Spaans, K. H.; Björnsson, H.; Pálsson, F.; Pinel, V.; Feigl, K. L.

    2014-09-01

    Surges are common at all the major ice caps in Iceland. Ice masses of gigatons may shift from the upper part of the outlet glacier towards the terminus in a few months, advancing the glacier front by up to several kilometres. The advancing ice front may be up to 100 m thick, increasing the load on crustal rocks correspondingly. We use the observed change in crustal loading during a surge of the western part of the Vatnajökull ice cap, Iceland, during 1993-1995 and the corresponding elastic crustal deformation, surveyed with interferometric synthetic aperture radar, to investigate the material properties of the solid Earth in this region. Crustal subsidence due to the surge reaches ˜75 mm at the edge of the Síðujökull outlet glacier. This signal is mixed with a broad uplift signal of ˜12 mm yr-1, relative to our reference area, caused by the ongoing retreat of Vatnajökull in response to climate change. We disentangle the two signals by linear inversion. Finite element modelling is used to investigate the elastic Earth response of the surge, as well as to confirm that no significant viscoelastic deformation occurred as a consequence of the surge. The modelling leads to estimates of the Young's modulus and Poisson's ratio of the underlying Earth. Comparison between the observed and modelled deformation fields is made using a Bayesian approach that yields the estimate of a probability distribution for each of the free parameters. Residuals indicate a good agreement between models and observations. One-layer elastic models result in a Young's modulus of 43.2-49.7 GPa (95 per cent confidence) and Poisson's ratio of 0-0.27, after removal of outliers. Our preferred model, with two elastic layers, provides a better fit to the whole surge signal. This model consists of a 1-km-thick upper layer with an average Young's modulus of 12.9-15.3 GPa and Poisson's ratio of 0.17, overlying a layer with an average Young's modulus of 67.3-81.9 GPa and Poisson's ratio of 0.25.

  10. The global chemical systematics of arc front stratovolcanoes: Evaluating the role of crustal processes

    Science.gov (United States)

    Turner, Stephen J.; Langmuir, Charles H.

    2015-07-01

    Petrogenetic models for convergent margins should be consistent with the global systematics of convergent margin volcanic compositions. A newly developed tool for compiling and screening data from the GEOROC database was used to generate a global dataset of whole rock chemical analyses from arc front stratovolcano samples. Data from 227 volcanoes within 31 volcanic arc segments were first averaged by volcano and then by arc to explore global systematics. Three different methods of data normalization produce consistent results that persist across a wide range of Mg# [Mg# =Mg / (Mg +Fe) ]. Remarkably coherent systematics are present among major and trace element concentrations and ratios, with the exception of three arcs influenced by mantle plumes and Peru/N. Chile, which is built on exceptionally thick crust. Chemical parameters also correlate with the thickness of the overlying arc crust. In addition to previously established correlations of Na6.0 with Ca6.0 and crustal thickness, correlations are observed among major elements, trace elements, and trace element ratios (e.g. La/Yb, Dy/Yb, Zr/Sm, Zr/Ti). Positive correlations include "fluid mobile," "high field strength," and "large ion lithophile" element groups, with concentrations that vary by a factor of five in all groups. Incompatible element enrichments also correlate well with crustal thickness, with the greatest enrichment found at arcs with the thickest crust. Intra-crustal processes, however, do not reproduce the global variations. High pressure fractionation produces intermediate magmas enriched in aluminum, but such magmas are rare. Furthermore, differences among magma compositions at various volcanic arcs persist from primitive to evolved compositions, which is inconsistent with the possibility that global variations are produced by crystal fractionation at any pressure. Linear relationships among elements appear to be consistent with mixing between depleted primary magma and an enriched contaminant

  11. Quality analysis of crustal tilt and strain observations in China's earthquakes in 2014

    Directory of Open Access Journals (Sweden)

    Zhiyao Chen

    2015-11-01

    Full Text Available This work analyzes the quality of crustal tilt and strain observations during 2014, which were acquired from 269 sets of ground tiltmeters and 212 sets of strainmeters. In terms of data quality, the water tube tiltmeters presented the highest rate of excellent quality, approximately 91%, and the pendulum tiltmeters and ground strainmeters yielded rates of 81% and 78%, respectively. This means that a total of 380 sets of instruments produced high-quality observational data suitable for scientific investigations and analyses.

  12. The VLBI Celestial Reference Frame of the NASA Crustal Dynamics Project

    Science.gov (United States)

    Ma, C.

    A celestial reference frame can be defined by precise positions of extragalactic radio sources using Mark III VLBI data available to the NASA Crustal Dynamics Project for geodynamic research. Seven years of such data have been analyzed to generate a catalogue of 101 sources with formal statistical errors between 0.01 and 0.77 ms in right ascension and between 0.2 and 9.3 mas in declination. The rotations and scatter of the positions from year to year are generally less than 1 mas.

  13. Crustal and lithospheric structure of the west Antarctic Rift System from geophysical investigations: A review

    Science.gov (United States)

    Behrendt, John C.

    1999-01-01

    The active West Antarctic Rift System, which extends from the continental shelf of the Ross Sea, beneath the Ross Ice Shelf and the West Antarctic Ice Sheet, is comparable in size to the Basin and Range in North America, or the East African rift systems. Geophysical surveys (primarily marine seismic and aeromagnetic combined with radar ice sounding) have extended the information provided by sparse geologic exposures and a few drill holes over the ice and sea covered area. Rift basins developed in the early Cretaceous accompanied by the major extension of the region. Tectonic activity has continued episodically in the Cenozoic to the present, including major uplift of the Transantarctic Mountains. The West Antarctic ice sheet, and the late Cenozoic volcanic activity in the West Antarctic Rift System, through which it flows, have been coeval since at least Miocene time. The rift is characterized by sparse exposures of late Cenozoic alkaline volcanic rocks extending from northern Victoria Land throughout Marie Byrd Land. The aeromagnetic interpretations indicate the presence of > 5 x 105 km2 (> 106 km3) of probable late Cenozoic volcanic rocks (and associated subvolcanic intrusions) in the West Antarctic rift. This great volume with such limited exposures is explained by glacial removal of the associated late Cenozoic volcanic edifices (probably hyaloclastite debris) concomitantly with their subglacial eruption. Large offset seismic investigations in the Ross Sea and on the Ross Ice Shelf indicate a ~ 17-24-km-thick, extended continental crust. Gravity data suggest that this extended crust of similar thickness probably underlies the Ross Ice Shelf and Byrd Subglacial Basin. Various authors have estimated maximum late Cretaceous-present crustal extension in the West Antarctic rift area from 255-350 km based on balancing crustal thickness. Plate reconstruction allowed crustal extension in late Cenozoic time is unlikely, alternate mechanisms have been proposed for the

  14. Flat-slab subduction, whole crustal faulting, and geohazards in Alaska: Targets for Earthscope

    Science.gov (United States)

    Gulick, S. P.; Pavlis, T. L.; Bruhn, R. L.; Christeson, G. L.; Freymueller, J. T.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Roeske, S.; Reece, R.; van Avendonk, H. J.; Worthington, L. L.

    2010-12-01

    Crustal structure and evolution illuminated by the Continental Dynamics ST. Elias Erosion and tectonics Project (STEEP) highlights some fundamental questions about active tectonics processes in Alaska including: 1) what are the controls on far field deformation and lithospheric stabilization, 2) do strike slip faults extend through the entire crust and upper mantle and how does this influence mantle flow, and 3) how does the transition from “normal” subduction of the Pacific along the Aleutians to flat slab subduction of the Yakutat Terrane beneath southeast and central Alaska to translation of the Yakutat Terrane past North American in eastern Alaska affect geohazard assessment for the north Pacific? Active and passive seismic studies and geologic fieldwork focusing on the Yakutat Terrane show that the Terrane ranges from 15-35 km thick and is underthrusting the North American plate from the St. Elias Mountains to the Alaska Range (~500 km). Deformation of the upper plate occurs within the offshore Pamplona Zone fold and thrust belt, and onshore throughout the Robinson Mountains. Deformation patterns, structural evolution, and the sedimentary products of orogenesis are fundamentally influenced by feedbacks with glacial erosion. The Yakutat megathrust extends beneath Prince William Sound such that the 1964 Mw 9.2 great earthquake epicenter was on this plate boundary and jumped to the adjacent Aleutian megathrust coseismically; this event illuminates the potential for transitional tectonic systems to enhance geohazards. The northern, southern, and eastern limits of the Yakutat microplate are strike-slip faults that, where imaged, appear to cut the entire crustal section and may allow for crustal extrusion towards the Bering Sea. Yakutat Terrane effects on mantle flow, however, have been suggested to cross these crustal features to allow for far-field deformation in the Yukon, Brooks Range, and Amerasia Basin. From the STEEP results it is clear that the Yakutat

  15. Recycling of crustal minerals into the upper mantle: evidence from ophiolites

    Science.gov (United States)

    Robinson, P. T.; Yang, J.; Trumbull, R.

    2009-05-01

    A wide variety of ultrahigh pressure and crustal minerals has been recovered from podiform chromitites of the Donqiao and Luobusa ophiolites of Tibet, the Ray-Iz ophiolite of the Polar Urals and the Semail ophiolite of Oman. Microdiamonds are abundant in the Luobusa, Donqiao and Ray-Iz ophiolites, coesite and kyanite occur in Luobusa and moissanite is present in all four ophiolites. Numerous crustal minerals, including zircon, corundum, quartz, almandine garnet, rutile, and feldspar are also present. The diamonds are mostly euhedral grains,100-200 µm across, commonly containing metallic and Mg-Fe silicate inclusions. One small grain occurs as an inclusion in an Os-Ir alloy. Coesite and kyanite are intergrown with each other on the rim of a grain of Ti-Fe alloy, and the coesite has a prismatic form suggesting it may be pseudomorphic after stishovite. Moissanite is common in all four ophiolites and occurs as small colorless, green or blue, vitreous fragments. Zircon grains range from 20 to 300 µm, and are mostly well rounded with very complex internal structures. They commonly contain low-pressure inclusions of quartz, rutile, orthoclase, mica, ilmenite and apatite. 206Pb/238U SIMS and SHRIMP dates for the zircons are mostly Paleozoic and Precambrian, far older than the ophiolites. The grains of quartz, almandine garnet, corundum and feldspar range up to about 0.5 mm and are moderately to well rounded. Smaller, angular fragments of such grains are also present. The rounded morphology of these grains, as well as the zircons, strongly suggests derivation from sedimentary material, presumably transported into the mantle by subduction. The microdiamonds and moissanite could also have been derived from crustal materials recycled into the mantle. We suggest that the various minerals were picked up by melts from which the chromitites precipitated and carried to shallow crustal levels. The preservation of such minerals, particularly quartz and coesite, in the mantle

  16. Extraction of crustal deformations and oceanic fluctuations from ocean bottom pressures

    Science.gov (United States)

    Ariyoshi, Keisuke; Nagano, Akira; Hasegawa, Takuya; Matsumoto, Hiroyuki; Kido, Motoyuki; Igarashi, Toshihiro; Uchida, Naoki; Iinuma, Takeshi; Yamashita, Yusuke

    2017-04-01

    It has been well known that megathrust earthquakes such as the 2004 Sumatra-Andaman Earthquake (Mw 9.1) and the 2011 the Pacific Coast of Tohoku Earthquake (Mw 9.0) had devastated the coastal areas in the western of Indonesia and in the north-eastern of Japan, respectively. To mitigate the disaster of those forthcoming megathrust earthquakes along Nankai Trough, the Japanese government has established seafloor networks of cable-linked observatories around Japan: DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis along the Nankai Trough) and S-net (Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench). The advantage of the cable-linked network is to monitor the propagation process of tsunami and seismic waves as well as seismic activity in real time. DONET contains pressure gauges as well as seismometers, which are expected to detect crustal deformations driven by peeling off subduction plate coupling process. From our simulation results, leveling changes are different sense among the DONET points even in the same science node. On the other hand, oceanic fluctuations such as melting ice masses through the global warming have so large scale as to cause ocean bottom pressure change coherently for all of DONET points especially in the same node. This difference suggests the possibility of extracting crustal deformations component from ocean bottom pressure data by differential of stacking data. However, this operation cannot be applied to local-scale fluctuations related to ocean mesoscale eddies and current fluctuations, which affect ocean bottom pressure through water density changes in the water column (from the sea surface to the bottom). Therefore, we need integral analysis by combining seismology, ocean physics and tsunami engineering so as to decompose into crustal deformation, oceanic fluctuations and instrumental drift, which will bring about high precision data enough to find geophysical phenomena. In this study

  17. Deep seismic investigation of crustal extensional structures in the Danish Basin along the ESTRID-2 profile

    DEFF Research Database (Denmark)

    Sandrin, Alessandro; Thybo, Hans

    2008-01-01

    The crust and uppermost mantle in the Danish Basin are investigated by modelling the P-wave velocity distribution along the north-south trending seismic profile ESTRID-2. Seismic tomography and ray inversion modelling demonstrate a variable depth to the top of the crystalline crust, from ~10 km...... to magmatic underplating. The occurrence of a large crustal mafic intrusion associated with magmatic underplating may be related to extensional/transtensional tectonism in the Tornquist Fan area in the Late Palaeozoic. The extensional event probably caused the opening of a plumbing system for intrusion...

  18. Crustal Structure across Rivera Plate and Jalisco Block (MEXICO): TsuJal Project

    Science.gov (United States)

    Nuñez-Cornu, F. J.; Nunez, D.; Barba, D. C., Sr.; Trejo, E.; Escalona, F.; Danobeitia, J.; Gutierrez Pena, Q. J.

    2015-12-01

    Located on the western margin of Mexico, the collision zone between Rivera, Cocos and North American plates is a complex tectonic collage with high seismic hazards and potential tsunamigenic sources. During the spring of 2014, within the framework of TSUJAL project, Spanish and Mexican scientists investigated this region with the main objective of defining the crustal architecture of this active margin and recognizing potential structural sources that can trigger earthquakes and tsunamis at the convergence between Rivera plate-Jalisco block with the North American Plate. To achieve these goals, a wide-ranging of geophysical data was acquired in this region both offshore and onshore. In this paper, we present the preliminary results obtained from this project about bathymetric, structural geology and wide-angle seismic data of the southern coast of Bahía de Banderas. A crustal P-wave velocity model for the southern coast of Bahía de Banderas was obtained using WAS data recorded by OBS and land seismic stations for more than 150 km across Rivera Plate and Jalisco Block. The thickness of the slab in this area is about 10 km and presents a dip angle about 8º. Continental crustal thickness below Puerto Vallarta is about 20 km, no evidence of continental Moho was found in this study. This model support that due to the convergence of Rivera Plate against Jalisco Block, the region of Bahía de Banderas is under strong crustal stresses that generate structural lineaments and have the same trends offshore and inland. Most of the seismicity reported can be associated to the main structural lineaments. The Banderas Canyon apparently is in an opening process from west to east, which seems to continue through the Rio Pitillal river valley. There is no seismic or morphological evidence to consider that the Banderas Canyon is a continuation of Vallarta Graben.South of María Cleofas Island, the SC marks the limit between RP and JB, possibly being the result of the RP against JB

  19. Evidence for Vertical Coherent Deformation in Eastern Tibet from Splitting of Crustal S Phases

    Science.gov (United States)

    Karalliyadda, S. C.; Weeraratne, D. S.; Silver, P. G.

    2007-12-01

    Regional shear wave phases recorded by stations in Yunnan Province and Eastern Tibet surrounding the Eastern Himalayan syntaxis are used to constrain seismic anisotropy at crustal depths which range from 45 km to 65 km, respectively. Shear wave splitting measurements were obtained using regional direct S phases recorded at stations operated by Carnegie Institution of Washington, Lehigh University, and MIT, with source depths that originate from 20 km to 55 km. S to P converted energy is avoided considering events with free surface incidence angles less than 37{°} and using records with low P energy. We apply a low pass filter with a corner frequency at 2.5 Hz to all records and correct for surface reflections using a free surface transform from previous methods. Anisotropy is small but well resolved for 14 records at 8 stations and indicate that delay times obtained for all stations are less than 0.4 {±} 0.05s. In Yunnan province the average delay time is 0.16 s but is twice this value in eastern Tibet at 0.31 s. The fast directions for all stations in Yunnan Province including KMI and CHTO (GSN) are consistent with fast directions for previous SKS studies, but with smaller delay times of 0.4s or less (where SKS are 1.0 - 1.5s). Stations in eastern Tibet display a {~}N-S azimuth roughly orthogonal to SKS studies in this area and may indicate sensitivity to cracks which form roughly parallel to the compressive stress direction. A N-S azimuth of anisotropy is also consistent with surface waves results for periods below 40s. By comparison with SKS splitting studies, we find that anisotropy in the crust is very small and contributes only about 15% to the total SKS splitting measurements, requiring about 1.0 - 1.2s of splitting to come from subcrustal depths. Such strong anisotropic fabric possibly present in the lithospheric mantle is inconsistent with a lower crustal flow model which predicts decoupling above the Moho. Consistently low splitting times for events

  20. Studying sub-crustal reflectors in SW-Spain with wide-angle profiles

    Science.gov (United States)

    Palomeras, Imma; Ayarza, Puy; Carbonell, Ramon; Afonso, JuanCarlos; Diaz, Jordi

    2017-04-01

    It is nowadays widely accepted that the mantle is highly heterogeneous and has lithologies that are capable of giving impedance enough to be observed in seismic data. Nevertheless, observing those impedance contrasts at mantle depths is a challenging problem. SW Iberia has been sampled by different deep vertical reflection and wide-angle reflection/refraction experiments ILIHA, IBERSEIS, and ALCUDIA, and hence provide a good opportunity to study seismically sub-crustal reflectors. These datasets have imaged a conspicuous sub-crustal reflector. This mantle reflector was first identified on the IBERSEIS wide angle reflection shot-gathers at large offsets (above 180 km). It was modeled as a boundary located between 61-72 km depth with a Vp increase from 8.2 km/s to 8.3 km/s. The fact that this reflector was not identified in the coincident vertical incidence dataset led us to interpret it as a gradient zone. A correlation with the 'Hales gradient zone', i.e. the boundary between spinel and garnet peridotites, was our preferred interpretation. The ALCUDIA experiment also shows prominent sub-crustal arrivals with the same characteristics as those observed in the IBERSEIS wide-angle data. However, these reflections also appear, locally and at 19 s TWT, in the vertical incidence dataset. In addition, the ALCUDIA wide-angle dataset shows a deeper reflector that maybe preliminarily associated with mantle anisotropy or even with the lithosphere-asthenosphere boundary. Both upper mantle reflectors are modeled at 65 km and 100 km depth, respectively, shallowing to the north to 55 km and 90 km depth. Integration of the information provided by the IBERSEIS and ALCUDIA datasets with older and lower resolution data from the ILIHA project, where three sub-crustal phases were identified in SW Iberia, allows us to conclude that, in this area, mantle reflectivity is outstanding. Also, modeling of all the datasets contributes to map, at a regional scale, the Hales discontinuity or

  1. Testing the Axial Dipole Hypothesis for the Moon by Modeling the Direction of Crustal Magnetization

    Science.gov (United States)

    Oliveira, Joana S.; Wieczorek, Mark A.

    2017-04-01

    Magnetic field maps of the Moon show that there are strong magnetic anomalies of crustal origin distributed heterogeneously across the lunar surface. However, the origin of the fields that magnetized the crust are not understood and could be the result of either a long-lived core generated dynamo or transient fields associated with large impact events. Core-dynamo models usually predict that the field would be predominantly dipolar, with the dipole axis aligned with the rotation axis. In this case, the direction of crustal magnetization would vary with planetary latitude, just as on Earth. We test this hypothesis by modeling the direction of crustal magnetization using spacecraft-derived magnetic field data. From the direction of magnetization, we calculate the corresponding paleopole, which we define as the north magnetic pole of a predominantly dipolar core-generated field when the anomaly was formed. The dipolar core field hypothesis will be confirmed if the paleopoles cluster in one or two regions. We use the Parker method, originally developed to study seamounts magnetism, to invert for the direction of crustal magnetization associated with isolated lunar magnetic anomalies. This method largely bypasses the non-uniqueness associated with specifying the geometry of the magnetic sources. The only assumption is that when the region acquired a remnant magnetization, the main field was constant in direction. In practice, unidirectional equivalent source dipoles are placed on the surface within a circle of specified radius over a region that encompasses an isolated anomaly. For an assumed direction of magnetization, we solve for the magnetic moments of the dipoles and determine the misfit between the model and observations using a non-negative least squares inversions approach. The inversion naturally finds those dipoles that are non-zero, as well as their intensities. For our inversions we use global gridded magnetic field maps at 30 km altitude with a resolution

  2. Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal

    Science.gov (United States)

    Wang, Huilin; Currie, Claire A.

    2017-08-01

    Mantle-based stresses have been proposed to explain the occurrence of deformation in the interior regions of continental plates, far from the effects of plate boundary processes. We examine how the gravitational removal of a dense mantle lithosphere root may induce deformation of the overlying crust. Simplified numerical models and a theoretical analysis are used to investigate the physical mechanisms for deformation and assess the surface expression of removal. Three behaviours are identified: (1) where the entire crust is strong, stresses from the downwelling mantle are efficiently transferred through the crust. There is little crustal deformation and removal is accompanied by surface subsidence and a negative free-air gravity anomaly. Surface uplift and increased free-air gravity occur after the dense root detaches. (2) If the mid-crust is weak, the dense root creates a lateral pressure gradient in the crust that drives Poiseuille flow in the weak layer. This induces crustal thickening, surface uplift and a minor free-air gravity anomaly above the root. (3) If the lower crust is weak, deformation occurs through pressure-driven Poiseuille flow and Couette flow due to basal shear. This can overthicken the crust, producing a topographic high and a negative free-air gravity anomaly above the root. In the latter two cases, surface uplift occurs prior to the removal of the mantle stress. The modeling results predict that syn-removal uplift will occur if the crustal viscosity is less than ∼1021 Pa s, corresponding to temperatures greater than ∼400-500 °C for a dry and felsic or wet and mafic composition, and ∼900 °C for a dry and mafic composition. If crustal temperatures are lower than this, lithosphere removal is marked by the formation of a basin. These results can explain the variety of surface expressions observed above areas of downwelling mantle. In addition, observations of the surface deflection may provide a way to constrain the vertical rheological

  3. Relation between relief and crustal structure in the Cantabrian Mountains (Spain) using DEM-GIS analysis

    Science.gov (United States)

    Llana-Fúnez, Sergio; Rodríguez-Rodríguez, Laura; Ballesteros, Daniel; María Díaz-Díaz, Luis; Valenzuela, Pablo; López-Fernández, Carlos; José Domínguez-Cuesta, María; Meléndez, Mónica; Jiménez-Sánchez, Montserrat; Fernández-Viejo, Gabriela

    2017-04-01

    The Cantabrian Mountains show a linear E-W trend parallel to the northern coast of Iberia peninsula, from the Pyrenees to Galicia, where it looses its trend and linearity. The western end of the linear segment of the orogen coincides with a change in the style of structures, accommodating the N-S shortening during the convergence between Europe and Iberia plates. We study the relief of the 230 km-long segment of the linear range between the Cantabria and Galicia re- gions, up to 2,650 m altitude. The bulk trend of the orogeny is controlled by the orientation of alpine thrusts that accommodate the shortening in relation to plate convergence. The Alpine Orogeny produced crustal thickening and the present day topography. Crustal thickness varies from 30 km in Eastern Cantabrian Mountains to 45-55 km at the Middle part of these mountains. The collision between European and African plates localized in northern Iberia from the Eocene to Oligocene and later migrated to southern Iberia during the Miocene. No major tectonic convergence was accommodated in the Cantabrians Mountains since the Oligocene, entering the orogen an erosional phase since then. The GIS-analysis present here, using 5 and 25 m-resolution DEMs by the Spanish National Geographical Institute, aims to identify the major features and to characterize the overall relief of the Cantabrians Mountains. In our preliminary approach, we present swath profiles, major river basins, watershed, longitudinal profiles of major rivers and hypsometric curves from selected areas that cover the studied orogen segment. Major tectonic structures control the location and orientation of the main watershed of the mountain range, but also the orientation of some local watersheds, e.g. associated to the Llanera thrust or the Ventaniella (strike-slip) fault. An unexpected result is that the average altitude along the water divide is 1,500 m, regardless of the large differences in crustal thickness along the study area. Most

  4. The Mars Crustal Magnetic Field Control of Plasma Boundary Locations and Atmospheric Loss: MHD Prediction and Comparison with MAVEN

    Science.gov (United States)

    Fang, Xiaohua; Ma, Yingjuan; Masunaga, Kei; Dong, Chuanfei; Brain, David; Halekas, Jasper; Lillis, Robert; Jakosky, Bruce M.; Connerney, Jack; Grebowsky, Joseph; hide

    2017-01-01

    We present results from a global Mars time-dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3-D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic changes with time. We develop a physics-based, empirical algorithm to effectively summarize the multidimensional crustal field distribution. It is found that by organizing the model results using this new approach, the Mars crustal field shows a clear, significant influence on both the IMB and the BS. Specifically, quantitative relationships have been established between the field distribution and the mean boundary distances and the cross-section areas in the terminator plane for both of the boundaries. The model-predicted relationships are further verified by the observations from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our analysis shows that the boundaries are collectively affected by the global crustal field distribution, which, however, cannot be simply parameterized by a local parameter like the widely used subsolar longitude. Our calculations show that the variability of the intrinsic crustal field distribution in Mars-centered Solar Orbital itself may account for approx.60% of the variation in total atmospheric loss, when external drivers are static. It is found that the crustal field has not only a shielding effect for atmospheric loss but also an escape-fostering effect by positively affecting the transterminator ion flow cross-section area.

  5. Accuracy Analysis of Precise Point Positioning of Compass Navigation System Applied to Crustal Motion Monitoring

    Science.gov (United States)

    Wang, Yuebing

    2017-04-01

    Based on the observation data of Compass/GPSobserved at five stations, time span from July 1, 2014 to June 30, 2016. UsingPPP positioning model of the PANDA software developed by Wuhan University,Analyzedthe positioning accuracy of single system and Compass/GPS integrated resolving, and discussed the capability of Compass navigation system in crustal motion monitoring. The results showed that the positioning accuracy in the east-west directionof the Compass navigation system is lower than the north-south direction (the positioning accuracy de 3 times RMS), in general, the positioning accuracyin the horizontal direction is about 1 2cm and the vertical direction is about 5 6cm. The GPS positioning accuracy in the horizontal direction is better than 1cm and the vertical direction is about 1 2cm. The accuracy of Compass/GPS integrated resolving is quite to GPS. It is worth mentioning that although Compass navigation system precision point positioning accuracy is lower than GPS, two sets of velocity fields obtained by using the Nikolaidis (2002) model to analyze the Compass and GPS time series results respectively, the results showed that the maximum difference of the two sets of velocity field in horizontal directions is 1.8mm/a. The Compass navigation system can now be used to monitor the crustal movement of the large deformation area, based on the velocity field in horizontal direction.

  6. Short note: Crustal deformation in the key stone network detected by satellite laser ranging

    Science.gov (United States)

    Schillak, S.; Wnuk, E.; Kunimori, H.; Yoshino, T.

    2006-03-01

    The paper presents the results of crustal deformation, as evidenced by changed station coordinates, in the Tokyo metropolitan area detected by the satellite laser ranging (SLR) technique. The coordinates of two Key Stone SLR stations, Tateyama and Kashima, were determined from 4 weeks of orbital arcs of the LAGEOS-1 and LAGEOS-2 satellites with respect to 16 SLR stations kept fixed in the ITRF2000 reference frame. The station coordinates were calculated using the NASA GEODYN-II orbital program. The orbital RMS-of-fit for both satellites was 16 mm. The standard deviation of the estimated positions was 3 mm. A jump of about 5 cm in the baseline length between the Kashima and Tateyama stations was detected in June August 2000 by VLBI and GPS techniques. This work confirms this crustal deformation as determined by SLR and vice versa. Analysis of coordinates of these stations shows that this effect was caused by a 4.5-cm displacement of the Tateyama station in the north-east direction. The change in the vertical component was not significant.

  7. Preliminary maps of crustal thickness and regional seismic phases for the Middle East and North Africa

    Energy Technology Data Exchange (ETDEWEB)

    Sweeney, J.J.

    1995-09-06

    As part of the development of regional seismic discrimination methods for the Middle East and North Africa (MENA) the author is building a database of information related to seismic propagation and crustal structure as well as associated geologic-tectonic and geophysical data. He hopes to use these data to construct and test models of regional seismic propagation and evaluate various detection/discrimination scenarios. To date, the database has been developed by building on a list of references for MENA provided by the Institute for the Study of the Continents (INSTOC) at Cornell University. To this list the author has added an equal number of references resulting from his own literature search which has emphasized papers dealing with seismicity and regional and teleseismic phase data. This paper represents an initial attempt to consolidate some of the information from the database into a form useful to researchers modeling regional seismic waveforms. The information compiled in this report is supplemental to the INSTOC database and has not been compiled anywhere else. What follows is a series of maps which illustrate the spatial variation of seismic phase velocities and crustal thickness. The text identifies the sources of information used in the map preparation. Data for the compilation of these maps has come from an initial search of the database as it presently exists and is not intended to be exhaustive. The author hopes that this initial exercise will help to identify areas and types of data that are deficient and help to focus future data gathering activities.

  8. Crustal growth history of the Korean Peninsula: Constraints from detrital zircon ages in modern river sediments

    Directory of Open Access Journals (Sweden)

    Taejin Choi

    2016-09-01

    Full Text Available U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS. The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. We obtained 515 concordant to slightly discordant zircon ages ranging from ca. 3566 to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic (249–79 Ma and Paleoproterozoic (2491–1691 Ma ages with subordinate Archean ages indicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage basins of the South Korean rivers and the crustal growth of the southern Korean Peninsula was focused in these two periods. Comparison of detrital zircon-age data between the North and South Korean river sediments reveals that the Paleoproterozoic zircon age distributions of both regions are nearly identical, while the Neoproterozoic–Paleozoic ages exist and the Mesozoic ages are dominant in southern Korean Peninsula. This result suggests that Precambrian terrains in Korea record the similar pre-Mesozoic magmatic history and that the influence of Mesozoic magmatism was mainly focused in South Korea.

  9. Evidence of Dynamic Crustal Deformation in Tohoku, Japan, From Time-Varying Receiver Functions

    Science.gov (United States)

    Porritt, R. W.; Yoshioka, S.

    2017-10-01

    Temporal variation of crustal structure is key to our understanding of Earth processes on human timescales. Often, we expect that the most significant structural variations are caused by strong ground shaking associated with large earthquakes, and recent studies seem to confirm this. Here we test the possibility of using P receiver functions (PRF) to isolate structural variations over time. Synthetic receiver function tests indicate that structural variation could produce PRF changes on the same order of magnitude as random noise or contamination by local earthquakes. Nonetheless, we find significant variability in observed receiver functions over time at several stations located in northeastern Honshu. Immediately following the Tohoku-oki earthquake, we observe high PRF variation clustering spatially, especially in two regions near the beginning and end of the rupture plane. Due to the depth sensitivity of PRF and the timescales over which this variability is observed, we infer this effect is primarily due to fluid migration in volcanic regions and shear stress/strength reorganization. While the noise levels in PRF are high for this type of analysis, by sampling small data sets, the computational cost is lower than other methods, such as ambient noise, thereby making PRF a useful tool for estimating temporal variations in crustal structure.

  10. Crustal history of Margarita Island (Venezuela) in detail: Constraint on the Caribbean plate-tectonic scenario

    Science.gov (United States)

    Stöckhert, Bernhard; Maresch, Walter V.; Brix, Manfred; Kaiser, Claudia; Toetz, Andreas; Kluge, Rolf; Krückhans-Lueder, Gabriela

    1995-09-01

    The pressure-temperature-time-deformation evolution for the crust of Margarita Island (Venezuela) has been established to allow comparison with current plate-tectonic models for the Caribbean region. On Margarita, the 12 recognizable stages of development can be summarized in terms of the following evolving tectonic settings: Protolith evolution as Aptian-Albian or older oceanic crust, as well as continental crust with Paleozoic basement (stages 1 and 2); accretion and high-pressure metamorphism (500 600 °C, 10 14 kbar) as the Margarita Complex in the deep level of a fore arc at 100 90 Ma (stage 3); ascent, cooling, and emplacement into the intermediate crustal level of a volcanic arc at 90 80 Ma (stage 4); transform plate-margin setting at a comparable level at 80 50 Ma (stage 5); second episode of rapid uplift and cooling (stages 6 and 7); and shallow crustal level close to transform plate margin from 50 Ma to present (stages 8 to 12). This complex sequence is in excellent agreement with plate-tectonic scenarios that require a Pacific origin for the Caribbean plate and eastward migration of the Margarita Complex and its correlatives along northern South America since the Cretaceous.

  11. Study of crustal structure and geological implications of southwestern margin of Northeast India

    Science.gov (United States)

    Saikia, Sowrav; Baruah, Santanu; Chopra, Sumer; Singh, Upendra K.; Gogoi, Bibhuti; Gohain, Himanata B.

    2017-10-01

    It is noticed that few geophysical studies have been carried out to decipher the crustal structure of southwestern part of the Northeast India comprising of Tripura fold belt and Bengal basin as compared to the Shillong plateau and the Brahmaputra basin. This region has a long history of seismicity that is still continuing. We have determined first-order crustal features in terms of Moho depths (H) and average VP/VS ratios (κ) using H-κ stacking technique. The inversion of receiver functions data yields near surface thick sedimentary layer in the Bengal basin, which is nearly absent in the Shillong plateau and Tripura fold belt. Our result suggests that the crust is thicker (38-45 km) in the Tripura fold belt region with higher shear-wave velocity in the lower crust than the Shillong plateau. The distribution of VP/VS ratio indicates heterogeneity throughout the whole region. While low to medium value of Poisson's ratio (1.69-1.75) indicates the presence of felsic crust in the Shillong plateau of the extended Indian Archean crust. The medium to high values of VP/VS ratio (> 1.780) in the Bengal basin and the Tripura fold belt region represent mafic crust during the formation of the Bengal delta and the Tripura fold belt creation in the Precambrian to the Permian age. The depth of the sediments in the Bengal basin is up to 8 km on its eastern margin, which get shallower toward its northeastern and southeastern margins.

  12. DEEP CRUSTAL STRUCTURE AND ESTIMATION OF MOHO IN THE LHASA TERRANE OF CENTRAL TIBET

    Directory of Open Access Journals (Sweden)

    Ul-Islam Md. Sultan

    2008-12-01

    Full Text Available Seismic attributes analysis is applied to INDEPTH II seismic profiles to develop a better understanding of the deep crustal structure and geodynamics of the Lhasa Terrane in the central Tibet area. Analyses indicate that the frequency anomalies are obtained over the range in between 0-30 Hz. Some area of the analyzed traces of the seismic profiles have shown dominated frequency anomaly approximately 10 Hz with little amount of other frequencies. The variation of frequency anomaly is shown to be the indication of theMoho depth of the area. EstimatedMoho depths are found very irregular and varying from20 kmto more than 136 km. The crust is thinner in southern, northern and eastern parts of the area while it is thicker in the western part having asymmetric nature in the central part. This variation might be the result of the complicated tectonic process of the Indian and Eurasian plates. Vertically downward pocket like frequency distributions and similar type frequency distributions at near and far depth are also observed in one of the analyzed sections. It might be indication of uprised asthenospheric matter which exchanged with lithosphere in subduction zones related to the multiple crustal uprising.

  13. Development of acceleration time histories for Semarang, Indonesia, due to shallow crustal fault earthquakes

    Science.gov (United States)

    Partono, Windu; Irsyam, Masyhur; Wardani, Sri Prabandiyani Retno

    2017-11-01

    Research on seismic, microzonation of Semarang is still ongoing. Following the research conducted by Team for Revision of Hazard Maps of Indonesia 2010, Lasem fault was the only fault that should be taken into account for seismic mitigation of Semarang. New research conducted by Team for Updating of Seismic Hazard Maps of Indonesia 2016 suggesting four new and closest shallow crustal fault sources (Rawapening, Weleri, Demak and Semarang Faults) which should be taken into account for seismic hazard mitigation of this city. Those four new seismic sources are typical reverse mechanism seismic sources. However Lasem fault is a typical strike slip mechanism seismic source. This paper presents the development of surface acceleration time histories due to three shallow crustal fault (Lasem, Semarang and Demak) earthquake sources with average magnitude 6.5 Mw. This research was performed by implementing de-aggregation hazard analysis, response spectral matching and site response analysis to obtain modified acceleration time histories. The modified acceleration time histories were developed due to inadequate data caused by those three fault sources. Surface acceleration time histories were calculated at 288 boring locations and then separated into three different time histories based on site class soil conditions (hard, medium and soft soil classes).

  14. Complex igneous processes and the formation of the primitive lunar crustal rocks

    Science.gov (United States)

    Longhi, J.; Boudreau, A. E.

    1979-01-01

    Crystallization of a magma ocean with initial chondritic Ca/Al and REE ratios such as proposed by Taylor and Bence (TB, 1975), is capable of producing the suite of primitive crustal rocks if the magma ocean underwent locally extensive assimilation and mixing in its upper layers as preliminary steps in formation of an anorthositic crust. Lunar anorthosites were the earliest permanent crustal rocks to form the result of multiple cycles of suspension and assimilation of plagioclase in liquids fractionating olivine and pyroxene. There may be two series of Mg-rich cumulate rocks: one which developed as a result of the equilibration of anorthositic crust with the magma ocean; the other which formed in the later stages of the magma ocean during an epoch of magma mixing and ilmenite crystallization. This second series may be related to KREEP genesis. It is noted that crystallization of the magma ocean had two components: a low pressure component which produced a highly fractionated and heterogeneous crust growing downward and a high pressure component which filled in the ocean from the bottom up, mostly with olivine and low-Ca pyroxene.

  15. Influence of a meteorological cycle in mid-crustal seismicity of the Nepal Himalaya

    Science.gov (United States)

    Kundu, Bhaskar; Vissa, Naresh Krishna; Panda, Dibyashakti; Jha, Birendra; Asaithambi, Renuhaa; Tyagi, Bhishma; Mukherjee, Sohinee

    2017-09-01

    The process of interseismic strain accumulation across the Nepal Himalaya is associated with micro seismicity (also called mid-crustal seismicity) which occurs along the mid-crustal ramp on the Main Himalayan Thrust (MHT). The seismicity shows strong annual periodicity in response to the annual stress variation of hydrological loads. We report dominance of annual periodicity in the eastern Nepal as compared to that of western Nepal, and overall annual periodicity dominance in the small magnitude earthquakes (Mw 0-3). Rainfall seismicity cross-correlation is significantly higher in the eastern Nepal region as compared to that of western Nepal with a prominent phase lag of 5-6 months with respect to the occurrence of monsoonal rainfall. Seasonal modulation can be explained by Coulomb failure stress model and fault resonance hypothesis induced by meteorological cycle. This new observation upholds the existing hypothesis that evaporation induced unloading in the Himalayan foothills and adjacent Indo-Gangetic plains during the post-monsoon period (i.e., during winter) add significant component of horizontal compression to the interseismic contraction at the MHT, which is the main driving mechanism for the seasonal modulation.

  16. Seasonal Mass Changes and Crustal Vertical Deformations Constrained by GPS and GRACE in Northeastern Tibet

    Directory of Open Access Journals (Sweden)

    Yuanjin Pan

    2016-08-01

    Full Text Available Surface vertical deformation includes the Earth’s elastic response to mass loading on or near the surface. Continuous Global Positioning System (CGPS stations record such deformations to estimate seasonal and secular mass changes. We used 41 CGPS stations to construct a time series of coordinate changes, which are decomposed by empirical orthogonal functions (EOFs, in northeastern Tibet. The first common mode shows clear seasonal changes, indicating seasonal surface mass re-distribution around northeastern Tibet. The GPS-derived result is then assessed in terms of the mass changes observed in northeastern Tibet. The GPS-derived common mode vertical change and the stacked Gravity Recovery and Climate Experiment (GRACE mass change are consistent, suggesting that the seasonal surface mass variation is caused by changes in the hydrological, atmospheric and non-tidal ocean loads. The annual peak-to-peak surface mass changes derived from GPS and GRACE results show seasonal oscillations in mass loads, and the corresponding amplitudes are between 3 and 35 mm/year. There is an apparent gradually increasing gravity between 0.1 and 0.9 μGal/year in northeast Tibet. Crustal vertical deformation is determined after eliminating the surface load effects from GRACE, without considering Glacial Isostatic Adjustment (GIA contribution. It reveals crustal uplift around northeastern Tibet from the corrected GPS vertical velocity. The unusual uplift of the Longmen Shan fault indicates tectonically sophisticated processes in northeastern Tibet.

  17. Seismic evidence for a possible deep crustal hot zone beneath Southwest Washington

    Science.gov (United States)

    Flinders, Ashton; Shen, Yang

    2017-01-01

    Crustal pathways connecting deep sources of melt and the active volcanoes they supply are poorly understood. Beneath Mounts St. Helens, Adams, and Rainier these pathways connect subduction-induced ascending melts to shallow magma reservoirs. Petrogenetic modeling predicts that when these melts are emplaced as a succession of sills into the lower crust they generate deep crustal hot zones. While these zones are increasingly recognized as a primary site for silicic differentiation at a range of volcanic settings globally, imaging them remains challenging. Near Mount Rainier, ascending melt has previously been imaged ~28 km northwest of the volcano, while to the south, the volcano lies on the margin of a broad conductive region in the deep crust. Using 3D full-waveform tomography, we reveal an expansive low-velocity zone, which we interpret as a possible hot zone, linking ascending melts and shallow reservoirs. This hot zone may supply evolved magmas to Mounts St. Helens and Adams, and possibly Rainier, and could contain approximately twice the melt volume as the total eruptive products of all three volcanoes combined. Hot zones like this may be the primary reservoirs for arc volcanism, influencing compositional variations and spatial-segmentation along the entire 1100 km-long Cascades Arc.

  18. On the development of the calc-alkaline and tholeiitic magma series: A deep crustal cumulate perspective

    Science.gov (United States)

    Chin, Emily J.; Shimizu, Kei; Bybee, Grant M.; Erdman, Monica E.

    2018-01-01

    Two distinct igneous differentiation trends - the tholeiitic and calc-alkaline - give rise to Earth's oceanic and continental crust, respectively. Mantle melting at mid-ocean ridges produces dry magmas that differentiate at low-pressure conditions, resulting in early plagioclase saturation, late oxide precipitation, and Fe-enrichment in mid-ocean ridge basalts (MORBs). In contrast, magmas formed above subduction zones are Fe-depleted, have elevated water contents and are more oxidized relative to MORBs. It is widely thought that subduction of hydrothermally altered, oxidized oceanic crust at convergent margins oxidizes the mantle source of arc magmas, resulting in erupted lavas that inherit this oxidized signature. Yet, because our understanding of the calc-alkaline and tholeiitic trends largely comes from studies of erupted melts, the signals from shallow crustal contamination by potentially oxidized, Si-rich, Fe-poor materials, which may also generate calc-alkaline rocks, are obscured. Here, we use deep crustal cumulates to "see through" the effects of shallow crustal processes. We find that the tholeiitic and calc-alkaline trends are indeed reflected in Fe-poor mid-ocean ridge cumulates and Fe-rich arc cumulates, respectively. A key finding is that with increasing crustal thickness, arc cumulates become more Fe-enriched. We propose that the thickness of the overlying crustal column modulates the melting degree of the mantle wedge (lower F beneath thick arcs and vice versa) and thus water and Fe3+ contents in primary melts, which subsequently controls the onset and extent of oxide fractionation. Deep crustal cumulates beneath thick, mature continental arcs are the most Fe-enriched, and therefore may be the "missing" Fe-rich reservoir required to balance the Fe-depleted upper continental crust.

  19. Crustal structure of the Carpathian orogen from receiver function analysis: how craton subduction and active delamination affect the crust

    Science.gov (United States)

    Petrescu, Laura; Tataru, Dragos; Grecu, Bogdan

    2017-04-01

    The Carpathian arc is an uncommon curved collisional system, involving the subduction of the Eastern European craton and the Proterozoic Moesian platform beneath younger European microplates. The Cenozoic collision led to the closure of the Tethys Oceanic basin, portions of which are actively breaking off or delaminating beneath the orogen, generating deep mantle earthquakes. Neogene volcanism, possibly related to subduction slab roll-back, also formed a band of presently extinct volcanoes in the back-arc region. The Carpathian embayment is thus an ideal laboratory to investigate crustal processes related to subduction of cratonic material, multiple plate junctions and active delamination. To better understand how the crustal structure changes from the Eastern European cratonic foreland, across the curved subduction zone, to the younger European microplates, we analyse teleseismic earthquakes recorded at broadband seismic stations located across eastern and southern Carpathians, in Romania and Moldova. We processed data from permanent seismic networks (The Romanian National Seismic Network) as well as data from temporary deployments such as CALIXTO (Carpathian Arc Lithosphere X-Tomography) and SCP (South Carpathian Project). Using extended multi-taper spectral division, we compute and analyse radial and transverse receiver functions. Energy on the transverse component may be an indicator of crustal anisotropy or the existence of intracrustal dipping interfaces. Using phase-weighted H-k stacking of receiver functions, we estimate the crustal thickness and the bulk crustal Poisson's ratio as well as the seismic sharpness of the Moho discontinuity. Furthermore, we invert receiver functions to obtain the S-wave velocity structure of the crust and upper mantle beneath individual stations, which provide concurrent information on the Moho nature. Our results provide a better understanding of crustal structure across complex collisional systems involving the subduction of

  20. Crustal deformation across the Southern Patagonian Icefield: GNSS observations and GIA models

    Science.gov (United States)

    Mendoza, Luciano; Richter, Andreas; Marderwald, Eric; Hormaechea, José Luis; Ivins, Erik; Perdomo, Raúl; Lange, Heiner; Schröder, Ludwig; Dietrich, Reinhard

    2017-04-01

    We present the geodetic observation and geodynamic interpretation of crustal deformation rates in a network of 43 GNSS sites covering the region of the Southern Patagonian Icefield (Argentina and Chile). Repeated and semi-permanent GNSS observations initiated in 1996 yield 3D site velocities within a terrestrial reference frame with mean accuracies of 1 mm/a and 6 mm/a for the horizontal and vertical components, respectively. These site velocities are interpreted with regard to the magnitude, patterns and primary driving processes of vertical and horizontal present-day crustal deformation (Richter et al. 2016). The vertical site velocities document a rapid uplift causally related to glacial-isostatic adjustment (GIA) reaching 4 cm/a. They yield now an unambiguous preference between two competing regional GIA models (Lange et al. 2014). Remaining discrepancies between the preferred model and our observations point toward an exceptionally low effective upper mantle viscosity and effects of lateral rheological heterogeneities. The extension and geometry of our network allow, for the first time, also a detailed analysis of the horizontal velocity components. An analysis of the horizontal strain-rate field reveals a complex composite, with compression dominating in the west and extension in the east. The observed velocities suggest significant contributions from three processes: GIA, a western interseismic tectonic deformation field related to plate subduction, and an extensional strain-rate field related to active Patagonian slab window tectonics. They document a dual interaction between the peculiar tectonic situation and the visco-elastic response to ice-load changes: First, a mechanical superposition of the characteristic patterns of each of the three processes, which results in the complex superposition of horizontal deformation revealed by our strain analysis. And second, the lateral differentiation of the glacial-isostatic response imposed by the three

  1. Hf isotope evidence for variable slab input and crustal addition in basalts and andesites of the Taupo Volcanic Zone, New Zealand

    DEFF Research Database (Denmark)

    Waight, Tod Earle; Troll, Valentin R.; Gamble, J.A.

    2017-01-01

    Crustal contamination complicates the identification of primary mantle-derived magma compositions in Continental arcs. However,when crustal processes and components arewell characterised, it is possible to extrapolate through continental arc magma compositional arrays towards the Hf and Nd isotop...

  2. Long-Span Continuous Self-Potential Measurements Around Earthquake Swarms for Monitoring Crustal Activity

    Science.gov (United States)

    Yoshimura, R.; Oshiman, N.; Yamazaki, K.; Uyeshima, M.; Ogawa, T.

    2008-12-01

    Earthquake swarm activity has been continuously observed around the southeastern flank of Ontake stratovolcano since 1976. A large earthquake with the depth about 2 km and a magnitude of 6.8 occurred in 1984 in the southeastern flank of the volcano. Recently, Kimata et al. (2004) revealed uplift ground deformation above the earthquake swarm area by using repeated leveling. Furthermore, MagnetoTelluric (MT) soundings estimated a low resistivity region with the depth about 2km beneath the uplift area (Kasaya et al., 2002). In order to investigate a relationship between tectonic movements and subsurface low resistivity zone, Yoshimura et al. (2007) carried out self-potential (SP) measurements from 2003 to 2005 around the earthquake swarm areas. As the result of SP measurements, a torus-shape positive SP anomaly has been detected at the eastern part of the survey profile. This anomaly is located between recent active clusters of earthquakes and near the ground uplift detected by Kimata et al. (2004). Given that the obtained anomaly delineates the subsurface fluid"fs motion due to thermal or crustal activities, it could be expected that the anomaly varies in association with fluctuation of crustal activities. In February 2007, we established a continuous SP observation network with the aim of monitoring the crustal/hydrothermal activity by reference to the obtained SP distribution. This network consists of 8 Pb- PbCl2 electrodes and uses metallic telephone lines as insulated cables for measuring SP. Voltage differences between electrodes are measured at an interval of 1 sec. This observation technique, called "Network-MT", has been developed to determine large-scale electrical conductivity structure and the spatial distribution of the telluric potentials (Uyeshima, 2007). As a preliminary result of longitudinal data analysis, night time daily median values showed remarkable stepwise SP time variations with relaxation time about 15 days in August 2007. Additionally

  3. Crustal Seismic Structure beneath Portugal (Western Iberia) and the role of Variscan Inheritance

    Science.gov (United States)

    Veludo, Idalina; Afonso Dias, Nuno; Fonseca, Paulo; Matias, Luís; Carrilho, Fernando; Haberland, Christian; Villaseñor, Antonio

    2017-04-01

    Mainland Portugal comprises most of the Western portion of the Iberian Peninsula, in a geodynamic setting associated with the Africa-Eurasia plate boundary. The crustal structure in Portugal is the result of a complex assemblage history of continental collision and extension with most of the surface is covered by rocks dating to the Variscan orogeny, the coastal ranges dominated by Mesozoic structures and Mesocenozoic basins covering partially the mainland. The impact and extension of this complex tectonic in the structure of the Iberian Lithosphere is still a matter of discussion, especially in its western part beneath Portugal. The existing knowledge relating the observed surface geology and lithospheric structures is sparse and sometimes incoherent, the relation between shallow and deep structures and their lateral extension still widely undetermined. Some questions still pertinent are the role and influence of the several tectonic units and their contacts in the present tectonic regime and in the stress field observed today, and the relation between the anomalous seismicity and associated crustal deformation rates with the inherited structure from past orogenies. In this study we present the results of a local earthquake tomographic study, performed to image this complex crustal structure down to 20 km depth. The relocation of the onshore seismicity recorded in the period 2000-2014 with the new 3D model allows cleansing some of the alignments and their correlation with some of the main active structures in Portugal enabling for the first time to correlate a large number of tectonic features to the small magnitude seismicity pattern. The seismicity distribution also displays a complex pattern, mainly reflecting the interaction between inherited Variscan structures with more recent fault systems created during the rifting stages of the Atlantic and diapir magmatic intrusions. The complex history of the assemblage of the crust beneath Western Iberia is well

  4. Geophysical evidence for the crustal variation and distribution of magmatism along the central coast of Mozambique

    Science.gov (United States)

    Mueller, Christian Olaf; Jokat, Wilfried

    2017-08-01

    For our understanding of the timing and geometry of the initial Gondwana break-up, still a consistent image of the crustal composition of the conjugated margins of central Mozambique and Antarctica and the location of their continent-ocean boundaries is missing. In this regard, a main objective is the explanation for the source of the different magnetic signature of the conjugate margins. Based on a revised investigation of wide-angle seismic data along two profiles across the Mozambican margin by means of an amplitude modelling, this study presents the crustal composition across and along the continental margin of central Mozambique. Supported by 2D magnetic modelling, the results are compared to the conjugate margin in Antarctica and allow new conclusions about their joined tectonic evolution. An observed crustal diversity between the north-eastern and south-western parts of the central Mozambican margin, testifies to the complex break-up history of this area. Conspicuous is the equal spatial extent of the HVLCB along the margin of 190-215 km. The onset of oceanic crust at the central Mozambican margin is refined to chron M38n.2n (164.1 Ma). Magnetic modelling supports the presence of reversed polarized SDRs in the continent-ocean transition that were mainly emplaced between 168.5 and 166.8 Ma (M42-M40). Inferred SDRs in the Riiser-Larsen Sea might be emplaced sometime between 166.8 and 164.1 Ma (M39-M38), but got overprinted by normal polarized intrusions of a late stage of rift volcanism, causing the opposite magnetic signature of the conjugate margins. The distribution of the magmatic material along the central coast of Mozambique clearly indicates the eastern extension of the north-eastern branch of the Karoo triple rift along the entire margin. The main magmatic phase affecting this area lasted for at least 12 Myr between 169 and 157 Ma, followed by the cease of the magmatism, perhaps due to the relative southwards motion of the magmatic centre.

  5. Geomorphic Response to Crustal Evolution of the Plate Boundary, northern California

    Science.gov (United States)

    Shi, X.; Kirby, E.; Furlong, K. P.

    2009-12-01

    The Coast Ranges in northern California are located within a developing transform plate boundary (San Andreas-Maacama-Bartlett Springs strike slip faults) and experience a crustal evolution driven by the migration of the Mendocino Triple Junction. How the landscape responds to the evolution of this plate boundary, however, is uncertain. Here, we analyze channel longitudinal profiles developed throughout the Coast Ranges to investigate the link between surface and deeper-seated processes. In particular, we focus on a crustal transition zone centered around the Little Lake Valley (Willits). Using the USGS 10m DEM to extract longitudinal stream profiles, we identify knickpoints and their spatial positions, calculate channel steepnesses and concavities, and analyze the pattern of knickpoint migration to explore possible driving mechanisms for landscape evolution. Our results reveal two first-order “domains” in the Coast Ranges. West of the Maacama fault system, drainages exhibit smooth, concave-up profiles with no discernable knickpoints. Preservation of relict patches of a high-elevation, low-relief landscape along the drainage divide between these coastal streams and inland watersheds (Eel and Russian Rivers) is consistent with progressive emergence of this region from below sea level, as indicated by relict shallow marine deposits (Ohlson Ranch Formation). East of the divide, tributaries of the Russian and Eel rivers exhibit knickpoints that separate downstream reaches of high gradient from lower-gradient headwater reaches. These are interpreted to reflect a transient increase in incision rates following either 1) stream capture, or 2) local vertical movements along the Maacama fault system. An example of this is found in the region east of Little Lake Valley, drainages are beheaded along the range front fault bounding the eastern side of the valley, suggesting relatively recent west-side down displacement along this fault system. Overall, our analysis suggests

  6. Resistant river basins as recorder of distributed crustal deformation: examples from New Zealand and Lebanon

    Science.gov (United States)

    Castelltort, S.; Goren, L.; Willett, S.; Champagnac, J.; Herman, F.

    2011-12-01

    Rivers are useful markers of crustal deformation because they deform together with the rocks over which they flow. For instance, at the scale of individual faults, offset rivers and alluvial fans have been used to reconstruct past slip rates(1), while the basins of major rivers have been utilized to estimate pervasive crustal strain at the continental scale(2). However, river basins have also been claimed to reorganize into similar equilibrium forms(3) independently of the tectonic regime. According to this latter view, river basins cannot serve as reliable markers of deformation since their boundaries adjust dynamically during deformation by processes of capture and divide migration. Here we show that both views are correct under different conditions, as different basins in the same tectonic field may or may not be persistent and record the history of deformation, depending on the relation between their geomorphic position and the nature and directionality of the strain field. To demonstrate this new understanding we study the planform of drainage basins along two major transpressive plate boundaries that partly show patterns that are spatially consistent with the assumed tectonic regime: the Alpine Fault in the South Island of New Zealand which marks the boundary between the Pacific and the Australian plates, and the Dead Sea Fault in Lebanon which strands the Africa-Arabia plate boundary. First we use a combination specific river basin modeling and planview morphometric analysis to unravel deformation from reorganization and identify the basins that may serve as reliable deformation markers. Then we use these reliable markers to constrain the slip rate over these two plate boundaries. Our analysis results show that, both in New Zealand and in Lebanon, a significant proportion of up to 55% of the plate motion over geological time scales is absorbed by distributed deformation away from the plate boundary. (1)--Allen, C. R. Transcurrent Faults in Continental Areas

  7. Crustal Models Assessment in Western Part of Romania Employing Active Seismic and Seismologic Methods

    Science.gov (United States)

    Bala, Andrei; Toma-Danila, Dragos; Tataru, Dragos; Grecu, Bogdan

    2017-12-01

    In the years 1999 - 2000 two regional seismic refraction lines were performed within a close cooperation with German partners from University of Karlsruhe. One of these lines is Vrancea 2001, with 420 km in length, almost half of them recorded in Transylvanian Basin. The structure of the crust along the seismic line revealed a very complicated crustal structure beginning with Eastern Carpathians and continuing in the Transylvanian Basin until Medias. As a result of the development of the National Seismic Network in the last ten years, more than 100 permanent broadband stations are now continuously operating in Romania. Complementary to this national dataset, maintained and developed in the National Institute for Earth Physics, new data emerged from the temporary seismologic networks established during the joint projects with European partners in the last decades. The data gathered so far is valuable both for seismology purposes and crustal structure studies, especially for the western part of the country, where this kind of data were sparse until now. Between 2009 and 2011, a new reference model for the Earth’s crust and mantle of the European Plate was defined through the NERIES project from existing data and models. The database gathered from different kind of measurements in Transylvanian Basin and eastern Pannonian Basin were included in this NERIES model and an improved and upgraded model of the Earth crust emerged for western part of Romania. Although the dataset has its origins in several periods over the last 50 years, the results are homogeneous and they improve and strengthen our image about the depth of the principal boundaries in the crust. In the last chapter two maps regarding these boundaries are constructed, one for mid-crustal boundary and one for Moho. They were build considering all the punctual information available from different sources in active seismic and seismology which are introduced in the general maps from the NERIES project for

  8. Crustal and lithospheric imaging of the Atlas Mountains of Morocco inferred from magnetotelluric data

    Science.gov (United States)

    Kiyan, D.; Jones, A. G.; Fullea, J.; Hogg, C.; Ledo, J.; Sinischalchi, A.; Campanya, J.; Picasso Phase II Team

    2010-12-01

    The Atlas System of Morocco is an intra-continental mountain belt extending for more than 2,000 km along the NW African plate with a predominant NE-SW trend. The System comprises three main branches: the High Atlas, the Middle Atlas, and the Anti Atlas. We present the results of a very recent multi-institutional magnetotelluric (MT) experiment across the Atlas Mountains region that started in September, 2009 and ended in February, 2010, comprising acquisition of broadband and long-period MT data. The experiment consisted of two profiles: (1) a N-S oriented profile crossing the Middle Atlas through the Central High Atlas to the east and (2) a NE-SW profile crossing the western High Atlas towards the Anti Atlas to the west. The MT measurements are part of the PICASSO (Program to Investigate Convective Alboran Sea System Overturn) and the concomitant TopoMed (Plate re-organization in the western Mediterranean: Lithospheric causes and topographic consequences - an ESF EUROCORES TOPO-EUROPE project) projects, to develop a better understanding of the internal structure and evolution of the crust and lithosphere of the Atlas Mountains. The MT data have been processed with robust remote reference methods and submitted to comprehensive strike and dimensionality analysis. Two clearly depth-differentiated strike directions are apparent for crustal (5-35 km) and lithospheric (50-150 km) depth ranges. These two orientations are roughly consistent with the NW-SE Africa-Eurasia convergence acting since the late Cretaceous, and the NNE-SSW Middle Atlas, where Miocene to recent Alkaline volcanism is present. Two-dimensional (2-D) smooth electrical resistivity models were computed independently for both 50 degrees and 20 degrees E of N strike directions. At the crustal scale, our preliminary results reveal a middle to lower-crustal conductive layer stretching from the Middle Atlas southward towards the High Moulouya basin. The most resistive (and therefore potentially thickest

  9. Characteristics of regional crustal deformation before 2016 Menyuan Ms6.4 earthquake

    Directory of Open Access Journals (Sweden)

    Weitao Chen

    2016-07-01

    Full Text Available On January 21, 2016, a strong earthquake with a magnitude of Ms6.4 happened at Menyuan, Qinghai Province of China. In almost the same place, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. In this paper, we analyze the characteristics of regional crustal deformation before the 2016 Menyuan Ms6.4 earthquake by using the data from 10 continuous Global Positioning System (GPS stations and 74 campaign-mode GPS stations within 200 km of this event: (a Based on the velocity field from over ten years GPS observations, a regional strain rate field is calculated. The results indicate that the crustal strain rate and seismic moment accumulation rate of the Qilian-Haiyuan active fault, which is the seismogenic tectonics of the event, are significantly higher than the surrounding regions. In a 20 km × 20 km area around the seismogenic region, the maximum and minimum principal strain rates are 21.5 nanostrain/a (NW–SE extension and −46.6 nanostrain/a (NE–SW compression, respectively, and the seismic moment accumulation rates is 17.4 Nm/a. The direction of principal compression is consistent with the focal mechanism of this event. (b Based on the position time series of the continuous GPS stations for a time-span of about 6 years before the event, we calculate the strain time series. The results show that the dilatation of the seismogenic region is continuously reduced with a “non-linear” trend since 2010, which means the seismogenic region has been in a state of compression. However, about 2–3 months before the event, both the dilatation and maximum shear strain show significant inverse trends. These abnormal changes of crustal deformation may reflect the non-linear adjustment of the stress–strain accumulation of the seismogenic region, when the accumulation is approaching the critical value of rupture.

  10. Coupling models of crustal deformation and mantle convection: An application of GeoFramework

    Science.gov (United States)

    Choi, E.; Thoutireddy, P.; Lavier, L.; Quenette, S.; Tan, E.; Gurnis, M.; Aivazis, M.; Appelbe, B.

    2004-12-01

    Crustal and mantle deformation are two closely coupled dynamical systems, usually solved in isolation. To numerically solve this problem, it is desirable to have both the crust and mantle as active components of the dynamics. However, materials composing the crust and mantle respond to loading differently and two different constitutive relations are necessary to describe the rheology of this system. Deformations also occur over a wide range of length scales: from a few 100 m for fault zones to well over 104 km for the largest scales involved in mantle convection. As a result, the numerical cost for a single model to resolve all of these spatial features while also incorporating distinct material types is prohibitive. Coupling two distinct modeling codes within a computational framework is a natural avenue to tackle the multi-material and multi-scale dynamics associated with the crust-mantle system. Using GeoFramework (http://geoframework.org), an extension of the Pyre, Python-based modeling framework, the SNAC and CitcomS codes are dynamically coupled. CitcomS has been used in variety of studies of mantle convection; this finite element package has been entirely reengineered within the Pyre environment. SNAC is based on the FLAC algorithm and is well-suited to modeling crustal deformation because it can deal with linear elastic, Maxwell viscoelastic, or elastoplastic rheology with a Mohr-Coulomb criterion. Using the Pyre-coupled SNAC and CitcomS codes, we run 3D numerical experiments of the extension of lithosphere in the presence of a rising mantle plume within a regional spherical geometry. The full thickness of the crust is simulated with SNAC and mantle convection with CitcomS. In the far field, deformation is partly driven by prescribed velocities described by two diverging plates around a single Euler pole. This specific setting for the problem is intended to help understand the evolution of the Red Sea and Afar triple junction. We will show the dynamic

  11. Characterizing the Crustal architecture of the Parnaiba basin with passive-source seismology

    Science.gov (United States)

    Coelho, Diogo; Julià, Jordi; Rodríguez Tribaldos, Verónica; White, Nicky

    2017-04-01

    Lithospheric-scale processes, such as the origin and evolution of large cratonic basins, can create big footprints or signatures in the subsurface that can be observed by geophysical means. With a huge potential for natural resources, the equatorial margin of NE Brazil has motivated many geophysical investigations by the oil industry. Our study area is the Parnaíba Basin, one of the largest cratonic basins of the world. The main goal of our study is to provide new images of the crust and lithosphere under the basin and highlight seismic discontinuities within, in order to improve our understanding of its architecture and help constrain models for its origin and evolution. A total of 9 broadband seismographic stations were installed within the PBAP project, a collaboration among several universities and BP Energy do Brasil, along an approximately 500 km-long transect across the basin, with interstation spacing of around 50 km. The receiver function technique is probably one of the most successful methodologies in broadband seismology for imaging of the crust and lithospheric mantle in continental areas, and we estimated crustal thickness and Vp/Vs ratio of the Parnaíba Basin by developing P-wave receiver functions from the acquired dataset. We also developed one-dimensional velocity models calculated from the joint inversion of P-wave receiver function and Rayleigh dispersion curves. Results from HK-Stacking, receiver function migration and joint inversion indicate the Moho dips gently toward the depocenter of the basin, displaying up to three different behaviors: A flat Moho in the depocenter of the basin, which showed the thickest crust (>42 km) and Vp/Vs ratio values arround 1,75; A thinning crust towards the eastern flank (<38 km), bounding with the Borborema Province, with Vp/Vs ratio of 1,74; An almost flat Moho with thickness of 40 km and Vp/Vs ratio around 1,72 on the western border, bounding with the Araguaia Belt. We also noted some mid crustal

  12. Crustal-Scale Images of the Continent-Ocean Transition Across the Eastern Canadian Margins

    Science.gov (United States)

    Louden, K.; Gerlings, J.

    2009-05-01

    The acquisition and analysis of ~10, 400-500-km-long, deep MCS reflection and wide-angle reflection/refraction (WAR/R) profiles across the eastern Canadian continental margins from Nova Scotia to Baffin Is. have been accomplished over the past 20 years during a number of joint Canadian and international programs. The combination of both reflectivity and velocity images from separate MCS and WAR/R profiles have detailed the large-scale patterns of crustal extension, mantle serpentinization and exhumation, and ocean crustal formation both within and between rifted segments from full thickness continental crust to oceanic crust produced by sea-floor spreading. A number of striking features are documented by these crustal-scale sections. In particular, a wide transition region with very thin seismic crust is delineated by a well-defined upper mantle zone with reduced velocities interpreted as partially serpentinized peridotite. The geological nature of the transitional crust is quite complex and may consist of various regions dominated by highly stretched continental crust, highly serpentinized continental mantle or thin ultra-slow spread ocean crust. It is difficult to define the nature of this region from its velocity structure alone, however, since it is only poorly resolved by standard travel-time methods. One robust characteristic that is generally observed is an abrupt change to typical ocean crust at the seaward edge of the transition zone. This boundary shows characteristic and coincident variations in both velocity structure and basement morphology. New results from the eastern margin of Flemish Cap demonstrate such a pattern particularly well. This observation suggests that once melt begins to form it causes an abrupt shift from a diffuse pattern of lithospheric extension to a focused zone of melt formation. Based on our profiles, we suggest that such transitions have occurred at a number of discrete pulses, which progress in age from south to north and may

  13. Precambrian Crustal Evolution of the Hudson Bay Region: Insights from Receiver Function Analysis (Invited)

    Science.gov (United States)

    Thompson, D. A.; Bastow, I. D.; Helffrich, G. R.; Kendall, J. M.; Wookey, J.; Snyder, D. B.; Eaton, D. W.

    2009-12-01

    The processes that formed, thickened and thinned the early Earth's crust remain poorly known. The onset of modern plate tectonics, for example, could be as far back as the Hadean or as late as the Neoproterozoic. In many cratons, vertical processes are believed to have been dominant (dome-and-keel tectonics, e.g. Pilbara craton), while others are hypothesised to have formed by the progressive accretion of different terranes (e.g. Superior craton). The Hudson Bay region represents one of the largest areas of Precambrian geology on the planet, with ages spanning 2 billion years (3.9-1.8 Ga). The western Churchill province contains the predominantly Paleo- to Mesoarchean Rae domain and the Neoarchean Hearne domain, and is welded to the Superior craton by the Paleoproterozoic Trans-Hudson Orogen, a Himalayan scale feature which extends for more than 4500 km along strike. The Churchill has received comparatively little scientific investigation due to its remote location and harsh climate. In order to test hypotheses on crustal formation and evolution during the Precambrian, teleseismic receiver functions have been analysed for more than 30 stations located on the key geological features in the vicinity of Hudson Bay. Across the entire Rae domain, a dominantly felsic crust with a sharp Moho is observed. Little evidence exists to interpret the vast extent of the felsic crust in terms of subduction related processes. Within the granite-greenstone terranes of the Hearne domain, a more intermediate bulk composition and complex Moho signature may be representative of an oceanic affinity for the crust, suggesting accretionary processes acted there. In the Quebec-Baffin Island region, bulk crustal Vp/Vs ratios are dominated by effects associated with the Trans-Hudson Orogen, and appear to map out the first-order shape of the indenting lower-plate. Correlation between terrane age and receiver function-derived crustal structure suggests that the crust in northern Canada was

  14. Crustal Deformation in Southcentral Alaska: The 1964 Prince William Sound Earthquake Subduction Zone

    Science.gov (United States)

    Cohen, Steven C.; Freymueller, Jeffrey T.

    2003-01-01

    This article, for Advances in Geophysics, is a summary of crustal deformation studies in southcentral Alaska. In 1964, southcentral Alaska was struck by the largest earthquake (moment magnitude 9.2) occurring in historical times in North America and the second largest earthquake occurring in the world during the past century. Conventional and space-based geodetic measurements have revealed a complex temporal-spatial pattern of crustal movement. Numerical models suggest that ongoing convergence between the North America and Pacific Plates, viscoelastic rebound, aseismic creep along the tectonic plate interface, and variable plate coupling all play important roles in controlling both the surface and subsurface movements. The geodetic data sets include tide-gauge observations that in some cases provide records back to the decades preceding the earthquake, leveling data that span a few decades around the earthquake, VLBI data from the late 1980s, and GPS data since the mid-1990s. Geologic data provide additional estimates of vertical movements and a chronology of large seismic events. Some of the important features that are revealed by the ensemble of studies that are reviewed in this paper include: (1) Crustal uplift in the region that subsided by up 2 m at the time of the earthquake is as much as 1 m since the earthquake. In the Turnagain Arm and Kenai Peninsula regions of southcentral Alaska, uplift rates in the immediate aftermath of the earthquake reached 150 mm/yr , but this rapid uplift decayed rapidly after the first few years following the earthquake. (2) At some other locales, notably those away the middle of the coseismic rupture zone, postseismic uplift rates were initially slower but the rates decay over a longer time interval. At Kodiak Island, for example, the uplift rates have been decreasing at a rate of about 7mm/yr per decade. At yet other locations, the uplift rates have shown little time dependence so far, but are thought not to be sustainable

  15. Layered crust-mantle transition zone below a large crustal intrusion in the Norwegian-Danish basin

    DEFF Research Database (Denmark)

    Sandrin, Alessandro; Nielsen, Lars; Thybo, Hans

    2009-01-01

    crust-mantle transition zone as solidified melts of mantle affinity, which were intruded into the lowermost crust. The layered zone is proposed to be associated with the extensional tectonism that occurred in the area in Late Carboniferous-Early Permian, which also caused the large crustal intrusion...

  16. A Monte Carlo model of crustal field influences on solar energetic particle precipitation into the Martian atmosphere

    Science.gov (United States)

    Jolitz, R. D.; Dong, C. F.; Lee, C. O.; Lillis, R. J.; Brain, D. A.; Curry, S. M.; Bougher, S.; Parkinson, C. D.; Jakosky, B. M.

    2017-05-01

    Solar energetic particles (SEPs) can precipitate directly into the atmospheres of weakly magnetized planets, causing increased ionization, heating, and altered neutral chemistry. However, strong localized crustal magnetism at Mars can deflect energetic charged particles and reduce precipitation. In order to quantify these effects, we have developed a model of proton transport and energy deposition in spatially varying magnetic fields, called Atmospheric Scattering of Protons and Energetic Neutrals. We benchmark the model's particle tracing algorithm, collisional physics, and heating rates, comparing against previously published work in the latter two cases. We find that energetic nonrelativistic protons precipitating in proximity to a crustal field anomaly will primarily deposit energy at either their stopping altitude or magnetic reflection altitude. We compared atmospheric ionization in the presence and absence of crustal magnetic fields at 50°S and 182°E during the peak flux of the 29 October 2003 "Halloween storm" SEP event. The presence of crustal magnetic fields reduced total ionization by 30% but caused ionization to occur over a wider geographic area.

  17. Crustal thickness variations across the Blue Ridge mountains, southern Appalachians: an alternative procedure for migrating wide-angle reflection data

    Science.gov (United States)

    Robert B. Hawman

    2008-01-01

    Migration of wide-angle reflections generated by quarry blasts suggests that crustal thickness increases from 38 km beneath the Carolina Terrane to 47–51 km along the southeastern flank of the Blue Ridge. The migration algorithm, developed for generating single-fold images from explosions and earthquakes recorded with isolated, short-aperture arrays, uses the localized...

  18. Sub-crustal earthquakes within the Australia-Pacific plate boundary zone beneath the Southern Alps, New Zealand

    Science.gov (United States)

    Boese, C. M.; Stern, T. A.; Townend, J.; Bourguignon, S.; Sheehan, A.; Smith, E. G. C.

    2013-08-01

    Sub-crustal earthquakes have been observed sporadically for ∼40 years in the central South Island of New Zealand. We report on 20 events recorded between December 2008 and February 2012 near the Alpine Fault in the continental collision zone between the Australian and Pacific plates. A subset of 18 events at depths of 47-74 km occurs south of Mt. Cook and together with recently reported tremor locations indicates along-strike variations in deformation behaviour along the plate boundary. The sub-crustal earthquakes south of Mt. Cook increase in depth, frequency and size southwards towards the Puysegur subduction zone. Focal mechanisms could be determined for 14 earthquakes and exhibit predominantly strike-slip and reverse faulting solutions. Stress inversion analysis of the focal mechanisms yields a stress field favouring oblique-reverse faulting. We interpret the geographic and vertical distributions of these sub-crustal events in relation to a previously proposed tectonic model of a remnant passive margin that formed south of New Zealand in the Eocene and was overridden when dextral strike-slip motion initiated on the Alpine Fault. We infer that sub-crustal earthquakes occur along the leading edge of this structure, which is attached to the continental Australian crust.

  19. Long-term exhumation of a Palaeoproterozoic orogen and the role of pre-existing heterogeneous thermal crustal properties

    DEFF Research Database (Denmark)

    McGregor, E.D.; Nielsen, S.B.; Stephenson, R.A.

    2013-01-01

    Ma. Modelling the 3D exhumation of a heterogeneous crust with flat topography demonstrates that some of the variability in observed fission-track ages could be attributed to heterogeneity in crustal heat production and thermal conductivity. The remaining variability in the observed dataset...

  20. Constraining ice mass loss from Jakobshavn Isbræ (Greenland) using InSAR-measured crustal uplift

    DEFF Research Database (Denmark)

    Liu, Lin; Wahr, John; Howat, Ian

    2012-01-01

    . Overall, our results suggest that despite the inherent difficulties of working with a signal that has significant large-scale components, InSAR-measured crustal deformation can be used to study the ice mass loss of a rapidly thinning glacier and its surrounding catchment, providing both a constraint...

  1. Variation of Crustal Shear Velocity Structure Along the Eastern Lau Back-Arc Spreading Center Constrained By Seafloor Compliance

    Science.gov (United States)

    Zha, Y.; Webb, S. C.; Dunn, R. A.

    2014-12-01

    Measurements of seafloor compliance, the deformation under long period (typically 30-300 s) ocean wave forcing, are primarily sensitive to crustal shear velocity structure. We analyze seafloor compliance from data collected from a subset of 50 broadband Ocean Bottom Seismographs (OBS) deployed at the Eastern Lau spreading center (ELSC) from 2009 to 2010. The ELSC is a 400-km-long back-arc spreading center lying closely to the Tonga subduction trench in the southwestern Pacific. Seafloor morphology, crustal seismic structure and lava composition data show rapid variations along the ridge as the ridge migrates away from the volcanic arc front to the north, indicating a decreasing influence of the subducting slab. We calculate seafloor compliance functions by taking the spectral transfer function between the vertical displacement and pressure signal recorded by the 4-component OBSs, which are equipped with differential pressure gauges (DPGs). In the ridge perpendicular direction, compliance amplitude vary by more than an order of magnitude from the ridge crest to older seafloor covered by sediment. Along the spreading ridge, compliance measured from on-axis sites increases southwards, indicative of a decrease in the upper crustal shear velocity possibly due to increasing porosity and a thickening extrusive layer [Jacobs et al., 2007; Dunn et al., 2013]. We apply a Markov Chain Monte Carlo method to invert the compliance functions for crustal shear velocities at various locations along the ELSC.

  2. Insight into NE Tibetan Plateau expansion from crustal and upper mantle anisotropy revealed by shear-wave splitting

    Science.gov (United States)

    Huang, Zhouchuan; Tilmann, Frederik; Xu, Mingjie; Wang, Liangshu; Ding, Zhifeng; Mi, Ning; Yu, Dayong; Li, Hua

    2017-11-01

    The northeastern Tibetan plateau margin is the current expansion border, where growth of the plateau is ongoing. We analyze shear-wave splitting at ChinArray stations in the NE Tibetan Plateau and its margin with the stable North Chine Craton. The measurements provide important information on the seismic anisotropy and deformations patterns in the crust and upper mantle, which can be used to constrain the expansion mechanism of the plateau. Along the margin and within the craton, the dominant NW-SE fast polarization direction (FPD) is NW-SE, subparallel to the boundary between the plateau and the North China Craton. The shear-wave splitting measurements on the NE Tibetan Plateau itself generally reflect two-layer anisotropy. The lower-layer anisotropy (with NW-SE FPDs) is consistent in the whole region and FPDs are the same as those in the North China Craton. The upper-layer FPDs are parallel to crustal motion rather than surface structures within the high plateau. The two-layer anisotropy implies the presence of deformed Tibetan lithosphere above the underthrusting North China Craton. The NE Tibetan shows similar deformation patterns at the surface (inferred from GPS) and within the mantle (inferred from shear-wave splitting), but significant crustal anisotropy (parallel to crustal motion) requires mid-lower crustal channel flow or detachment to drive further tectonic uplift of the plateau.

  3. Crustal age domains in the Kibaran belt of SW-Uganda: Combined zircon geochronology and Sm Nd isotopic investigation

    Science.gov (United States)

    Buchwaldt, Robert; Toulkeridis, Theofilos; Todt, Wolfgang; Ucakuwun, Elias K.

    2008-04-01

    Combination of geochemistry, Nd mean crustal residence ages and single zircon ages reveal distinct provinces not recognized previously within the Kibaran belt of SW-Uganda. Geochemical analyses (HFSE and REE) of four granitoids, namely the Ntungamo, Chitwe, Rwentobo and Kamwezi from the Karagwe Tinfield have been interpreted to be mainly composed of melt components from subduction modified parts of the continental lithospheric mantle. In addition we can demonstrate, from these distinctive batholiths crystallization ages that lead to the result of three age groups, one at around 1566 Ma, the second at 1444 Ma to and the third clusters between 1329 Ma and 1363 Ma. The ɛNd( t) values from the now precisely dated intrusions of the Kibaran belt indicate subsequently two distinctive groups. The older granites have ɛNd( t) values of -20.1 to -23.1 and Nd mean crustal residence ages, based on a depleted mantle model, from 3.52 Ga to 3.84 Ga while the younger granite batholiths show lower ɛNd( t) values of -10.1 to -14.0 and Nd mean crustal residence ages from 2.86 Ga to 3.06 Ga, respectively. The distinct geochemical, geochronological and isotopic characteristics and the unrelated geological evolution reconstructed from these data strongly implies that the two now adjacent Precambrian complexes were geologically unrelated crustal packages prior to high grade metamorphism and, as such, represent "suspect terranes" which were most probably brought together during a middle Proterozoic collision event.

  4. Imaging Yellowstone plume-lithosphere interactions from inversion of ballistic and diffusive Rayleigh wave dispersion and crustal thickness data

    Science.gov (United States)

    Stachnik, J. C.; Dueker, K.; Schutt, D. L.; Yuan, H.

    2008-06-01

    Diffusive and ballistic Rayleigh wave dispersion data from three PASSCAL seismic deployments are combined with crustal thickness constraints from receiver function analysis to produce a high-resolution shear velocity image of the Yellowstone hot spot track crust and uppermost mantle. This synoptic image shows the following crustal features: the eastern Snake River Plain (ESRP) high-velocity midcrustal layer, low-velocity lower crust beneath the 4.0-6.6 Ma Heise caldera field, high-velocity lower crust beneath the fashion governed by preexisting lower crustal strength heterogeneity. Within the northern Wyoming province, the so-called 7.x km/s lower crustal magmatic layer is found to extend westward to the N-S oriented pre-Cambrian rift margin. The high-velocity, hence high-density, 7.x layer beneath the imaged by body wave tomograms, after being sheared to horizontal by plate drift, is manifest as a very low velocity (3.9 km/s) layer that is only about 110 km wide. The ESRP mantle lithosphere has been thinned to about 28 km thickness by the plume's transport of heat and magma upward, lateral advection of the lower lithosphere by plume shear, and ongoing lithospheric dilatation.

  5. The crustal structure of the Southern Nain and Makkovik Provinces of Labrador deriverd from seismic refraction data

    DEFF Research Database (Denmark)

    Funck, T.; Hansen, A.K.; Reid, Ian Derry

    2008-01-01

    A refraction seismic profile was used to determine the crustal structure across the Nain/ Makkovik boundary, and to look for an offshore continuation of the  Nain Plutonic Suite (NPS). Velocity models were developed from forward and inverse modeling of travel times. There are. In the Saglek block...

  6. Seismic-wave attenuation associated with crustal faults in the new madrid seismic zone.

    Science.gov (United States)

    Hamilton, R M; Mooney, W D

    1990-04-20

    The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones.

  7. Gravity anomaly and crustal structure characteristics in North-South Seismic Belt of China

    Science.gov (United States)

    Shen, Chongyang; Xuan, Songtbai; Yang, Guangliang; Wu, Guiju

    2017-04-01

    The North-South Seismic Belt (NSSB) is the binary system boundary what is formed by the western Indian plate subduction pushing and the eastern west Pacific asthenosphere rising, and it is one of the three major seismic belts (Tianshan, Taiwan and NSSB) and mainly located between E102°and E107°. And it is mainly composed of topographic gradient zones, faults, cenozoic basins and strong earthquake zones, which form two distinct parts of tectonic and physical features in the west and east. The research results of geophysical and deep tectonic setting in the NSSB show that it is not only a gravity anomaly gradient zone, it is but also a belt of crustal thickness increasing sharply westward of abrupt change. Seismic tomography results show that the anomaly zone is deeper than hundreds of kilometers in the NSSB, and the composition and structure of the crust are more complex. We deployed multiple Gravity and GNSS synchronous detection profiles in the NSSB, and these profiles crossed the mainly faults structure and got thousands of points data. In the research, source analysis, density structure inversion, residual gravity related imaging and normalized full gradient methods were used, and analyzed gravity field, density and their structure features in different positions, finally obtained the crustal density structure section characteristics and depth structure differences. The research results showed that the gravity Bouguer anomaly is similar to the existing large scale result. The Bouguer anomaly is rising significantly from west to east, its trend variation coincides well with the trend change of Moho depth, which is agreeing with the material flows to the peripheral situation of the Tibetan plateau. The obvious difference changes of the residual anomaly is relative to the boundary of structure or main tectonics, it's also connected with the stop degree of the eurasian plate when the material migrates around. The density structure of the gravity profiles mainly

  8. Crustal Stress and Strain Energy Density Rates in South Korea Deduced from GPS Observations

    Directory of Open Access Journals (Sweden)

    Shuanggen Jin Pil-Ho Park

    2006-01-01

    Full Text Available An accurate measurement and understanding of horizontal stress rates within the earth¡¦s crust is important for providing fundamental insights into the mechanisms driving plate motion and intraplate tectonic activity. In this paper, the stress field within the crust of the South Korean peninsula is obtained from observed displacement rates based on 4-year continuous GPS observations (2000 - 2004. Results show that the South Korean peninsula is under both compression and extensional stress regimes with maximum shear stress rate being in the mid part of the study area coinciding with the geologically defined Honam Shear Zone (HSZ and relatively highly seismically active zone. In addition, the variation rate of strain energy density, an important index reflecting the intensity of crustal activity, is further derived, and its distribution indicates high earthquake potential in the mid-part as well as the north and northeast edges of the crust of the South Korean peninsula.

  9. EARLY PRECAMBRIAN CRUSTAL EVOLUTION OF THE BELOMORIAN AND TRANS-NORTH CHINA OROGENS AND SUPERCONTINENTS RECONSTRUCTION

    Directory of Open Access Journals (Sweden)

    A. I. Slabunov

    2017-01-01

    Full Text Available Comparative analysis of the crustal evolution of the Early Precambrian Belomorian and Trans-North China orogens (Fig. 1 has shown [Slabunov et al., 2015] that: Both belts were formed by the superposition of two Precambrian orogenies. The earth crust of the Belomorian belt was produced during the Mesoarchaean to Neoarchaean Belomorian collisional orogeny [Slabunov, 2008; Slabunov et al., 2006] and then was reworked during the Palaeoproterozoic Lapland-Kola collisional orogeny [Daly at al., 2006; Balagansky et al., 2014]. The earth crust of the Trans-North China orogen was formed during a Neoarchean accretionary orogeny and then was reworked during a Paleoproterozoic collisional orogeny [Zhao et al., 2012; Guo et al., 2012, 2005]. The Lapland granulite belt is the core of the Lapland-Kola Palaeoproterozoic collisional orogen in the Fennoscandian shield and the Khondolite belt occupies the same tectonic position in a Palaeoproterozoic collisional orogen in the North China craton.

  10. Sensitivity analysis of crustal correction for calculation of lithospheric mantle density from gravity data

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2016-01-01

    We investigate how uncertainties in seismic and density structure of the crust propagate to uncertainties in mantle density structure. The analysis is based on interpretation of residual upper-mantle gravity anomalies which are calculated by subtracting (stripping) the gravitational effect...... of the crust from the observed satellite gravity field data (GOCE Direct release 3). Thus calculated residual mantle gravity anomalies are caused mainly by a heterogeneous density distribution in the upper mantle. Given a relatively small range of expected compositional density variations in the lithospheric...... mantle, knowledge on uncertainties associated with incomplete information on crustal structure is of utmost importance for progress in gravity modelling. Uncertainties in the residual upper-mantle gravity anomalies result chiefly from uncertainties in (i) seismic VP velocity-density conversion...

  11. Seismic refraction investigations on the crustal structure of the western Jameson Land Basin, East Greenland

    Science.gov (United States)

    Fechner, Notker; Jokat, Wilfried

    1996-07-01

    In 1990, a combined land-sea experiment in the Hall Bredning, Scoresby Sund (East Greenland) revealed new information about the crustal structure of the Jameson Land Basin. The sediments and the upper and lower crust have been imaged by a 710-km-long network of seismic refraction lines. Our data indicate that the crust-mantle boundary is at a depth of 24 km close to the western coast of Jameson Land and deepens to 31 km toward the western termination of Hall Bredning. The sediments thin from 8-km thickness in the east to almost 0 km close to Milne Land. Our cross sections indicate that Jameson Land is an asymmetrical, half-graben shaped sedimentary basin with a N-S striking axis.

  12. Monitoring crustal movements in northern Tianshan Mountain based on GPS technology

    Directory of Open Access Journals (Sweden)

    A.V. Vilayev

    2017-05-01

    Full Text Available Monitoring results for the period 2009–2014 by ten standard GPS stations allowed to determine the crustal movements of seismically active region in south-eastern Kazakhstan. Maps of movement velocity were made in geocentric coordinate system and in reference system of the Eurasian continent. GPS points displacements reflect the features of modern deformation processes that are notable in the high seismic activity region. The structure of the velocity field divergence qualitatively confirms major deformation in the sublatitudinal direction which is parallel to the main ridge of the northern Tianshan Mountain. The epicenters of earthquakes are in agreement with the border areas of compression–tension, as well as the allocated areas of multidirectional rotary motion. The conclusion is that GPS monitoring of the movements of the Earth's crust can be used to evaluate the territory's stress–strain state for the purpose of seismic zoning and seismic risk assessment.

  13. Geology of the Icy Galilean Satellites: Understanding Crustal Processes and Geologic Histories Through the JIMO Mission

    Science.gov (United States)

    Figueredo, P. H.; Tanaka, K.; Senske, D.; Greeley, R.

    2003-01-01

    Knowledge of the geology, style and time history of crustal processes on the icy Galilean satellites is necessary to understanding how these bodies formed and evolved. Data from the Galileo mission have provided a basis for detailed geologic and geo- physical analysis. Due to constrained downlink, Galileo Solid State Imaging (SSI) data consisted of global coverage at a -1 km/pixel ground sampling and representative, widely spaced regional maps at -200 m/pixel. These two data sets provide a general means to extrapolate units identified at higher resolution to lower resolution data. A sampling of key sites at much higher resolution (10s of m/pixel) allows evaluation of processes on local scales. We are currently producing the first global geological map of Europa using Galileo global and regional-scale data. This work is demonstrating the necessity and utility of planet-wide contiguous image coverage at global, regional, and local scales.

  14. Precise tremor source locations and amplitude variations along the lower-crustal central San Andreas Fault

    Science.gov (United States)

    Shelly, David R.; Hardebeck, Jeanne L.

    2010-01-01

    We precisely locate 88 tremor families along the central San Andreas Fault using a 3D velocity model and numerous P and S wave arrival times estimated from seismogram stacks of up to 400 events per tremor family. Maximum tremor amplitudes vary along the fault by at least a factor of 7, with by far the strongest sources along a 25 km section of the fault southeast of Parkfield. We also identify many weaker tremor families, which have largely escaped prior detection. Together, these sources extend 150 km along the fault, beneath creeping, transitional, and locked sections of the upper crustal fault. Depths are mostly between 18 and 28 km, in the lower crust. Epicenters are concentrated within 3 km of the surface trace, implying a nearly vertical fault. A prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6.0 Parkfield earthquake.

  15. Limits on crustal differential stress in southern California from topography and earthquake focal mechanisms

    Science.gov (United States)

    Luttrell, Karen; Smith-Konter, Bridget

    2017-10-01

    The in situ crustal stress field fundamentally governs, and is affected by, the active tectonic processes of plate boundary regions, yet questions remain about the characteristics of this field and the implications for active faults in the upper crust. We estimate the magnitude of differential stress at seismogenic depth in southern California by balancing in situ orientation indicated by earthquake focal mechanisms against the stress imposed by topography, which tends to resist the motion of strike-slip faults. Our results indicate that most regions require differential stress of at least 20 MPa at seismogenic depth. In the areas of most rugged topography along the San Andreas Fault System, differential stress at seismogenic depth must exceed 62 MPa consistent with differential stress estimates from complimentary methods. This furthermore suggests pore pressure must be less than lithostatic and that coefficient of friction cannot be very low (i.e. coefficient of static friction >0.3).

  16. The Sarmatian crustal segment: Precambrian correlation between the Voronezh Massif and the Ukrainian Shield across the Dniepr-Donets Aulacogen

    Science.gov (United States)

    Shchipansky, Andrey A.; Bogdanova, Svetlana V.

    1996-12-01

    Sarmatia is the southernmost crustal segment of the East European Precambrian Craton. The Phanerozoic Dniepr-Donets Aulacogen (DDA) subdivides it into unequal halves, the Ukrainian Shield in the south and the Voronezh Massif in the north. Correlation between the Ukrainian Shield and the Voronezh Massif is reviewed, the overall structure and age-province subdivision of Sarmatia are assessed, and constraints are imposed on displacement along the DDA. It is shown that differences in the trends of the principal basement structures, highlighted by magnetic anomalies outlining Palaeoproterozoic banded iron formations, are a consequence of the heterogeneous structure of the Archaean-Palaeoproterozoic basement rather than the kinematics of the opening of the DDA. Only minor right-lateral displacement along the DDA has occurred. The main crustal units of the Ukrainian Shield, i.e. the Azov, Middle Dniepr and Ingul-Ingulets Blocks, correlate excellently with the Oskol, Sumy and Sevsk Blocks of the Voronezh Massif, which allows the definition of three coherent Oskol-Azov, Sumy-Dniepr and Sevsk-Ingulets crustal domains. Presently available radiometric datings show that these three domains all have Archaean crustal ages of 3.65-3.0, 3.2-3.1 and 3.1-2.8 Ga, respectively. The inter-domain boundaries appear largely to have existed already in the Archaean, but were subsequently masked by Palaeoproterozoic deformation and overlain by Proterozoic cover and nappe piles. Amongst the three crustal domains of central and eastern Sarmatia, the Oskol-Azov and Sevsk-Ingulets ones have been reworked substantially in the Palaeoproterozoic, while the Sumy-Dniepr Domain acted as a stable cratonic unit, although apparently rotating anti-clockwise between 2.3 and 2.1 Ga ago. The Palaeoproterozoic banded iron belts of Sarmatia can be subdivided into the cratonic-margin Krivoy Rog type and the interior, intra-domain Oskol type. The former outline the cratonic Sumy-Dniepr Domain, while the latter

  17. New Perspectives on Ophiolite Formation: Evidence from Ultrahigh Pressure (UHP), Highly Reduced and Crustal-type Minerals in Podiform Chromitites

    Science.gov (United States)

    Robinson, P. T.; Yang, J.

    2014-12-01

    Separated and in situ ultrahigh pressure (UHP), highly reduced and crustal-type minerals are common in podiform chromitites of the Luobusa and Dongqiao ophiolites, Tibet and the Ray-Iz ophiolite of the Polar Urals, Russia. Highly reduced and crustal-type minerals have also been recovered from the Oman ophiolite. UHP minerals include diamond, coesite-stishovite and kyanite, whereas highly reduced minerals are mainly moissanite (SiC), native elements (e.g., Si, Fe, Cr, Al, Ti, Mn, W, Ta) and a wide variety of metallic alloys. Crustal-type minerals are represented by various combinations of zircon, corundum, almandine garnet, kyanite, andalusite, quartz, K-feldspar, plagioclase, apatite, amphibole, rutile, and titanite. Most in-situ grains are hosted in small, circular to irregular patches of amorphous carbon within grains of magnesiochromite, indicating the former presence of a C-rich fluid, either during or after crystallization of the chromite. The recovered zircons are typically rounded to sub-rounded grains with complex internal structures indicating polyphase growth. Their trace element contents and low-pressure inclusion assemblages (quartz, muscovite, K-feldspar, apatite, ilmenite, rutile) indicate a continental crustal origin. The zircons have SIMS U-Pb ages that are generally much older than the host ophiolite (total range: 90 to 2500 Ma). The presence of numerous crustal minerals, particularly zircon, suggests derivation from metasedimentary rocks subducted into the mantle. The preservation of UHP, highly reduced and crustal-type minerals in chromitites implies effective isolation from the mafic melts that formed the ophiolites and chromitites. Clearly, the formation of ophiolites and podiform chromitites must be a complex, multistage process involving crystallization of magnesiochromite grains at depth in the upper mantle, upwelling of the host peridotites and chromitites, capture of mantle wedges above suprasubduction zones, further crystallization and

  18. Anomalous crustal movements with low seismic efficiency - Campi Flegrei, Italy and some examples in Japan

    Directory of Open Access Journals (Sweden)

    A. Nazzaro

    2002-06-01

    Full Text Available Campi Flegrei is a unique volcanic region located near Naples, Italy. Anomalous crustal movements at Pozzuoli in Campi Flegrei have been documented since the Roman period. The movements were gradual and have continued to the present, occasionally accompanying swarms of local earthquakes and volcanic eruptions. Generally the movements proceed with low seismicity. After the 1538 eruption of Monte Nuovo, Pozzuoli had subsided monotonously, but it changed to uplift abruptly in 1969. The uplift accelerated in 1983 and 1984 reaching more than 2 m, and thereafter began to subside. Many discussions of this event have been published. In Japan, we have examples of deformations similar to those at Campi Flegrei, mainly in volcanic areas, and rarely in non-volcanic areas. The former includes Iwojima, Miyakejima and Aira caldera while the latter is represented by Cape Omaezaki. Iwojima is a volcano island, and its secular uplifts since the 18th century are recognized as an unusual event. Miyakejima volcano and Aira caldera exhibited anomalous movements with low seismicity after their eruptions. Cape Omaezaki is not situated in volcanic zone but near a subduction zone, and gradually and continuously subsides as a precursor to a large earthquake. In such cases as Campi Flegrei and the Japanese localities, we would question whether the deformations are accompanied by normal seismicity or low seismicity. To examine quantitatively the relationship between seismicity and related deformation, seismic efficiency is generally useful. The crustal deformations in all the regions cited above are characterized by exceptionally low seismic efficiencies. In the present paper, the deformations at Pozzuoli and Iwojima are mainly described and a comparative discussion among these and other localities in Japan is supplemented. It is concluded that such anomalous phenomena in volcanic areas are attributable to peculiar rheological aspects of the material composing the local

  19. Scaling of Mixing Rate in Mantle Convection Models: Influence of Plate Tectonics, Melting and Crustal Production

    Science.gov (United States)

    Tackley, Paul

    2017-04-01

    It is generally thought that the early Earth's mantle was hotter than today, which using conventional convective scalings should have led to vigorous convection and mixing. Geochemical observations, however, suggest that mixing was not as rapid as would be expected, leading to the suggestion that early Earth had stagnant lid convection [Debaille et al., 2003]. Additionally, the mantle's thermal evolution is difficult to explain using conventional scalings because early heat loss would have been too rapid, which has led to the hypothesis that plate tectonics convection does not follow the conventional convective scalings [Korenaga, 2003]. One physical process that could be important in this context is partial melting leading to crustal production, which has been shown to have the major effects of buffering mantle temperature and carrying a significant fraction of the heat from hot mantle [Nakagawa & Tackley, 2012], making plate tectonics easier [Lourenco et al., 2016], and causing compositional differentiation of the mantle that can buffer core heat loss [Nakagawa & Tackley, 2010]. Here, the influence of this process on mantle mixing is examined, using secular thermo-chemical models that simulate Earth's evolution over 4.5 billion years. Mixing is quantified both in terms of how rapidly stretching occurs, and in terms of dispersion: how rapidly initially close heterogeneities are dispersed horizontally and vertically through the mantle. It is found that convection with plate tectonics, melting and crustal production does not follow the conventional Nu-Ra and velocity-Ra scalings derived from boundary-layer theory, and thus mixing in the early Earth is much less rapid than earlier thought. Reasons for this will be analysed in this presentation.

  20. Geomagnetic Crustal field Anomalies over small countries (Austria and Albania) according to regional and global models

    Science.gov (United States)

    Peqini, Klaudio; Duka, Bejo

    2017-04-01

    Austria and Albania are comparably small countries, geographically mostly elongated respectively in longitude and latitude. Using data from repeat stations on these countries and their neighboring countries, the regional spatial-temporal (ST) model for each country is build by polynomial expansion in time, latitude and longitude of the geomagnetic field components. The residuals between the observed values of the components of the magnetic field and those predicted by the model are interpreted as local anomalies of the Crustal/Lithosphere geomagnetic field. Using different global models (CM5, POMME-9, EMM2015, CHAOS-6), that are expansion in spherical harmonics up to maximum degree Lmax, the geomagnetic field contribution of internal sources at any place of the region (Austria or Albania) at any time (within the time interval of the respective model validity) can be calculated. These global models consider the spherical harmonics contribution from degree L = 1 to Lc as the Core field and the spherical harmonics contribution from the degree L = Lc + 1 to Lmax as Crust/Lithosphere static field, i.e. there is not considered the induced magnetization of the Crust/Lithosphere. We have calculated the crustal contribution in each region by different ways: by calculating the residuals between observed values and predicted values by the different models (up to Lmax) and then averaging these residuals; by calculating the residuals between the observed values and values predicted from the nuclear part (contribution from L = 1 to Lc) of different models; by the direct calculations of the models (considering contribution from L = Lc + 1 to Lmax). The results from different models and different ways for Austrian and Albanian regions will be compared. Especially the results for the total field (F) will be compared with available aeromagnetic and ground anomalies maps of the regions.

  1. Crustal Seismic Attenuation in Germany Measured with Acoustic Radiative Transfer Theory

    Science.gov (United States)

    Gaebler, Peter J.; Eulenfeld, Tom; Wegler, Ulrich

    2017-04-01

    This work is carried out in the context of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). As part of this treaty a verification regime was introduced to detect, locate and characterize nuclear explosion testings. The study of seismology can provide essential information in the form of broadband waveform recordings for the identification and verification of these critical events. A profound knowledge of the Earth's subsurface between source and receiver is required for a detailed description of the seismic wave field. In addition to underground parameters such as seismic velocity or anisotropy, information about seismic attenuation values of the medium are required. Goal of this study is the creation of a comprehensive model of crustal seismic attenuation in Germany and adjacent areas. Over 20 years of earthquake data from the German Central Seismological Observatory data archive is used to estimate the spatial dependent distribution of seismic intrinsic and scattering attenuation of S-waves for frequencies between 0.5 and 20 Hz. The attenuation models are estimated by fitting synthetic seismogram envelopes calculated with acoustic radiative transfer theory to observed seismogram envelopes. This theory describes the propagation of seismic S-energy under the assumption of multiple isotropic scattering, the crustal structure of the scattering medium is hereby represented by a half-space model. We present preliminary results of the spatial distribution of intrinsic attenuation represented by the absorption path length, as well as of scattering attenuation in terms of the mean free path and compare the outcomes to results from previous studies. Furthermore catalog magnitudes are compared to moment magnitudes estimated during the inversion process. Additionally site amplification factors of the stations are presented.

  2. Determining relative bulk viscosity of kilometre-scale crustal units using field observations and numerical modelling

    Science.gov (United States)

    Gardner, Robyn L.; Piazolo, Sandra; Daczko, Nathan R.

    2017-11-01

    Though the rheology of kilometre-scale polymineralic rock units is crucial for reliable large-scale, geotectonic models, this information is difficult to obtain. In geotectonic models, a layer is defined as an entity at the kilometre scale, even though it is heterogeneous at the millimetre to metre scale. Here, we use the shape characteristics of the boundaries between rock units to derive the relative bulk viscosity of those units at the kilometre scale. We examine the shape of a vertically oriented ultramafic, harzburgitic-lherzolitic unit, which developed a kilometre-scale pinch and swell structure at mid-crustal conditions ( 600 °C, 8.5 kbar), in the Anita Shear Zone, New Zealand. The ultramafic layer is embedded between a typical polymineralic paragneiss to the west, and a feldspar-quartz-hornblende orthogneiss, to the east. Notably, the boundaries on either side of the ultramafic layer give the ultramafics an asymmetric shape. Microstructural analysis shows that deformation was dominated by dislocation creep (n = 3). Based on the inferred rheological behaviour from the field, a series of numerical simulations are performed. Relative and absolute values are derived for bulk viscosity of the rock units by comparing boundary tortuosity difference measured on the field example and the numerical series. Our analysis shows that during deformation at mid-crustal conditions, paragneisses can be 30 times less viscous than an ultramafic unit, whereas orthogneisses have intermediate viscosity, 3 times greater than the paragneisses. If we assume a strain rate of 10- 14 s- 1 the ultramafic, orthogneiss and paragneiss have syn-deformational viscosities of 3 × 1022, 2.3 × 1021 and 9.4 × 1020 Pa s, respectively. Our study shows pinch and swell structures are useful as a gauge to assess relative bulk viscosity of rock units based on shape characteristics at the kilometre scale and in non-Newtonian flow regimes, even where heterogeneity occurs within the units at the

  3. Macroseismic intensity investigation of the November 2014, M=5.7, Vrancea (Romania crustal earthquake

    Directory of Open Access Journals (Sweden)

    Angela Petruta Constantin

    2016-11-01

    Full Text Available On November 22, 2014 at 21:14:17 local hour (19:14:17 GMT a  ML=5.7 crustal earthquake occurred in the area of Marasesti city of Vrancea county (Romania - the epicenter was located at north latitude 45.87° and east longitude 27.16°, with a focal depth of 39 km. This earthquake is the main shock of a sequence that started with this and lasted until the end of January. During the sequence, characterized by the absence of foreshocks, a number of 75 earthquakes were recorded in 72 hours, the largest of which occurred in the same day with the main shock, at 22:30 (ML= 3.1. The crustal seismicity of Vrancea seismogenic region is characterized by moderate earthquakes with magnitudes that have not exceeded MW 5.9, this value being assigned to an earthquake that occurred in historical times on March 1, 1894 (Romplus catalogue. Immediately after the 2014 earthquake occurrence, the National Institute for Earth Physics (NIEP sent macroseismic questionnaires in all affected areas, in order to define the macroseismic field of ground shaking. According to macroseismic questionnaires survey, the intensity of epicentral area reached VI MSK, and the seismic event was felt in all the extra-Carpathian area. This earthquake caused general panic and minor to moderate damage to the buildings in the epicentral area and the northeast part of country. The main purpose of this paper is to present the macroseismic map of the earthquake based on the MSK-64 intensity scale.

  4. Thermal and petrologic constraints on lower crustal melt accumulation under the Salton Sea Geothermal Field

    Science.gov (United States)

    Karakas, Ozge; Dufek, Josef; Mangan, Margaret T.; Wright, Heather M.; Bachmann, Olivier

    2017-06-01

    In the Salton Sea region of southern California (USA), concurrent magmatism, extension, subsidence, and sedimentation over the past 0.5 to 1.0 Ma have led to the creation of the Salton Sea Geothermal Field (SSGF)-the second largest and hottest geothermal system in the continental United States-and the small-volume rhyolite eruptions that created the Salton Buttes. In this study, we determine the flux of mantle-derived basaltic magma that would be required to produce the elevated average heat flow and sustain the magmatic roots of rhyolite volcanism observed at the surface of the Salton Sea region. We use a 2D thermal model to show that a lower-crustal, partially molten mush containing rate) given extension rates at or below the current value of ∼0.01 m/yr (Brothers et al., 2009). These regions of partial melt are a natural consequence of a thermal regime that scales with average surface heat flow in the Salton Trough, and are consistent with seismic observations. Our results indicate limited melting and assimilation of pre-existing rocks in the lower crust. Instead, we find that basalt fractionation in the lower crust produces derivative melts of andesitic to dacitic composition. Such melts are then expected to ascend and accumulate in the upper crust, where they further evolve to give rise to small-volume rhyolite eruptions (Salton Buttes) and fuel local spikes in surface heat flux as currently seen in the SSGF. Such upper crustal magma evolution, with limited assimilation of hydrothermally altered material, is required to explain the slight decrease in δ18 O values of zircons (and melts) that have been measured in these rhyolites.

  5. Crustal structure of the Iberian Peninsula and surrounding regions from ambient noise tomography

    Science.gov (United States)

    Villasenor, A.

    2015-12-01

    We present new high-resolution images of the crust in the Iberian Peninsula and surrounding regions using seismic ambient noise. We have compiled continuous recordings of all permanent broadband stations and temporary experiments in the region (IberArray, WILAS, PYROPE, PICASSO) from 2007 to 2014. This dataset consists of more than 400 broadband stations, although not all of them were operating simultaneously. We cross-correlate the three components these continuous recordings between all station pairs to obtain empirical Green's functions (EFGs). From these EGFs we measure group and phase velocities of the fundamental mode Rayleigh and Love waves, and also obtain estimates of Rayleigh wave ellipticity. We then perform a 2D tomographic inversion of the dispersion measurements to obtain phase and group velocity maps of Rayleigh and Love waves for periods from 4 to 40 seconds. The short period dispersion and ellipticity maps show excellent correlation with surface features (i.e. sedimentary basins, internal zones of mountain ranges, and stable regions), while maps for longer periods are a good proxy for crustal thickness. Due to the high station density of the dataset used we are able to image the entire Iberian Peninsula with unprecedented resolution, resolving small scale structures such as the West Alboran and Lower Tagus basins, the high anomaly associated with the Ronda-Beni Bousera peridotites, etc. We also investigate the existence of azimuthal anisotropy of Rayleigh wave velocities as a function of period (i.e. depth) . Given the good correlation of the new dispersion maps with gravity anomalies, estimates of crustal thickness from receiver functions, and P-wave velocities from local earthquake tomography, our ultimate objective is to obtain an integrated model of shear-wave structure that fits all these datasets.

  6. Multi-dimensional Crustal and Lithospheric Structure of the Atlas Mountains of Morocco by Magnetotelluric Imaging

    Science.gov (United States)

    Kiyan, D.; Jones, A. G.; Fullea, J.; Ledo, J.; Siniscalchi, A.; Romano, G.

    2014-12-01

    The PICASSO (Program to Investigate Convective Alboran Sea System Overturn) project and the concomitant TopoMed (Plate re-organization in the western Mediterranean: Lithospheric causes and topographic consequences - an ESF EUROSCORES TOPO-EUROPE project) project were designed to collect high resolution, multi-disciplinary lithospheric scale data in order to understand the tectonic evolution and lithospheric structure of the western Mediterranean. The over-arching objectives of the magnetotelluric (MT) component of the projects are (i) to provide new electrical conductivity constraints on the crustal and lithospheric structure of the Atlas Mountains, and (ii) to test the hypotheses for explaining the purported lithospheric cavity beneath the Middle and High Atlas inferred from potential-field lithospheric modeling. We present the results of an MT experiment we carried out in Morocco along two profiles: an approximately N-S oriented profile crossing the Middle Atlas, the High Atlas and the eastern Anti-Atlas to the east (called the MEK profile, for Meknes) and NE-SW oriented profile through western High Atlas to the west (called the MAR profile, for Marrakech). Our results are derived from three-dimensional (3-D) MT inversion of the MT data set employing the parallel version of Modular system for Electromagnetic inversion (ModEM) code. The distinct conductivity differences between the Middle-High Atlas (conductive) and the Anti-Atlas (resistive) correlates with the South Atlas Front fault, the depth extent of which appears to be limited to the uppermost mantle (approx. 60 km). In all inverse solutions, the crust and the upper mantle show resistive signatures (approx. 1,000 Ωm) beneath the Anti-Atlas, which is the part of stable West African Craton. Partial melt and/or exotic fluids enriched in volatiles produced by the melt can account for the high middle to lower crustal and uppermost mantle conductivity in the Folded Middle Atlas, the High Moulouya Plain and the

  7. Seismicity and crustal structure at the Mendocino triple junction, Northern California

    Energy Technology Data Exchange (ETDEWEB)

    Dicke, M.

    1998-12-01

    A high level of seismicity at the Mendocino triple junction in Northern California reflects the complex active tectonics associated with the junction of the Pacific, North America, and Gorda plates. To investigate seismicity patterns and crustal structure, 6193 earthquakes recorded by the Northern California Seismic Network (NCSN) are relocated using a one-dimensional crustal velocity model. A near vertical truncation of the intense seismic activity offshore Cape Mendocino follows the strike of the Mattole Canyon fault and is interpreted to define the Pacific plate boundary. Seismicity along this boundary displays a double seismogenic layer that is attributed to interplate activity with the North America plate and Gorda plate. The interpretation of the shallow seismogenic zone as the North America - Pacific plate boundary implies that the Mendocino triple junction is situated offshore at present. Seismicity patterns and focal mechanisms for events located within the subducting Gorda pl ate are consistent with internal deformation on NE-SW and NW-SE trending rupture planes in response to north-south compression. Seismic sections indicate that the top of the Gorda plate locates at a depth of about 18 Km beneath Cape Mendocino and dips gently east-and southward. Earthquakes that are located in the Wadati-Benioff zone east of 236{sup o}E show a change to an extensional stress regime indicative of a slab pull force. This slab pull force and scattered seismicity within the contractional forearc region of the Cascadia subduction zone suggest that the subducting Gorda plate and the overriding North America plate are strongly coupled. The 1992 Cape Mendocino thrust earthquake is believed to have ruptured a blind thrust fault in the forearc region, suggesting that strain is accumulating that must ultimately be released in a potential M 8+ subduction earthquake.

  8. Lake level observations to detect crustal tilt: San Andreas Lake, California, 1979-1989

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, R.J.; Johnston, M.J.S.; Myren, G.D. (Geological Survey, Menlo Park, CA (USA)); Murray, T. (Cascades Volcano Observatory, Vancouver, WA (USA))

    1989-07-01

    A pair precision lake level gauging stations, installed in 1978, have been monitoring differential crustal uplift (crustal tilt) at San Andreas lake, California, near the suspected epicenter on the San Andreas fault of the M = 8.3, 1906 San Francisco earthquake. The stations are installed in the lake with a 4.2 km station separation parallel to the San Andreas fault. The gauging stations use quartz pressure transducers that are capable of detecting intermediate to long-term vertical displacements greater than 0.4 mm relative to a fluid surface. Differencing data from the two sites reduces the noise contributed by atmospheric pressure, temperature, and density changes, and isolates the relative elevation changes between the ends of the lake. At periods less than 20 minutes, the differenced data are dominated by lake seiches which have a fundamental mode at a period of 13 {plus minus} 0.3 minutes. These seiche harmonics can be filtered or predicted and removed from the data. Wind shear, typically lasting several days, can generate apparent short term tilt of the lake and large seiche amplitudes. The tilt noise power spectrum obtained from these data decreases by about 15 dB/decade of frequency. Monthly averages of the data between 1979-1989 indicate a tilt rate of 0.02 {plus minus} 0.08 microradians/yr (down S34{degree}E). No measurable horizontal tilt has apparently occurred in this region of the San Andreas fault during the last decade, however, measurements of trilateration networks show this region to be undergoing a horizontal strain of 0.6 {plus minus} 0.2 {mu}strain/yr.

  9. Crustal Structure in the Western Part of Romania from Local Seismic Tomography

    Science.gov (United States)

    Zaharia, Bogdan; Grecu, Bogdan; Popa, Mihaela; Oros, Eugen; Radulian, Mircea

    2017-12-01

    The inner part of the Carpathians in Romania belongs to the Carpathians-Pannonian system bordered by the Eastern Carpathians to the north and east, Southern Carpathians to the south and Pannonian Basin to the west. It is a complex tectonic region with differential folding mechanisms, post-collisional kinematics, rheology and thermal properties, including within its area the Apuseni Mountains and the Transylvanian Basin. The purpose of this study is to map the 3-D structure of the crust over this region on the basis of local earthquake data. Input data were recorded during the South Carpathian Project (2009–2011), a successful collaboration between the Institute of Geophysics and Tectonics of the University of Leeds and the National Institute for Earth Physics (NIEP), Romania. A temporary array of 32 broadband seismic stations (10 CMG-40T, 8 CMG-3T and 14 CMG-6TD) was installed across the western part of Romania (spaced at 40 to 50 km intervals) during the project. In addition, 25 stations deployed in the eastern Hungary and Serbia was considered. P- and S-wave arrivals are identified for all the selected events (minimum 7 phases per event with reasonable signal/noise ratio). All the events are first relocated using Joint Hypocentre Determination (JHD) technique. Then the well-located events were inverted to determine the crustal structure using LOTOS algorithm. The lateral variations of the crustal properties as resulted from the tomography image are interpreted in correlation with the station corrections estimated by JHD algorithm and with the post-collisional evolution of the Carpathians-Pannonian system.

  10. 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.

  11. Rapid crustal exhumation and mantle-melt extraction: Where has the crust gone?

    Science.gov (United States)

    Alvarez-Valero, A. M.; Jagoutz, O.; Manthei, C.

    2012-04-01

    The emplacement of the Beni Bousera and Ronda ultramafic massifs of the Betico-Rifean belt (N Morocco-S Spain) has been discussed for several decades. These massifs are among the largest exposures of mantle rocks on Earth's surface, which obviously confers a special interest for mantle research in Earth Sciences. We present an integrated study of mantle and the surrounding crustal material of Beni Bousera in order to understand the interplay between melt percolation and emplacement of the ultramafic rocks and their relationships to the surrounding crust. Here we focus specifically on detailed petrological studies coupled with phase diagram modeling to elucidate the tectono-metamorphic history of the surrounding granulites. We then compare and relate these results to our understanding of the evolution of the Beni Bousera mantle rocks. The orogenic lherzolite of the ultramafic massif is surrounded by mostly metapelitic high-grade granulites (with local mylonitic layers) that are rimmed in turn by a successive sequence of lower metamorphic grade, from gneisses (with minor migmatites) to schists. The northern part of the massif offers exceptional exposures of a continuous lithospheric section from the ultramafics, via the Moho to the whole granulite packet by showing within the latter the preservation of two pressure events at fairly constant HT of c. 750 °C. A prograde higher-pressure episode (> 12 kbar) is characterized by equilibrium micro-domains with Grt+Bt+Ky+Rt followed by a lower-pressure (c. 5kbar) symplectic assemblage of Crd+Spl. This reveals a dramatic decompression event registered within less than 2 kms of crustal thickness. These results together with structures, numerical modelling and geochronology will extend the knowledge of the mechanisms of mantle emplacement in particular and global tectonics in general.

  12. Crustal structure and regional tectonics of SE Sweden and the Baltic Sea

    Energy Technology Data Exchange (ETDEWEB)

    Milnes, A.G. [Bergen Univ. (Norway). Dept. of Geology; Gee, D.G.; Lund, C.E. [Uppsala Univ. (Sweden). Dept. of Earth Sciences

    1998-11-01

    In this desk study, the available geophysical and geological data on the crustal structure and regional tectonics of the wider surroundings of the Aespoe site (SE Sweden and adjacent parts of the Baltic Sea) are compiled and assessed. The aim is to contribute to the knowledge base for long-term rock mechanical modeling, using the Aespoe site as a proxy for a high-level radioactive waste repository site in Swedish bedrock. The geophysical data reviewed includes two new refraction/wide-angle reflection seismic experiments carried out within the EUROBRIDGE project, in addition to the numerous earlier refraction seismic profiles. The BABEL normal-incidence deep seismic profile is also considered. New geological data, presented at EUROBRIDGE workshops, and in recent SGU publications, are reviewed for the same area. In combination with the seismic data, these provide a base for interpreting the present composition and structure, and the Palaeoproterozoic-Mesoproterozoic evolution, of the crustal segment within which the Aespoe site lies - the Smaaland mega-block. This is characterized by having undergone little regionally significant deformation or magmatism since Neoproterozoic times (the last 1000 million years). It is shown that, at this scale of observation (of the order of 100 km), the long-term rheology of the lithosphere can be argued from a relatively tight observational network, when combined with the results of earlier SKB studies (seismo-tectonics, uplift patterns, state of stress, heat flow) and published research. Although many uncertainties exist, the present state of knowledge would suffice for first exploratory calculations and sensitivity studies of long-term, large-scale rock mechanics 101 refs, 22 figs

  13. Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting

    Science.gov (United States)

    Gouiza, Mohamed; Hall, Jeremy; Welford, J. Kim

    2017-04-01

    The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia-Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic-Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4-16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow.

  14. A First Crustal Model beneath Portugal from Teleseismic Rayleigh Wave Ellipticity Inversion

    Science.gov (United States)

    Attanayake, Januka; Ferreira, Ana M. G.; Berbellini, Andrea; Morelli, Andrea

    2017-04-01

    Accurate seismic crustal models are important for interpreting seismicity and tectonics and predicting strong ground motion. These interpretations and predictions are particularly important in regions prone to significant seismic hazard such as Portugal, where considerable destruction has taken place from large on- and offshore earthquakes (e.g. 1755 M 8 Lisbon and 1909 Benavente M 6.0 earthquakes). The lack of high quality countrywide broadband data in the past has hindered quantitative characterization of regional Earth structure in Portugal. Due to a significant expansion of the Portuguese seismic network, however, a large volume of data is accumulating since 2006. We used this new high quality dataset to measure multi-period Rayleigh Wave Ellipticity (RWE), which we inverted to build the first seismic crustal model beneath Portugal. RWE is defined by the Horizontal-to-Vertical (H/V) amplitude ratio at a given seismic station, and theoretical studies demonstrate it to be strongly sensitive to the structure immediately beneath that particular station. We measured teleseismic RWE between 15 s and 60 s from 33 permanent and temporary stations in Portugal and inverted it for shear wave velocity (Vs) structure of the crust using a fully non-linear Monte Carlo method. Our results show that both RWE and Vs are spatially correlated with surface geology. Notably, sedimentary basins produced by Mesozoic rifting (e.g. Lusitanian Basin (LB) and the Lower Tagus-Sado Basin (LTSB)) are correlated with higher RWE (lower Vs). Similar high RWE values are observed in the interior of Central Iberian Zone (CIZ), which is an older metamorphic belt. We interpret this to be the signature of an extensional episode that the CIZ has undergone possibly simultaneous to the Mesozoic rift event. The Galicia-Tras-os-Montes-Zone (GTMZ)- a Paleozoic metamorphic belt - in Northern Portugal exhibits the lowest RWE (highest Vs), whereas other metamorphic terrains have RWE intermediate to Basins and

  15. Crustal Variations in the Axial Low Velocity Zone Between the Siqueiros and Clipperton Transform Faults, East Pacific Rise

    Science.gov (United States)

    Wilcock, W. S.; Toomey, D. R.; Detrick, R. S.

    2002-12-01

    As part of the 1997 UNDERSHOOT seismic experiment, three rise-perpendicular profiles were collected across the East Pacific Rise between the Siqueiros and Clipperton transform faults. The southern line at 8°42'N lies at the center of an inflated segment south of the 9°03'N overlapping spreading center (OSC); the middle line at 9°18'N coincides with anomalously thick crust just to the north of the OSC; and the northern line at 9°50'N overlies a bathymetrically shallow segment near the site of recent eruptions. The lines extend at least 55 km off-axis and each comprises 200-400 airgun shots that were recorded by 6-7 seafloor receivers. We have used a two-dimensional tomography algorithm to invert crustal phases and Moho reflections for models of the P-wave velocity structure. For each line, we first inverted the non-rise crossing paths for off-axis structure and crustal thickness. We then interpolated the results to derive a starting model for axial inversions. Using a creeping method, we successively incorporated crustal phases that pass above the axial magma chamber (AMC), crustal phases that pass below the AMC, and Moho reflections. Since the ray geometry is two-dimensional, the width of the axial low velocity zone (LVZ) is not well resolved. We chose to squeeze the solutions by damping velocity perturbations at nodes that are more than 4-6 km off-axis. The root mean squared residuals are about 0.025 s for rise-crossing crustal phases and 0.03-0.04 s for sub-axial Moho reflections. The structure of the LVZ appears substantially different in the three models. Immediately beneath the AMC, the LVZ has the highest amplitude along the 9°50'N profile. In contrast, the LVZ in the lowermost crust has its largest amplitude along the 9°18'N profile where the crustal thickness requires that the melt supply is highest. The lower crustal LVZ beneath the 9°50'N profile is less pronounced than at the other two sites and is significantly skewed to the east. The differences

  16. Quantitative restoration the Gulf of Mexico continental margins based on a newly-derived, basin-wide, crustal thickness map

    Science.gov (United States)

    Nguyen, L. C.; Mann, P.

    2016-12-01

    For decades, one of the main difficulties for understanding the tectonic evolution of the Gulf of Mexico (GOM) is quantifying the amount of crustal thinning of its deeply-buried and salt-covered continental margins formed during the Triassic-Jurassic rifting. In this study, we present a new crustal thickness map for the entire GOM and its surrounding areas based on integration of: 1) depth to basement compilation of previous seismic refraction and well data; and 2) regional estimation of Moho depths from 3D gravity inversion. Gravity modeling of salt thickness and Moho depth provide new constraints on crustal thickness in areas where refraction and well data are not available from both the US and Mexican GOM. Our derived crustal thickness map shows a zone of stretched continental crust with an average thickness of 20 km extending 700 km from the Ouachita foldbelt to the Sigsbee escarpment and in a 200-km-wide zone along the north and NW edge of the Yucatan block. To fully reconstruct the GOM to its pre-rift stage, we first close the late Jurassic oceanic part of the deep GOM using the traces of oceanic transform faults mapped from satellite gravity data. We then use our crustal thickness map to restore the thinned continental crust of the conjugate margins. Restoring the Yucatan block in a NW-SE direction produces the optimal, closed-fit model which supports a two-phase, GOM opening concept with early asymmetrical rifting across a broader, more extended, North American lower plate ( 250 km) in the northern, US GOM and a narrower, less extended, Yucatan upper plate ( 100 km) in the southern, Mexican GOM. Our full-fit reconstruction shows a single, post-rift Louann-Campeche salt-filled sag basin and re-aligned Paleozoic magnetic trends between the Yucatan block and Florida.

  17. A tale of two orogens: Crustal processes in the Proterozoic Trans-Hudson and Grenville Orogens, eastern Canada

    Science.gov (United States)

    Darbyshire, F. A.; Bastow, I. D.; Petrescu, L.; Gilligan, A.; Thompson, D. A.

    2017-08-01

    The Precambrian core of North America was assembled in the Proterozoic by a series of collisions between Archean cratons. Among the orogenic belts, two stand out due to their significant spatial extent. The Paleoproterozoic Trans-Hudson Orogen (THO) and Mesoproterozoic Grenville Orogen extend for thousands of kilometers along strike and hundreds of kilometers across strike. Both have been compared to the present-day Himalayan-Karakoram-Tibetan Orogen (HKTO). Over the last 20-30 years, active and passive source seismic studies have contributed a wealth of information about the present-day crustal structure and composition of the two orogens in Canada. The Proterozoic orogenic crust is generally thicker than that of neighboring Archean terranes, with a more variable Moho character, ranging from relatively sharp to highly diffuse. Both orogens have a prominent high-velocity lower crustal layer, consistent with long-term preservation of a partially eclogitized root at the base of the crust and similar to that inferred beneath the western HKTO. Crustal structure in the northern THO strongly resembles the lower crustal structure of the HKTO, suggesting that Moho depths may have reached 60-70 km when the orogen was active. A prominent midcrustal discontinuity beneath the central Grenville Province and changes in the patterns of seismic anisotropy in the THO crust beneath Hudson Bay provide geophysical evidence that lower crustal flow likely played a role in the evolution of both orogens, similar to that inferred beneath the present-day HKTO. The seismic evidence from Canada supports the notion of tectonic uniformitarianism, at least as far back as the Paleoproterozoic.

  18. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    Energy Technology Data Exchange (ETDEWEB)

    Syuhada, E-mail: hadda9@gmail.com [Graduate Research on Earthquake and Active Tectonics (GREAT), Bandung Institute of Technology, Jalan Ganesha 10, Bandung 40132 (Indonesia); Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia); Hananto, Nugroho D.; Handayani, Lina [Research Centre for Geotechnology - Indonesian Institute of Sciences (LIPI), Jl. Sangkuriang (Kompleks LIPI) Bandung 40135 (Indonesia); Puspito, Nanang T; Yudistira, Tedi [Faculty of Mining and Petroleum Engineering ITB, Jalan Ganesha 10, Bandung 40132 (Indonesia); Anggono, Titi [Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia)

    2015-04-24

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  19. Neoproterozoic to Paleozoic Geological Evolution of Mongolia: Constraints on Modes of "Crustal Growth" in the Central Asian Orogenic Belt

    Science.gov (United States)

    Macdonald, F. A.; Bold, U.; Smith, E.; Olin, P. H.; Crowley, J. L.; Schmitz, M. D.

    2012-12-01

    The Central Asian Orogenic Belt (CAOB) is widely considered the largest area of Phanerozoic juvenile crustal growth on Earth. However, the timing and nature of the orogenic events in the core of the CAOB in Mongolia has remained poorly constrained due to a dearth of detailed geological and geochronological studies. To bridge this gap and test models of crustal growth, here we refine the sequencing of geological events by focusing on the formation and destruction of Neoproterozoic and Paleozoic tectonic basins. Mongolia's basins record a complete Neoproterozoic to Cambrian Wilson cycle with rifting of the Mongolian continent at ca. 700 Ma, the development of a Cryogenian to Ediacaran thermally subsiding passive margin, an arc-continent collision at ca. 520 Ma, and a continent-arc-continent collision at ca. 500 Ma. During this collisional orogeny, that is the Cambrian Altaids, crustal growth occurred largely through the obduction of ophiolites. Rifting of the southern margin occurred during the Ordovician Period, with the development of a Silurian passive margin. Oblique northwest-dipping subduction was initiated during the Devonian and resulted in a transpressional accretionary orogen. The CAOB culminated with a continent-arc-continent collision and the accretion of the North China and Tarim Blocks in the latest Permian. The Devonian to early Permian accretionary orogen is associated not only with voluminous plutonism, but also, major translational structures oblique to the margin resulting in the appearance of many accreted terranes. These data are consistent with existing coarse Hf and Nd isotopic data, but also provide a framework for future detailed studies. Although our geological constraints suggest distinct periods of apparent crustal growth through either collisional or accretionary orogenies, net crustal growth after accounting for recycling is equivocal.

  20. DigitalCrust – a 4D data system of material properties for transforming research on crustal fluid flow

    Science.gov (United States)

    Fan, Yin; Richard, Steve; Bristol, R. Sky; Peters, Shanan; Ingebritsen, Steven E.; Moosdorf, Nils; Packman, Aaron I.; Gleeson, Tom; Zazlavsky, Ilya; Peckham, Scott; Murdoch, Larry; Cardiff, Michael; Tarboton, David; Jones, Norm; Hooper, Richard; Arrigo, Jennifer; Gochis, David; Olson, John

    2015-01-01

    Fluid circulation in the Earth's crust plays an essential role in surface, near surface, and deep crustal processes. Flow pathways are driven by hydraulic gradients but controlled by material permeability, which varies over many orders of magnitude and changes over time. Although millions of measurements of crustal properties have been made, including geophysical imaging and borehole tests, this vast amount of data and information has not been integrated into a comprehensive knowledge system. A community data infrastructure is needed to improve data access, enable large-scale synthetic analyses, and support representations of the subsurface in Earth system models. Here, we describe the motivation, vision, challenges, and an action plan for a community-governed, four-dimensional data system of the Earth's crustal structure, composition, and material properties from the surface down to the brittle–ductile transition. Such a system must not only be sufficiently flexible to support inquiries in many different domains of Earth science, but it must also be focused on characterizing the physical crustal properties of permeability and porosity, which have not yet been synthesized at a large scale. The DigitalCrust is envisioned as an interactive virtual exploration laboratory where models can be calibrated with empirical data and alternative hypotheses can be tested at a range of spatial scales. It must also support a community process for compiling and harmonizing models into regional syntheses of crustal properties. Sustained peer review from multiple disciplines will allow constant refinement in the ability of the system to inform science questions and societal challenges and to function as a dynamic library of our knowledge of Earth's crust.

  1. A Sintaxe da Janela

    Directory of Open Access Journals (Sweden)

    Luís Antônio Jorge

    1993-12-01

    Full Text Available A preocupação fundamenta! do trabalho é de caráter ontológico: esboçar o problema das significações apriorísticas e autônomas dos elementos que compõem a sintaxe arquitetônica. O trabalho elege um desses elementos: a janela. Este artigo parte da aproximação histórica entre a janela e a secção da pirâmide visual, construção imaginária da teoria da perspectiva renascentista. A consideração da janela na linguagem arquitetônica implica reconhecer uma ambigüidade essencial: a janela deve inserir-se ordenadamente no plano da parede - raciocínio típico da modenatura - mas também relacionar-se com a imagem vista através dela, que extrapola o plano, ressaltando a tridimensionalidade - herança da perspectiva renascentista, fundamentada no espaço euclidiano. Ver janela ou ver através da janela são alternativas que se colocam tanto ao observador interno ao edifício, quanto ao externo. Texto de duplaface, a sintaxe da janela versa sobre o relacionamento desses dois lados

  2. Crustal formation in the Nanling Range, South China Block: Hf isotope evidence of zircons from Phanerozoic granitoids

    Science.gov (United States)

    Shu, Xu-Jie; Wang, Xiao-Lei; Sun, Tao; Chen, Wei-Feng; Shen, Wei-Zhou

    2013-09-01

    Granitic rocks are the principle agent of crustal differentiation, therefore their origins yield important information on crustal formation and reworking. An extensive survey of zircon Hf isotopes from granitic rocks in a large region can provide a profile of crustal characteristics that may be further linked to previous crustal evolution. In this study, we measured U-Pb ages and Hf isotope compositions of zircon grains extracted from twenty-five Jurassic, five Triassic and two Ordovician granitic plutons from the Nanling Range, South China Block (SCB). Combined with the published Lu-Hf isotopic data for the granitic rocks in the studied and adjacent areas, three domains with different crustal formation histories have been identified in the southern part of the SCB: eastern side, middle part and western side. The eastern side extends to the coastal area of the SCB, with dominant Hf crustal model ages (TDM2) in zircons falling within the range of 2.2-1.6 Ga. The middle part is partly coincided with the low-Nd model age belt proposed by Chen and Jahn (1998), with zircon Hf TDM2 ranging from 1.6 to 1.0 Ga. The western side covers the westernmost Nanling Range and the western end of the Jiangnan orogen, in which the granitoids have zircon Hf TDM2 model ages spanning 2.2-1.8 Ga. The Paleo- to Meso-Proterozoic model ages of the Phanerozoic granitoids in the Nanling Range imply a long-term crustal reworking. Zircons from the western and eastern sides have an average ɛHf(155 Ma) at around -10, about 4 epsilon units lower than the middle part (ɛHf(155 Ma) = -6). Hf TDM2 histogram from the western Nanling Range is similar to that of the Neoproterozoic granitoids in northern Guangxi Province to the west but much lower to the granites in the middle part to the east. The eastern side has a broader range of Hf model ages in zircons, with the main peak low to ca 1.6 Ga, suggesting the reworking of Mesoproterozoic crust. However, granitoids in the middle part have zircon Hf TDM2

  3. Alps, Carpathians and Dinarides-Hellenides: about plates, micro-plates and delaminated crustal blocks

    Science.gov (United States)

    Schmid, Stefan

    2014-05-01

    Before the onset of Europe-Africa continental collision in the Dinarides-Hellenides (around 60Ma) and in the Alps and Western Carpathians (around 35 Ma), and at a large scale, the dynamics of orogenic processes in the Mediterranean Alpine chains were governed by Europe-Africa plate convergence leading to the disappearance of large parts of intervening oceanic lithosphere, i.e. the northern branch of Neotethys along the Sava-Izmir-Ankara suture and Alpine Tethys along the Valais-Magura suture (Schmid et al. 2008). In spite of this, two major problems concerning the pre-collisional stage are still poorly understood: (1) by now we only start to understand geometry, kinematics and dynamics of the along-strike changes in the polarity of subduction between Alps-Carpathians and Dinarides-Hellenides, and (2) it is not clear yet during exactly which episodes and to what extent intervening rifted continental fragments such as, for example, Iberia-Briançonnais, Tisza, Dacia, Adria-Taurides moved independently as micro-plates, and during which episodes they remained firmly attached to Europa or Africa from which they broke away. As Europe-Africa plate convergence slowed down well below 1 cm/yr at around 30 Ma ago these pre-collisional processes driven by plate convergence on a global scale gave way to more local processes of combined roll-back and crustal delamination in the Pannonian basin of the Carpathian embayment and in the Aegean (as well as in the Western Mediterranean, not discussed in this contribution). In the case of the Carpathian embayment E-directed roll back totally unrelated to Europe-Africa N-S-directed convergence, started at around 20 Ma ago, due to the presence relict oceanic lithosphere in the future Pannonian basin that remained un-subducted during collision. Due to total delamination of the crust from the eastward rolling back European mantle lithosphere the anticlockwise rotating ALCAPA crustal block, consisting of Eastern Alps and Western Carpathian

  4. Crustal deformation evidences for viscous coupling and fragmented lithosphere at the Nubia-Iberia plate boundary (Western Mediterranean)

    Science.gov (United States)

    Palano, Mimmo; González, Pablo J.; Fernández, José

    2016-04-01

    A spatially dense crustal velocity field, based on up to 15 years of GNSS observations at more than 380 sites and extensively covering the Iberian Peninsula and Northern Africa, allow us to provide new insights into two main tectonic processes currently occurring in this area. We detected a slow large-scale clockwise rotation of the Iberian Peninsula with respect to a local pole located closely to the northwestern sector of the Pyrenean mountain range (Palano et al., 2015). Although this crustal deformation pattern could suggest a rigid rotating lithosphere block, this model would predict significant shortening along the Western (off-shore Lisbon) and North Iberian margin which cannot totally ruled out but currently is not clearly observed. Conversely, we favour the interpretation that this pattern reflects the quasi-continuous straining of the ductile lithosphere in some sectors of South and Western Iberia in response to viscous coupling of the NW Nubia and Iberian plate boundary in the Gulf of Cádiz. Furthermore, the western Mediterranean basin appears fragmented into independent crustal tectonic blocks, which delimited by inherited lithospheric shear structures and trapped within the Nubia-Eurasia collision, are currently accommodating most of the plate convergence rate. Among these blocks, an (oceanic-like western) Algerian one is currently transferring a significant fraction of the Nubia-Eurasia convergence rate into the Eastern Betics (SE Iberia) and likely causing the eastward motion of the Baleares Promontory. Most of the observed crustal ground deformation can be attributed to processes driven by spatially variable lithospheric plate forces imposed along the Nubia-Eurasia convergence boundary. Nevertheless, the observed deformation field infers a very low convergence rates as observed also at the eastern side of the western Mediterranean, along the Calabro Peloritan Arc, by space geodesy (e.g. Palano, 2015). References Palano M. (2015). On the present

  5. Collision vs. subduction-related magmatism: Two contrasting ways of granite formation and implications for crustal growth

    Science.gov (United States)

    Moyen, J.-F.; Laurent, O.; Chelle-Michou, C.; Couzinié, S.; Vanderhaeghe, O.; Zeh, A.; Villaros, A.; Gardien, V.

    2017-04-01

    Earth's continental crust is dominantly made of buoyant, felsic igneous material (granitoids), that was ultimately extracted from the mantle as a result of Earth's differentiation. Since felsic melts are not in chemical equilibrium with the mantle, they can originate either from melting of older crustal lithologies, or from differentiation of a primitive mantle melt; only the latter case will contribute to crustal growth. To understand the mechanisms of continental crust growth and differentiation through time, it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites. In modern Earth, granitoids are chiefly generated in convergent plate boundaries (subduction and collision). This paper examines the granitic suites in a late-collision environment, the Variscan French Massif Central (FMC), and compares them with the suites found in an oceanic arc. We therefore describe, and compare, two end-members sites of granite generation. In the FMC, several main types of granites are described. Muscovite and Cordierite bearing Peraluminous Granites (resp. MPG and CPG) contain large amounts of inherited zircons, and their chemistry demonstrates that their sources were older crustal material (resp. metasediments and metaigneous). On the other hand, Potassic Calc-alkaline Granites (KCG), associated to potassic diorites (vaugnerites) do not contain inherited zircons, and ultimately derive from the vaugnerites. The vaugnerites in turn form by partial melting of a mantle contaminated by the regional crust. Therefore, although they are isotopically similar to the crust, the KCG are net contributors to crustal growth. Thus we conclude that although late-orogenic settings are dominated by crustal melting and recycling, they may be sites of net crustal growth, even though this is not visible from isotopes only. In contrast, arc granitoids are purely or almost purely mantle derived. However, the preservation

  6. The Yellowstone-Snake River Plain Seismic Profiling Experiment: Crustal structure of the Eastern Snake River Plain

    Science.gov (United States)

    Braile, L. W.; Smith, R. B.; Ansorge, J.; Baker, M. R.; Sparlin, M. A.; Prodehl, C.; Schilly, M. M.; Healy, J. H.; Mueller, St.; Olsen, K. H.

    1982-04-01

    Seismic refraction profiles recorded along the eastern Snake River Plain (ESRP) in southeastern Idaho during the 1978 Yellowstone-Snake River Plain cooperative seismic profiling experiment are interpreted to infer the crustal velocity and attenuation (Q-1) structure of the ESRP. Travel-time and synthetic seismogram modeling of a 250 km reversed refraction profile as well as a 100 km detailed profile indicate that the crust of the ESRP is highly anomalous. Approximately 3 to 6 km of volcanic rocks (with some interbedded sediments) overlie an upper-crustal layer (compressional velocity ≅6.1 km/s) which thins southwestward along the ESRP from a thickness of 10 km near Island Park Caldera to 2 to 3 km beneath the central and southwestern portions of the ESRP. An intermediate-velocity (≅6.5 km/s) layer extends from ≅10 to ≅20 km depth. A thick (≅22 km) lower crust of compressional velocity 6.8 km/s, a total crustal thickness of ≅42 km, and a Pn velocity of ≅7.9 km/s is observed in the ESRP, similar to the western Snake River Plain and the Rocky Mountains Provinces. High attenuation is evident on the amplitude corrected seismic data due to low-Q values in the volcanic rocks (Qp = 20 to 200) and throughout the crust (Qp = 160 to 300). Based on these characteristics of the crustal structure and volcanic-age progression data, it is suggested that the ESRP has resulted from an intensive period of intrusion of mantle-derived basaltic magma into the upper crust generating explosive silicic volcanism and associated regional uplift and caldera collapse. This activity began about 15 m.y. ago in southwestern Idaho and has migrated northeast to its present position at Yellowstone. Subsequent cooling of the intruded upper crust results in the 6.5 km/s velocity intermediate layer. Crustal subsidence and periodic basaltic volcanism as represented by the ESRP complete the sequence of crustal evolution.

  7. Continental velocity through Precambrian times: The link to magmatism, crustal accretion and episodes of global cooling

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    J.D.A. Piper

    2013-01-01

    Full Text Available Quasi-integrity of continental crust between Mid-Archaean and Ediacaran times is demonstrated by conformity of palaeomagnetic poles to near-static positions between ∼2.7–2.2 Ga, ∼1.5–1.2 Ga and ∼0.75–0.6 Ga. Intervening data accord to coherent APW loops turning at “hairpins” focused near a continental-centric location. Although peripheral adjustments occurred during Early Proterozoic (∼2.2 Ga and Grenville (∼1.1 Ga times, the crust retained a low order symmetrical crescent-shaped form constrained to a single global hemisphere until break-up in Ediacaran times. Conformity of palaeomagnetic data to specific Eulerian parameters enables definition of a master Precambrian APW path used to estimate the root mean square velocity (vRMS of continental crust between 2.8 and 0.6 Ga. A long interval of little polar movement between ∼2.7 and 2.2 Ga correlates with global magmatic shutdown between ∼2.45 and 2.2 Ga, whilst this interval and later slowdown at ∼0.75–0.6 Ga to velocities of <2 cm/year correlate with episodes of widespread glaciation implying that these prolonged climatic anomalies had an internal origin; the reduced input of volcanically-derived atmospheric greenhouse gases is inferred to have permitted freeze-over conditions with active ice sheets extending into equatorial latitudes as established by low magnetic inclinations in glaciogenic deposits. vRMS variations through Precambrian times correspond to the distribution of U-Pb ages in orogenic granitoids and detrital zircons and demonstrate that mobility of continental crust has been closely related to crustal tectonism and incrementation. Both periods of near-stillstand were followed by rapid vRMS recording massive heat release from beneath the continental lid at ∼2.2 and 0.6 Ga. The first coincided with the Lomagundi-Jatuli isotopic event and led to prolonged orogenesis accompanied by continental flooding and reconfiguration of the crust on the Earth

  8. Towards seismic data inversion for crustal thermo-chemical structure: what thermodynamics say

    Science.gov (United States)

    Diaferia, Giovanni; Cammarano, Fabio

    2017-04-01

    Unraveling the temperature distribution and composition of Earth's Crust is key to understanding its origin, evolution and mechanical behavior. Models of compressional (VP) and shear (VS) velocity and the mapping of seismic discontinuities are derived from seismological studies and interpreted in terms of temperature and composition. Nonetheless seismic models require approximations and assumptions that can be geologically inconsistent or poorly justified. Moreover, the relationship between the seismic and material properties of rocks are often non-linear and non-unique. A better and more quantitative understanding of rock behavior with respect to temperature, pressure, composition and water content is necessary, to clarify the limits and feasibility of seismic methods in inferring geological features. We use thermodynamic modeling to predict bulk seismic velocities and densities of proposed (both dry and hydrous) compositions for the upper, middle and lower crust in the Italian province, at varying temperature and pressure. A comparison is made with the VP and VS from the EPCrust model (Molinari & Morelli, 2011) and the ones from Molinari et al. (2015), based on ambient noise surface wave inversion. We find that different dry compositions proposed for the Italian crust would be seismically indistinguishable. The variation induced by a different composition is always lower than that caused by temperature and water content. Moreover, a mechanical mix of different chemical compositions produces bulk seismic properties which correspond, within errors, to what obtained by modeling their average composition. For these reasons, a global composition for the Crust (i.e Rudnick and Gao [2003]) can be used as a reasonable approximation. The presence of water, although important to retrieve the correct crustal mineralogy, does not affect significantly seismic velocities in a large P-T range. Only felsic, upper crustal compositions with water content >0.25 wt%, show a drastic

  9. Crustal and Lithospheric Structure of the Western Mediterranean: Pds Receiver Function Results from the PICASSO Experiment

    Science.gov (United States)

    Thurner, S.; Palomeras, I.; Levander, A.

    2012-12-01

    The Betic Mountains in southern Spain, the Gibraltar Arc, the Alboran Sea, and the Rif and Atlas Mountains in northern Africa comprise the western Mediterranean tectonic region, which has been affected by simultaneous extension and compression throughout the Cenozoic. Multiple geodynamic models have been invoked to explain the coeval compressional and extensional tectonic processes, including slab roll-back (Royden, 1993; Lonergan and White, 1997; Gutscher et al., 2002), accompanied and followed by lithospheric convective downwelling (Seber et al., 1996; Calvert et al., 2000), and delamination (Platt et al., 1996). We use Ps teleseismic receiver functions to investigate the crustal and lithospheric structure throughout this region. PICASSO (Program to Investigate Convective Alboran Sea System Overturn) is a multi-disciplinary, international investigation seeking to improve our understanding of the geodynamics of the western Mediterranean. The PICASSO deployment includes 89 broadband stations distributed linearly from central Spain to the Morocco-Algeria border. For this study we supplemented the PICASSO dataset with data from six other Moroccan, Spanish, Portuguese, and German networks in the region. Using 167 events (M > 6.0) recorded at a total of 240 stations we calculated 1 Hz and 2Hz receiver functions. The receiver functions were then CCP stacked to create a 3D image volume of the region. The Pds receiver functions indicate crustal thicknesses between ~42-47 km in southern Spain beneath the Betic Mountains and ~35-45 km across the Gibraltar Strait. Beneath both the Rif and Betic Mountains we observe complex crustal structures, including two strong positive arrivals around Moho depth (~50 km). A number of models can explain this feature, including those associated thrust systems in each region. In Morocco, along a NW-SE transect from the Gibraltar Strait across the Atlas Mountains, we observe thick crust in the north beneath the Rif Mountains and to the south

  10. Crustal deformation pattern of the Morocco-Iberian area: constraints from 14 years of GPS measurements

    Science.gov (United States)

    Palano, Mimmo; González, Pablo; Fernandez, Josè

    2014-05-01

    We present an improved rendition of crustal motion field of the Morocco-Iberian area, based on an extensive GPS dataset covering about 14 years of observations from 1999.00 up to 2013.79 in order to provide a detailed spatial resolution of geodetic velocity and strain-rate fields. In particular, we included all available data from public continuous GPS stations, considering also data coming from networks developed mainly for mapping, engineering and cadastre purposes. In addition to continuous GPS sites, we included data from 31 episodic GPS sites located in Morocco with surveys spanning the 1999-2006 time interval, whose data are available through the UNAVCO archive (www.unavco.org). All GPS data were processed by using the GAMIT/GLOBK software, taking into account precise ephemerides from the IGS (International GNSS Service; http://igscb.jpl.nasa.gov) and Earth orientation parameters from the International Earth Rotation Service (http://www.iers.org). To improve the overall configuration of the network and tie the regional measurements to an external global reference frame, data coming from more than 25 continuously operating global tracking stations, largely from the IGS and EUREF permanent networks, were introduced in the processing. All stations were organized (and processed) into seven sub-networks of about 40-50 sites each, on average, sharing a few common sites to provide ties between them. Finally, by using the GLORG module of GLOBK, the GAMIT-solutions and their full covariance matrices were combined to estimated a consistent set of positions and velocities in the ITRF2008 reference frame by minimizing the horizontal velocity of the continuously operating global tracking stations mentioned above. To adequately investigate the crustal deformation pattern over the study area, we aligned our estimated GPS velocities to an Eurasian and a Nubian fixed reference frames. In addition, by taking into account the observed GPS horizontal velocity field and

  11. Deep-crustal seismicity in volcanic regions by fluid-enhanced wallrock embrittlement

    Science.gov (United States)

    Sisson, T. W.; Power, J. A.

    2013-12-01

    Spatial association of deep long-period (DLP) seismicity with volcanoes [1,2], spectral frequencies resembling shallow events attributed to fluid motions, and temporal associations with some eruptions, prompt the interpretation that DLPs mark the locations of magma, or magma with percolating exsolved vapor, in the mid and lower crust. However, various factors are more consistent with the events taking place in the walls surrounding the hot aseismic cores of deep magmatic systems, due to expelled magmatic fluids elevating pore pressures and reducing wall rock brittle strengths, or possibly in largely solidified peripheral intrusions embrittled by interstitial residual melt. First, although exceptions are known, deep seismic events are typically displaced to one or more sides of the locus of volcanism. Compilation of >1000 mid to deep crustal DLP and volcano tectonic events from the Aleutian arc, plotted as radial distance from the respective volcanic locus vs. depth, shows a minimum of events beneath the volcanic loci, encased in a downward broadening halo of events, typically displaced about 6 km to the sides of the volcanic locus. Lateral offsets of deep events are also well established for volcanoes of the Washington Cascades [3], averaging 7.5×4.5(1σ) km, and for some centers in California [1]. Second, while mafic parental magmas can have high concentrations of H2O (CO2 concentrations are comparatively negligible), H2O is highly soluble at mid to lower crustal pressures and will not exsolve appreciably until advanced crystallization and second boiling. Deep vapor exsolution will proceed gradually, delayed well after replenishment events, due to slow cooling and crystallization in the hot deep crust. Exsolution dominantly at high crystallinities argues against bubbles moving through largely liquid replenishing magmas as a major cause of DLPs. Third, isotherms around the mid to deep crustal portions of magmatic systems will propagate outward with time1/2 due to

  12. Genealogias da alegria

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    Bruno Vasconcelos de Almeid

    2009-08-01

    Full Text Available Genealogias da Alegria tem por objetivo rastrear conceitos e construir planos sobre os quais podemos pensar a alegria como campo problemático. Trata-se de traçar linhas e acoplar fragmentos históricos e literários com a finalidade de subsidiar a discussão contemporânea em torno da alegria. O procedimento genealógico vale-se de trechos das obras de Calímaco e Luciano de Samósata, da elegia erótica romana e da alegria cristã. O passo seguinte consiste em rastrear o pensamento da alegria na obra de Gilles Deleuze, especialmente em três momentos: uma passagem de Diferença e Repetição, um trecho dos Diálogos extraído de Da Superioridade da Literatura Anglo-americana e a comunicação Pensamento Nômade no Colóquio de Cerisy. A alegria não se define como sentimento ou emoção; ao contrário, está ligada à premissa de afirmação da vida e ao caráter trágico da existência.

  13. Shallow crustal structure of eastern-central Trans-Mexican Volcanic Belt.

    Science.gov (United States)

    Campos-Enriquez, J. O.; Ramón, V. M.; Lermo-Samaniego, J.

    2015-12-01

    Central-eastern Trans-Mexican Volcanic Belt (TMVB) is featured by large basins (i.e., Toluca, Mexico, Puebla-Tlaxcala, Libres-Oriental). It has been supposed that major crustal faults limit these basins. Sierra de Las Cruces range separates the Toluca and Mexico basins. The Sierra Nevada range separates Mexico basin from the Puebla-Tlaxcala basin. Based in gravity and seismic data we inferred the Toluca basin is constituted by the Ixtlahuaca sub-basin, to the north, and the Toluca sub-basin to the south, which are separated by a relative structural high. The Toluca depression is more symmetric and bounded by sub-vertical faults. In particular its eastern master fault controlled the emplacement of Sierra de Las Cruces range. Easternmost Acambay graben constitutes the northern and deepest part of the Ixtlahuaca depression. The Toluca-Ixtlahuaca basin is inside the Taxco-San Miguel de Allende fault system, and limited to the west by the Guerrero terrane which continues beneath the TMVB up to the Acambay graben. Mexico basin basement occupies an intermediate position and featured by a relative structural high to the north-east, as established by previous studies. This relative structural high is limited to the west by the north-south Mixhuca trough, while to the south it is bounded by the east-west Copilco-Xochimilco-Chalco sub-basin. The Puebla-Tlaxcala basin basement is the shallowest of these 3 tectonic depressions. In general, features (i.e., depth) and relationship between these basins, from west to east, are controlled by the regional behavior of the Sierra Madre Oriental fold and thrust belt basement (i.e., Oaxaca Complex?). This study indicates that an active east-west regional fault system limits to the south the TMVB (from the Nevado de Toluca volcano through the Popocatepetl volcano and eastward along southern Puebla-Tlaxcala basin). The Tenango and La Pera fault systems constituting the western part of this regional fault system coincide with northern

  14. Subsidence history, crustal structure and evolution of the Nogal Rift, Northern Somalia

    Science.gov (United States)

    Ali, M. Y.; Watts, A. B.

    2013-12-01

    Seismic reflection profile, gravity anomaly, and biostratigraphic data from deep exploration wells have been used to determine the tectonic subsidence, structure and evolution of the Nogal basin, Northern Somalia, one of a number of ENE-WSW trending early Mesozoic rifts that formed prior to opening of the Gulf of Aden. Backstripping of biostratigraphic data at the Nogal-1 and Kali-1 wells provides new constraints on the age of rifting, and the amount of crustal and mantle extension. The tectonic subsidence and uplift history at the wells can be generally explained as a consequence of two, possibly three, major rifting events. The first event initiated in the Late Jurassic (~156 Ma) and lasted for ~10 Myr. We interpret the rift as a late stage event associated with the break-up of Gondwana and the separation of Africa and Madagascar. The second event initiated in the Late Cretaceous (~80 Ma) and lasted for ~20 Myr. This event probably correlates with a rapid increase in spreading rate on the ridges separating the African and Indian and African and Antarctica plates and a contemporaneous slowing down of Africa's plate motion. The backstripped tectonic subsidence data can be explained by a multi-rift extensional model with a stretching factor, β, in the range 1.17-1.38. The third and most recent event occurred in the Oligocene (~32 Ma) and lasted for ~10 Myr. This rift only developed at the centre of the basin close to Nogal-1 well, and is related to the opening of the Gulf of Aden. The amount of crustal thinning inferred at the Kali-1 well is consistent with the results of Process-Oriented Gravity and Flexure (POGM) modelling, assuming an elastic thickness of ~30 km. The thinning at the Nogal-1 well, however, is greater by ~ 7 km than predicted suggesting that the basin may be locally underplated by magmatic material. Irrespective, POGM suggests the transition between thick crust beneath Northern Somalia to thin crust beneath the Indian Ocean forms a ~500 km wide

  15. Deep crustal structure of the northeastern margin of the Arabian plate from seismic and gravity data

    Science.gov (United States)

    Pilia, Simone; Ali, Mohammed; Watts, Anthony; Keats, Brook; Searle, Mike

    2017-04-01

    The United Arab Emirates-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cainozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (7060 cubic inches, 116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s and a thick sedimentary package in the offshore. Furthermore, the velocity model reveals a highly stretched crust with the Moho discontinuity lying at about 20 km. A prestack depth-migrated profile (about 50 km long) coincident with the offshore part

  16. Crustal structure at the western end of the North Anatolian Fault Zone from deep seismic sounding

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    B. Baier

    2001-06-01

    Full Text Available The first deep seismic sounding experiment in Northwestern Anatolia was carried out in October 1991 as part of the "German - Turkish Project on Earthquake Prediction Research" in the Mudurnu area of the North Anatolian Fault Zone. The experiment was a joint enterprise by the Institute of Meteorology and Geophysics of Frankfurt University, the Earthquake Research Institute (ERI in Ankara, and the Turkish Oil Company (TPAO. Two orthogonal profiles, each 120 km in length with a crossing point near Akyazi, were covered in succession by 30 short period tape recording seismograph stations with 2 km station spacing. 12 shots, with charge sizes between 100 and 250 kg, were fired and 342 seismograms out of 360 were used for evaluation. By coincidence an M b = 4.5 earthquake located below Imroz Island was also recorded and provided additional information on Moho and the sub-Moho velocity. A ray tracing method orginally developed by Weber (1986 was used for travel time inversion. From a compilation of all data two generalized crustal models were derived, one with velocity gradients within the layers and one with constant layer velocities. The latter consists of a sediment cover of about 2 km with V p » 3.6 km/s, an upper crystalline crust down to 13 km with V p » 5.9 km/s, a middle crust down to 25 km depth with V p » 6.5 km/s, a lower crust down to 39 km Moho depth with V p » 7.0 km/s and V p » 8.05 km/s below the Moho. The structure of the individual profiles differs slightly. The thickest sediment cover is reached in the Izmit-Sapanca-trough and in the Akyazi basin. Of particular interest is a step of about 4 km in the lower crust near Lake Sapanca and probably an even larger one in the Moho (derived from the Imroz earthquake data. After the catastrophic earthquake of Izmit on 17 August 1999 this significant heterogeneity in crustal structure appears in a new light with regard to the possible cause of the Izmit earthquake. Heterogeneities in

  17. Effect of small-scale heterogeneities on interpretation of crustal compositions exemplified by a layered anorthosite

    Science.gov (United States)

    Semprich, J.; Vrijmoed, J. C.

    2015-02-01

    The composition of the lower crust has a significant effect on geodynamic processes because it influences physical rock properties such as densities and seismic velocities. Compositional differences in lower crustal rocks are potentially large and exist on the scales of centimeters up to kilometers resulting in non-unique seismic and gravity data. While larger heterogeneities can be detected as reflections on seismic profiles, irregular small-scale compositional variations are not likely to be discovered, but will influence the averaged seismic velocities and densities of an area. The extent and effects of such small-scale heterogeneities are explored on an exposed high-grade layered anorthositic body by providing a detailed field map, petrological descriptions, pycnometry measurements as well as whole rock and mineral analyses combined with thermodynamic phase equilibria calculations. To evaluate the results of our thermodynamic calculations, densities and mineral modes obtained from the modeled phase equilibria are compared to measured densities and estimated mineral modes from rock samples. The proportion of mafic to ultramafic (plagioclase-poor) rocks in the mapped field area amounts to 10-15% but higher proportions of these rock types in the lower crust are feasible. To further study the effects of compositional variations, we have generated mixtures of mafic to ultramafic and anorthositic/intermediate rocks until the average properties of these mixtures are comparable to those of mafic granulites (3000-3100 kg/m3; 7.1-7.3 km/s). Mixtures of anorthosite with 40-45% and of tonalite with 50-60% high-grade mafic to ultramafic rocks yield average densities and seismic velocities similar to mafic granulites although they still contain 50-60 vol.% plagioclase. Hence small-scale mixing of certain rock types may result in the overestimation of the proportion of mafic (garnet) granulites in the lithologic interpretation of crustal compositions from seismic data. Since

  18. Crustal structure of the Northwestern Iranian Plateau revealed by ambient noise tomography

    Science.gov (United States)

    Jiang, M.; Chen, L.; Ai, Y.; Talebian, M.; Ghods, A.; Sobouti, F.

    2015-12-01

    The Iranian Plateau was formed during the collision of the Arabian plate and Eurasia plate since ~30 Ma following the closure of the Neo-Tethys ocean. Comparing with the Tibetan Plateau to the east, the Iranian Plateau has lower elevation, thinner crust and less internal deformation. Whether these differences can be attributed to two successive stages of a common continent-continent collision process or two different orogenic processes is still under debate. Detailed information of structures at depth can provide key constraints on this debate and is essential for understanding the formation of the plateau. To investigate the deep structure of the Iranian Plateau, we operated a temporary seismic array in northwestern Iran from October 2013 to October 2014, under a collaborative project named CIGSIP (China-Iran Geological and Geophysical Survey in the Iranian Plateau). This array started from the south of the Zagros belt, trending northeastward and ending at the coast area of the southern Caspian Sea. Using the continuous seismic data recorded by this seismic array of the CIGSIP project, we adopted ambient noise tomography to image the 3-D crustal shear velocity structure beneath the sampled area in northwestern Iran. To stabilize the inversion for shear velocities, we incorporated the prior constraints on the depths of the Moho and strong intra-crustal discontinuities from teleseismic receiver functions recorded by the same array. Systematic comparisons were further conducted among images with and without depth constraints incorporated and with various initial models adopted in the inversion, indicating that the resultant shear velocity images reveal robust structural features beneath the study area. Our results show that bounding by the Main Zagros Thrust (MZT), the crust exhibits different structural features on the two sides. Low velocity anomalies are mainly confined to the south of the MZT. The crust north of MZT is characterized by high velocities. Low

  19. InSAR Observations and Finite Element Modeling of Crustal Deformation Around a Surging Glacier, Iceland

    Science.gov (United States)

    Spaans, K.; Auriac, A.; Sigmundsson, F.; Hooper, A. J.; Bjornsson, H.; Pálsson, F.; Pinel, V.; Feigl, K. L.

    2014-12-01

    Icelandic ice caps, covering ~11% of the country, are known to be surging glaciers. Such process implies an important local crustal subsidence due to the large ice mass being transported to the ice edge during the surge in a few months only. In 1993-1995, a glacial surge occurred at four neighboring outlet glaciers in the southwestern part of Vatnajökull ice cap, the largest ice cap in Iceland. We estimated that ~16±1 km3 of ice have been moved during this event while the fronts of some of the outlet glaciers advanced by ~1 km.Surface deformation associated with this surge has been surveyed using Interferometric Synthetic Aperture Radar (InSAR) acquisitions from 1992-2002, providing high resolution ground observations of the study area. The data show about 75 mm subsidence at the ice edge of the outlet glaciers following the transport of the large volume of ice during the surge (Fig. 1). The long time span covered by the InSAR images enabled us to remove ~12 mm/yr of uplift occurring in this area due to glacial isostatic adjustment from the retreat of Vatnajökull ice cap since the end of the Little Ice Age in Iceland. We then used finite element modeling to investigate the elastic Earth response to the surge, as well as confirm that no significant viscoelastic deformation occurred as a consequence of the surge. A statistical approach based on Bayes' rule was used to compare the models to the observations and obtain an estimate of the Young's modulus (E) and Poisson's ratio (v) in Iceland. The best-fitting models are those using a one-kilometer thick top layer with v=0.17 and E between 12.9-15.3 GPa underlain by a layer with v=0.25 and E from 67.3 to 81.9 GPa. Results demonstrate that InSAR data and finite element models can be used successfully to reproduce crustal deformation induced by ice mass variations at Icelandic ice caps.Fig. 1: Interferograms spanning 1993 July 31 to 1995 June 19, showing the surge at Tungnaárjökull (Tu.), Skaftárjökull (Sk.) and S

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

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    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

  1. Dating High Temperature Mineral Fabrics in Lower Crustal Granulite Facies Rocks

    Science.gov (United States)

    Stowell, H. H.; Schwartz, J. J.; Tulloch, A. J.; Klepeis, K. A.; Odom Parker, K.; Palin, M.; Ramezani, J.

    2015-12-01

    Granulite facies rocks may record strain that provides a record of compressional and/or extensional crustal events in hot orogenic cores and the roots of magmatic arcs. Although the precise timing of these events is important for constructing tectonic histories, it is often difficult to determine due to uncertain relationships between isotopic signatures, mineral growth, and textural features that record strain. In addition, there may be large uncertainties in isotope data due to intracrystalline diffusion and multiple crystallization events. L-S tectonites in lower crustal rocks from Fiordland, NZ record the early stages of extensional collapse of thickened magmatic arc crust. The precise age of these fabrics is important for constraining the timing of extension that led to opening of the Tasman Sea. High temperature granulite facies L-S fabrics in garnet reaction zones (GRZ) border syn- to post-deformational leucosomes. U-Pb zircon, Lu-Hf garnet, and Sm-Nd garnet ages, and trace elements in these phases indicate the complexity of assigning precise and useful ages. Zircon have soccer ball morphology with patchy and sector zoned CL. Zircon dates for igneous host and adjacent GRZ range over ca. 17 Ma. 236U-208Pb LA-ICP-MS are 108-125 Ma, N=124 (host & GRZ); however, chemical abrasion (CA) shifts GRZ dates ca. 2 Ma older. 236U-208Pb SHRIMP-RG dates cluster in 2 groups: 118.5±0.8 Ma, N=23 and 111.0±0.8 Ma, N=6. CA single crystal TIMS dates also fall into 2 groups: 117.6±0.1 Ma, N=4 and 116.6±0.2 Ma N=4. Garnet isochron ages determined from coarse garnet selvages adjacent to leucosomes range from 112.8±2.2 (147Sm-143Nd, 10 pts.) to 114.8±3.5 (177Lu-176Hf, 6 pts.) Ma. Zircon dates from all methods show ranges (>10 Ma) and 2 distinct populations. Host and GRZ zircon cannot be readily distinguished by age, lack younger rims, but have distinct Th/U trends and Eu/Eu* vs. Hf ratios. Difference in zircon trace element composition indicates either early leucosome

  2. Moon-Mercury: Large impact structures, isostasy and average crustal viscosity

    Science.gov (United States)

    Schaber, G.G.; Boyce, J.M.; Trask, N.J.

    1977-01-01

    Thirty-five craters and basins larger than 200 km in diameter are recognized on the imaged portion (45%) of Mercury. If the unimaged portion of the planet is similarly cratered, a total of 78 such impact features may be present. Sixty-two craters and basins 200 km in diameter are recognized on the moon, a body with only half the cross-sectional area of Mercury. If surface areas are considered, however, Mercury is cratered only 70% as densely as the moon. The density of impact craters with diameters greater than 400 km on Mercury is only 30% of that on the moon, and for craters with diameters between 400 and 700 km, the density on Mercury is only 21% of the lunar crater density. The size-frequency distribution curve for the large Mercurian craters follows the same cumulative -2 slope as the lunar curve but lies well below the 10% surface saturation level characteristic of the lunar curve. This is taken as evidence that the old heavily cratered terrain on Mercury is, at least presently, not in a state of cratering equilibrium. The reduced density of large craters and basins on Mercury relative to the moon could be either a function of the crater-production rates on these bodies or an effect of different crustal histories. Resurfacing of the planet after the basin-forming period is ruled out by the presence of 54 craters and basins 100 km in diameter and larger (on the imaged portion of Mercury) that have either well-defined or poorly-defined secondary-crater fields. Total isostatic compensation of impact craters ???800 km in diameter indicates that the average viscosity of the Mercurian crust over the past 4+ aeons was the same as that for the moon (???1026.5 P). This calculated viscosity and the distribution of large craters and basins suggest that either the very early crustal viscosity on Mercury was less than that of the moon and the present viscosity greater, or the differences in large crater populations on the two bodies is indeed the result of variations in

  3. Crustal Structure across The Southwest Longmenshan Fault Zone from Seismic Wide Angle Reflection/Refraction Profile

    Science.gov (United States)

    Tian, Xiaofeng; Wang, Fuyun; Wang, Shuaijun; Duan, Yonghong

    2014-05-01

    The Lushan eathquake, which epicenter and focal depth were at 30.308° N, 102.888° E, and 14.0 km, is the latest intense earthquake occurring in the southwest section of the Longmenshan fault zone after the Ms 8.0 Wenchuan earthquake in 2008. According to the emergency field observations, the slip distribution of the Lushan earthquake was concentrated at the hypocenter, and did not rupture to the surface(Chen et al, 2013). The rupture history constrained by inverting waveforms showed that the causative fault plane of the Lushan event is apparently not a simple extension of either the Pengguan fault or the Beichuan fault that ruptured during the 2008 Mw 8.0 Wenchuan earthquake. The focal mechanism using the Cut and Paste algorithm showed this event occurred on a high dip-angle fault, but its dip angle is not steep enough to rupture the surface. All these research is not independent on the heterogeneous crust structure of the Longmenshan fault zone. A 450 km-long wide-angle reflection/refraction profile executed during September and October 2013. This experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of crust and uppermost mantle beneath the Southwest Longmenshan fault zone. This seismic profile extends from the west Sichuan Plain, through the Longmenshan Fault zone, and into the west Sichuan Plateau. We observed clear Pg, refraction Phase from the upper crust, Pi1/Pi2/Pi3, reflection/refraction Phase from intra-crust, PmP, reflection from the Moho boundary, and the Pn phase, refraction Phase from uppermost mantle. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. The model shows the crustal thickness of the region is very variable. The Moho topography varies more than 10km in the southwest

  4. Crustal structure and seismotectonics of central Sicily (southern Italy): new constraints from instrumental seismicity

    Science.gov (United States)

    Sgroi, Tiziana; de Nardis, Rita; Lavecchia, Giusy

    2012-06-01

    In this paper, we propose a new model of the crustal structure and seismotectonics for central Sicily (southern Italy) through the analysis of the depth distribution and kinematics of the instrumental seismicity, occurring during the period from 1983 to 2010, and its comparison with individual geological structures that may be active in the area. The analysed data set consists of 392 earthquakes with local magnitudes ranging from 1.0 to 4.7. We defined a new, detailed 1-D velocity model to relocate the earthquakes that occurred in central Sicily, and we calculated a Moho depth of 37 km and a mean VP/VS ratio of 1.73. The relocated seismic events are clustered mainly in the area north of Caltanissetta (e.g. Mainland Sicily) and in the northeastern sector (Madonie Mountains) of the study area; only minor and greatly dispersed seismicity is located in the western sector, near Belice, and along the southern coast, between Gela and Sciacca. The relocated hypocentral distribution depicts a bimodal pattern: 50 per cent of the events occur within the upper crust at depths less than ˜16 km, 40 per cent of the events occur within the middle and depth crust, at depths between 16 and 32 km, and the remaining 10 per cent occur at subcrustal depths. The energy release pattern shows a similar depth distribution. On the basis of the kinematic analysis of 38 newly computed focal plane solutions, two major geographically distinct seismotectonic domains are distinguished: the Madonie Mountain domain, with prevalent extensional and extensional-oblique kinematics associated with upper crust Late Pliocene-Quaternary faulting, and the Mainland Sicily domain, with prevalent compressional and compressional-oblique kinematics associated with thrust faulting, at mid to deep crust depth, along the north-dipping Sicilian Basal Thrust (SBT). The stress inversion of the Mainland Sicily focal solutions integrated with neighbouring mechanisms available in the literature highlights a regional

  5. Crustal structure of the Gujarat region, India: New constraints from the analysis of teleseismic receiver functions

    Science.gov (United States)

    Chopra, Sumer; Chang, Tao-Ming; Saikia, Sowrav; Yadav, R. B. S.; Choudhury, Pallabee; Roy, Ketan Singha

    2014-12-01

    In this study, receiver function analysis is carried out at 32 broadband stations spread all over the Gujarat region, located in the western part of India to image the sedimentary structure and investigate the crustal composition for the entire region. The powerful Genetic Algorithm technique is applied to the receiver functions to derive S-velocity structure beneath each site. A detail image in terms of basement depths and Moho thickness for the entire Gujarat region is obtained for the first time. Gujarat comprises of three distinct regions: Kachchh, Saurashtra and Mainland. In Kachchh region, depth of the basement varies from around 1.5 km in the eastern part to 6 km in the western part and around 2-3 km in the northern part to 4-5 km in the southern part. In the Saurashtra region, there is not much variation in the depth of the basement and is between 3 km and 4 km. In Gujarat mainland part, the basement depth is 5-8 km in the Cambay basin and western edge of Narmada basin. In other parts of the mainland, it is 3-4 km. The depth of Moho beneath each site is obtained using stacking algorithm approach. The Moho is at shallower depth (26-30 km) in the western part of Kachchh region. In the eastern part and epicentral zone of the 2001 Bhuj earthquake, large variation in the Moho depths is noticed (36-46 km). In the Saurashtra region, the crust is more thick in the northern part. It varies from 36-38 km in the southern part to 42-44 km in the northern part. In the mainland region, the crust is more thick (40-44 km) in the northern and southern part and is shallow in Cambay and Narmada basins (32-36 km). The large variations of Poisson's ratio across Gujarat region may be interpreted as heterogeneity in crustal composition. High values of σ (∼0.30) at many sites in Kachchh and few sites in Saurashtra and Mainland regions may be related to the existence of high-velocity lower crust with a mafic/ultramafic composition and, locally, to the presence of partial melt

  6. Crustal Structure Beneath the Tibetan Plateau Using Receiver Functions and Surface Wave Dispersion Observations

    Science.gov (United States)

    Diehl, T.; Ammon, C. J.; Mejia, J.

    2002-12-01

    Despite substantial effort, some uncertainty in the bulk crustal geology beneath the Tibetan Plateau remains. Recent experiments have provided a wealth of seismic data for investigating structures within the Tibetan lithosphere. We investigate the subsurface Tibetan geology using receiver functions from the 1991-1992 Passive Source and the 1997-1999 INDEPTH III experiments. We have completed joint inversions of surface-wave dispersion and select receiver functions for the older data and plan to explore and invert receiver functions from select stations from the INDEPTH III experiment. The combination of receiver functions with surface-wave dispersion does much to improve P- and S-velocity structure resolution, but modeling is most appropriate for relatively simple structures. We begin our analyses with the depth-velocity stacking estimation of Zhu and Kanamori [2000] where we attempt to extract thickness, P-velocity, and Vp/Vs ratios compatible with the move-out of the Ps conversion and multiples from velocity contrasts within the lithosphere. Again, the main limitation of the technique is the assumption of a simple structure to insure consistency with a set of straightforward travel-time equations used to compute arrival-time move-out (as a function of incident-wave ray parameter). Poisson's ratio values from the 1991-1992 deployment were difficult to extract because of complex structure. The station with simplest response, WNDO, suggests a ratio of 0.28 beneath the north-central Plateau, which is slightly above average for continental crust. These results are lower than some earlier values which suggested that the lower crust beneath central and northern Tibet may contain substantial partial melt. The joint inversion of the simplest available receiver functions, and global long-period and local short-period surface-wave dispersion observations suggests that the crustal thickness for the northern Plateau ranges from 60-70 km (stations ERDO, BUDO, TUNL). Thickness

  7. Barents Sea Crustal and Upper Mantle Structure from Deep Seismic and Potential Field Data

    Science.gov (United States)

    Aarseth, I.; Mjelde, R.; Breivik, A. J.; Minakov, A.; Huismans, R. S.; Faleide, J. I.

    2016-12-01

    The Barents Sea basement comprises at least two different domains; the Caledonian in the west and the Timanian in the east. Contrasting interpretations have been published recently, as the transition between these two domains is not well constrained. Interpretations of new high-quality magnetic data covering most of the SW Barents Sea challenged previous studies of the Late Paleozoic basin configurations in the western and central Barents Sea. Two major directions of Caledonian structures have been proposed by different authors: N-S and SW-NE. Two regional ocean bottom seismic (OBS) profiles, crossing these two major directions, were acquired in 2014.The primary goal in this project is to locate the main Caledonian suture in the western Barents Sea, as well as the possible Barentsia-Baltica suture postulated further eastwards. High velocity anomalies associated with Caledonian eclogites are particularly interesting as they may be related to Caledonian suture zones. The collapse of the Caledonian mountain range predominantly along these suture zones is expected to be closely linked to the deposition of Devonian erosional products, and subsequent rifting is likely to be influenced by inheritance of Caledonian trends. P-wave travel-time modelling is done by use of a combined ray-tracing and inversion scheme, and gravity modelling has been used to support the seismic model. The results indicate high P-wave velocities (mostly over 4 km/s) close to the seafloor as well as high velocity (around 6 km/s) zones at shallow depths which are interpreted as volcanic sills. The crustal transect reveals areas of complex geology and velocity inversions. Strong reflections from within the crystalline crust indicate a heterogeneous basement terrain. Gravity modelling agrees with this, as several blocks with variable densities had to be introduced in order to reproduce the observed gravity anomalies. Refractions from the top of the crystalline basement together with reflections from

  8. Deep crustal structure of the UAE-Oman mountain belt from seismic and gravity data

    Science.gov (United States)

    Pilia, S.; Tanveer, M.; Ali, M.; Watts, A. B.; Searle, M. P.; Keats, B. S.

    2016-12-01

    The UAE-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cenozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s, underlain by a thin layer of slower material (about 4.5 km/s). Furthermore, the velocity model reveals a Moho depth that rises from ca 30 km in the west to ca 20 km in the east. A poststack depth-migrated profile (about 50 km long) coincident with the offshore part of the refraction

  9. THE RELATIONSHIP BETWEEN THE SEPTEMBER 2017 MARS GLOBAL AURORA EVENT AND CRUSTAL MAGNETIC FIELDS

    Science.gov (United States)

    Nasr, Camella-Rosa; Schneider, Nick; Connour, Kyle; Jain, Sonal; Deighan, Justin; Jakosky, Bruce; MAVEN/IUVS Team

    2018-01-01

    In September 2017, the Imaging UltraViolet Spectrograph (IUVS) on the MAVEN spacecraft observed global aurora on Mars caused by a surprisingly strong solar energetic particle event. Widespread “diffuse aurora” have previously been detected on Mars through more limited observations (Schneider et al., Science 350, (2015); DOI: 10.1126/science.aad0313), but recent observations established complete coverage of the observable portion of Mars’ nightside. The aurora was global due to Mars’s lack of a global magnetic field, which allowed energetic electrons from the Sun to directly precipitate into the atmosphere. On September 11th, IUVS detected aurora more than 25 times brighter than any prior IUVS observation, with high SNR detections of aurora at the limb and against the disk of the planet. Fainter auroral emission was seen around the nightside limb over 13 orbits spanning nearly 3 days.On September 14th, during the declining phase of the event, faint linear features and patches were detected by the spacecraft, which were higher than the noise floor, with a similar spatial distribution to “discrete aurora” patches observed on Mars by the SPICAM instrument on the Mars Express spacecraft (Bertaux et al., Nature 435, doi :10.1038/nature03603). Discrete aurora occur near areas of the crust affected by the magnetism left over from Mars’ once-strong dipole field. Emission is limited to regions of the crustal magnetic field where the field lines are likely to be open to solar wind interactions. Those regions are concentrated in Mars’ southern hemisphere centered on 180 degrees east longitude.We studied the localized emissions on 14 September to determine whether there might be a connection between the observed diffuse aurora event and discrete auroral processes. First, we investigated the localized emissions to confirm that the observed signal was consistent with expected auroral spectra. Second, their locations were projected on a map of the crustal magnetic

  10. Integration of GPS and InSAR Data for Optimal 3-Dimensional Crustal Deformation Map

    Science.gov (United States)

    Shen, Z.; Liu, Z.

    2016-12-01

    GPS and InSAR are complementary to each other for crustal deformation monitoring, We develop an algorithm to integrate the two data sets for the production of 3-dimensional crustal motion map. In the algorithm point-based discrete GPS measurements are first interpolated to produce continuous 3-D vector map at chosen grids covered by the InSAR data. The interpolation is based on an algorithm of Shen et al. [2015], which takes into account of GPS station distance, network density and configuration for data weighting. A Gaussian distance weighting function and a Voronoi cell spatial weighting function are used in the interpolation. The amount of weighting and degree of smoothing can be spatially variable and optimally determined based on in situ data strength. This approach can effectively smooth out the incoherencies in discretized GPS velocity data. At the locations where both InSAR and interpolated GPS data are available, optimal 3-D components are solved for using a weighted least square method. The InSAR data are weighted by their LOS uncertainties. The GPS interpolated data are weighted by their re-estimated uncertainties assuming a uniform smoothing instead of variable smoothing used for data interpolation as mentioned above, to ensure that the uncertainty estimates reflect the in situ data strength consistently and not biased by uneven degree of smoothing. Including InSAR data from both ascending and descending viewing geometry, if available, provides improved constraint on the 3-D deformation when integrating with GPS data. We apply this algorithm to a test region in southern California covering most of the active faults in the region such as the San Andreas, San Jacinto, and Garlock. We use LOS rate data derived from 18 years of ERS-Envisat InSAR data, and a combination of continuous and campaign GPS data of more than two decades of time span. Our preliminary result shows that the GPS and InSAR data are generally consistent for the horizontal velocities at

  11. Seismogenesis of the lower crustal intraplate earthquakes occurring in Kachchh, Gujarat, India

    Science.gov (United States)

    Mandal, Prantik; Pandey, O. P.

    2011-08-01

    Large intraplate continental earthquakes like the 1811-12 New Madrid (M w ⩾ 8.0) and the 2001 Bhuj (Mw7.7) were highly destructive because they occurred in strong crust, but the mechanisms underlying their seismogenesis are not understood. Here we show, using local earthquake velocity tomography, and joint inversion of receiver functions and surface wave group velocity dispersion that the crust and uppermost mantle beneath the 2001 Bhuj earthquake region of western India is far more complex than hitherto known through previous studies. A new image of the crust and underlying mantle lithosphere indicates the presence of a 18-km thick high velocity (Vp: 7.15-8.11 km/s) differentiated crustal and mantle magmatic layer above a hot and thin lithosphere (only 70 km) in the epicentral region of 2001 Bhuj earthquake. This magmatic layer begins at the depth of 24 km and continues down to 42 km depth. Below this region, brittle-ductile transition reaches as deep as the Moho (˜34 km) due to the possible presence of olivine rich mafic magma. Our 1-D velocity structure envisages an initial phase of plume activity (Deccan plume at 65 m.y. ago) resulting in basaltic magma in the eclogitic layers at sub-lithospheric levels, wherein they were subjected to crystallization under ultra-high pressure conditions. Our study also delineates an updoming of Moho (˜4-7 km) as well as asthenosphere (˜6-10 km) below the Kachchh rift zone relative to surrounding areas, suggesting the presence of a confined body of partial melts below the lithosphere-asthenosphere boundary. Restructuring of this warm and thin lithosphere may have been caused due to rifting (at 184 and 88 m.y. ago) and tholeiitic and alkalic volcanism related to the Deccan Traps K/T boundary event (at 65 m.y. ago). Recent study of isotopic ratios proposed that the alkalic basalts found in Kachchh are generated from a CO 2 rich lherzolite partial melts in the asthenosphere that ascended along deep lithospheric rift faults

  12. The InSAR Italy portal for open access to crustal deformation data

    Science.gov (United States)

    Salvi, Stefano; Tolomei, Cristiano; Pezzo, Giuseppe; Lanari, Riccardo; Pepe, Antonio; Marchetti, Pier Giorgio; Della Vecchia, Andrea; Mantovani, Simone

    2014-05-01

    InSAR Italy is a web portal devised to provide open access services to crustal deformation data measured using multitemporal SAR Interferometry techniques over the Italian territory. It is an evolution of the VELISAR initiative, promoted in 2006 by the Istituto Nazionale di Geofisica e Vulcanologia, and originally participated by IREA-CNR and TRE srl. InSAR Italy was developed tailoring the Multi-sensor Evolution Analysis (MEA) environment, an Earth Observation and geospatial data analysis tool empowered with OGC standard interfaces. The web interface allows an easy browsing of the ground deformation maps obtained for each satellite image dataset, leading to a clear picture and improved analysis of the displacement time series over single pixels or large areas. Web Coverage Service (WCS) and Web Coverage Processing Service (WCPS) are used to access and process the maps, respectively. The crustal deformation data are provided by INGV and IREA-CNR as products of publicly-funded research projects, and are disseminated in compliance with the national legislation on the Open Data Access; metadata associated to the products are published according to the INSPIRE specifications. The information provided through InSAR Italy is mainly based on InSAR data maintained in the ESA archives, in particular from the ERS satellites for the 1992-2000 period, and ENVISAT for the period 2003-2010, however, ground velocity maps obtained from COSMO-SkyMed data will also be released in the near future. The InSAR Italy deformation maps consist of time series of ground displacement at resolution varying between 5 and 80 m, and the relative mean velocity values. The data sets can be queried and mean velocities can be recalculated over user-defined time periods, to account for possible non-linear displacement trends. The MEA spatiotemporal data analysis capability allows to investigate deformation phenomena occurring at very different spatial scales, from single buildings to entire regions

  13. some morphological effects related to a non-uniform uplifting of crustal blocks in Northern Sicily (Central Mediterranean)

    Science.gov (United States)

    Nigro, Fabrizio; Renda, Pietro; Favara, Rocco

    2010-05-01

    We can distinguish two morphological evolutions of the drainage basins which develop in the earth's sectors subjected to uplift and tilting, in relationship to their antecedence or subsequence in comparison to the tectonic process. If this process begins in concomitance with a geomorphic cycle the main valleys of the drainage basins will longitudinally be developed according to the tilting direction which the crustal block is subjected. But if the non-uniform vertical movement develops in a sector already characterized by the presence of a idrographic network, this can be influenced in its pattern in various ways. A crustal block contemporarily subject to uplift and tilting will be characterized to its inside, at the end of this process, by more elevated and less elevated sectors. The erosive ground processes suffer this non-uniform vertical movement and since it gradually develops in time, landforms, as valleys of drainage basins, will suffer analogous variations. If pre-existing, the slopes of the valleys will be subjected to tilting also and one of the characteristics in the evolution of the reliefs connected with the uplift and the tilting of crustal blocks are represented by the progressive asymmetry of the slopes of a valley. The uplift and the tilting of the block progressively determines a difference of inclination of the slopes of the incising valley. This effect is given by the progressive incision and migration of the axis of the valley that it determines slopes with crests to different middle elevation between the right side and that left. The erosional process that determines him with the uplift and the tilting of the crustal blocks are characterized by a greater erosion rate in the sectors of head of the slope that is mostly raised. Likewise, the migration of the river consistent with the tilting direction determines a greater rate of erosion along one of the banks. The general morphometric result can be that of the individualization of slopes that

  14. Evaluating the relative roles of crustal growth and recycling through continental arc magmatism in the Ross orogen, Antarctica

    Science.gov (United States)

    Hagen-Peter, Graham; Cottle, John

    2017-04-01

    There remains much debate about the mechanisms of the growth and differentiation of continental crust over geologic time, although the geochemical resemblance between continental crust and arc magmatism around the world make subduction-related magmatism a conspicuous candidate. It's clear that both juvenile magmatism and crustal recycling occur at convergent margins, but is it difficult to quantify the roles of these two end-member processes. This is particularly challenging in continental arc settings, where magmas ascend through and interact with thick continental lithosphere of variable—and usually unknown—age and composition. We assess the relative magnitudes of crustal growth and recycling in a 500-km-long segment of the Ross orogen of Antarctica—an archetypal example of a long-lived "Cordilleran-style" continental arc—utilizing an extensive set of zircon Hf (˜70 samples) and whole rock Nd and Sr (15 samples) isotopic data for igneous rocks ranging from gabbro to granite. Initial ɛNd and 87Sr/86Sr values range from +0.1 to -10.3 and ˜0.7044 to 0.7137, respectively. Initial ɛHf values (weighted means of individual analyses from each sample) are predominately negative—ranging from +3.5 to -12.3—potentially interpreted as reflecting a dominant crustal component in the source of the granitoids. However, inherited zircon domains provide evidence for significantly less radiogenic ancient crust in the unexposed basement of the orogen. Additionally, primitive samples (SiO2 69) range in initial ɛHf from approximately +0.8 to -4.0, representing juvenile magmatism with enriched isotopic compositions. While a broader range and lower ɛHf values (+3.5 to -12.3) in more evolved samples from large granitic plutons likely reflect variable degrees of crustal assimilation during differentiation, overlap with the isotopic compositions of primitive samples permits differentiation with relatively minor degrees of crustal assimilation. This qualitative

  15. Sr, Nd, and Pb isotopes in Proterozoic intrusives astride the Grenville Front in Labrador - Implications for crustal contamination and basement mapping

    Science.gov (United States)

    Ashwal, L. D.; Wooden, J. L.; Emslie, R. F.

    1986-01-01

    Trace element and Pb, Sr, and Nd isotopic compositions of anorthosites and related rocks, and of younger mafic dikes from Harp Lake and Mealy Mountains in Labrador, Canada are estimated and compared. The effects of crustal component contaminants on the isotopic compositions of the dikes are investigated. The correlation between the isotopic data and the crustal contamination model is studied. It is observed that for Harp Lake the initial Sr ratios are higher and the Nd values are lower than Mealy samples, and the data do not correspond to the crustal contamination model; however, the Pb isotope data favor a crustal contamination model. It is noted that the Labrador segment of the Grenville Front appears to coincide with the southern margin of the Archean North Atlantic craton, and may represent a pre mid-Proterozoic suture.

  16. Neoarchean (2.5–2.8 Ga crustal growth of the North China Craton revealed by zircon Hf isotope: A synthesis

    Directory of Open Access Journals (Sweden)

    Andong Wang

    2012-03-01

    Full Text Available The crustal growth of the North China Craton (NCC during the Neoarchean time (2.5–2.8 Ga is a hotly controversial topic, with some proposing that the main crustal growth occurred in the late Neoarchean (2.5–2.6 Ga, in agreement with the time of the magmatism, whereas others suggest that the main crustal accretion took place during early Neoarchean time (2.7–2.8 Ga, consistent with the time of crustal-formation of other cratons in the world. Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC. In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC. The results suggest that both 2.7–2.8 Ga and 2.5–2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested. The Eastern block is characterized by the main 2.7–2.8 Ga crustal growth with local new crustal-formation at 2.5–2.6 Ga, and the Yinshan block is characterized by ∼2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group. Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some ∼2.6 Ga and minor Early- to Middle-Archean crustal components, and the crustal accretion in the Trans-North China Orogen (TNCO has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy. Zircon Hf isotope compositions, coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO, and the evolution and tectonic division of the NCC is more complex than previously proposed, probably involving multi-stage crustal growth and subduction processes

  17. Using a Genetic Algorithm to Model Broadband Regional Waveforms for Crustal Structure in the Western United States

    Science.gov (United States)

    Bhattacharyya, Joydeep; Sheehan, Anne F.; Tiampo, Kristy; Rundle, John

    1999-01-01

    In this study, we analyze regional seismograms to obtain the crustal structure in the eastern Great Basin and western Colorado plateau. Adopting a for- ward-modeling approach, we develop a genetic algorithm (GA) based parameter search technique to constrain the one-dimensional crustal structure in these regions. The data are broadband three-component seismograms recorded at the 1994-95 IRIS PASSCAL Colorado Plateau to Great Basin experiment (CPGB) stations and supplemented by data from U.S. National Seismic Network (USNSN) stations in Utah and Nevada. We use the southwestern Wyoming mine collapse event (M(sub b) = 5.2) that occurred on 3 February 1995 as the seismic source. We model the regional seismograms using a four-layer crustal model with constant layer parameters. Timing of teleseismic receiver functions at CPGB stations are added as an additional constraint in the modeling. GA allows us to efficiently search the model space. A carefully chosen fitness function and a windowing scheme are added to the algorithm to prevent search stagnation. The technique is tested with synthetic data, both with and without random Gaussian noise added to it. Several separate model searches are carried out to estimate the variability of the model parameters. The average Colorado plateau crustal structure is characterized by a 40-km-thick crust with velocity increases at depths of about 10 and 25 km and a fast lower crust while the Great Basin has approximately 35- km-thick crust and a 2.9-km-thick sedimentary layer.

  18. Along-Axis Structure and Crustal Construction Processes of Spreading Segments in Iceland: Implications for Magmatic Rifts

    Science.gov (United States)

    Siler, D. L.; Karson, J. A.

    2017-10-01

    Magmatic rift systems are composed of discrete spreading segments defined by morphologic, structural, and volcanic features that vary systematically along strike. In Iceland, structural features mapped in the glaciated and exhumed Miocene age upper crust correlate with analogous features in the seismically and volcanically active neovolcanic zone. Integrating information from both the active rift zones and ancient crust provides a three-dimensional perspective of crustal structure and the volcanic and tectonic processes that construct crust along spreading segments. Crustal exposures in the Skagi region of northern Iceland reveal significant along-strike variations in geologic structure. The upper crust at exhumed magmatic centers (segment centers) is characterized by a variety of intrusive rocks, high-temperature hydrothermal alteration, and geologic evidence for kilometer-scale subsidence. In contrast, the upper crust along segment limbs, which extend along strike from magmatic centers, is characterized by thick sections of gently dipping lava flows, cut by varying proportions of subvertical dikes. This structure implies relatively minor upper crustal subsidence and lateral dike intrusion. The differing modes of subsidence beneath segment centers and segment limbs require along-axis mass redistribution in the underlying upper, middle, and lower crust during crustal construction. This along-axis material transport is accomplished through lateral dike intrusion in the upper crust and by along-axis flow of magmatic to high-temperature solid-state gabbroic material in the middle and lower crust. These processes, inferred from outcrop evidence in Skagi, are consistent with processes inferred to be important during active rifting in Iceland and at analogous magmatic oceanic and continental rifts.

  19. Correlations of Strong Martian Crustal Magnetic Fields With Valley Networks and Phyllosilicate Exposures: Implications for Magnetic Sources

    Science.gov (United States)

    Hood, L. L.; Harrison, K. P.; Langlais, B.; Lillis, R. J.; Poulet, F.

    2009-05-01

    A broad spatial correlation between strong martian crustal magnetic fields and the valley networks, which are indicative of surface water erosion, has previously been reported. In this paper, we report initial evidence for a correlation of phyllosilicate exposures identified to date using Mars Express OMEGA data with strong crustal fields and valley networks in the Noachian southern highlands. Two separate statistical methods confirm the significance of the phyllosilicate exposure correlation. Like the valley networks and crustal fields, the phyllosilicate exposures are distributed north and east of Hellas in the southern highlands but are nearly absent within, south, and west of this basin. Similarly, they are present north and west of Argyre but are sparse within, south, and east of this basin. All three tend to occur mainly at low paleolatitudes as inferred from magnetic anomaly modeling by several groups. We interpret the correlation to imply that the strongest crustal magnetization formed primarily while liquid water was present in the martian upper crust. The source of the water could have been from above (precipitation) or from below (mantle outgassing). A likely explanation is that the production in magnetic source regions of efficient remanence carriers was enhanced in the presence of magmatic heat through hydrothermal chemical processes. For example, magnetite production could have been enhanced through serpentinization. Geologic evidence suggests that magmatic intrusions occurred commonly in the upper highland crust during the Noachian. If these intrusions occurred in the form of dikes and/or dendritic conduits over regions as large as 200 - 600 km during time periods less than the dynamo reversal time scale, then magnetic source regions with dimensions comparable to those inferred from orbital data could be accounted for.

  20. Far-field crustal movements before and after the 2011 Ms9. 0 Japan earthquake from GPS observations

    Directory of Open Access Journals (Sweden)

    Gu Guohua

    2011-08-01

    Full Text Available The paper gives an analysis of the displacement time series before and after the March 11, 2011 Ms9. 0 east Japan earthquake and co-seismic displacements observed at continuous GPS stations in and around China. The results showed a broad-scaled related elastic-rebound process and some premonitory horizontal crustal movements to this earthquake over this vast area.

  1. Regional variations of crustal thickness along the eastern edge of the Tibetan plateau and their tectonic implications

    Science.gov (United States)

    Kang, D.; YU, C.; TAO, K.; Chen, W.; Liu, Q.; Chen, J.; Zheng, X.; Ning, J.

    2011-12-01

    Using data from a massive array of xyz broadband seismographs deployed in the Sichuan-Yunnan Region, southwestern China, we applied the method of Virtual Deep Seismic Sounding (VDSS; Tseng et al., 2009) to investigate regional variations in crustal thickness near the eastern edge of Tibet. VDSS takes advantage of the deep-penetrating power of teleseismic waves and is very robust in determining the overall thickness of crust. It uses SV-to-P conversion off the free surface as a virtual source near each receiver to generate strong, post-critical reflections such as the SsPmp phase off the Moho. Preliminary results indicate that there are no abrupt changes in crustal thickness beneath major fault zones such as Longmen Shan fold-and-thrust belt (where the devastating Wenchuan earthquake sequence occurred in 2008), the largely strike-slip Xianshuihe fault system, and the largely strike-slip Anninghe fault zone. When compared with predictions from Airy isostasy, crustal thicknesses of the stable Sichuan basin (35 km to 44 km) and of the southern Chuan-Dian block (about 50 km to 60 km), fall within expected ranges. However, crustal thicknesses beneath the marginal area of northern Chuan-Dian (40 km to 47 km) block and the marginal area of Songpan-Ganze terrane (about 30 km) are much thinner than expected (by 15 km to 30 km), calling for active tectonic support from the mantle lithosphere. Tseng, T.-L., W.-P. Chen, et al. Northward thinning of Tibetan crust revealed by virtual seismic profiles. Geophysical Research Letters, 2009, 36(24): L24304.

  2. Meshfree Finite Element Technique for Geoscience Research: A New Tool for Modeling Earthquake-induced Crustal Deformation

    Science.gov (United States)

    Tsukanov, I.; Wdowinski, S.

    2008-12-01

    Meshfree (or meshless) Finite Element (FE) may sound as an oxymoron, but it is an emerging modeling technique with many advantages. The method still uses elements, just as the standard (meshed) techniques. However, the elements are set by a grid that does not necessarily conform to the geometry of the modeled object. In the contrast to standard FEMs, in our meshfree method the object's geometry is represented by the distances to the boundaries. Distance to the boundary is an intrinsic property of any geometric object, and it provides a natural way to represent the geometric information and satisfy boundary conditions exactly. Because meshfree methods do not require spatial meshing that conforms to the geometric model, they provide the needed geometrical flexibility lacking in standard FE methods. However, the treatment of boundary conditions becomes more challenging. The meshfree FE technique is used in variety of engineering applications, such as heat transfer, structural analysis, shape-material optimization and stress analysis of acquired models. So far, this very promising technique had a very minor impact in geoscience research. Only three geoscience papers used the meshfree technique in their research. We have started utilizing this flexible numerical modeling tool to study earthquake-induced crustal deformation. So far, we used 3-D elastic models to simulate interseismic deformation due to a buried dislocation. Our preliminary results show an excellent fit with analytical dislocation models. We plan to continue developing the application of the meshfree technique to crustal deformation studies, in order to generate a modeling tool that can easily incorporate complicated geometries (faults, topography, and crustal units), geometrical changes over time, complicated rheologies, and heterogeneous crustal properties.

  3. The effect of large reservoirs impoundment to the spatial and temporal variations of regional crustal deformation in Hubei Province, China

    Directory of Open Access Journals (Sweden)

    Wenbin Shen

    2016-09-01

    Full Text Available The total capacity of Three Gorges Reservoir (TGR and Danjiangkou Reservoir (DJR is large and has significant seasonal fluctuations, which give rise to crustal instability. In this research, we focus on studying the temporal and spatial variation of crustal deformation in Hubei Province caused by reservoir impoundment of TGR and DJR. The Digital Elevation Model, historical hydrological information, GPS monitoring data and load-induced deformation model are combined to monitor the crustal deformation. The modeled results indicate that in the trapezoidal area between the TGR and DJR, the average vertical deformations at different latitudes have different variation tendencies. The vertical deformation modulus and fluctuation amplitude are larger at the latitude of 33°N/32.5°N from 2003 to 2006 and at the latitude of 31°N/32.5°N from 2008 to 2014, while the latter are much larger than the former. Moreover, from 2008 to 2014, the frequency and the intensity of seismic activities are all enhanced significantly in this region. The modeled results at the GPS sites are consistent with the vertical displacement of GPS monitoring results in trends and the waveform. It can be inferred that the seasonal deformation is elastic. The horizontal deformation components have the same variation trends with that at each GPS monitoring station, which demonstrates that the whole region is moving toward the southeast. The spatial variation of crustal deformation demonstrates that the impoundment of TGR in 2003 causes significant vertical displacements, with the maximum modulus of 32 mm downward located in Xiangjiang River's estuary. When the water storage increases, the maximum value will become larger, and the location will move toward the upstream. Besides, the earthquakes occurred more frequently in the region with maximum deformation modulus.

  4. Crustal structure beneath the High Lava Plains of eastern Oregon and surrounding regions from receiver function analysis

    Science.gov (United States)

    Eagar, Kevin C.; Fouch, Matthew J.; James, David E.; Carlson, Richard W.

    2011-02-01

    We analyze teleseismic P-to-S receiver functions to image crustal structure beneath the High Lava Plains (HLP) of eastern Oregon and surrounding regions. Coverage from 206 broadband seismic stations provides the first opportunity to resolve variations in crustal composition, thickness, and heterogeneity on scales of a few km in depth and tens of km laterally across the HLP region. We utilize both H - κ stacking and a new Gaussian-weighted common conversion point stacking technique. We find crust that is ≥40 km thick beneath the Cascades, Idaho Batholith, and Owyhee Plateau and thinner (˜31 km) crust beneath the HLP and northern Great Basin. Low Poisson's ratios of ˜0.240 characterize the granitic crust beneath the Idaho Batholith, while the Owyhee Plateau exhibits values of ˜0.270, typical of average continental crust. The Owyhee Plateau is a thick simple crustal block with distinct edges at depth. The western HLP exhibits high average values of 0.304, typical for regions of widespread basaltic volcanism. Combined with other geological and geophysical observations, the areas of abnormally high Poisson's ratios (˜0.320) and low-velocity zones in the crust beneath north-central and southern Oregon are consistent with the presence of partial melt on either side of the HLP trend, suggesting a central zone where crustal melts have drained to the surface, perhaps enabled by the Brothers Fault Zone. Thicker crust and an anomalous N-S band of low Poisson's ratios (˜0.252) skirting the Steens Mountain escarpment is consistent with residuum from a midcrustal magma source of the massive flood basalts, supporting the view of extensive mafic underplating and intraplating of the crust from Cenozoic volcanism.

  5. Seismic and gravity modelling of crustal structure in the Central Graben, North Sea. Observations along MONA LISA profile 3

    Science.gov (United States)

    Nielsen, L.; Balling, N.; Jacobsen, B. H.; MONA LISA Working Group

    2000-12-01

    High quality wide-angle and deep normal-incidence seismic data sets recorded during the MONA LISA (Marine and Onshore North Sea Acquisition for Lithospheric Seismic Analysis) experiment have allowed detailed crustal investigations in the area of the Central Graben and south-eastern North Sea to be conducted. An integrated velocity-density model based on a joint inversion of traveltimes and gravity data is presented for the crust and uppermost mantle along MONA LISA line 3, which crosses the Central Graben approximately perpendicular to its strike direction. This model shows pronounced crustal thinning and associated Moho uplift beneath the deepest part of the Central Graben. In the graben area, Moho is interpreted to be situated at 25 km depth and the crystalline crust is about a factor of 2 thinner than in the surrounding crustal provinces, where Moho is interpreted to reach depths between 32 and 36 km. Maximum thickness of the sedimentary column in the Central Graben is 10-11 km. The mass deficit of the thick sediments is compensated by the Moho uplift. The modelled Moho coincides with the base of lower crustal reflectivity observed in the coincident normal-incidence seismic section. Good overall agreement between the integrated velocity-density model and the normal-incidence data is observed. The migrated deep seismic reflection section recorded to 26 s traveltime contains deep west-ward and east-ward dipping events symmetric about the deepest part of the Central Graben. These dipping upper mantle reflections may be linked to extensional processes that formed the Central Graben. At least one of the upper mantle dipping reflectors may be a reactivated structure formed originally during Caledonian collision.

  6. Crustally derived granites in Dali, SW China: new constraints on silicic magmatism of the Central Emeishan Large Igneous Province

    Science.gov (United States)

    Zhu, Bei; Peate, David W.; Guo, Zhaojie; Liu, Runchao; Du, Wei

    2017-10-01

    We have identified a new crustally derived granite pluton that is related to the Emeishan Large Igneous Province (ELIP). This pluton (the Wase pluton, near Dali) shows two distinct SHRIMP zircon U-Pb age groups ( 768 and 253 Ma). As it has an intrusive relationship with Devonian limestone, the younger age is interpreted as its formation, which is related to the ELIP event, whereas the 768 Ma Neoproterozoic-aged zircons were inherited from Precambrian crustal component of the Yangtze Block, implying the pluton has a crustally derived origin. This is consistent with its peraluminous nature, negative Nb-Ta anomaly, enrichment in light rare earth elements, high 87Sr/86Sr(i) ratio (0.7159-0.7183) and extremely negative ɛ(Nd)(i) values (-12.15 to -13.70), indicative of melts derived from upper crust materials. The Wase pluton-intruded Devonian strata lie stratigraphically below the Shangcang ELIP sequence, which is the thickest volcanic sequence ( 5400 m) in the whole ELIP. The uppermost level of the Shangcang sequence contains laterally restricted rhyolite. Although the rhyolite has the same age as the Wase pluton, its geochemical features demonstrate a different magma origin. The rhyolite displays moderate 87Sr/86Sr(i) (0.7053), slightly negative ɛ(Nd)(i) (-0.18) and depletions in Ba, Cs, Eu and Sr, implying derivation from differentiation of a mantle-derived mafic magma source. The coexistence of crustally and mantle-derived felsic systems, along with the robust development of dike swarms, vent proximal volcanics and thickest flood basalts piles in Dali, shows that the Dali area was probably where the most active Emeishan magmatism had once existed.

  7. Seismic evidence of crustal heterogeneity beneath the northwestern Deccan volcanic province of India from joint inversion of Rayleigh wave dispersion measurements and P receiver functions

    Science.gov (United States)

    Deshpande, Akshaya; Mohan, Gollapally

    2017-04-01

    The northwestern Deccan volcanic province (NWDVP) of India, encompassing the Saurashtra peninsula and the adjoining Gulf of Cambay, is investigated through joint inversion of surface wave dispersion measurements and teleseis- mic P receiver functions, to estimate the crustal and shallow upper mantle shear wave velocity (Vs) structure. The Mw ˜ 7.7 Bhuj earthquake and the post Bhuj regional events, recorded during the period 2001-2010 at 7 stations along 37 source-receiver paths were used along with 35 teleseismic events. A joint curve fitting inversion technique is applied to obtain a best fit for the fundamental mode Rayleigh wave group velocity dispersion curves for time periods 5-50 s and high quality crustal P wave receiver functions obtained at each station. Significant crustal heterogeneity is observed within the study region with the average crustal Vs ranging from 3.5 km/s to 3.8 km/s with the paths cutting across the Gulf of Cambay exhibiting large reduction in shear wave velocities. Utilizing the average crustal Vs ≈ 3.66 km/s estimated for Saurashtra, together with the average crustal P wave velocity (Vp) ≈ 6.54 km/s derived independently through deep seismic sounding studies, yields a bulk Vp/Vs ratio of 1.786 or an equivalent crustal Poisson's ratio of 0.271. A major contribution to the high Poisson's ratio comes from the 12 to 16 km thick lower crustal layers with shear velocities ranging from 3.8 km/s to 4.19 km/s suggesting widespread magmatic underplating due to emplacement of mafic cumulates in the lower crust. The shallow uppermost mantle shear velocities are in the range 4.2-4.5 km/s averaging 4.36 km/ s, which is less than that observed for the Indian shield, indicating the effects of residual thermal anomaly. The variation in the crustal Vs, high Poisson's ratios and low upper mantle shear velocities reflect the thermal and compositional effects of the Deccan volcanism which are manifested in terms of pervasive presence of mafic dykes

  8. Crustal growth and episodic reworking over one billion years in the Capricorn Orogen, Western Australia: evidence from Lu-Hf and O isotope data

    Science.gov (United States)

    Jahn, Inalee; Clark, Chris; Reddy, Steve; Taylor, Rich

    2017-04-01

    Fundamental to understanding the generation and evolution of a crustal block is knowledge of the relationship between additions of new material from the mantle, and the extent of crustal recycling [1]. Hafnium isotope ratios can be used to characterise relative contributions from mantle, crustal and recycled reservoirs within magmas. Oxygen isotopes can be used to constrain the extent of crustal interaction during magma emplacement. When used in conjunction, they can help unravel multiple crystallisation histories of a crustal block, and follow the source composition through magma evolution. The Capricorn Orogen records the Paleoproterozoic collision of the Yilgarn and Pilbara Cratons to form the West Australian Craton, and over one billion years of subsequent intracontinental crustal reworking. U-Pb zircon geochronology records three discrete tectono-magmatic events which resulted in voluminous granitic magmatism: the 2005-1975 Ma Glenburgh Orogeny, the 1820-1770 Ma Capricorn Orogeny, and the 1680-1620 Ma Durlacher Orogeny [2]. We present U-Pb, Lu-Hf and δ18O isotopic data from zircon from 50 samples of granites and granitoids from the Capricorn Orogen to provide constraints on the crustal evolution of the Paleoproterozoic crust. Our results confirm crustal growth by juvenile mantle input was limited to the Glenburgh Orogeny associated with the amalgamation of the West Australian Craton, while all subsequent Paleoproterozoic magmatism was primarily derived from significant reworking of the pre-existing crustal components. Time-sliced maps showing the variation in Hf and O isotopes can be used to image crustal evolution in space and time, and are particularly useful in constraining the spatial and temporal extent of juvenile magmatic additions to the crust. These maps suggest that crustal growth was concentrated along, or in the terranes adjacent to, the Yilgarn Craton margin. Our results are in agreement with previous isotopic studies [3], and provide additional

  9. Evidence for multiple mechanisms of crustal contamination of magma from compositionally zoned plutons and associated ultramafic intrusions of the Alaska Range

    Science.gov (United States)

    Reiners, P.W.; Nelson, B.K.; Nelson, S.W.

    1996-01-01

    Models of continental crustal magmagenesis commonly invoke the interaction of mafic mantle-derived magma and continental crust to explain geochemical and petrologic characteristics of crustal volcanic and plutonic rocks. This interaction and the specific mechanisms of crustal contamination associated with it are poorly understood. An excellent opportunity to study the progressive effects of crustal contamination is offered by the composite plutons of the Alaska Range, a series of nine early Tertiary, multiply intruded, compositionally zoned (peridotite to granite) plutons. Large initial Sr and Nd isotopic contrasts between the crustal country rock and likely parental magmas allow evaluation of the mechanisms and extents of crustal contamination that accompanied the crystallization of these ultramafic through granitic rocks. Three contamination processes are distinguished in these plutons. The most obvious of these is assimilation of crustal country rock concurrent with magmatic fractional crystallization (AFC), as indicated by a general trend toward crustal-like isotopic signatures with increasing differentiation. Second, many ultramafic and mafic rocks have late-stage phenocryst reaction and orthocumulate textures that suggest interaction with felsic melt. These rocks also have variable and enriched isotopic compositions that suggest that this felsic melt was isotopically enriched and probably derived from crustal country rock. Partial melt from the flysch country rock may have reacted with and contaminated these partly crystalline magmas following the precipitation and accumulation of the cumulus phenocrysts but before complete solidification of the magma. This suggests that in magmatic mush (especially of ultramafic composition) crystallizing in continental crust, a second distinct process of crustal contamination may be super-imposed on AFC or magma mixing involving the main magma body. Finally, nearly all rocks, including mafic and ultramafic rocks, have (87Sr

  10. The role of lower-crustal hydration in the tectonic evolution of the Colorado Plateau

    Science.gov (United States)

    Porter, Ryan; Hoisch, Thomas; Holt, William E.

    2017-08-01

    Geologists have long debated the timing and mechanism for uplift of the Colorado Plateau with numerous hypotheses proposed to explain each. We use surface wave tomography to examine the lithospheric structure of the Colorado Plateau and surrounding regions and combine these data with thermodynamic modeling to better constrain lower crustal composition, water content, and density. Our results show that about 15% ( 290 m) of the modern plateau elevation can be supported isostatically by hydration of the lower crust, which reduces the overall density of the lithosphere. Hydration of the Colorado Plateau lithosphere likely occurred due to dewatering of the Farallon slab during flat-slab subduction. Subsequent warming and extension have likely further reduced the density of the crust along the plateau margins by as much as 110 kg/m3. This is likely a result of extension encroaching into the plateau and small-scale convection occurring within the mantle surrounding the plateau, and may help explain the high topography on the margins of the plateau.

  11. Crustal and upper mantle structure of stable continental regions in North America and northern Europe

    Science.gov (United States)

    Masse, R.P.

    1987-01-01

    From an analysis of many seismic profiles across the stable continental regions of North America and northern Europe, the crustal and upper mantle velocity structure is determined. Analysis procedures include ray theory calculations and synthetic seismograms computed using reflectivity techniques. The P wave velocity structure beneath the Canadian Shield is virtually identical to that beneath the Baltic Shield to a depth of at least 800 km. Two major layers with a total thickness of about 42 km characterize the crust of these shield regions. Features of the upper mantle of these region include velocity discontinuities at depths of about 74 km, 330 km, 430 km and 700 km. A 13 km thick P wave low velocity channel beginning at a depth of about 94 km is also present. A number of problems associated with record section interpretation are identified and a generalized approach to seismic profile analysis using many record sections is described. The S wave velocity structure beneath the Canadian Shield is derived from constrained surface wave data. The thickness of the lithosphere beneath the Canadian and Baltic Shields is determined to be 95-100 km. The continental plate thickness may be the same as the lithospheric thickness, although available data do not exclude the possibility of the continental plate being thicker than the lithosphere. ?? 1987 Birkha??user Verlag.

  12. Evidence of crustal contamination, sediment, and fluid components in the campanian volcanic rocks

    Science.gov (United States)

    Paone, A.

    2004-01-01

    The Campanian Volcanic Subprovince is part of the classic western potassic volcanic province of the Italian Peninsula. The Campanian volcanic products show the effects of shallow assimilation and fractional crystallisation, and the contribution of regional crustal sources (e.g., Hercynian basement-Calabrian crust). The Roccamonfina, Campi Flegrei, and Ventotene volcanic rocks are characterised by wide isotopic and geochemical variations. Such variations appear to reflect both AFC processes and chemical heterogeneity in the upper mantle that may be linked to subduction processes. Mixing curves (Th/Ce-, Ba/K- and Eu/Eu*-143Nd/144Nd) linking sediments and mantle end-members account for the variations in the Campanian Subprovince volcanic rocks with a sediment contribution of 2-10%. The upper mantle sources for the low- and high-K rocks at Roccamonfina have been constrained on the basis of a multi-element normalised diagram. The two sources require different amounts of sediment in the mantle wedge (LK???2% versus HK???10%) and a fluid component probably from altered ocean crust to explain the fluid mobile elements. Low-K Roccamonfina rocks are geochemically similar to those from Campi Flegrei, Ventotene, and Somma-Vesuvius, suggesting a similar proportion of sediment in their upper mantle source regions. ?? 2004 B.V. All rights reserved.

  13. Vertical Crustal Motion Derived from Satellite Altimetry and Tide Gauges, and Comparisons with DORIS Measurements

    Science.gov (United States)

    Ray, R. D.; Beckley, B. D.; Lemoine, F. G.

    2010-01-01

    A somewhat unorthodox method for determining vertical crustal motion at a tide-gauge location is to difference the sea level time series with an equivalent time series determined from satellite altimetry, To the extent that both instruments measure an identical ocean signal, the difference will be dominated by vertical land motion at the gauge. We revisit this technique by analyzing sea level signals at 28 tide gauges that are colocated with DORIS geodetic stations. Comparisons of altimeter-gauge vertical rates with DORIS rates yield a median difference of 1.8 mm/yr and a weighted root-mean-square difference of2.7 mm/yr. The latter suggests that our uncertainty estimates, which are primarily based on an assumed AR(l) noise process in all time series, underestimates the true errors. Several sources of additional error are discussed, including possible scale errors in the terrestrial reference frame to which altimeter-gauge rates are mostly insensitive, One of our stations, Male, Maldives, which has been the subject of some uninformed arguments about sea-level rise, is found to have almost no vertical motion, and thus is vulnerable to rising sea levels. Published by Elsevier Ltd. on behalf of COSPAR.

  14. Imaging of upper crustal structure beneath East Java-Bali, Indonesia with ambient noise tomography

    Science.gov (United States)

    Martha, Agustya Adi; Cummins, Phil; Saygin, Erdinc; Sri Widiyantoro; Masturyono

    2017-12-01

    The complex geological structures in East Java and Bali provide important opportunities for natural resource exploitation, but also harbor perils associated with natural disasters. Such a condition makes the East Java region an important area for exploration of the subsurface seismic wave velocity structure, especially in its upper crust. We employed the ambient noise tomography method to image the upper crustal structure under this study area. We used seismic data recorded at 24 seismographs of BMKG spread over East Java and Bali. In addition, we installed 28 portable seismographs in East Java from April 2013 to January 2014 for 2-8 weeks, and we installed an additional 28 seismographs simultaneously throughout East Java from August 2015 to April 2016. We constructed inter-station Rayleigh wave Green's functions through cross-correlations of the vertical component of seismic noise recordings at 1500 pairs of stations. We used the Neighborhood Algorithm to construct depth profiles of shear wave velocity (Vs). The main result obtained from this study is the thickness of sediment cover. East Java's southern mountain zone is dominated by higher Vs, the Kendeng basin in the center is dominated by very low Vs, and the Rembang zone (to the North of Kendeng zone) is associated with medium Vs. The existence of structures with oil and gas potential in the Kendeng and Rembang zones can be identified by low Vs.

  15. Crustal seismic structure beneath the Deccan Traps area (Gujarat, India), from local travel-time tomography

    Science.gov (United States)

    Prajapati, Srichand; Kukarina, Ekaterina; Mishra, Santosh

    2016-03-01

    The Gujarat region in western India is known for its intra-plate seismic activity, including the Mw 7.7 Bhuj earthquake, a reverse-faulting event that reactivated normal faults of the Mesozoic Kachchh rift zone. The Late Cretaceous Deccan Traps, one of the largest igneous provinces on the Earth, cover the southern part of Gujarat. This study is aimed at bringing light to the crustal rift zone structure and likely origin of the Traps based on the velocity structure of the crust beneath Gujarat. Tomographic inversion of the Gujarat region was done using the non-linear, passive-source tomographic algorithm, LOTOS. We use high-quality arrival times of 22,280 P and 22,040 S waves from 3555 events recorded from August 2006 to May 2011 at 83 permanent and temporary stations installed in Gujarat state by the Institute of Seismological Research (ISR). We conclude that the resulting high-velocity anomalies, which reach down to the Moho, are most likely related to intrusives associated with the Deccan Traps. Low velocity anomalies are found in sediment-filled Mesozoic rift basins and are related to weakened zones of faults and fracturing. A low-velocity anomaly in the north of the region coincides with the seismogenic zone of the reactivated Kachchh rift system, which is apparently associated with the channel of the outpouring of Deccan basalt.

  16. Investigation of long period crustal deformation on the inactive branch of the North Anatolian Fault Zone

    Science.gov (United States)

    Akay, G.; Ozener, H.

    2009-05-01

    The western part of North Anatolian Fault (NAF) bifurcates around Mudurnu into two fault segments: northern and southern branch. The latter bifurcates again at west of Pamukova and creates middle strand. This study aimed to analyze crustal movement along the middle strand near Iznik which is considered as inactive fault. We focused on a microgeodetic network called General Command of Mapping-Istanbul Technical University (GCM-ITU) network around this segment. In order to obtain displacement values, five campaigns performed on the network which were used in the study. The displacements of the stations were estimated relative to the fixed stations located at the south of the network. The coordinates of the stations were calculated from the triangulation measurements realized in 1941 and 1963, trilateration measurements in 1981, and GPS campaigns in 2004 and 2007. Then, mean displacements of the network ranging between 7 mm/yr and 18 mm/yr were obtained for these years. In the second part of the study, the GPS data were re-processed by adding three stations from Marmara Continuous GPS Network (MAGNET). Details of MAGNET can be found Ergintav et al. (2002). Estimated displacements were ranging between 3 mm/yr and 13 mm/yr for 2004 and 2007. TUBI station of IGS network was taken as stable.

  17. Investigation of long period crustal deformation on the inactive branch of the North Anatolian Fault Zone

    Directory of Open Access Journals (Sweden)

    G. Akay

    2009-05-01

    Full Text Available The western part of North Anatolian Fault (NAF bifurcates around Mudurnu into two fault segments: northern and southern branch. The latter bifurcates again at west of Pamukova and creates middle strand. This study aimed to analyze crustal movement along the middle strand near Iznik which is considered as inactive fault. We focused on a microgeodetic network called General Command of Mapping-Istanbul Technical University (GCM-ITU network around this segment. In order to obtain displacement values, five campaigns performed on the network which were used in the study. The displacements of the stations were estimated relative to the fixed stations located at the south of the network. The coordinates of the stations were calculated from the triangulation measurements realized in 1941 and 1963, trilateration measurements in 1981, and GPS campaigns in 2004 and 2007. Then, mean displacements of the network ranging between 7 mm/yr and 18 mm/yr were obtained for these years.

    In the second part of the study, the GPS data were re-processed by adding three stations from Marmara Continuous GPS Network (MAGNET. Details of MAGNET can be found Ergintav et al. (2002. Estimated displacements were ranging between 3 mm/yr and 13 mm/yr for 2004 and 2007. TUBI station of IGS network was taken as stable.

  18. Free-air and Bouguer gravity anomalies and the Martian crustal dichotomy

    Science.gov (United States)

    Frey, Herbert; Bills, Bruce G.; Kiefer, Walter S.; Nerem, R. Steven; Roark, James H.; Zuber, Maria T.

    1993-01-01

    Free-air and Bouguer gravity anomalies from a 50x50 field, derived from re-analysis of Viking Orbiter and Mariner 9 tracking data and using a 50x50 expansion of the current Mars topography and the GSFC degree 50 geoid as the equipotential reference surface, with the Martian crustal dichotomy are compared. The spherical harmonic topography used has zero mean elevation, and differs from the USGS maps by about 2 km. In this field the dichotomy boundary in eastern Mars lies mostly at -1 to -2 km elevation. Bouguer gravity anomalies are shown on a map of Noachian, Hesperian, and Amazonian age terrains, simplified from current geologic maps. The map is centered at 300 deg W to show the continuity of the dichotomy boundary. Contour interval is 100 mgals. Gravity and topography were compared along approximately 40 profiles oriented parallel to the dichotomy boundary topographic gradient, to determine how the geophysical character of the boundary changes along its length and what this implies for its origin and development.

  19. Crustal velocity structure of the Apennines (Italy from P-wave travel time tomography

    Directory of Open Access Journals (Sweden)

    A. Amato

    1996-06-01

    Full Text Available In this paper we provide P-wave velocity images of the crust underneath the Apennines (Italy, focusing on the lower crustal structure and the Moho topography. We inverted P-wave arrival times of earthquakes which occurred from 1986 to 1993 within the Apenninic area. To overcome inversion instabilities due to noisy data (we used bulletin data we decided to resolve a minimum number of velocity parameters, inverting for only two layers in the crust and one in the uppermost mantle underneath the Moho. A partial inversion of only 55% of the overall dataset yields velocity images similar to those obtained with the whole data set, indicating that the depicted tomograms are stable and fairly insensitive to the number of data used. We find a low-velocity anomaly in the lower crust extending underneath the whole Apenninic belt. This feature is segmented by a relative high-velocity zone in correspondence with the Ortona-Roccamonfina line, that separates the northern from the southern Apenninic arcs. The Moho has a variable depth in the study area, and is deeper (more than 37 km in the Adriatic side of the Northern Apennines with respect to the Tyrrhenian side, where it is found in the depth interval 22-34 km.

  20. Determination of crustal thickness under Tibet from gravity-gradient data

    Science.gov (United States)

    Chen, Wenjin

    2017-08-01

    We develop a novel regional inversion algorithm to determinate the Moho geometry from the gravity-gradient data. The procedure involves two steps. Firstly, the refined gravity-gradient data, which comprise mainly the gravitational signal of the Moho geometry, are obtained from applying the gravimetric forward modeling by using a tesseroid method. Secondly, the refined gravity-gradient data are used to find the Moho depth. The functional relationship between the (known) refined gravity-gradient data and the (unknown and sought) Moho depth is defined by means of the (nonlinear) Fredholm integral equation of the first kind, which is further linearized by means of applying a Taylor series. To stabilize the inverse solution of the system of observation equations, the Tikhonov regularization is applied. The developed algorithm is tested at the study area of Tibet characterized by the largest crustal thickness. Results of the gravimetric inversion (for the uniform and variable Moho density contrast models) have a relatively good agreement with the seismic model (CRUST1.0) at the level of expected uncertainties of about 5 km without the presence of a significant systematic bias.

  1. Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

    Energy Technology Data Exchange (ETDEWEB)

    Martha, Agustya Adi [Meteorological, Climatological and Geophysical Agency, Jakarta (Indonesia); Graduate Research on Earthquakes and Active Tectonics, Institut Teknologi Bandung, Bandung (Indonesia); Widiyantoro, Sri [Global Geophysics Group, Institut Teknologi Bandung, Bandung (Indonesia); Center for Disaster Mitigation, Institut Teknologi Bandung, Bandung (Indonesia); Cummins, Phil; Saygin, Erdinc [Research School of Earth Sciences, Australian National University, Canberra (Australia); Masturyono [Meteorological, Climatological and Geophysical Agency, Jakarta (Indonesia)

    2015-04-24

    East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images.

  2. Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

    Science.gov (United States)

    Martha, Agustya Adi; Widiyantoro, Sri; Cummins, Phil; Saygin, Erdinc; Masturyono

    2015-04-01

    East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images.

  3. The crustal structure beneath The Netherlands derived from ambient seismic noise

    Science.gov (United States)

    Yudistira, Tedi; Paulssen, Hanneke; Trampert, Jeannot

    2017-11-01

    This work presents the first comprehensive 3-D model of the crust beneath The Netherlands. To obtain this model, we designed the NARS-Netherlands project, a dense deployment of broadband stations in the area. Rayleigh and Love wave group velocity dispersion was measured from ambient noise cross-correlations. Azimuthally anisotropic group velocity maps were then constructed and the isotropic part was used to determine a shear wave speed model that includes the effects of radial anisotropy. Employing the Neighbourhood Algorithm for the depth inversion, we obtained probabilistic estimates of the radially anisotropic model parameters. We found that the variations in the thickness of the top layer largely match the transition from sediments of Permian age to those of Carboniferous age. Regions of high faulting density such as the West Netherlands Basin and Roer Valley Graben are recognized in our model by their negative radial anisotropy (VSH - VSV < 0). The model has a mid-crustal discontinuity at a depth of around 13 km and the average Moho depth is 33 km, with most of its depth variations within 2 km. Specifically, a localized Moho uplift to a depth of 29 km is found within Roer Valley Graben, in the Campine region in Belgium. Furthermore, our Rayleigh and Love wave group velocity data at periods of around 20 s show evidence for azimuthal anisotropy with a NW-SE fast direction. This anisotropy is likely related to NW-SE rock fabric in the lower crust thought to originate from the Caledonian deformation.

  4. Connecting crustal seismicity and earthquake-driven stress evolution in Southern California

    Science.gov (United States)

    Pollitz, Fred F.; Cattania, Camilla

    2017-08-01

    Tectonic stress in the crust evolves during a seismic cycle, with slow stress accumulation over interseismic periods, episodic stress steps at the time of earthquakes, and transient stress readjustment during a postseismic period that may last months to years. Static stress transfer to surrounding faults has been well documented to alter regional seismicity rates over both short and long time scales. While static stress transfer is instantaneous and long lived, postseismic stress transfer driven by viscoelastic relaxation of the ductile lower crust and mantle leads to additional, slowly varying stress perturbations. Both processes may be tested by comparing a decade-long record of regional seismicity to predicted time-dependent seismicity rates based on a stress evolution model that includes viscoelastic stress transfer. Here we explore crustal stress evolution arising from the seismic cycle in Southern California from 1981 to 2014 using five M≥6.5 source quakes: the M7.3 1992 Landers, M6.5 1992 Big Bear, M6.7 1994 Big Bear, M7.1 1999 Hector Mine, and M7.2 2010 El Mayor-Cucapah earthquakes. We relate the stress readjustment in the surrounding crust generated by each quake to regional seismicity using rate-and-state friction theory. Using a log likelihood approach, we quantify the potential to trigger seismicity of both static and viscoelastic stress transfer, finding that both processes have systematically shaped the spatial pattern of Southern California seismicity since 1992.

  5. Tectonics and crustal structure of the Saurashtra peninsula: based on Gravity and Magnetic data

    Science.gov (United States)

    Mishra, A. K.; Singh, A.; Singh, U. K.

    2016-12-01

    The Saurashtra peninsula is located at the North Western margin of the Indian shield which occurs as a horst block between the rifts namely as Kachchh, Cambay and Narmada. It is important because of occurrence of moderate earthquake and presence of mesozoic sediments below the Deccan trap. The maps of bouguer gravity anomaly and the total intensity magnetic anomalies of Saurashtra have delineated six circular gravity highs of magnitudes 40-60 mGal and 800-1000 nT respectively. In order to understand the location, structure and depth of the source body, methods like continuous wavelet transform (CWT), Euler deconvolution and power spectrum analysis have been implemented in the potential field data. The CWT and Euler deconvolution give 16-18 km average depth of volcanic plug in Junagadh and Rajula region. From the power spectrum analysis, it is found that average Moho depth in the Saurashtra is about 36-38 km. Keeping the constraints obtained from geophysical studies like borehole, deep seismic survey, receiver function analysis and geological information, combined gravity and magnetic modeling have been performed. Detailed crustal structure of the Saurashtra region has been delineated along two profiles which pass from prominent geological features Junagadh and Rajula volcanic plugs respectively.

  6. Research on Recent GPS Crustal Deformation Characteristics in the Northeastern Edge of Qinghai-Tibet Plateau

    Science.gov (United States)

    Ma, Haiping; Wu, Yanqiang; Feng, Jian’gang; Xu, Rong; Wu, Shayi; Wang, Qian

    2017-10-01

    Based on the GPS data in the northeastern edge of Qinghai-Tibet Plateau, the velocity field and the extension change rate of baseline between stations are analyzed. The crustal movement characteristics and their dynamic changes in this region are discussed. The result indicates that the baseline in the regions demonstrates an overall characteristic of shrinking in the NE direction and extending in the NW direction; The extrusion of Bayan Har Block in SE direction since 2009 has amplified obviously, which leads to the enhancement of correlated movement in SE direction in the NW side of Longmenshan Fault. In addition, Tianzhu empty regions and the area near the epicenter of Menyuan Ms6.4 earthquake in 2016 are right in the boundary of this differentiated movement. Recently, a certain amount of strain energy might have been accumulated in the nearby area of the northern margin of Alkin Fault Zone, west boundary of Erdos Block and west to105°N on Northern Xiqinling Fault. The seismic risk in the west and east section of the intersecting area between Bayan Har Block and Qaidam Block is high. The west section of Northern Xiqinling Fault belongs to the inner ring of clockwise vortex and possesses medium-strong seismic risk.

  7. Role of crustal and slab components in the Northern Volcanic Zone of the Andes (Ecuador) constrained by Sr-Nd-O isotopes

    OpenAIRE

    Hidalgo, S.; Gerbe, M. C.; Martin, H.; Samaniego, Pablo; Bourdon, E.

    2012-01-01

    A combined approach based on trace elements, radiogenic (Sr-Nd) and stable (O) isotopes allows us to discuss the role of crustal assimilation and mantle metasomatism in Quaternary Ecuadorian magmatism. Magmas emplaced in the Eastern Cordillera have high Sr isotopic ratios and relatively high delta O-18 values, which reflect crustal assimilation (6-13 vol.%) of igneous and metamorphic Palaeozoic and Mesozoic rocks during ascent and storage in the continental crust. However, in the Volcanic Fro...

  8. Crustal seismic anisotropy beneath Shillong plateau - Assam valley in North East India: Shear-wave splitting analysis using local earthquakes

    Science.gov (United States)

    Sharma, Antara; Baruah, Santanu; Piccinini, Davide; Saikia, Sowrav; Phukan, Manoj K.; Chetia, Monisha; Kayal, J. R.

    2017-10-01

    We present crustal anisotropy estimates constrained by shear wave splitting (SWS) analysis using local earthquakes in the Shillong plateau and Assam valley area, North East India (NE India) region. Splitting parameters are determined using an automated cross-correlation (CC) method. We located 330 earthquakes recorded by 17 broadband seismic stations during 2001-2014 in the study area. Out of these 330 events, seismograms of 163 events are selected for the SWS analysis. Relatively small average delay times (0.039-0.084 s) indicate existence of moderate crack density in the crust below the study area. It is found that fast polarization directions vary from station to station depending on the regional stress system as well as geological conditions. The spatial pattern of crustal anisotropy in the area is controlled mostly by tectonic movement of the Indian plate towards NE. Presence of several E-W and N-S trending active faults in the area also play an important role on the observed pattern of crustal anisotropy.

  9. Structural evolution of a composite middle to lower crustal section: The Sierra de Pie de Palo, northwest Argentina

    Science.gov (United States)

    Mulcahy, S. R.; Roeske, S. M.; McClelland, W. C.; Jourdan, F.; Iriondo, A.; Renne, P. R.; Vervoort, J. D.; Vujovich, G. I.

    2011-02-01

    The Sierra de Pie de Palo of northwest Argentina preserves middle to lower crustal metamorphic rocks that were penetratively deformed during Ordovician accretion of the Precordillera terrane to the Gondwana margin. New structural, petrologic, and geochronologic data from a 40 km structural transect reveals that the Sierra de Pie de Palo preserves a middle to lower crustal ductile thrust complex consisting of individual structural units and not an intact ophiolite and cover sequence. Top-to-the-west thrusting occurred intermittently on discrete ductile shear zones from ˜515 to ˜417 Ma and generally propagated toward the foreland with progressive deformation. Ordovician crustal shortening and peak metamorphic temperatures in the central portion of the Sierra de Pie de Palo were synchronous with retro-arc shortening and magmatic flare-up within the Famatina arc. Accretion of the Precordillera terrane resulted in the end of arc flare-up and the onset of synconvergent extension by ˜439 Ma. Continued synextensional to postextensional convergence was accommodated along progressively lower grade shear zones following terrane accretion and the establishment of a new plate margin west of the Precordillera terrane. The results support models of Cordilleran orogens that link voluminous arc magmatism to periods of regional shortening. The deformation, metamorphic, and magmatic history within the Sierra de Pie de Palo is consistent with models placing the region adjacent to the Famatina margin in the middle Cambrian and not as basement to the Precordillera terrane.

  10. Crustal and uppermost mantle structure of southern Norway: results from surface wave analysis of ambient seismic noise and earthquake data

    Science.gov (United States)

    Köhler, Andreas; Weidle, Christian; Maupin, Valérie

    2012-12-01

    We use ambient seismic noise and earthquake recordings on a temporary regional network in southern Norway to produce Rayleigh and Love wave phase velocity maps from 3 to 67 s period. Local dispersion curves are then jointly inverted for a 3-D shear wave velocity model of the region. We perform a two-step inversion approach. First, a direct search, Monte Carlo algorithm is applied to find best fitting isotropic velocity depth profiles. Those profiles are then used as initial models for a linearised inversion which takes into account radial anisotropy in the shear wave structure. Results reveal crustal as well as uppermost mantle structures in the studied region. Velocity anomalies in the upper crust are rather small in amplitude and can in most parts be related to surface geology in terms of rock densities. Old tectonic units like the Oslo Graben (300-240 Ma) and the Caledonian nappes (440-410 Ma) are clearly imaged. Furthermore, we find clear indications for localized crustal anisotropy of about 3 per cent. Despite generally poor resolution of interface depths in surface wave inversion, we find lateral variation of crustal thickness in agreement with previous studies. We are able to confirm and locate the transition from a slow lithospheric upper mantle underneath southern Norway to a fast shield-like mantle towards Sweden.

  11. Crustal structure beneath the Paleozoic Parnaíba Basin revealed by airborne gravity and magnetic data, Brazil

    Science.gov (United States)

    de Castroa, David L.; Fuck, Reinhardt A.; Phillips, Jeffrey D.; Vidotti, Roberta M.; Bezerra, Francisco H. R.; Dantas, Elton L.

    2014-01-01

    The Parnaíba Basin is a large Paleozoic syneclise in northeastern Brazil underlain by Precambrian crystalline basement, which comprises a complex lithostructural and tectonic framework formed during the Neoproterozoic–Eopaleozoic Brasiliano–Pan African orogenic collage. A sag basin up to 3.5 km thick and 1000 km long formed after the collage. The lithologic composition, structure, and role in the basin evolution of the underlying basement are the focus of this study. Airborne gravity and magnetic data were modeled to reveal the general crustal structure underneath the Parnaíba Basin. Results indicate that gravity and magnetic signatures delineate the main boundaries and structural trends of three cratonic areas and surrounding Neoproterozoic fold belts in the basement. Triangular-shaped basement inliers are geophysically defined in the central region of this continental-scale Neoproterozoic convergence zone. A 3-D gravity inversion constrained by seismological data reveals that basement inliers exhibit a 36–40.5 km deep crustal root, with borders defined by a high-density and thinner crust. Forward modeling of gravity and magnetic data indicates that lateral boundaries between crustal units are limited by Brasiliano shear zones, representing lithospheric sutures of the Amazonian and São Francisco Cratons, Tocantins Province and Parnaíba Block. In addition, coincident residual gravity, residual magnetic, and pseudo-gravity lows indicate two complex systems of Eopaleozoic rifts related to the initial phase of the sag deposition, which follow basement trends in several directions.

  12. How plume-ridge interaction shapes the crustal thickness pattern of the Réunion hotspot track

    Science.gov (United States)

    Bredow, Eva; Steinberger, Bernhard; Gassmöller, Rene; Dannberg, Juliane

    2017-08-01

    The Réunion mantle plume has shaped a large area of the Earth's surface over the past 65 million years: from the Deccan Traps in India along the hotspot track comprising the island chains of the Laccadives, Maldives, and Chagos Bank on the Indian plate and the Mascarene Plateau on the African plate up to the currently active volcanism at La Réunion Island. This study addresses the question how the Réunion plume, especially in interaction with the Central Indian Ridge, created the complex crustal thickness pattern of the hotspot track. For this purpose, the mantle convection code ASPECT was used to design three-dimensional numerical models, which consider the specific location of the plume underneath moving plates and surrounded by large-scale mantle flow. The results show the crustal thickness pattern produced by the plume, which altogether agrees well with topographic maps. Especially two features are consistently reproduced by the models: the distinctive gap in the hotspot track between the Maldives and Chagos is created by the combination of the ridge geometry and plume-ridge interaction; and the Rodrigues Ridge, a narrow crustal structure which connects the hotspot track and the Central Indian Ridge, appears as the surface expression of a long-distance sublithospheric flow channel. This study therefore provides further insight how small-scale surface features are generated by the complex interplay between mantle and lithospheric processes.

  13. Crustal Seismic Structure along the East Pacific Rise 8° 20'N to 10° 10'N: Crustal melt accumulation and its relation to Mantle Melt Delivery, Tectonic Segmentation, Seafloor Geology and Hydrothermal Activity

    Science.gov (United States)

    Christopher, L. M.; Dunn, R.; Toomey, D.; Wilcock, W.; Detrick, R.

    2003-12-01

    The UNDERSHOOT seismic experiment was designed to test competing magma supply models for the East Pacific Rise (EPR). P-wave energy that traverses the ridge within the crust allows us to map the variability of magma storage within the crust along the entire length of the transform-bounded segment of the EPR between the Siqueiros and Clipperton fracture zones. This 200-km-long section of ridge exhibits several small discontinuities of the bathymetric structure and one large overlapping spreading center (OSC) at 9° 03'N. Earlier work has shown that the ridge is underlain by a shallow melt lens at approximately 1.5 km depth and by a prominent low velocity zone (4-8 km wide) that extends from the melt lens downwards into the mantle. This low velocity zone is indicative of high temperatures and a partially molten region of up to 10-40 percent magma storage. During the undershoot experiment P-wave crustal refractions and Moho reflections uniformly sampled this low-velocity zone along the entire length of this transform-bounded ridge segment. We use this data to tomographically image variations of the low-velocity zone along the ridge, including crustal thickness variations, and by inference variations in magma storage and supply. We jointly solve for the three-dimensional velocity structure of the crust and crustal thickness using a newly developed tomographic technique. While vertical resolution is poor beneath the rise, the high density of crossing ray paths, over a wide range of angles, provides excellent constraints on lateral variations in velocity structure. Initial results of this study do not reveal a discontinuity in the crustal low-velocity region beneath the OSC as expected by some models of OSC formation. This result correlates with a mantle tomographic image [Dunn et al., 2001] which likewise does not reveal a discontinuity in the mantle level low-velocity region just beneath the OSC. Our results, in combination with tomographic images of the uppermost

  14. Traumatologia da coluna cervical

    OpenAIRE

    Silva, Cíntia da Costa Silvano,1989-

    2013-01-01

    Estima-se que mais de três milhões de pacientes com suspeita de lesão traumática da Coluna Cervical (CC) são atendidos nos serviços de urgência dos Estado Unidos da América (EUA), por ano. O mecanismo de trauma da CC é, numa grande parte das situações, incerto. A sua determinação depende maioritariamente dos padrões morfológicos da lesão e é indiretamente determinado a partir dos achados radiológicos. Uma lesão clinicamente significativa da CC é definida como qualquer fratura, luxação o...

  15. Subduction initiation and recycling of Alboran domain derived crustal components prior to the intra-crustal emplacement of mantle peridotites in the Westernmost Mediterranean: isotopic evidence from the Ronda peridotite

    Science.gov (United States)

    Varas-Reus, María Isabel; Garrido, Carlos J.; Bosch, Delphine; Marchesi, Claudio Claudio; Acosta-Vigil, Antonio; Hidas, Károly; Barich, Amel

    2014-05-01

    During Late Oligocene-Early Miocene different domains formed in the region between Iberia and Africa in the westernmost Mediterranean, including thinned continental crust and a Flysch Trough turbiditic deposits likely floored by oceanic crust [1]. At this time, the Ronda peridotite likely constituted the subcontinental lithospheric mantle of the Alboran domain, which mantle lithosphere was undergoing strong thinning and melting [2] [3] coevally with Early Miocene extension in the overlying Alpujárride-Maláguide stacked crust [4, 5]. Intrusive Cr- rich pyroxenites in the Ronda massif records the geochemical processes occurring in the subcontinental mantle of the Alboran domain during the Late Oligocene [6]. Recent isotopic studies of these pyroxenites indicate that their mantle source was contaminated by a subduction component released by detrital crustal sediments [6]. This new data is consistent with a subduction setting for the late evolution of the Alboran lithospheric mantle just prior to its final intracrustal emplacement in the early Miocene Further detailed structural studies of the Ronda plagioclase peridotites-related to the initial stages of ductile emplacement of the peridotite-have led to Hidas et al. [7] to propose a geodynamic model where folding and shearing of an attenuated mantle lithosphere occurred by backarc basin inversion followed by failed subduction initiation that ended into the intracrustal emplacement of peridotite into the Alboran wedge in the earliest Miocene. This hypothesis implies that the crustal component recorded in late, Cr-rich websterite dykes might come from underthrusted crustal rocks from the Flysch and/or Alpujárrides units that might have been involved in the earliest stages of this subduction initiation stage. To investigate the origin of crustal component in the mantle source of this late magmatic event recorded by Cr-pyroxenites, we have carried out a detail Sr-Nd-Pb-Hf isotopic study of a variety of Betic

  16. Cartografia da paisagem alterada

    Directory of Open Access Journals (Sweden)

    Simone Cortezão

    2011-04-01

    Full Text Available O presente trabalho de pesquisa surge da investigação de paisagens alteradas, áreas pós-industriais e da geografia urbana que é conformada pela indústria. A preocupação principal é revê-las como espaço de investigação crítica sob o ponto de vista particular, integradas às noções da peculiar natureza industrial com suas consequentes transformações na paisagem, além das relações do indivíduo com esse novo meio produzido. “Cartografia da paisagem alterada” é uma pesquisa que indicia a paisagem alterada em pelo menos dois estratos: um que é o da construção da geografia da cidade pela indústria, e o outro que é a paisagem alterada subjetivamente, o que configura uma crítica e uma reação à conformação sócio geográfica em outros parâmetros - da proximidade, da experiência vivida e da construção de um vocabulário próprio.  A pesquisa teórica sobre áreas pós-industriais, associada a referências nas artes e arquitetura, constitui o primeiro estrato. Teorias e procedimentos artísticos de Robert Smithson, Joseph Beuys e Rem Koolhaas fornecem material para o segundo, mediante a pesquisa do cotidiano no lugar, a região do Vale do Aço, que se configura em um guia - glossário

  17. Flow of ultra-hot Precambrian orogens and the making of crustal layering in Phanerozoic orogenic plateaux

    Science.gov (United States)

    Chardon, Dominique; Gapais, Denis; Cagnard, Florence; Jayananda, Mudlappa; Peucat, Jean-Jacques

    2010-05-01

    Reassessment of structural / metamorphic properties of ultra-hot Precambrian orogens and shortening of model weak lithospheres support a syn-convergence flow mode on an orogen scale, with a large component of horizontal finite elongation parallel to the orogen. This orogen-scale flow mode combines distributed shortening, gravity-driven flow, lateral escape, and three-dimensional mass redistribution of buried supracrustal rocks, magmas and migmatites in a thick fluid lower crust. This combination preserves a nearly flat surface and Moho. The upper crust maintains a nearly constant thickness by real-time erosion and near-field clastic sedimentation and by ablation at its base by burial of pop-downs into the lower crust. Steady state regime of these orogens is allowed by activation of an attachment layer that maintains kinematic compatibility between the thin and dominantly plastic upper crust and a thick "water bed" of lower crust. Because very thin lithospheres of orogenic plateaux and Precambrian hot orogens have similar thermomechanical structures, bulk orogenic flow comparable to that governing Precambrian hot orogens should actually operate through today's orogenic plateaux as well. Thus, syn-convergence flow fabrics documented on exposed crustal sections of ancient hot orogens that have not undergone collapse may be used to infer the nature of flow fabrics that are imaged by geophysical techniques beneath orogenic plateaux. We provide a detailed geological perspective on syn-convergence crustal flow in relation to magma emplacement and partial melting on a wide oblique crustal transition of the Neoarchean ultra-hot orogen of Southern India. We document sub-horizontal bulk longitudinal flow of the partially molten lower crust over a protracted period of 60 Ma. Bulk flow results from the interplay of (1) pervasive longitudinal transtensional flow of the partially molten crust, (2) longitudinal coaxial flow on flat fabrics in early plutons, (3) distributed, orogen

  18. Antecedentes da adocao da computacao em nuvem: efeitos da infraestrutura, investimento e porte

    National Research Council Canada - National Science Library

    Prospero Sanchez, Otavio; Cappellozza, Alexandre

    2012-01-01

    ... em infraestrutura de Tecnologia da Informacao (TI). Paradoxalmente, ao mesmo tempo em que surge o beneficio para as organizacoes da possibilidade de executarem computacao em nuvem, os decisores deparam-se com o dilema advindo da possibilidade...

  19. Incipient Crustal Stretching across AN Active Collision Belt: the Case of the Siculo-Calabrian Rift Zone (central Mediterranean)

    Science.gov (United States)

    Catalano, S.; Tortorici, G.; Romagnoli, G.; Pavano, F.

    2012-12-01

    In the Central Mediterranean, the differential roll-back of the subducting Nubia Plate caused the Neogene-Quaternary extrusion of the Calabrian arc onto the oceanic Ionian slab, and the opening of the oceanic Tyrrhenian Basin, in the overriding Eurasia Plate. The differential motion at the edges of the arc was largely accommodated along transform faults that propagated across the orogenic belt. Since the Late Quaternary, the southern edge of the arc has been replaced by the roughly N-S oriented Siculo-Calabrian Rift Zone (SCRZ) that formed as the NNW-directed normal faults of NE Sicily, crossing the orogenic belt, have linked the NNE-oriented Tyrrhenian margin of southern Calabria with the NNW-trending Africa-Ionian boundary of southeastern Sicily. Our study focused on the Sicily shoulder of the SCRZ, where the transition zone between the extensional belt and the still active Nubia-Eurasia convergent margin is characterized by two distinct mobile crustal wedges, both lying on an upwarped Mantle, where a re-orientations of the σ1 is combined with volcanism (e.g. Etna, Aeolian islands) and a huge tectonic uplift. In southeastern Sicily, the Hyblean-Etnean region evolved, since about 0.85 Ma, as an indipendent crustal wedge, moving towards the NNW and pointing to the active Mt. Etna volcano. A local ENE crustal stretching accompanied the traslation of the block and pre-dated the ESE-oriented extension governing the propagation of the southernmost branch of the SCR, which started at about 330 ka B.P.. Similarly, the Peloritani-Aeolian region, flanked by the 125 ka-old NE-Sicily branch of the rift zone, represents a mostly submerged crustal wedge that migrates towards the NE, diverging from the rest of the Sicily collision zone and pointing to the Stromboli volcano. The Peloritani-Aeolian block is characterized by the occurrence of a wide central NE-oriented collapsed basin contoured by an actively uplifting region, whose tectonic boundaries are evidenced by a sharp

  20. The 1978 Yellowstone-Eastern Snake River Plain Seismic Profiling Experiment: Crustal structure of the Yellowstone Region and experiment design

    Science.gov (United States)

    Smith, R. B.; Schilly, M. M.; Braile, L. W.; Ansorge, J.; Lehman, J. L.; Baker, M. R.; Prodehl, C.; Healy, J. H.; Mueller, S.; Greensfelder, R. W.

    1982-04-01

    In 1978 a major seismic profiling experiment was conducted in the Yellowstone-eastern Snake River Plain region of Idaho and Wyoming. Fifteen shots were recorded that provided coverage to distances of 300 km. In this paper, travel time and synthetic seismogram modeling was used to evaluate an average P wave velocity and apparent Q structure of the crust from two seismic profiles (reversed) across the Yellowstone National Park region. This area includes the well-known hydrothermal features of Yellowstone National Park (geysers, fumeroles, etc.), a large collapse caldera, and extensive silicic volcanism of Quaternary age—features attributed to shallow crustal sources of magma. The averaged crustal structure for this region as interpreted from the seismic data consists of (1) a highly variable, near-surface layer approximately 2 km thick with variable velocities of 3.0 to 4.8 km/s and a low apparent Q of 30 that is interpreted to be composed of weathered rhyolites and sedimentary infill, (2) an upper crustal layer 3 to 4 km thick with variable velocities of 4.9 to 5.5 km/s and apparent Q of 50 to 200 that is thought to represent the accumulation of the Pleistocene-Quaternary rhyolite flows, ash flow tuffs, and possible Paleozoic and Precambrian metamorphic equivalents, (3) the crystalline, upper crust that is characterized by a laterally inhomogeneous layer that varies in velocity from 4.0 to 6.1 km/s, averaging 5 km thick with a Q of 300. This layer appears to be a cooling but still hot body of granitic composition beneath the Yellowstone caldera. It is thought to be a remnant of the magma chambers that produced the Quaternary silicic volcanic rocks of the Yellowstone Plateau and may still be a major contributor to the high heat flow, (4) a laterally homogeneous intermediate crustal layer 8 to 10 km thick with a velocity of 6.5 km/s and apparent Q of 100 to 300, (5) a homogeneous 25-km-thick lower crust with a velocity of 6.7 to 6.8 km/s and an apparent Q of 300

  1. MACIEZ DA CARNE BOVINA

    Directory of Open Access Journals (Sweden)

    Antonio Bento Mancio

    2006-10-01

    Full Text Available Dentre as características de qualidade da carne bovina, a maciez assume posição de destaque, sendo considerada a característica organoléptica de maior influência na aceitação da carne por parte dos consumidores. A dureza da carne pode ser dividida em dureza residual, causada pelo tecido conjuntivo e outras proteínas do estroma, e dureza de actomiosina, causada pelas proteínas miofibrilares. Dentre os fatores que influenciam a maciez da carne, podem ser destacados a genética, a raça, a idade ao abate, o sexo, a alimentação, o uso de agentes hormonais (?-adrenérgicos e os tratamentos post-mortem. A qualidade final da carne é resultante de tudo o que aconteceu com o animal durante toda a cadeia produtiva. Devem-se assegurar procedimentos adequados de transporte, armazenamento, manipulação, exposição e preparo da carne, a fim de se obter um produto de melhor qualidade. PALAVRAS-CHAVE: Calpaínas, calpastatina, qualidade da carne, rigor mortis, tecido muscular.

  2. GERONTOLOGIA: ESTADO DA ARTE

    Directory of Open Access Journals (Sweden)

    Vera M.A.Tordino Brandão

    2010-02-01

    Full Text Available O Programa de Gerontologia da PUC desenvolve pesquisas focando o ser na perspectiva do envelhecimento. As atividades são interdisciplinares e reúnem docentes, alunos e ex-alunos. Nesta mesa redonda apresentamos um panorama sobre estes estudos. Na área da educação e comunicação o foco está centrado na longevidade e na preparação e representação social da velhice. São ressaltadas como temáticas: a formação continuada de profissionais e pesquisadores; o significado da religiosidade/espiritualidade ao longo da trajetória, e sua repercussão na qualidade de vida do idoso; os programas sócio-educacionais para idosos e concepções sobre educação; o monitoramento da mídia na cobertura da crescente longevidade e seus impactos. Em identidade e modos de morar reflete-se sobre soluções planejadas e sua adequação para a inclusão do envelhecimento populacional como questão fundamental, que implica a elaboração de novas políticas, investigações e, especialmente, apresenta-se como questão a ser analisada, refletida e vivenciada pela sociedade em geral. Quanto à saúde, o Programa desenvolve várias pesquisas numa abordagem interdisciplinar tendo como objetos de estudo: a terapia assistida com animais direcionada a idosos com diagnóstico de Alzheimer; o acompanhamento terapêutico e o atendimento psicoterapêutico em grupo, a aplicação da técnica de Calatonia em idosos moradores de ILPI, além da investigação sobre impasses clínicos no idoso frágil. Palavras-chave: gerontologia, longevidade, envelhecimento

  3. CONDICIONANTES DA COMPETITIVIDADE EMPRESARIAL

    Directory of Open Access Journals (Sweden)

    José Luiz Contador

    2010-03-01

    Full Text Available Este trabalho examina teoricamente os fatores determinantes da competitividade do produto e do negócio, imprescindíveis à elaboração de estratégias competitivas que visam à obtenção e sustentação de vantagens competitivas. Esse tema é objeto tanto da área de marketing estratégico quanto da de estratégia empresarial. Nas duas áreas, há um ponto de consenso que afirma que a empresa deve diferenciar sua oferta para conquistar e manter vantagem competitiva. Mas, os estudos conduzidos por meio do modelo de Campos e Armas da Competição revelaram que a empresa pode diferenciar seu produto e/ou serviço de modo mais amplo, levando em consideração, na formulação da sua estratégia competitiva, também o campo da competição, quer do produto, quer dela própria. Assim, o objetivo deste artigo é evidenciar que, para a empresa ser competitiva, além de diferenciar seu produto e/ou seu serviço no sentido tradicional, ela precisa: 1 diferenciar seu produto incluindo a definição em quais campos vai competir em cada segmento; e 2 escolher as armas da competição que irá utilizar e definir a intensidade de cada arma. Para atingir tal objetivo, foram necessários vários conceitos do modelo de Campos e Armas da Competição: campo da competição, arma da competição, tese do modelo, configuração dos campos da competição, campo coadjuvante, produto coadjuvante e par produto-mercado. Como uma proposta inovadora sempre desperta dúvida, é mostrado o processo de validação do modelo de Campos e Armas da Competição e são discutidas sua universalidade, consistência e completude.

  4. Simulations of crustal anatexis: Implications for the growth and differentiation of continental crust

    Science.gov (United States)

    Raia, Federica; Spera, Frank J.

    1997-10-01

    There is overwhelming and incontrovertible petrological and geophysical evidence for the significant role played by mantle-derived mafic magma in the generation and growth of continental crust. Likewise, intrusion of mafic magmas beneath or into continental crust is very likely the major source of enthalpy that drives intracrustal differentiation. A simple dynamical model has been constructed to examine the critical factors that govern the evolution and time-scale of crustal anatexic events when driven by basaltic magma underplating or injection into crust. Critical factors include the intensity of the enthalpy input (i.e., the power dissipated) and the rheological properties, bulk composition and compositional structure of the source rocks undergoing partial fusion. We have performed numerical simulations to evaluate these factors using phase equilibria and thermochemical and transport property data applicable to the binary eutectic system CaAl2Si2O8-CaMgSi2O6 as a rough analog to study anatexis of mafic lower crust. The role of enthalpy power is tested by varying the enthalpy (or temperature) along the base of the crustal block while maintaining a fixed temperature at the top. As ratio Tbot/Ttop increases modestly from 1.05 to 1.15, the average fraction of melt at steady state in the anatexic region increases from 50% to 75%. Time to attain steady state scales inversely with Tbot/Ttop with an increase by a factor of 2 for a 10% decrease in Tbot/Ttop. Typical anatexic timescales are in the range 103 to 105 years for length scales in range 102 to 103 m. The consequences of different rheological models, especially the importance of Darcy percolative flow relative to en masse flow within the partial melt region was also investigated. A value of the solid fraction called the critical value (ƒscrit) is set such that for 00.5) relatively large volumes of nearly homogeneous melt are rapidly generated. In distinction, for ƒscrit small, more enthalpy is stored in the

  5. Quantification of crustal deformation based on analysis of Persistent Scatterer Interferometry of W-Crete

    Science.gov (United States)

    Rieger, S.; Adam, N.; Friedrich, A. M.

    2012-04-01

    Persistent Scatterer Interferometry (PSI) is a powerful tool for detecting crustal deformation processes such as strain accumulation along convergent margins during the interseismic period. This technique allows the detection of vertical motion of the Earth's surface with millimeter accuracy at wide spatial coverage of hundreds of km2. Persistent Scatterers (PSs) are phase stable point scatterers with a consistent and strong reflectivity observed over a long time (Ferretti et al., IEEE GRSS, 2001). We used the PSI Wide Area Product (PSI WAP) of the German Aerospace Center (DLR) for the detection of the vertical surface motion of the western part of the island of Crete. Therefore, we used data of the radar satellites ERS-1 and ERS-2 of the European Space Agency (ESA). The western part of the island of Crete is covered by 39 Synthetic Aperture Radar (SAR) images acquired between 1992 and 2000 of the ERS Track 193. The island of Crete is located adjacent to the Hellenic subduction zone, which is currently one of the most seismically active regions in Europe. Historical records document a devastating earthquake on July 21st, 365 A.D. near the island of Crete. (M > 8.5, Stiros, Quat. Int., 2010). The event resulted in coseismic uplift of the western part of the island of Crete of up to 9 m (Pirazolli et al., JGR, 1996). By analyzing the vertical surface motion of SW-Crete during the interseismic period we are able to determine whether the hypocenter of the 365 A.D. earthquake was located on the subduction interface or on a fault in the overriding plate (Shaw et al., Nature Geosci., 2008). If the 365 A.D. earthquake occurred along the subduction interface, then the region (W-Crete) experiencing coseismic uplift should undergo interseismic subsidence and vice versa (Hyndman & Wang, JGR 1993). The results of the PSI WAP analysis for W-Crete indicate uplift of the SW corner of the island of up to 5 mm/yr in the line-of-sight (LOS). The central part of W-Crete is more or

  6. Crustal Deformation Caused by Earthquake Detected by InSAR Technique Using ALOS/PALSAR Data

    Science.gov (United States)

    Miyagi, Y.; Nishimura, Y.; Takahashi, H.; Shimada, M.

    2007-12-01

    The Japan Aerospace Exploration Agency (JAXA) launched the Advanced Land Observing Satellite (ALOS), which is commonly called 'Daichi' in Japanese, on 24th January 2006. This satellite has the Phased Array type L- band Synthetic Aperture Radar (PALSAR) following the mission of the Japanese Earth Resource Satellite-1 (JERS-1). The PALSAR is an advanced SAR sensor with up to 10 m of spatial resolution and variable off-nadir angle. The ALOS/PALSAR can determine the position and attitude with high accuracy by use of mounted dual frequency GPS system and high precision star trackers, and L-band SAR sensor is suitable to observe even heavily-vegetated area. Therefore it is expected much better coherent SAR images than the JERS-1 and the other previous C-band SAR satellites, and major step forward for InSAR (Interferometric SAR) technique. Actually, several outstanding results from InSAR measurements have been reported for the period after the launch. In 2007, two big earthquakes causing some damages on the periphery occurred in Japan. One is M6.7 Noto Peninsula earthquake on 25th March 2007, and the other is M6.8 off the Chuetsu region earthquake on 16th July 2007. Because both seismic faults inferred from these earthquakes are located at shallow depth beneath the bottom of the sea near the coast, obvious crustal deformation in a land area were detected by PALSAR data. In Japan, there is a dense nation-wide GPS network (GEONET) composed of more than 1200 GPS sites established and operated by Geographical Survey Institute and a lot of seismometers. Similarly GPS and seismometer could detect signals caused by the earthquakes, so these are noticeable cases from the standpoint of a comparison among various kinds of data. A remote sensing techniq