Le Cambrien basal (Étage Fortunien, env. 535 Ma) de la Formation de Kuanchuanpu dans la Province chinoise du Shaanxi, contient une grande variété de Small Shelly Fossils (SSF) préservés grâce à une phosphatisation secondaire. On y trouve les éléments exosquelettiques de groups animaux très variés mais également des embryons et stades larvaires conservés en trois dimensions et interprétés par les auteurs précédents comme de possible cnidaires. Cette faune dans son ensemble est une source d’informations exceptionnelle sur les toutes premières étapes de la diversification animal avant qu’elle n’atteigne son plein développement (ex : au cours du Cambrien inférieur, Série 2, Étage 3). Nous avons exploré ici la morphologie de ces organismes fossiles submillimétriques au moyen de la Microscopie Électronique à Balayage (SEM) et de techniques microtomographiques aux rayons X (Computed X-ray Microtomography, XTM et Synchrotron X-ray Microtomography, SRXTM), testé les hypothèses concernant leurs possibles affinités avec les cnidaires et analysé leur possible relations phylogénétiques avec les groups actuels de cnidaires. Parmi ces fossiles, certains (ex : Olivooides et formes apparentées) peuvent être raisonnablement considérées comme des cnidaires sur la base de leur anatomie interne, leur symétrie radiale et leurs caractères externes, et pourraient appartenir au groupes-souche des Scyphozoa, Cubozoa et Anthozoa. Des représentants des groupescouronne Scyphozoa, Cubozoa, Anthozoa et Hydrozoa semblent apparaître plus tard dans l’évolution des cnidaires (pas avant le Cambrien inférieur Série 2, Étage 3) comme l’indiquent les méduses du gisement exceptionnel (Lagerstätte) de Chengjiang (env. 521 Ma) qui ressemblent en tout point aux méduses actuelles et possédaient déjà un système sensorial sophistiqué. Notre étude met en lumière une série de caractères atypiques chez les cnidaires ancestraux de Kuanchuanpu: 1) la coexistence de divers modes de symétrie, 2) la prédominance de la symétrie pentaradiale, 3) l’existence d’un mode de développement direct (apparemment sans larve planula) contrastant ainsi avec tous les cnidaires actuels et 4) une taille corporelle très petite compatible avec un mode de vie meiobenthique / The lowermost Cambrian (Fortunian Stage; ca. 535 Ma) Kuanchuanpu Formation from China contains a great variety of secondarily phosphatized Small Shelly Fossils such as exoskeletal elements of various animal groups but also yields three-dimension allypreserved embryos and larval stages interpreted as cnidarians by previous authors. This biota is an exceptional source of information on the early steps of animal biodiversification before its full development (e.g. early Cambrian, Series 2, Stage 3).We explored the morphology of these sub-millimetric fossil organisms by means of Scanning Electron Microscopy (SEM), Computed X-ray Microtomography (XTM) and Synchrotron X-ray Microtomography (SRXTM), and tested their cnidarian affinities and analyzed their possible relation to modern cnidarian groups. Some of them (e.g.Olivooides and related forms) can be reasonably considered as cnidarians based on their internal anatomy, radial symmetry and external features, and may belong to the stem groups Scyphozoa, Cubozoa and Anthozoa. Crown-group scyphozoans,cubozoans, anthozoans and hydrozoans seem to appear later in the evolution of cnidarians, not before Stage 3, Series 2 of the early Cambrian as indicated by the jellyfish from the Chengjiang Lagerstätte (ca. 521 Ma) which closely resemble modern tetraradial medusae and possessed sophisticated sensory organs. Our study highlights some important “atypical” features of the ancestral cnidarians from the Kuanchuanpubiota such as 1) the co-existence of diverse symmetry patterns, 2) the prevalence of pentaradial symmetry, 3) a possible direct development (with no planula larva) contrasting with all modern cnidarians and 4) a small body size consistent with ameiobenthic lifestyle

L'ordre faible sur un groupe de Coxeter W est un ordre partiel sur les éléments de W, intervenant dans de nombreux domaines de la combinatoire algébrique. Dans cette thèse, on propose un nouveau modèle général pour l'étude de cet ordre ainsi que d'autres ensembles ordonnés affiliés, et on explore diverses conséquences aussi bien algébriques que combinatoires de cette construction. On commence, dans le chapitre 3, par étudier une version restreinte de ce modèle. Plus précisément, on explique comment on peut associer un ensemble ordonné (aussi appelé « poset » à tout graphe orienté, simple, acyclique et muni d'une valutation sur ses sommets (aussi appelé « graphe valué »). On montre ensuite que ces posets sont en général des semi-treillis inférieurs, des treillis quand le graphe est fini, et on donne une formule explicite pour les valeurs de leurs fonctions de Möbius. On prouve ensuite que l'ordre faible sur les groupes de Coxeter de type A, B et A, le « flag weak order », ainsi que le treillis des idéaux supérieurs et inférieurs de tout poset fini peuvent être décrit avec notre modèle. Cette description amène naturellement à associer une série quasi-symétrique à chaque élément de An et An et on montre que cette série est en fait la série de Stanley associée. On présente dans le chapitre 4 les résultats centraux de la thèse, en effet on y introduit la généralisation de la construction faite au chapitre précédent au cas de tout graphe valué, c'est-à-dire sans condition s'acyclicité et de simplicité. On s'affranchit également de certaines contraintes imposées par la définition du chapitre 3, ce qui nous permet d'associer à tout graphe valué un treillis complet, et non plus un semi-treillis. En particulier, les semi-treillis du chapitre 3 se retrouvent naturellement plongés dans un treillis complet. Ceci nous amène à nous intéresser à des conjectures de Dyer portant sur l'étude d'une extension de l'ordre faible sur tout groupe de Coxeter (entre autres, il est conjecturé que ces extensions sont des treillis complets). On construit alors, à l'aide de notre formalisme, des extensions de l'ordre faible ayant beaucoup des propriétés conjecturalement attachées aux extensions de Dyer, et contenant ces dernières comme sous-poset. On conjecture que l'une de ces extensions coïncide avec celle de Dyer, et on fournit des outils pour le tester. Finalement, on étudie diverses conséquences de notre théorie : la construction d'extensions des semi-treillis cambriens (fin du chapitre 4), la construction d'un nouveau modèle combinatoire pour le treillis de Tamari et m-Tamari (chapitre 5), et enfin on propose une application à la combinatoire des tableaux (chapitre 6) / Weak order on a Coxeter group W is a partial order on W appearing in many areas of algebraic combinatorics. In this thesis, we propose a new general model for the study of the weak order and other related partially ordered sets (also called “posets”) and we explore various algebraic and combinatorial consequences of this construction. We begin with studying a restricted version of this model in Chapter 3. More precisely, we explain how one can associate a poset to any simple acyclic digraph together with a valuation on its vertices (also called “valued digraph”). We then prove that these posets are complete meet semi-lattices in general, complete lattices when the underlying digraph is finite, and we give an explicit formula to compute the value of their Möbius functions. Then, we show that the weak order on Coxeter groups of type A, B and A, the flag weak order, and the up-set (resp. down-set) lattices of any finite poset can be described within this theory. This description naturally leads to associate a quasi-symmetric function to any element of An And An, and we demonstrate that this function is in fact the corresponding Stanley symmetric function. In Chapter 4 we introduce the main results of this thesis. Indeed, we introduce in this chapter the generalization of the construction made in Chapter 3 to the case of any valued digraph, that is without the simplicity and acyclicity condition. Furthermore, this new definition allows us to get rid of some constraints of the definition of Chapter 3, allowing us to associate a complete lattice to each valued digraph. In particular, the meet semi-lattices of Chapter 3 are naturally extended into complete lattices. This leads us to the study of some conjectures of Dyer about the properties of an extension of the weak order having a lot of the properties conjecturally attached to Dyer’s extensions, and we prove that each one of our extensions contains Dyer’s extension as a sub-poset. We make the conjecture that one of this extension coincide with the one of Dyer, and we provide tools in order to test this conjecture. Finally, we study various consequences of out theory : we provide extensions of Cambrian semi-lattices into complete lattices (end of Chapter 4), we construct a new combinatorial model for Tamari and m-Tamari lattices (Chapter 5), and we finish with an application to tableaux combinatorics (Chapter 6)

No description available.

The importance of the Musgrave Province in continental reconstructions of Proterozoic Australia is only beginning to be appreciated. The Mesoproterozoic Musgrave Province sits in a geographically central location within Australia and is bounded by older and more isotopically evolved regions including the Gawler Craton of South Australia and Arunta Region of the Northern Territory. Understanding the crustal growth and deformation mechanisms involved in the formation of the Musgrave Province, and also the nature of the basement that separates these tectonic elements, allows for greater insight into defining the timing and processes responsible for the amalgamation of Proterozoic Australia. The ca. 1.60-1.54 Ga Musgravian Gneiss preserves geochemical and isotopic signatures related to ongoing arc-magmatism in an active margin between the North Australian and South Australian Cratons (NAC and SAC). Characteristic geochemical patterns of the Musgravian Gneiss include negative anomalies in Nb, Ti, and Y, and are accompanied by steep LREE patterns. Also characteristic of the Musgravian Gneiss is its juvenile Nd isotopic composition (ɛNd1.55 values from -1.2 to +0.9). The juvenile isotopic signature of the Musgravian Gneiss separates it from the bounding comparitively isotopically evolved terranes of the Arunta Region and Gawler Craton. The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti-bearing minerals and garnet. Circa 1.40 Ga metasedimentary rocks of the eastern Musgrave Province also record vital evidence for determining Australia.s location and fit within a global plate reconstruction context during the late Mesoproterozoic. U-Pb detrital zircon and Sm-Nd isotopic data from these metasedimentary rocks suggests a component of derivation from sources outside of the presently exposed Australian crust. Best fit matches come from rocks originating from eastern Laurentia. Detrital zircon ages range from Palaeoproterozoic to late Mesoproterozoic, constraining the maximum depositional age of the metasediments to approximately 1.40 Ga, similar to that of the Belt Supergroup in western Laurentia. The 1.49-1.36 Ga detrital zircons in the Musgrave metasediments are interpreted to have been derived from the voluminous A-type suites of Laurentia, as this time period represents a “magmatic gap” in Australia, with an extreme paucity of sources this age recognized. The metasedimentary rocks exhibit a range of Nd isotopic signatures, with ɛNd(1.4 Ga) values ranging from -5.1 to 0.9, inconsistent with complete derivation from Australian sources, which are more isotopically evolved. The isotopically juvenile ca. 1.60-1.54 Ga Musgravian Gneiss is also an excellent candidate for the source of the abundant ca. 1.6-1.54 Ga detrital zircons within the lower sequences of the Belt Supergroup. If these interpretations are correct, they support a palaeogeographic reconstruction involving proximity of Australia and Laurentia during the pre-Rodinia Mesoproterozoic. This also increases the prospectivity of the eastern Musgrave Province to host a metamorphised equivalent of the massive Pb-Zn-Ag Sullivan deposit. The geochemical and isotopic signatures recorded in mafic-ultramafic rocks can divulge important information regarding the state of the sub continental lithospheric mantle (SCLM). The voluminous cumulate mafic-ultramafic rocks of the ca. 1.08 Ga Giles Complex record geochemical and Nd-Sr isotopic compositions consistent with an enriched parental magma. Traverses across three layered intrusions, the Kalka, Ewarara, and Gosse Pile were geochemically and isotopically analysed. Whole rock samples display variably depleted to enriched LREE patterns when normalised to chondrite ((La/Sm)N = 0.43-4.72). Clinopyroxene separates display similar depleted to enriched LREE patterns ((La/Sm)N = 0.37-7.33) relative to a chondritic source. The cumulate rocks display isotopically evolved signatures (ɛNd ~-1.0 to .5.0 and ɛSr ~19.0 to 85.0). Using simple bulk mixing and AFC equations, the Nd-Sr data of the more radiogenic samples can be modelled by addition of ~10% average Musgrave crust to a primitive picritic source, without need for an enriched mantle signature. Shallow decompressional melting of an asthenospheric plume source beneath thinned Musgravian lithosphere is envisaged as a source for the parental picritic magma. A model involving early crustal contamination within feeder zones is favoured, and consequently explorers looking for Ni-Cu-Co sulphides should concentrate on locating these feeder zones. Few absolute age constraints exist for the timing of the intracratonic Petermann Orogeny of the Musgrave Province. The Petermann Orogeny is responsible for much of the lithospheric architecture we see today within the Musgrave Province, uplifting and exhuming large parts along crustal scale E-W trending fault/shear systems. Isotopic and geochemical analysis of a suite of stratigraphic units within the Neoproterozoic to Cambrian Officer Basin to the immediate south indicate the development of a foreland architecture at ca. 600 Ma. An excursion in ɛNd values towards increasingly less negative values at this time is interpreted as representing a large influx of Musgrave derived sediments. Understanding the nature of the basement separating the SAC from the NAC and WAC is vital in constructing models of the amalgamation of Proterozoic Australia. This region is poorly understood as it is overlain by the thick sedimentary cover of the Officer Basin. However, the Coompana Block is one place where basement is shallow enough to be intersected in drillcore. The previously geochronologically, geochemically, and isotopically uncharacterised granitic gneiss of the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. U-Pb LA-ICPMS dating of magmatic zircons provides an age of ca. 1.50 Ga, interpreted as the crystallisation age of the granite protolith. The samples have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. ɛNd values are high with respect to surrounding exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The tectonic environment into which the granite was emplaced is also unclear, however one possibility is emplacement within an extensional environment represented by interlayered basalts and arenaceous sediments of the Coompana Block. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the “Australian magmatic gap” of ca. 1.52-1.35 Ga, and is a possible source for detrital ca. 1.50 zircons found within sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1261003 / Thesis(PhD)-- University of Adelaide, School of Earth and Environmental Sciences, 2006

The importance of the Musgrave Province in continental reconstructions of Proterozoic Australia is only beginning to be appreciated. The Mesoproterozoic Musgrave Province sits in a geographically central location within Australia and is bounded by older and more isotopically evolved regions including the Gawler Craton of South Australia and Arunta Region of the Northern Territory. Understanding the crustal growth and deformation mechanisms involved in the formation of the Musgrave Province, and also the nature of the basement that separates these tectonic elements, allows for greater insight into defining the timing and processes responsible for the amalgamation of Proterozoic Australia. The ca. 1.60-1.54 Ga Musgravian Gneiss preserves geochemical and isotopic signatures related to ongoing arc-magmatism in an active margin between the North Australian and South Australian Cratons (NAC and SAC). Characteristic geochemical patterns of the Musgravian Gneiss include negative anomalies in Nb, Ti, and Y, and are accompanied by steep LREE patterns. Also characteristic of the Musgravian Gneiss is its juvenile Nd isotopic composition (ɛNd1.55 values from -1.2 to +0.9). The juvenile isotopic signature of the Musgravian Gneiss separates it from the bounding comparitively isotopically evolved terranes of the Arunta Region and Gawler Craton. The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti-bearing minerals and garnet. Circa 1.40 Ga metasedimentary rocks of the eastern Musgrave Province also record vital evidence for determining Australia.s location and fit within a global plate reconstruction context during the late Mesoproterozoic. U-Pb detrital zircon and Sm-Nd isotopic data from these metasedimentary rocks suggests a component of derivation from sources outside of the presently exposed Australian crust. Best fit matches come from rocks originating from eastern Laurentia. Detrital zircon ages range from Palaeoproterozoic to late Mesoproterozoic, constraining the maximum depositional age of the metasediments to approximately 1.40 Ga, similar to that of the Belt Supergroup in western Laurentia. The 1.49-1.36 Ga detrital zircons in the Musgrave metasediments are interpreted to have been derived from the voluminous A-type suites of Laurentia, as this time period represents a “magmatic gap” in Australia, with an extreme paucity of sources this age recognized. The metasedimentary rocks exhibit a range of Nd isotopic signatures, with ɛNd(1.4 Ga) values ranging from -5.1 to 0.9, inconsistent with complete derivation from Australian sources, which are more isotopically evolved. The isotopically juvenile ca. 1.60-1.54 Ga Musgravian Gneiss is also an excellent candidate for the source of the abundant ca. 1.6-1.54 Ga detrital zircons within the lower sequences of the Belt Supergroup. If these interpretations are correct, they support a palaeogeographic reconstruction involving proximity of Australia and Laurentia during the pre-Rodinia Mesoproterozoic. This also increases the prospectivity of the eastern Musgrave Province to host a metamorphised equivalent of the massive Pb-Zn-Ag Sullivan deposit. The geochemical and isotopic signatures recorded in mafic-ultramafic rocks can divulge important information regarding the state of the sub continental lithospheric mantle (SCLM). The voluminous cumulate mafic-ultramafic rocks of the ca. 1.08 Ga Giles Complex record geochemical and Nd-Sr isotopic compositions consistent with an enriched parental magma. Traverses across three layered intrusions, the Kalka, Ewarara, and Gosse Pile were geochemically and isotopically analysed. Whole rock samples display variably depleted to enriched LREE patterns when normalised to chondrite ((La/Sm)N = 0.43-4.72). Clinopyroxene separates display similar depleted to enriched LREE patterns ((La/Sm)N = 0.37-7.33) relative to a chondritic source. The cumulate rocks display isotopically evolved signatures (ɛNd ~-1.0 to .5.0 and ɛSr ~19.0 to 85.0). Using simple bulk mixing and AFC equations, the Nd-Sr data of the more radiogenic samples can be modelled by addition of ~10% average Musgrave crust to a primitive picritic source, without need for an enriched mantle signature. Shallow decompressional melting of an asthenospheric plume source beneath thinned Musgravian lithosphere is envisaged as a source for the parental picritic magma. A model involving early crustal contamination within feeder zones is favoured, and consequently explorers looking for Ni-Cu-Co sulphides should concentrate on locating these feeder zones. Few absolute age constraints exist for the timing of the intracratonic Petermann Orogeny of the Musgrave Province. The Petermann Orogeny is responsible for much of the lithospheric architecture we see today within the Musgrave Province, uplifting and exhuming large parts along crustal scale E-W trending fault/shear systems. Isotopic and geochemical analysis of a suite of stratigraphic units within the Neoproterozoic to Cambrian Officer Basin to the immediate south indicate the development of a foreland architecture at ca. 600 Ma. An excursion in ɛNd values towards increasingly less negative values at this time is interpreted as representing a large influx of Musgrave derived sediments. Understanding the nature of the basement separating the SAC from the NAC and WAC is vital in constructing models of the amalgamation of Proterozoic Australia. This region is poorly understood as it is overlain by the thick sedimentary cover of the Officer Basin. However, the Coompana Block is one place where basement is shallow enough to be intersected in drillcore. The previously geochronologically, geochemically, and isotopically uncharacterised granitic gneiss of the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. U-Pb LA-ICPMS dating of magmatic zircons provides an age of ca. 1.50 Ga, interpreted as the crystallisation age of the granite protolith. The samples have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. ɛNd values are high with respect to surrounding exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The tectonic environment into which the granite was emplaced is also unclear, however one possibility is emplacement within an extensional environment represented by interlayered basalts and arenaceous sediments of the Coompana Block. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the “Australian magmatic gap” of ca. 1.52-1.35 Ga, and is a possible source for detrital ca. 1.50 zircons found within sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1261003 / Thesis(PhD)-- University of Adelaide, School of Earth and Environmental Sciences, 2006

The importance of the Musgrave Province in continental reconstructions of Proterozoic Australia is only beginning to be appreciated. The Mesoproterozoic Musgrave Province sits in a geographically central location within Australia and is bounded by older and more isotopically evolved regions including the Gawler Craton of South Australia and Arunta Region of the Northern Territory. Understanding the crustal growth and deformation mechanisms involved in the formation of the Musgrave Province, and also the nature of the basement that separates these tectonic elements, allows for greater insight into defining the timing and processes responsible for the amalgamation of Proterozoic Australia. The ca. 1.60-1.54 Ga Musgravian Gneiss preserves geochemical and isotopic signatures related to ongoing arc-magmatism in an active margin between the North Australian and South Australian Cratons (NAC and SAC). Characteristic geochemical patterns of the Musgravian Gneiss include negative anomalies in Nb, Ti, and Y, and are accompanied by steep LREE patterns. Also characteristic of the Musgravian Gneiss is its juvenile Nd isotopic composition (ɛNd1.55 values from -1.2 to +0.9). The juvenile isotopic signature of the Musgravian Gneiss separates it from the bounding comparitively isotopically evolved terranes of the Arunta Region and Gawler Craton. The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti-bearing minerals and garnet. Circa 1.40 Ga metasedimentary rocks of the eastern Musgrave Province also record vital evidence for determining Australia.s location and fit within a global plate reconstruction context during the late Mesoproterozoic. U-Pb detrital zircon and Sm-Nd isotopic data from these metasedimentary rocks suggests a component of derivation from sources outside of the presently exposed Australian crust. Best fit matches come from rocks originating from eastern Laurentia. Detrital zircon ages range from Palaeoproterozoic to late Mesoproterozoic, constraining the maximum depositional age of the metasediments to approximately 1.40 Ga, similar to that of the Belt Supergroup in western Laurentia. The 1.49-1.36 Ga detrital zircons in the Musgrave metasediments are interpreted to have been derived from the voluminous A-type suites of Laurentia, as this time period represents a “magmatic gap” in Australia, with an extreme paucity of sources this age recognized. The metasedimentary rocks exhibit a range of Nd isotopic signatures, with ɛNd(1.4 Ga) values ranging from -5.1 to 0.9, inconsistent with complete derivation from Australian sources, which are more isotopically evolved. The isotopically juvenile ca. 1.60-1.54 Ga Musgravian Gneiss is also an excellent candidate for the source of the abundant ca. 1.6-1.54 Ga detrital zircons within the lower sequences of the Belt Supergroup. If these interpretations are correct, they support a palaeogeographic reconstruction involving proximity of Australia and Laurentia during the pre-Rodinia Mesoproterozoic. This also increases the prospectivity of the eastern Musgrave Province to host a metamorphised equivalent of the massive Pb-Zn-Ag Sullivan deposit. The geochemical and isotopic signatures recorded in mafic-ultramafic rocks can divulge important information regarding the state of the sub continental lithospheric mantle (SCLM). The voluminous cumulate mafic-ultramafic rocks of the ca. 1.08 Ga Giles Complex record geochemical and Nd-Sr isotopic compositions consistent with an enriched parental magma. Traverses across three layered intrusions, the Kalka, Ewarara, and Gosse Pile were geochemically and isotopically analysed. Whole rock samples display variably depleted to enriched LREE patterns when normalised to chondrite ((La/Sm)N = 0.43-4.72). Clinopyroxene separates display similar depleted to enriched LREE patterns ((La/Sm)N = 0.37-7.33) relative to a chondritic source. The cumulate rocks display isotopically evolved signatures (ɛNd ~-1.0 to .5.0 and ɛSr ~19.0 to 85.0). Using simple bulk mixing and AFC equations, the Nd-Sr data of the more radiogenic samples can be modelled by addition of ~10% average Musgrave crust to a primitive picritic source, without need for an enriched mantle signature. Shallow decompressional melting of an asthenospheric plume source beneath thinned Musgravian lithosphere is envisaged as a source for the parental picritic magma. A model involving early crustal contamination within feeder zones is favoured, and consequently explorers looking for Ni-Cu-Co sulphides should concentrate on locating these feeder zones. Few absolute age constraints exist for the timing of the intracratonic Petermann Orogeny of the Musgrave Province. The Petermann Orogeny is responsible for much of the lithospheric architecture we see today within the Musgrave Province, uplifting and exhuming large parts along crustal scale E-W trending fault/shear systems. Isotopic and geochemical analysis of a suite of stratigraphic units within the Neoproterozoic to Cambrian Officer Basin to the immediate south indicate the development of a foreland architecture at ca. 600 Ma. An excursion in ɛNd values towards increasingly less negative values at this time is interpreted as representing a large influx of Musgrave derived sediments. Understanding the nature of the basement separating the SAC from the NAC and WAC is vital in constructing models of the amalgamation of Proterozoic Australia. This region is poorly understood as it is overlain by the thick sedimentary cover of the Officer Basin. However, the Coompana Block is one place where basement is shallow enough to be intersected in drillcore. The previously geochronologically, geochemically, and isotopically uncharacterised granitic gneiss of the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. U-Pb LA-ICPMS dating of magmatic zircons provides an age of ca. 1.50 Ga, interpreted as the crystallisation age of the granite protolith. The samples have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. ɛNd values are high with respect to surrounding exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The tectonic environment into which the granite was emplaced is also unclear, however one possibility is emplacement within an extensional environment represented by interlayered basalts and arenaceous sediments of the Coompana Block. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the “Australian magmatic gap” of ca. 1.52-1.35 Ga, and is a possible source for detrital ca. 1.50 zircons found within sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1261003 / Thesis(PhD)-- University of Adelaide, School of Earth and Environmental Sciences, 2006

Made available in DSpace on 2015-02-24T19:48:36Z (GMT). No. of bitstreams: 1 RobertoGO_Capa_ate_pag82.pdf: 4449318 bytes, checksum: a8a67621781bd4f76c4e2c0361bcc6a2 (MD5) Previous issue date: 2008-07-27 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The Borborema Province (BP) is a geologic domain located in Northeastern Brazil. The BP is limited at the south by the S?o Francisco craton, at the west by the Parna?ba basin, and both at the north and east by coastal sedimentary basins. Nonetheless the BP surface geology is well known, several key aspects of its evolution are still open, notably: i)its tectonic compartmentalization established after the Brasiliano orogenesis, ii) the architecture of its cretaceous continental margin, iii) the elastic properties of its lithosphere, and iv) the causes of magmatism and uplifting which occurred in the Cenozoic. In this thesis, a regional coverage of geophysical data (elevation, gravity, magnetic, geoid height, and surface wave global tomography) were integrated with surface geologic information aiming to attain a better understanding of the above questions. In the Riacho do Pontal belt and in the western sector of the Sergipano belt, the neoproterozoic suture of the collision of the Sul domain of the BP with the Sanfranciscana plate (SFP) is correlated with an expressive dipolar gravity anomaly. The positive lobule of this anomaly is due to the BP lower continental crust uplifting whilst the negative lobule is due to the supracrustal nappes overthrusting the SFP. In the eastern sector of the Sergipano belt, this dipolar gravity anomaly does not exist. However the suture still can be identified at the southern sector of the Maranc? complex arc, alongside of the Porto da Folha shear zone, where the SFP N-S geophysical alignments are truncated. The boundary associated to the collision of the Cear? domain of the BP with the West African craton is also correlated with a dipolar gravity anomaly. The positive lobule of this anomaly coincides with the Sobral-Pedro II shear zone whilst the negative lobule is associated with the Santa Quit?ria magmatic arc. Judging by their geophysical signatures, the major BP internal boundaries are: i)the western sector of the Pernambuco shear zone and the eastern continuation of this shear zone as the Congo shear zone, ii) the Patos shear zone, and iii) the Jaguaribe shear zone and its southwestern continuation as the Tatajuba shear zone. These boundaries divide the BP in five tectonic domains in the geophysical criteria: Sul, Transversal, Rio Grande do Norte, Cear?, and M?dio Corea?. The Sul domain is characterized by geophysical signatures associated with the BP and SFP collision. The fact that Congo shear zone is now proposed as part of the Transversal domain boundary implies an important change in the original definition of this domain. The Rio Grande do Norte domain presents a highly magnetized crust resulted from the superposition of precambrian and phanerozoic events. The Cear? domain is divided by the Senador Pompeu shear zone in two subdomains: the eastern one corresponds to the Or?s-Jaguaribe belt and the western one to the Cear?-Central subdomain. The latter subdomain exhibits a positive ENE-W SW gravity anomaly which was associated to a crustal discontinuity. This discontinuity would have acted as a rampart against to the N-S Brasiliano orogenic nappes. The M?dio Corea? domain also presents a dipolar gravity anomaly. Its positive lobule is due to granulitic rocks whereas the negative one is caused by supracrustal rocks. The boundary between M?dio Corea? and Cear? domains can be traced below the Parna?ba basin sediments by its geophysical signature. The joint analysis of free air anomalies, free air admittances, and effective elastic thickness estimates (Te) revealed that the Brazilian East and Equatorial continental margins have quite different elastic properties. In the first one 10 km < Te < 20 km whereas in the second one Te ? 10 km. The weakness of the Equatorial margin lithosphere was caused by the cenozoic magmatism. The BP continental margin presents segmentations; some of them have inheritance from precambrian structures and domains. The segmentations conform markedly with some sedimentary basin features which are below described from south to north. The limit between Sergipe and Alagoas subbasins coincides with the suture between BP and SFP. Te estimates indicates concordantly that in Sergipe subbasin Te is around 20 km while Alagoas subbasin has Te around 10 km, thus revealing that the lithosphere in the Sergipe subbasin has a greater rigidity than the lithosphere in the Alagoas subbasin. Additionally inside the crust beneath Sergipe subbasin occurs a very dense body (underplating or crustal heritage?) which is not present in the crust beneath Alagoas subbasin. The continental margin of the Pernambuco basin (15 < Te < 25 km) presents a very distinct free air edge effect displaying two anomalies. This fact indicates the existence in the Pernambuco plateau of a relatively thick crust. In the Para?ba basin the free air edge effect is quite uniform, Te ? 15 km, and the lower crust is abnormally dense probably due to its alteration by a magmatic underplating in the Cenozoic. The Potiguar basin segmentation in three parts was corroborated by the Te estimates: in the Potiguar rift Te ? 5 km, in the Aracati platform Te ? 25 km, and in the Touros platform Te ? 10 km. The observed weakness of the lithosphere in the Potiguar rift segment is due to the high heat flux while the relatively high strength of the lithosphere in the Touros platform may be due to the existence of an archaean crust. The Cear? basin, in the region of Munda? and Icara? subbasins, presents a quite uniform free air edge effect and Te ranges from 10 to 15 km. The analysis of the Bouguer admittance revealed that isostasy in BP can be explained with an isostatic model where combined surface and buried loadings are present. The estimated ratio of the buried loading relative to the surface loading is equal to 15. In addition, the lower crust in BP is abnormally dense. These affirmations are particularly adequate to the northern portion of BP where adherence of the observed data to the isostatic model is quite good. Using the same above described isostatic model to calculate the coherence function, it was obtained that a single Te estimate for the entire BP must be lower than 60 km; in addition, the BP north portion has Te around 20 km. Using the conventional elastic flexural model to isostasy, an inversion of crust thickness was performed. It was identified two regions in BP where the crust is thickened: one below the Borborema plateau (associated to an uplifting in the Cenozoic) and the other one in the Cear? domain beneath the Santa Quit?ria magmatic arc (a residue associated to the Brasiliano orogenesis). On the other hand, along the Cariri-Potiguar trend, the crust is thinned due to an aborted rifting in the Cretaceous. Based on the interpretation of free air anomalies, it was inferred the existence of a large magmatism in the oceanic crust surrounding the BP, in contrast with the incipient magmatism in the continent as shown by surface geology. In BP a quite important positive geoid anomaly exists. This anomaly is spatially correlated with the Borborema plateau and the Maca?-Queimadas volcanic lineament. The integrated interpretation of geoid height anomaly data, global shear velocity model, and geologic data allow to propose that and Edge Driven Convection (EDC) may have caused the Cenozoic magmatism. The EDC is an instability that presumably occurs at the boundary between thick stable lithosphere and oceanic thin lithosphere. In the BP lithosphere, the EDC mechanism would have dragged the cold lithospheric mantle into the hot asthenospheric mantle thus causing a positive density contrast that would have generated the main component of the geoid height anomaly. In addition, the compatibility of the gravity data with the isostatic model, where combined surface and buried loadings are present, together with the temporal correlation between the Cenozoic magmatism and the Borborema plateau uplifting allow to propose that this uplifting would have been caused by the buoyancy effect of a crustal root generated by a magmatic underplating in the Cenozoic / A Prov?ncia Borborema (PB) ? um dom?nio geol?gico-estrutural localizado no Nordeste do Brasil, limitado a sul pelo Cr?ton do S?o Francisco, a oeste pela Bacia do Parna?ba e a norte e leste pelas bacias costeiras. Embora bastante estudada por geologia de superf?cie, na PB ainda est?o em aberto aspectos importantes de sua evolu??o, notadamente: i) a sua compartimentagem tect?nica ap?s a Orog?nese Brasiliana, ii) a arquitetura da margem continental implantada no Cret?ceo, iii) as propriedades el?sticas de sua litosfera, e iv) as causas do magmatismo e do soerguimento no Cenoz?ico. Esta Tese empregou dados geof?sicos de cobertura regional (eleva??o, gravimetria, magnetometria, altura geoidal e tomografia), para aportar informa??es de geologia profunda aos problemas acima colocados. A sutura gerada pela colis?o neoproteroz?ica entre o Dom?nio Sul da PB e a Placa Sanfranciscana (PSF) ? marcada, na Faixa Riacho do Pontal e no oeste da Faixa Sergipana, por uma forte anomalia gravim?trica dipolar, cujo pico positivo corresponde ao al?amento da crosta inferior da PB e o negativo corresponde ?s nappes de supracrustais empurradas sobre a PSF. Na regi?o leste da Faixa Sergipana n?o h? assinaturas gravim?tricas que indiquem cavalgamento e flexura de placas, mas a interpreta??o de truncamentos de assinaturas geof?sicas de dire??o N-S da PSF permite localizar a sutura na margem sul do complexo de arco Maranc?, ao longo da Z. C. Porto da Folha. Por sua vez, o limite colisional do Dom?nio Cear? da PB com o Cr?ton Oeste-Africano, ao longo da Z. C. Sobral-Pedro II, ? tamb?m marcado por uma anomalia gravim?trica dipolar, cujo pico positivo coincide com a Z. C. Sobral-Pedro II, e o negativo coincide com o arco magm?tico de Santa Quit?ria. A julgar pela express?o geof?sica, os limites internos mais importantes da PB s?o: i) a Z. C. Pernambuco Oeste e sua continua??o na Z. C. Congo, ii) a Z. C. Patos e iii) a Z. C. Jaguaribe e sua continua??o na Z. C. Tatajuba. Estes limites dividem a PB em cinco grandes dom?nios geof?sicos-tect?nicos: Sul (ou Externo), Transversal, Rio Grande do Norte, Cear? e M?dio Corea?. O Dom?nio Sul ? marcado por assinaturas geof?sicas associadas ? colis?o da PB com a PSF. O Dom?nio Transversal teve a sua concep??o original de limites modificada porque a parte leste do seu limite sul foi associada com a Z. C. Congo. O Dom?nio Rio Grande do Norte apresenta a crosta mais magn?tica da PB, com superposi??o de fontes pr?-cambrianas e faneroz?icas. No Dom?nio Cear?, a Z. C. Senador Pompeu ? o divisor de dois subdom?nios: o leste corresponde ? Faixa Or?s-Jaguaribe e o oeste corresponde ao Cear?-Central, onde ocorre uma assinatura gravim?trica interpretada como uma descontinuidade crustal de dire??o ENE-WSW, que funcionou como um anteparo para as nappes brasilanas, com sentido de deslocamento para sul. O Dom?nio M?dio Corea? apresenta uma anomalia gravim?trica dipolar, cujo pico positivo est? associado com rochas granul?ticas, e o negativo com rochas supracrustais. A assinatura geof?sica do seu limite com o Dom?nio Cear? ? evidente, apesar dos sedimentos da Bacia do Parna?ba. A an?lise conjunta da anomalia ar-livre, admit?ncia ar-livre e estimativas da espessura el?stica efetiva (Te) evidenciou que as margens Leste e Equatorial possuem propriedades el?sticas bastante diferentes: enquanto a primeira tem Te entre 10 e 20 km, a segunda tem Te em torno ou inferior a 10 km. Essa diferen?a ? devida ao enfraquecimento da litosfera da Margem Equatorial produzida pelo magmatismo cenoz?ico. A margem continental da PB apresenta segmenta??es que incorporaram heran?as das estruturas e dos dom?nios pr?-cambrianos, que se correlacionam com os limites conhecidos das bacias. Descrevendo de sul para norte, o limite da separa??o da Bacia Sergipe - Alagoas em duas sub-bacias coincide com a sutura entre o Dom?nio Sul da PB e a PSF; as estimativas de Te indicam, concordantemente, que a Sub-bacia Sergipe (Te ? 20 km) se instalou em uma litosfera mais resistente do que a da Sub-bacia Alagoas (Te ? 10 km). Adicionalmente, no interior da crosta da Sub-bacia Sergipe ocorre um grande corpo denso (underplating ou heran?a crustal?) que n?o continua na Sub-bacia Alagoas. A margem da Bacia de Pernambuco (15 < Te < 25 km) apresenta caracter?sticas diferentes das outras bacias costeiras, porque no Plat? de Pernambuco h? duas anomalias do efeito de borda , o que indica a exist?ncia no plat? de uma crosta continental afinada, contudo ainda relativamente espessa. A Bacia da Para?ba se apresenta bastante uniforme, com Te em torno de 15 km, e possui uma crosta inferior relativamente densa, que foi interpretada como uma modifica??o por underplating magm?tico relacionado com o magmatismo cenoz?ico. A segmenta??o da Bacia Potiguar em tr?s partes ? corroborada pelas estimativas de Te: Rifte Potiguar (Te ? 5 km), Plataforma de Aracati (Te ? 25 km) e Plataforma de Touros (Te ? 10 km). A fragilidade da litosfera na regi?o do Rifte Potiguar est? associada com fluxo t?rmico atual alto, e a resist?ncia relativamente maior da Plataforma de Touros pode ser devida a uma crosta arqueana. A margem da Bacia do Cear?, no trecho das sub-bacias Munda? e Icara?, possui anomalia ar-livre uniforme, com Te entre 10 e 15 km. A an?lise da admit?ncia Bouguer revelou que a condi??o isost?tica da PB ? compat?vel com um modelo em que ocorrem carregamentos combinados na superf?cie e na base da crosta, com a carga da base 15 vezes maior que a do topo. Em adi??o, a PB possui uma crosta inferior anormalmente densa. Estas afirma??es s?o especialmente adequadas para a parte norte da PB porque a? a ader?ncia dos dados observados ao modelo ? maior. Para o mesmo modelo isost?tico e usando a fun??o coer?ncia, estimou-se que a Te da PB deve ser inferior a 60 km, embora sua por??o norte tenha Te de apenas 20 km. A invers?o de espessura de crosta, usando o modelo isost?tico com carga apenas na superf?cie, indicou que existem na PB duas regi?es de espessamento: uma abaixo do Planalto da Borborema (de origem cenoz?ica) e a outra no Dom?nio Cear?, sob o arco magm?tico de Santa Quit?ria (vestigial do Pr?-cambriano). Por outro lado, ocorre um afinamento ao longo do Trend Cariri-Potiguar, que representa o registro no interior do continente de um rifteamento cret?ceo abortado. A interpreta??o das anomalias ar-livre de fontes oce?nicas levou ? proposi??o de que ocorreu um volumoso magmatismo na ?rea oce?nica adjacente ? PB, ao contr?rio da ?rea continental, como indicam as informa??es de geologia de superf?cie. A PB apresenta uma expressiva anomalia positiva de ge?ide, com correla??o espacial com o Planalto da Borborema e o Alinhamento Macau-Queimadas. A integra??o de dados de tomografia de ondas superficiais e de anomalias residuais de ge?ide permitiu interpretar que uma convec??o em pequena escala (Edge Driven Convection-EDC), gerada na interface entre a raiz da litosfera continental fria e o manto quente da ?rea oce?nica, pode ter sido a causa do magmatismo cenoz?ico. O mecanismo de EDC teria causado o arrasto do manto litosf?rico continental frio para dentro do manto astenosf?rico quente, ocasionando assim contraste positivo de densidade, que seria uma componente importante da origem da anomalia de ge?ide. A compatibilidade dos dados gravim?tricos da PB com o modelo isost?tico que combina carregamentos no topo e na base da crosta, e a correla??o temporal entre o magmatismo cenoz?ico e o soerguimento do planalto, permite propor que o soerguimento deste ocorreu por causa do empuxo provocado pela raiz da crosta, produzida por um underplating magm?tico no Cenoz?ico

The Arabian–Nubian Shield (ANS) represents a major site of juvenile Neoproterozoic crustal addition on Earth and documents Neoproterozoic tectonics bracketed by two supercontinent cycles, namely the fragmentation of Rodinia and the amalgamation of Gondwana. There is general consensus that the ANS formed by juvenile magmatic arc accretion and subsequent shield–wide post–tectonic magmatism. However, detailed understanding about the timing of events and the nature of magma sources in parts of the shield are lacking. To date, there are no isotopic data from the Paleozoic sedimentary sequences of the ANS, except those from the northern part. New zircon U–Pb, δ18O and whole–rock Nd isotopes are presented for plutonic rocks from the eastern Ethiopia, Yemen and southernmost Arabian Shield in Saudi Arabia. This thesis also presents the first combined in situ zircon U–Pb–O–Hf isotope data on the Cambrian–Ordovician sandstones of the Arabian Shield. The results are used to elucidate the crustal evolution of these parts of the ANS and to evaluate terrane correlations. Specifically, the nature of crustal growth, i.e., relative proportions of juvenile magmatic additions vs. crustal reworking, nature of the magma source and mechanism of crust formation (plume material vs. subduction zone enrichment) and understanding the provenance of the Cambrian–Ordovician sandstone sequences were important research questions addressed. The results from Paper I suggest that the eastern Ethiopian Precambrian basement is dominated by reworking of pre-Neoproterozoic supracrustal material unlike contemporaneous rocks in the remaining parts of Ethiopia— indicating the presence of two distinct lithospheric blocks of contrasting isotopic compositions in Ethiopia. Metamorphic age distributions suggest that the eastern Ethiopian block was amalgamated with the juvenile Western Ethiopian Shield during ca. 580–550 Ma. Importantly, the suture between them may represent the northern continuation of a major suture identified further south in Africa along which Gondwana amalgamated. Similarly, the Abas terrane in Yemen (Paper II) is dominated by reworking of pre–Neoproterozoic crust and shows age and isotopic compositions that are inconsistent with the Afif terrane of Saudi Arabia, precluding correlation between the two regions. The trace element systematics of plutonic rocks from the southernmost Arabian Shield (paper III) point to enrichment due to subduction component, bear no evidence of a plume component, and are consistent with the adakite-like chemistry of some of the subduction–related plutonic samples. This reinforces the notion that the shield grew through juvenile magmatic arc additions. The combined zircon U–Pb–O–Hf data of the Cambrian–Ordovician sandstones (Paper IV) indicate their derivation from both the adjacent juvenile ANS and the more southerly crustal blocks that are dominated by reworking of pre–Neoproterozoic crust. The remarkable similarity in age spectra and homogeneity of Cambrian sandstones deposited across the northern margin of Gondwana point to continental–scale sediment mixing and dispersal regulated by the supercontinent cycle. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

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