In this article, we document a detailed analytical characterisation of zircon M127, a homogeneous 12.7 carat gemstone from Ratnapura, Sri Lanka. Zircon M127 has TIMS-determined mean U-Pb radiogenic isotopic ratios of 0.084743 +/- 0.000027 for Pb-206/U-238 and 0.67676 +/- 0.00023 for Pb-207/U-235 (weighted means, 2s uncertainties). Its Pb-206/U-238 age of 524.36 +/- 0.16 Ma (95% confidence uncertainty) is concordant within the uncertainties of decay constants. The delta O-18 value (determined by laser fluorination) is 8.26 +/- 0.06 parts per thousand VSMOW (2s), and the mean Hf-176/Hf-177 ratio (determined by solution ICP-MS) is 0.282396 +/- 0.000004 (2s). The SIMS-determined delta Li-7 value is -0.6 +/- 0.9 parts per thousand (2s), with a mean mass fraction of 1.0 +/- 0.1 mu g g(-1) Li (2s). Zircon M127 contains similar to 923 mu g g(-1) U. The moderate degree of radiation damage corresponds well with the time-integrated self-irradiation dose of 1.82 x 10(18) alpha events per gram. This observation, and the (U-Th)/He age of 426 +/- 7 Ma (2s), which is typical of unheated Sri Lankan zircon, enable us to exclude any thermal treatment. Zircon M127 is proposed as a reference material for the determination of zircon U-Pb ages by means of SIMS in combination with hafnium and stable isotope (oxygen and potentially also lithium) determination.

Orientador: Ticiano José Saraiva dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-18T11:36:53Z (GMT). No. of bitstreams: 1 Ancelmi_MatheusFernando_M.pdf: 13152442 bytes, checksum: 9332eaa1da5b9097c8fe1da5caf15557 (MD5) Previous issue date: 2011 / Resumo: Na porção NW da Província Borborema, Domínio Ceará Central, a existência de retroeclogitos posicionados a oeste do Arco Magmático de Santa Quitéria são importantes registros geológicos para caracterização geotectônica, principalmente pelo fato destes tipos de rochas comumente marcarem zonas de subducção oceânica e colisão de blocos continentais. Com mapeamento geológico, em escala 1:10.000, e estudo petrográfico foram caracterizados dezenas de lentes de retroeclogitos numa faixa N-S ao longo de mais de 16 km. Tais rochas estão encaixadas em gnaisses orto- e paraderivados, e raramente associadas a rochas cálcio-silicáticas. O retrometamorfismo ocorreu de forma heterogênea nestes corpos metamáficos, sendo mais intenso nas bordas devido sua interação com fluídos contidos nos gnaisses encaixantes. Assim, são sugeridas as seguintes reações de retrometamorfismo: 1º) Grt + Cpx + Qtz + H2O ? Pl + Amp ou Grt + Cpx + Rt + Qtz + H2O ? Amp + Ilm + Pl; 2°) Omp ? Di + Pl; 3º) Grt + Di + Pl + H2O ? Amp; 4°) Grt + Pl + Qtz + H2O ? Grt2 + Pl (An) + Amp. Cabendo ressaltar a incipiente formação de Fe(Mg)- clorita e actinolita que são minerais de fácies xisto verde. Já os gnaisses encaixantes estão migmatizados e apresentam a paragênese de sillimanita (depois de cianita) + granada + biotita + álcali-feldspato + rutilo + quartzo ± plagioclásio, típica de fácies granulito de alta pressão. Estas associações compõem a Faixa Eclogítica de Forquilha, que estruturalmente está em contato tectônico de empurrão com faixas dominantemente constituídas por metapelitos e pequenas porções de metacalcários e metamáficas com diferentes graus metamórficos pertencentes ao Grupo Ceará. Estudos anteriores mostraram que a idade do protólito destes retroeclogitos é de ca. 1,57 Ga, com dois eventos de metamorfismo entre 650 a 630 Ma e 620 a 600 Ma. Para avaliar a relação destes retroeclogitos e suas encaixantes, foi realizado um estudo de proveniência de sedimentos, baseado em U-Pb (LA-ICP-MS) em zircões detríticos e isótopos de Nd, que identificou que esta bacia recebeu sedimentos continentais exclusivamente de fontes paleoproterozóicas com picos entre 2,0 e 2,2 Ga. A idade máxima de sedimentação é estimada em ca. 1850 Ma e os embasamentos paleoproterozóicos do Domínio Ceará Central e do Domínio Rio Grande do Norte são as prováveis fontes de sedimentos em uma margem passiva ou uma bacia intracratônica. Adicionalmente, estudo de proveniência foi realizado nas rochas do Grupo Ceará, e neste caso os zircões detríticos mostraram um espectro de idades desde o Paleoproterozóico até o Neoproterozóico. Zircões mais jovens que ca. 650 Ma possuem característica de grãos metamórficos por conta da baixa razão Th/U e textura do tipo ovóide e soccer ball. A idade máxima de deposição foi estimada pelo zircão que forneceu a idade de 659 ± 4 Ma (206Pb/238U, Th/U = 0,56), indicando que esta bacia teve um curto período de existência (ca. 15 Ma), sendo possivelmente parte de um ambiente de margem ativa. Estes dados e as relações de campo mostram que a Faixa Eclogítica de Forquilha foi exumada e colocada tectonicamente com unidades de cobertura de uma margem ativa / Abstract: In the NW Borborema Province, Ceará Central Domain, retrograded eclogites occur in the west side of the Santa Quitéria Magmatic Arc. These high-pressure metamafic rocks are important geological features, due to the fact that this type of rock is typical of subduction and collisional zones. Based on 1:10.000 geological map and petrography of the lithological units established in this work, it is possible to character that the Forquilha retrograded eclogites occur along more than 16 km in a N-S trend belt. These metamafic rocks are enclosed in migmatized ortho- and paragnaisses, and rarely in calc-silicate rocks. The retrogressive metamorphism occurred heterogeneously on these metamafic bodies, being more intensive at the outer parts and obliterating higher mineral paragenesis, possibly due to a greater interaction with fluids of the host rocks. Thus, it is suggested the following retrometamophic reactions: 1º) Grt + Cpx + Qtz + H2O ? Pl + Amp or Grt + Cpx + Rt + Qtz + H2O ? Amp + Ilm + Pl; 2°) Omp ? Di + Pl; 3º) Grt + Di + Pl + H2O ? Amp; 4°) Grt + Pl + Qtz + H2O ? Grt2 + Pl (An) + Amp, besides the incipient formation of Fe(Mg)-chlorite and actinolite that are typical of greenschist facies conditions. The paragneisses that enclose these rocks are migmatized and present the mineral paragenesis of sillimanite (after kyanite) + garnet + biotite + alkali-feldspar + rutile + quartz ± plagioclase, which is typical of high-pressure granulite facies conditions. Together, these rocks establish the Forquilha Eclogite Zone, which is in tectonic contact with rocks of Ceará Group that are dominantly constitute by metapelites and minor portions of metacalcareous and metamafic rocks metamorphosed in different levels. Previous geochronological studies on these retrograded eclogites show a ca. 1.57 Ga protolith age, and two metamorphic ages ranging from 650 to 630 Ma and 620 to 600 Ma. A sediment provenance study, based on LA-ICPMS detrital zircon U-Pb ages and whole rock Nd isotopic data, were performed on the metasedimentary rocks that host these retrograded eclogites, in order to determine the maximum depositional age and the possible sources of sediment material. The zircon age distribution, Nd isotopic rations and TDM model ages demonstrated that these rocks exclusively received sediments from Paleoproterozoic sources older than ca. 1.85 Ga, with peaks at 2.0 to 2.2 Ga. The Paleoproterozoic basement of Rio Grande do Norte Domain and Ceará Central Domain are estimated as the main possible sources of sediments on a passive margin or intracratonic basin. It also was analyzed detrital zircons of non-migmatized metasedimentary rocks of Ceará Group, which are in tectonic contact with FEZ. In this case, the samples showed an age distribution from Paleoproterozoic to Neoproterozoic. Zircons grains younger than 650 Ma present low Th/U ratio, and ovoid and soccer ball textures typical of metamorphic grains. Because of this, the maximum deposition age of this sequence is constrained by the youngest zircon grain dated at 659 ± 4 Ma (206Pb/238U age, Th/U = 0.56), what indicates that this sedimentary basin had a short life (ca. 15 Ma) and possible have been part of an active margin setting. These data and structural field observations suggest that the FEZ was exhumed and tectonically juxtaposed with cover units of a active margin setting / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

The tectonic evolution of northern Ellesmere Island is dominated by the accretion of the Pearya Terrane and the progressive reworking of materials from the Pearya Terrane and the northern Caledonides. Geochronology from a suite of seven Succession I orthogneiss samples defines a range of earliest Neoproterozoic ages from 962 ± 6 Ma to 974 ± 8 Ma. Geochemistry of both zircon and whole rock samples reveal a complex magmatic history tapping multiple sources. The rocks include both I and S type granitoids, with silica contents ranging from 62% to 73%. Trace element geochemistry reveals LILE enrichment decoupled from low to depleted HFSE values, suggestive of an origin above a subduction zone. Isotope geochemistry supports input from juvenile and evolved materials, with εNd(i) values between -1 and -4.6, and a similar range for εHf from zircon. The northern elements of the Caledonian Orogen preserve a record of magmatism in the c. 985 Ma to 920 Ma range. These ages are also observed in orthogneiss units of the south central Brooks Range and Farewell terrane, Alaska. The Pearya Terrane orthogneiss units and those currently dispersed in Alaska are interpreted to have originated near or on the eastern margin of Greenland and record post-Rodinia assembly subduction outboard of the supercontinent. Succession II (Trettin, 1987) of the Pearya Terrane represents variably metamorphosed metasedimentary rocks of Proterozoic to early Paleozoic age. These units are structurally juxtaposed with Succession I orthogneiss and Paleozoic sedimentary units of the Pearya Terrane. Detrital zircon age spectra from seven samples of Neoproterozoic meta-sedimentary rocks reveal three groups defined by observed dominant age peaks and youngest observed age populations. Group I includes three quartzite samples and contains numerous c. 1100 Ma to 1800 Ma peaks, with the youngest population at c. 1050 Ma. Two samples of immature meta-sandstone form Group II, defined by a dominant c. 970 Ma age peak. Two samples from the diamictite unit below the Deutchers Glacier thrusts form Group III, with a similar pattern of c. 1000 Ma to 1800 Ma age peaks to Group I; however, this group includes a small population of c. 600 Ma to 700 Ma grains as well. The ubiquitous Mesoproterozoic ages reflect a Grenvillian-Sveconorwegian provenance. These data are consistent with detrital zircon datasets from other North Atlantic-Arctic Caledonide terranes, reinforcing stratigraphic links between the Pearya Terrane and the northern Caledonides. The utility of the Pearya Terrane dataset is multiplied by probable links to Circum-Arctic and Cordilleran terranes, many of which contain similar populations of Mesoproterozic-aged detrital zircon. U/Pb ages and Hf isotopic data from detrital zircon suites sampled from Ordovician to Carboniferous sedimentary rock of the Pearya Terrane and northern Ellesmere Island record define the background for terranes translating along the northeastern Laurentian margin in the Paleozoic. Ordovician to Silurian clastic sediments deposited on the Pearya Terrane record pre terrane accretion provenance dominated by recycling of the metaigneous and metasedimentary Proterozoic basement as well as an Ordovician arc source. The provenance of Late Devonian sediments deposited during the Ellesmerian Orogen is dominated by similar recycled materials, with new sources derived from Paleoproterozoic domains of the Canadian-Greenland shield and documented late Devonian granitoids emplaced the Canadian Arctic Islands and Arctic Alaska. The basal Sverdrup Basin records increasing proportions of Paleoprtoerozoic and Archean aged grains relative to Mesoproterozoic ages, suggestive of increased contributions from the Laurentian craton and no little detritus exotic to Laurentia. Detrital zircon age spectra from Devonian to Carboniferous sediments in the northern Cordilleran clastic wedge and western Canadian Arctic Islands contain abundant exotic zircon likely derived from the Caledonian and Timanian Orogens. This variance of sediment provenance indicates that the eastern Canadian Arctic Island were isolated from non-Laurentian or Caledonian detritus, and that sources of the exotic Timanian zircon reconstruct farther west along the margin.

The St. Cyr klippe hosts well preserved to variably retrogressed eclogites found as sub-meter to hundreds of meter scale lenses within quartzofeldspathic schists in the Yukon-Tanana terrane, Canadian Cordillera. The St. Cyr area consists of structurally imbricated, polydeformed, and polymetamorphosed units of continental arc and oceanic crust. The eclogite-bearing quartzofeldspathic schists form a 30 by 6 kilometer thick, northwest-striking, coherent package. The schists consist of metasediments and felsic intrusives that are intercalated on the tens of meter scale. The presence of phengite and Permian age zircon crystallized under eclogite facies metamorphic conditions indicates that the eclogite was metamorphosed in situ with its quartzofeldspathic host. I investigated the metamorphic evolution of the eclogite-facies rocks in the St. Cyr klippe using isochemical phase equilibrium thermodynamic (pseudosection) modeling. I constructed P-T pseudosections in the system Na2O-K2O-CaO-FeO-O2-MnO-MgO-Al2O3-SiO2-TiO2-H2O for the bulk-rock composition of an eclogite and a host metatonalite. In combination with petrology and mineral compositions, St. Cyr eclogites followed a five-stage clockwise P-T path. Peak pressure conditions for the eclogites and metatonalites reached up to 3.2 GPa, well within the coesite stability field, indicating the eclogites reached ultrahigh-pressure conditions. Decompression during exhumation occurred with a corresponding temperature increase. SHRIMP-RG zircon dating shows that the protolith of the eclogites formed within the Yukon-Tanana terrane during early, continental arc activity, between 364 and 380 Ma, while the metatonalite protolith formed at approximately 334 Ma, during the Little Salmon Cycle of the Klinkit phase of Yukon-Tanana arc activity. Both the eclogites and the metatonalites were then subducted to mantle depths and metamorphosed to ultrahigh-pressure conditions during the late Permian, between 266 and 271 Ma. The results of our study suggest portions of the Yukon-Tanana terrane were subducted to high-pressure and ultrahigh-pressure conditions. This is the first report of ultrahigh-pressure metamorphism in the accreted terranes of the North American Cordillera. Petrological, geochemical, geochronological, and structural relationships link the eclogites at St. Cyr to other eclogite localities in Yukon, indicating the high-pressure assemblages form a larger lithotectonic unit within the Yukon-Tanana terrane.

Migmatites are a common rock type in the Adirondack Mountains, NY. We analyzed a single sample of biotite-garnet-sillimanite paragneiss with foliation parallel leucosome along Route 22 south of Whitehall, NY in order to determine the timing of melting using both in-situ monazite and zircon U/Pb geochronology from the restite and leucosome layers of the same rock. Monazite was analyzed via in-situ EMPA on the Ultrachron microprobe at the University of Massachusetts. Zircon was analyzed via LA-ICP-MS (in-situ and mounted mineral separates) at the LaserChron Center. Monazite analyses from the restite yielded six compositionally distinct populations with dates of 1178 ± 16, 1139 ± 4, 1064 ± 6, 1049 ± 4, 1030 ± 5, and 1004 ± 10 Ma. Yttrium and heavy REEs decrease in monazite in two steps: one dramatic drop from ca. 1150 to 1065 Ma and another between ca. 1065 and 1050, interpreted to reflect two periods of garnet growth and melting. Analyses from the restite zircon separate yielded a significant single peak near 1050 Ma. These zircon grains exhibit fir-tree sector zoning texture which is interpreted to indicate crystallization from melt. Monazite from leucosome yielded a unimodal population at ca. 1050 Ma, however, backscatter images document alteration of monazite to apatite on the edges of the grains, and abundant uranothorite inclusions. Leucosome zircon analyses yielded a ca. 1150 Ma population from cores and a 1050 Ma population from rims. Cathodoluminescence imaging reveals that the zircon rims have textures indicative of fluid alteration. The data are consistent with these rocks undergoing two periods of melting. The first event at ca. 1150 Ma may have involved a non-garnet producing melting reaction, such as muscovite dehydration-melting. The second event at 1065 Ma involved significant garnet growth, interpreted to represent biotite dehydration-melting. Subsequently, the rocks underwent hydrothermal alteration at 1050 Ma. Monazite grains with dates at 1030 ± 5 and 1004 ± 10 Ma have higher yttrium concentrations suggesting garnet breakdown and monazite growth during decompression and retrograde metamorphism. A combination of monazite and zircon dating techniques from each compositional layer is necessary to constrain leucosome-restite relationships and to accurately interpret the timing of melting from migmatites that have experienced multiple phases of melting.

This Dissertation combines the investigation of the sedimentological impacts of the Deepwater Horizon (DwH) blowout event in the deep-sea benthos, with the refinement and advancement of methods and approaches for high-resolution investigations of events preserved in sedimentary records. An approach that combined, rapid collection of cores, a continued annual time series collection of cores, and high-resolution sampling and analyses, in particular short-lived Radioisotopes (SLRad), enabled the temporal resolution required to detect the sedimentary response to the short-duration DwH event, and evaluate post-event sedimentation patterns at a comparable time scale (months). The collection of 179 sediment cores from 80 sites between the fall of 2010 and 2016 included four sites that were utilized as an annual time-series collection to define the sedimentary response to the DwH blowout event and how the sedimentary system evolved/recovered post-event. High-resolution (2mm) sub-sampling was utilized to maximize the temporal resolution of analyses and age control using SLRad. The rapid collection of cores to define the immediate benthic impact(s), as well as the use of time-sensitive indicators of the event that may degrade over time, as well as indicators for very short time scale (months) sedimentation, such as 234Thxs. 234Thxs inventories and mass accumulation rates (MAR’s) were one of the most diagnostic characteristics of the sedimentary response. The DwH blowout event led to a Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) event that caused a depositional pulse to the seafloor. This was defined by increased sedimentation rates and the shutdown of bioturbation as indicated by 234Thxs inventories and MAR’s. The annual collection of sediment cores as a time-series allowed for continued high-resolution analyses and use of 234Thxs to determine post-event sedimentation rates and baselines on monthly time scales for direct comparison to the depositional pulse. Within ~one year sedimentation rates decreased and within three years site specific return of bioturbation occurred and sedimentation rates on monthly scale (234Thxs) stabilized. Also, within ~three years the sedimentary signature of the depositional pulse became undetectable with respect to sediment texture and composition possibly due to dilution of this indicator by mixing/bioturbation and/or compaction of the event layer. Without the use of high-resolution sampling and geochronological tools such as 234Thxs the depositional pulse would not have been detected in the sedimentary system. The continued use of these high-resolution methods allowed for further defining the magnitude of the sedimentary response to the DwH event as well as provide baseline sedimentation patterns at a monthly time scale. The annual time series defines the post-event evolution of the sedimentary system as well as the assessment of the post-depositional alterations that influence the integration and preservation of such sedimentation events in the sedimentary record. This includes the potential for re-mobilization of event sediments, potential re-exposure of ecosystems to contaminated sediments and redistribution of event sediments. Alternatively, burial and alteration of the sedimentary signature over time influences the preservation potential of sedimentation events such as DwH, with decreasing ability to detect events due to bioturbation, degradation of signature and compaction. The refinement of methodology and approaches, in particular short-lived radioisotope (SLRad) geochronology, allowed for the high-resolution determination of the sedimentary impacts of the DwH blowout event. In turn, the opportunity to investigate the DwH event in real time provided the opportunity to advance high-resolution methodologies in an applied fashion. Continued refinement of high-resolution approaches and methods, in particular geochronologies, will allow for the detection of short-duration and subtle sedimentary events in real time as well as in the sedimentary record. Through the application of such approaches and methods to real events, these methods can be further refined and assessed for their utility and limitations.

<div> <div> <div> <p>The combination of field-based studies and numerical modeling provides a robust tool for evaluating geologic and geodynamic processes along a convergent margin. Complex and persistent tectonic activity and a novel suite of geophysical observations make the southern Alaskan convergent margin a key region to evaluate these processes through both basin analysis studies and geodynamic modeling. This conceptual approach is utilized to explore the active driving forces of surface deformation throughout southcentral Alaska, as well as the geologic record of regional Cenozoic tectonic processes. </p> <p>New sedimentologic, chronostratigraphic, and provenance data from strata that crop out within the central Alaska Range document a previously unrecognized stage of Eocene – early Miocene strike-slip basin development along the northern side of the central Denali fault system. This stage was followed by Miocene-Pliocene deformation and exhumation of the central Alaska Range, and basin development and northward sediment transport into the Tanana foreland basin. This portion of the study provides insight into Cenozoic tectonics and basin development in the central Alaska Range. </p> <p>How transpressional tectonics are manifest in the modern-day, in combination with shallow subduction processes, are not well understood for the southern Alaskan convergent margin. Simulations of the 3-D deformation of this region allow for investigation of the complex relationship between these tectonic processes and surface deformation. Results from this study display the far-field affect that strong plate coupling along the shallowly subducting Yakutat slab has on the surface deformation of southcentral Alaska. Our models also show that partitioning of this convergence is observed along the Denali fault system. Additionally, our results indicate the subducting slab is segmented into separate Pacific, Yakutat and Wrangell slab segments. This variation in slab structure exerts control on the upper plate response to shallow subduction.</p> </div> </div> </div>

The North Caribou Terrane forms the core of Superior Province and records a protracted history of crustal growth and modification. At the centre of the North Caribou Terrane, lies the North Caribou greenstone belt, which is surrounded by granitoids of diverse compositions and ages. This study reports whole-rock geochemistry, zircon and titanite geochronology, and hornblende geobarometry on these plutonic rocks. Although zircons as old as 3132 ± 7 Ma were found, the main magmatic pulse occurred between 2880 and 2830 Ma, and geobarometry indicates tectonic thickening during this period. This was followed by widespread hydrothermal alteration and limited magmatism from 2760 to 2680 Ma, and shallow, brittle-ductile intrusions at circa 2630 Ma. From 2730 to 2630 Ma, intrusions were emplaced at increasingly shallow crustal levels. All of the rocks, except for the youngest pegmatitic intrusions, show similar patterns in major and trace elements, with a general trend toward more evolved compositions through time. These patterns indicate that the granitoids record mostly reworking of early intrusions, which is also consistent with patterns observed in the geochronology.

No description available.

The Paşalar fauna includes 56 mammalian species of European. Asian, African and North American origin. Evidence provided on the stage-of-evolution of the primates Sivapithecus darwini and cf. Kenyapithecus, the rodent Turkomys pasalarensis, insectivores, carnivores, rhinos, suids and ruminants suggests that Paşalar is correlative with the Late Langhian marine stage and European Mammal Neogene Zone 6., circa 15 Ma (million years ago). A review of the Paşalar fauna's biogeographic history suggests that it was aggregated by a succession of pulsed intercontinental geographic extensions tied to global sea-level lowering events during the earlier half of the Miocene.