Sample records for accessory minerals zircon

  1. Accessory mineral records of tectonic environments? (Invited)

    NASA Astrophysics Data System (ADS)

    Storey, C.; Marschall, H. R.; Enea, F.; Taylor, J.; Jennings, E. S.

    2010-12-01

    Accessory mineral research continues to gather momentum as we seek to unleash their full potential. It is now widely recognised that robust accessory minerals, such as zircon, rutile, titanite, allanite and monazite, are archives of important trace elements that can help deduce metamorphic reaction history in metapelites, metabasites and other rock types. Moreover, they are important carriers of certain trace elements and govern or influence the products of partial melting and of fluid-rock interaction (e.g. magmas and mineralisation) in settings like subduction zones and hydrothermal systems. Perhaps most importantly, they can often be dated using the U-Th-Pb system. More recently, radiogenic (Lu-Hf, Sm-Nd, Rb-Sr) and stable (O) isotope systems have been applied and have further pushed the utility of accessory mineral research. In this talk I will discuss some of these advances towards one particular aim: the use of detrital accessory minerals for fingerprinting tectonic environments. This is a particularly laudable aim in Precambrian rocks, for which the preservation potential of orogenic belts and fossil subduction zones and their diagnostic metamorphic rocks is low. The implication is that our understanding of plate tectonics, particularly in the Archaean, is biased by the preserved in-tact rock record. An analogy is that Jack Hills zircons record evidence of Earth’s crust some 400 Ma before the preserved rock record begins. I will focus on some recent advances and new data from rutile and also the mineral inclusion record within zircon, which shows great promise for petrologic interpretation.

  2. Gold in Accessory Zircon (the Kozhim Massif, Subpolar Urals)

    NASA Astrophysics Data System (ADS)

    Denisova, Yuliya; Pystin, Aleksandr

    2017-12-01

    The crystals of zircon due to their resistance to external impact of various processes can reveal information about the environment of their formation and the inclusions observed of them. Zircon contains different mineral inclusions: biotite, plagioclase, quartz, apatite, etc. However, there is no information about gold inclusions in the zircons from granites of the Sudpolar Urals. The study results of the inclusions of gold in accessory zircon of the Kozhim granitic massif are presented in this paper. The studied mineral is a dark-brown translucent short-prismatic crystal containing the inclusion of gold and the allocations of quartz. According to studies, the inclusion of gold formed during the growth of zircon and it is the gold covered with a thin film of oxide gold. It was confirmed that the crystallization of the studied zircon occurred at a temperature of 800°C and above on the stage of formation of granites of Kozhim massif. The assumption is made about the additional temperature in the course of which was caused by decreasing of temperature up to 700° C and below during postmagmatic stage.

  3. Hunting for eruption ages in accessory minerals

    NASA Astrophysics Data System (ADS)

    Vazquez, J. A.

    2012-12-01

    A primary goal in geochronology is to provide precise and accurate ages for tephras that serve as chronostratigraphic markers for constraining the timing and rates of volcanism, sedimentation, climate change, and catastrophic events in Earth history. Zircon remains the most versatile accessory mineral for dating silicic tephras due to its common preservation in distal pyroclastic deposits, as well as the robustness of its U-Pb and U-series systems even after host materials have been hydrothermally altered or weathered. Countless studies document that zircon may be complexly zoned in age due to inheritance, contamination, recycling of antecrysts, protracted crystallization in long-lived magma reservoirs, or any combination of these. Other accessory minerals such as allanite or chevkinite can retain similar records of protracted crystallization. If the goal is to date the durations of magmatic crystallization, differentiation, and/or magma residence, then these protracted chronologies within and between accessory minerals are a blessing. However, if the goal is to date the timing of eruption with high precision, i.e., absolute ages with millennial-scale uncertainties, then this age zoning is a curse. Observations from ion microprobe 238U-230Th dating of Pleistocene zircon and allanite provide insight into the record of near-eruption crystallization in accessory minerals and serve as a guide for high-precision whole-crystal dating. Although imprecise relative to conventional techniques, ion probe analysis allows high-spatial resolution 238U-230Th dating that can document multi-millennial age distributions at the crystal scale. Analysis of unpolished rims and continuous depth profiling of zircon from small and large volume eruptions (e.g., Coso, Mono Craters, Yellowstone) reveals that the final several micrometers of crystallization often yield ages that are indistinguishable from associated eruption ages from the 40Ar/39Ar or (U-Th)/He methods. Using this approach, we

  4. Accessory minerals and subduction zone metasomatism: a geochemical comparison of two mélanges (Washington and California, U.S.A.)

    USGS Publications Warehouse

    Sorensen, Sorena S.; Grossman, Jeffrey N.

    1993-01-01

    Data from the Gee Point and Catalina mélanges suggest that the accessory minerals titanite, rutile, apatite, zircon and REE-rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction-related fluid-rock interaction. Mobilization of incompatible elements, and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid-rich metamorphic environments in subduction zones.

  5. Geochemical contrasts between Late Triassic ore-bearing and barren intrusions in the Weibao Cu-Pb-Zn deposit, East Kunlun Mountains, NW China: constraints from accessory minerals (zircon and apatite)

    NASA Astrophysics Data System (ADS)

    Zhong, Shihua; Feng, Chengyou; Seltmann, Reimar; Li, Daxin; Dai, Zhihui

    2017-12-01

    The Weibao copper-lead-zinc skarn deposit is located in the northern East Kunlun terrane, NW China. Igneous intrusions in this deposit consist of barren diorite porphyry (U-Pb zircon age of 232.0 ± 2.0 Ma) and ore-bearing quartz diorite and pyroxene diorite (U-Pb zircon ages of 223.3 ± 1.5 and 224.6 ± 2.9 Ma, respectively). Whole-rock major and trace element and accessory mineral (zircon and apatite) composition from these intrusions are studied to examine the different geochemical characteristics of ore-bearing and barren intrusions. Compared to the barren diorite porphyry, the ore-bearing intrusions have higher Ce4+/Ce3+ ratios of zircon and lower Mn contents of apatite, indicating higher oxidation state. Besides, apatite from the ore-bearing intrusions shows higher Cl contents and lower F/Cl ratios. These characteristics collectively suggest the higher productivity of ore-bearing quartz diorite and pyroxene diorite. When compared with ore-bearing intrusions from global porphyry Cu deposits, those from Cu-Pb-Zn skarn deposits display lower Ce4+/Ce3+ and EuN/EuN* ratios of zircon and lower Cl and higher F/Cl ratios of apatite. We conclude that these differences reflect a general geochemical feature, and that zircon and apatite composition is a sensitive tool to infer economic potential of magmas and the resulting mineralization types in intrusion-related exploration targets.

  6. Identification and significance of accessory minerals from a bituminous coal

    USGS Publications Warehouse

    Finkelman, R.B.; Stanton, R.W.

    1978-01-01

    A scanning electron microscope (SEM) has been used to study the in situ accessory minerals in polished blocks and pellets of petrographically analysed samples of the Waynesburg coal (hvb). Individual grains from the low-temperature ash (LTA) of the same coal were also studied. The visual resolution of the SEM permitted the detection of submicron mineral grains, which could then be analysed by the attached energy-dispersive system. Emphasis was placed on the highly reflective grains in the carbominerite bands. Among the most abundant accessory minerals observed were rutile, zircon, and rare-earth-bearing minerals. Small (1-5 ??m) particles of what may be authigenic iron-rich chromite and a nickel silicate form rims on quartz grains. The SEM also permits the observation of grain morphology and mineral intergrowths. These data are useful in determining authigenicity and diagenic alteration. Substances in density splits of LTA include authigenic, detrital, extraterrestrial magnetite, tourmaline, and evaporite (?) minerals, and a fluorine-bearing amphibole. This analytical approach allows the determination of specific sites for many of the trace elements in coals. In the Waynesburg coal, most of the chromium is in the iron-chromium rims, the fluorine is in the amphibole, and the rare-earth elements are in rare-earth-bearing minerals. The ability to relate trace-element data to specific minerals will aid in predicting the behaviour of elements in coal during combustion, liquefaction, gasification, weathering, and leaching processes. This ability also permits insight into the degree of mobility of these elements in coal and provides clues to sedimentological and diagenetic conditions. ?? 1978.

  7. Late-stage magmatic to deuteric/metasomatic accessory minerals from the Cerro Boggiani agpaitic complex (Alto Paraguay Alkaline Province)

    NASA Astrophysics Data System (ADS)

    Comin-Chiaramonti, Piero; Renzulli, Alberto; Ridolfi, Filippo; Enrich, Gaston E. R.; Gomes, Celso B.; De Min, Angelo; Azzone, Rogério G.; Ruberti, Excelso

    2016-11-01

    This work describes rare accessory minerals in volcanic and subvolcanic silica-undersaturated peralkaline and agpaitic rocks from the Permo-Triassic Cerro Boggiani complex (Eastern Paraguay) in the Alto Paraguay Alkaline Province. These accessory phases consist of various minerals including Th-U oxides/silicates, Nb-oxide, REE-Sr-Ba bearing carbonates-fluorcarbonates-phosphates-silicates and Zr-Na rich silicates. They form a late-stage magmatic to deuteric/metasomatic assemblage in agpaitic nepheline syenites and phonolite dykes/lava flows made of sodalite, analcime, albite, fluorite, calcite, ilmenite-pyrophanite, titanite and zircon. It is inferred that carbonatitic fluids rich in F, Na and REE percolated into the subvolcanic system and metasomatically interacted with the Cerro Boggiani peralkaline and agpaitic silicate melts at the thermal boundary layers of the magma chamber, during and shortly after their late-stage magmatic crystallization and hydrothermal deuteric alteration.

  8. Contrasting accessory mineral behavior in minimum-temperature melts: Empirical constraints from the Himalayan metamorphic core

    NASA Astrophysics Data System (ADS)

    Cottle, John M.; Larson, Kyle P.; Yakymchuk, Chris

    2018-07-01

    Medium-grained leucogranite in the Tama Kosi region of the Nepalese Himalayan Metamorphic Core yields a relatively narrow range of monazite 208Pb/232Th dates with a dominant population at 21.0 Ma inferred to represent crystallization of an early plutonic phase. In contrast, the pegmatitic portion of the same intrusive complex, that cross-cuts the medium-grained leucogranite, contains zircon, monazite and xenotime that each display near-identical age spectra, recording semi-continuous (re-)crystallization from 27.5 Ma to 21.0 Ma, followed by a 2 m.y. hiatus then further (re-)crystallization between 19.4 and 18.6 Ma. The "gap" in pegmatite dates corresponds well to the crystallization age of the older leucogranite, whereas the end of accessory phase growth in the pegmatite coincides with the onset of regional-scale cooling. Detailed textural, trace element and thermochronologic data indicate that the range of zircon, monazite and xenotime dates recorded in the pegmatite reflect inherited components that underwent semi-continuous (re-)crystallization during metamorphism and/or anatexis in the source region(s), whereas dates younger than the hiatus indicate accessory phase recrystallization, related to both fluid influx and a concomitant increase in temperature. In contrast, the lack of an inherited component(s) in the medium-grained leucogranite phase is inferred to be a result of complete dissolution during partial melting. A model is proposed in which influx of heat and H2O-rich fluids associated with early leucogranite emplacement temporarily delayed zircon and monazite and xenotime crystallization, respectively. These data highlight the importance of measuring spatially resolved dates, trace elements and textural patterns from multiple accessory minerals combined with model constraints to better understand the often-complex crystallization history of anatectic melts in collisional orogens.

  9. Magmatic origin and fluid alteration versus inheritance: Complex history of accessory minerals from I-type granites from northern Victoria Land (Antarctica)

    NASA Astrophysics Data System (ADS)

    Menneken, M.; John, T.; Läufer, A.; Berndt, J.; Henjes-Kunst, F.; Giese, J.

    2016-12-01

    When reconstructing the formation and evolution of Earths earliest crust, one is still heavily reliant on information that can be gathered from detrital zircon grains, which have been proven to be a useful tool concerning the various isotopic, chemical, and mineralogical features that can be utilized within. However, detailed investigations have shown that some of these tracers might be prone to alteration and will not necessarily reflect conditions during formation [1, 2]. In this study, zircons and their host rocks from the Granite Harbour Intrusives (GHI) of northern Victoria Land, Antarctica, have been investigated with respect to regional evolution of continental crust as well as the reliability of zircon as a recorder of crustal formation. Here we present U-Pb, δ18O, trace element and inclusion data of zircons from Cambro-Ordovician granitoids, as well as geochemical analyses of accessory apatites. Our initial results show that even in I-type granitoids with a presumably simple formation history, U-Pb-age data and related isotopic, chemical, or mineralogical features have to be evaluated carefully in order to constrain the timing of magmatic events, inheritance or fluid alteration events. They do, for example, incorporate a large portion of recycled material, which is clearly reflected by a strong component of inherited U-Pb-zircon ages, but can also be inferred by comparing main- and trace-element compositions of apatite inclusions in zircon with accessory apatites. Apatite inclusions from all investigated samples for example, are clearly higher in F concentration, than their accessory counterparts. However, not all zircon grains record the youngest event, emphasizing that not only alteration might be a key factor to consider when evaluating zircon characteristics with respect to their host rock, but also, the timing and preservation of predating features. [1] Rasmussen et al. (2011) Metamorphic replacement of mineral inclusions in detrital zircon from Jack

  10. Accessory Mineral Records of Early Earth Crust-Mantle Systematics: an Example From West Greenland

    NASA Astrophysics Data System (ADS)

    Storey, C. D.; Hawkesworth, C. J.

    2008-12-01

    Conditions for the formation and the nature of Earth's early crust are enigmatic due to poor preservation. Before c.4 Ga the only archives are detrital minerals eroded from earlier crust, such as the Jack Hills zircons in western Australia, or extinct isotope systematics. Zircons are particularly powerful since they retain precise records of their ages of crystallisation, and the Lu-Hf radiogenic isotope and O stable isotope systematics of the reservoir from which they crystallised. In principle, this allows insight into the nature of the crust, the mantle reservoir from which the melt was extracted and any reworked material incorporated into that melt. We have used in situ methods to measure U-Pb, O and Lu-Hf within single zircon crystals from tonalitic gneisses from West Greenland in the vicinity of the Isua Supracrustal Belt. They have little disturbed ages of c.3.8 Ga, mantle-like O isotope signatures and Lu-Hf isotope signatures that lie on the CHUR evolution line at 3.8 Ga. These samples have previously been subjected to Pb isotope feldspar and 142Nd whole rock analysis and have helped constrain models in which early differentiation of a proto-crust must have occurred. The CHUR-like Lu-Hf signature, along with mantle-like O signature from these zircons suggests juvenile melt production at 3.8 Ga from undifferentiated mantle, yet the other isotope systems preclude this possibility. Alternatively, this is further strong evidence for a heterogeneous mantle in the early Earth. Whilst zircons afford insight into the nature of the early crust and mantle, it is through the Sm-Nd system that the mantle has traditionally been viewed. Titanite often contains several thousand ppm Nd, making it amenable to precise analysis, and is a common accessory phase. It has a reasonably high closure temperature for Pb and O, and it can retain cores with older ages and distinct REE chemistry. It is often the main accessory phase alongside zircon, and it is the main carrier of Nd

  11. Trace element geochemistry of zircons from mineralizing and non-mineralizing igneous rocks related to gold ores at Yanacocha, Peru

    NASA Astrophysics Data System (ADS)

    Koleszar, A. M.; Dilles, J. H.; Kent, A. J.; Wooden, J. L.

    2012-12-01

    Zircons record important details about the evolution of magmatic systems, are relatively insensitive to alteration, and have been used to investigate the geochemistry, temperature, and oxidation state of volcanic and plutonic system. We examine zircons that span 6-7 m.y. of calc-alkaline volcanic activity in the Yanacocha district of northern Peru, where dacitic intrusions are associated with high-sulfidation gold deposits. The 14.5-8.4 Ma Yanacocha Volcanics include cogenetic lavas and pyroclastic rocks and are underlain by the andesites and dacites of the Calipuy Group, the oldest Cenozoic rocks in the region. We present data for magmatic zircons from the Cerro Fraile dacitic pyroclastics (15.5-15.1 Ma) of the Calipuy Group, and multiple eruptive units within the younger Yanacocha Volcanics: the Atazaico Andesite (14.5-13.3 Ma), the Quilish Dacite (~14-12 Ma), the Azufre Andesite (12.1-11.6 Ma), the San Jose Ignimbrite (11.5-11.2 Ma), and the Coriwachay Dacite (11.1-8.4 Ma). Epithermal high sulfidation (alunite-bearing) gold deposits are associated with the dacite intrusions of the Coriwachay and Quilish Dacites. Zircons from the non-mineralizing rocks typically have lower Hf concentrations and record Ti-in-zircon temperatures that are ~100°C hotter than zircons from the mineralizing intrusions. Temperatures recorded by zircons from the mineralizing intrusions are remarkably similar to those of the underlying Cerro Fraile dacite pyroclastics, but the zircons discussed here generally record SHRIMP-RG 206Pb/238U ages within error of previously published Ar-Ar eruption ages (eliminating antecrystic or xenocrystic origins). These observations suggest that zircons in the mineralizing intrusions form after greater extents of crystallization (and thus record elevated Hf concentrations and lower temperatures) than do zircons in the non-mineralized deposits. Unlike zircons from mineralized units associated with the porphyry Cu(Mo) deposits in Yerington, Nevada, which

  12. Crustal Zircons from the Podiform Chromitites in Luobusa Ophiolite, Tibet

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.; Komiya, T.; Maruyama, S.

    2004-12-01

    For the past decade, diamonds and unusual mineral asemblages were reported in podiform chromitites of the Luobusa ophiolite, southern Tibet, China (Bai 1993, Bai 2000, Yan 2001) by heavy mineral separation. These include (1) native elements, (2) alloys, (3) carbide, (4) platinium group elements (PGE) and arsenides, (5) silicates (6) oxide, (7) carbonates, (8) minerals with unusual compositons. Despite many questions as to these minerals above still remain open, these mineral inclusions would provide us the important infomation on the formation of the podiform chromitites. In this study, over 100 zircons were discovered by heavy mineral separation of podiform chromitite in Luobusa ophiolite. The discovery of accessory zircons in chromitites allowed us to date the formation of the chromitite and history of tectonic evolutions. Here we report the U-Pb age and mineral inclusions of zircons and discuss with unusually old age zircons. 20 zircon grains in chromitites from No. 1 site were analyzed. Zircons from the chromitites in Luobusa ophiolite are usually euhedral-subhedral and some are rounded. Cathodoluminescence images of these zircons indicate that some zircons have clear oscillatory zoning, whereas other zircons show apparent homogeneous overgrowth. U-Pb dating of these zircons by LA-ICP-MS yielded two different ages. One group has relatively younger age, 107-534Ma, which plots nearly on a concordia line. Another group has older age 1460-1822Ma, which plots off the concordia line. There is insignificant difference of apparent ages within a single zircon grain. For example, a zircon has 1650 Ma in the core, whereas does 1654 Ma in the rim. We identified several mineral inclusions, quartz, feldspar, mica, apatite, within both yonger and older zircons using laser-Raman spectrometry and EPMA. No high-pressure minerals or mantle minerals were identified. This means that these unusually old zircons were formed in low-pressure crustal emvironment. Where did the zircons

  13. Crystallization of accessory phases in magmas by local saturation adjacent to phenocrysts

    USGS Publications Warehouse

    Bacon, C.R.

    1989-01-01

    Accessory minerals commonly occur attached to or included in the major crystalline phases of felsic and some intermediate igneous rocks. Apatite is particularly common as inclusions, but Fe-Ti oxides, pyrrhotite, zircon, monazite, chevkinite and xenotime are also known from silicic rocks. Accessories may nucleate near the host crystal/ liquid interface as a result of local saturation owing to formation of a differentiated chemical boundary layer in which accessory mineral solubility would be lower than in the surrounding liquid. Differentiation of this boundary layer would be greatest adjacent to ferromagnesian phenocrysts, especially Fe-Ti oxides; it is with oxides that accessories are most commonly associated in rocks. A boundary layer may develop if the crystal grows more rapidly than diffusion can transport incorporated and rejected elements to and from the phenocryst. Diffusion must dominate over convection as a mode of mass transfer near the advancing crystal/liquid interface in order for a boundary layer to exist. Accumulation of essential structural constituent elements of accessory minerals owing to their slow diffusion in evolved silicate melt also may force local saturation, but this is not a process that applies to all cases. Local saturation is an attractive mechanism for enhancing fractionation during crystallization differentiation. If accessory minerals attached to or included in phenocrysts formed because of local saturation, their host phenocrysts must have grown rapidly when accessories nucleated in comparison to lifetimes of magma reservoirs. Some inconsistencies remain in a local saturation origin for accessory phases that cannot be evaluated without additional information. ?? 1989.

  14. Progress integrating ID-TIMS U-Pb geochronology with accessory mineral geochemistry: towards better accuracy and higher precision time

    NASA Astrophysics Data System (ADS)

    Schoene, B.; Samperton, K. M.; Crowley, J. L.; Cottle, J. M.

    2012-12-01

    It is increasingly common that hand samples of plutonic and volcanic rocks contain zircon with dates that span between zero and >100 ka. This recognition comes from the increased application of U-series geochronology on young volcanic rocks and the increased precision to better than 0.1% on single zircons by the U-Pb ID-TIMS method. It has thus become more difficult to interpret such complicated datasets in terms of ashbed eruption or magma emplacement, which are critical constraints for geochronologic applications ranging from biotic evolution and the stratigraphic record to magmatic and metamorphic processes in orogenic belts. It is important, therefore, to develop methods that aid in interpreting which minerals, if any, date the targeted process. One promising tactic is to better integrate accessory mineral geochemistry with high-precision ID-TIMS U-Pb geochronology. These dual constraints can 1) identify cogenetic populations of minerals, and 2) record magmatic or metamorphic fluid evolution through time. Goal (1) has been widely sought with in situ geochronology and geochemical analysis but is limited by low-precision dates. Recent work has attempted to bridge this gap by retrieving the typically discarded elution from ion exchange chemistry that precedes ID-TIMS U-Pb geochronology and analyzing it by ICP-MS (U-Pb TIMS-TEA). The result integrates geochemistry and high-precision geochronology from the exact same volume of material. The limitation of this method is the relatively coarse spatial resolution compared to in situ techniques, and thus averages potentially complicated trace element profiles through single minerals or mineral fragments. In continued work, we test the effect of this on zircon by beginning with CL imaging to reveal internal zonation and growth histories. This is followed by in situ LA-ICPMS trace element transects of imaged grains to reveal internal geochemical zonation. The same grains are then removed from grain-mount, fragmented, and

  15. Elemental Analysis of Zircon by High Mass Resolution USGS-Stanford SHRIMP-RG: Measuring and Evaluating Ti-in-zircon Temperatures and Compositional Characteristics

    NASA Astrophysics Data System (ADS)

    Wooden, J. L.; Mazdab, F. K.; Claiborne, L. L.; Miller, C. F.; Barth, A. P.

    2006-12-01

    High mass resolution of SHRIMP-RG permits measurement of a large set of trace elements for zircon, including 48Ti, Sc, and Nb (requiring better than 9,000 MR) and Be, B, F, P, 49Ti, V, Y, all the REE, Hf, Th, and U (Mazdab and Wooden 2006). A 15-20 micron spot allows analysis of numerous discrete CL zones from single zircons with minimal contributions from unknown material below the exposed surface. Data from suites of zircons from more than 20 individual granitoid samples suggest several general observations: (1) Temperatures calculated by Ti-in-zircon (Watson et al 2006) are entirely compatible with petrologic constraints; uncertainty in a(TiO2) introduces uncertainty in calculated T, but for reasonable values between 0.5 and 0.8 T's consistently fall between 650 and 900 C, mostly in the lower half of the range; (2) T can vary by 150-200 C within suites of zircons from individual samples and even in single zircons, where zonation may be normal (high to low, core to rim), reverse (low to high) or fluctuating; (3) Hf concentrations increase with decreasing T because of Zr/Hf fractionation between zircon and melt (Claiborne et al in press); (4) Many elements and element ratios show a co-variation with T and Hf concentration e.g., Th/U and MREE/HREE decrease with increasing Hf and decreasing T. Hf concentrations can continue to increase after a minimum T is reached, indicating continuing zircon growth from remaining (near eutectic?) melt. Yb/Gd (steepness of the HREE pattern) is an excellent monitor of fractionation, particularly at lower T (below 750 C) where the ratio increases rapidly. This trend may result from co-fractionation of accessory minerals and/or be driven by the thermodynamics of crystal growth, and/or may involve other factors and processes as yet poorly understood. Magmatic zircons commonly have a negative Eu anomaly of about 0.5 or lower which may change little or become more pronounced with falling T; anomalies probably reflect feldspar

  16. Contrasting Granite Metallogeny through the Zircon Record: A Case Study from Myanmar.

    PubMed

    Gardiner, Nicholas J; Hawkesworth, Chris J; Robb, Laurence J; Whitehouse, Martin J; Roberts, Nick M W; Kirkland, Christopher L; Evans, Noreen J

    2017-04-07

    Granitoid-hosted mineral deposits are major global sources of a number of economically important metals. The fundamental controls on magma metal fertility are tectonic setting, the nature of source rocks, and magma differentiation. A clearer understanding of these petrogenetic processes has been forged through the accessory mineral zircon, which has considerable potential in metallogenic studies. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset from the paired Cu-Au (copper) and Sn-W (tin) magmatic belts in Myanmar. Copper arc zircons have juvenile εHf (+7.6 to +11.5) and mantle-like δ 18 O (5.2-5.5‰), whereas tin belt zircons have low εHf (-7 to -13) and heavier δ 18 O (6.2-7.7‰). Variations in zircon Hf and U/Yb reaffirm that tin belt magmas contain greater crustal contributions than copper arc rocks. Links between whole-rock Rb/Sr and zircon Eu/Eu* highlight that the latter can monitor magma fractionation in these systems. Zircon Ce/Ce* and Eu/Eu* are sensitive to redox and fractionation respectively, and here are used to evaluate zircon sensitivity to the metallogenic affinity of their host rock. Critical contents of Sn in granitic magmas, which may be required for the development of economic tin deposits, are marked by zircon Eu/Eu* values of ca. ≤0.08.

  17. Tracking hydrothermal alteration and mineralization in rock-forming and accessory minerals from the Lyon Mountain Granite and related iron oxide apatite (IOA) ores from the Adirondack Mountains, New York State

    NASA Astrophysics Data System (ADS)

    Buchanan, A.; Hanchar, J. M.; Steele-MacInnis, M. J.; Crowley, J. L.; Valley, P. M.; Fisher, C. M.; Fedo, C.; Piccoli, P. M.; Fournelle, J.

    2012-12-01

    The Lyon Mountain granite (LMG) is located in the northeastern Adirondack Mountains in New York State and hosts several low-titanium iron oxide apatite (IOA) ore deposits. The ores are predominately hosted by perthite bearing granite, which has been extensively altered to albite and microcline granite by Na and K metasomatism. This alteration results in several distinct groups of rocks that are dominated by either K or Na addition and a group composed of mixed Na and K addition. The different groups of altered perthite also lie on a trend suggestive of addition of Fe to each, consistent with a secondary mineralization origin. Previous work showed that the host rocks of the IOA ores have zircon with ~1150 Ma cores and 1060-1050 Ma rims and whole grains. This study aims to further constrain the timing of LMG emplacement, subsequent hydrothermal alteration, and Fe mineralization through geochemical analysis of the major, minor, and accessory phases and geochronology of accessory phases. SIMS analyses of zircon from several of the IOA ores reveal at least two periods of growth after LMG magmatism, at 1039 +/- 4.4 Ma and 1016 +/- 7 Ma to 1000 +/- 9 Ma. In situ EMPA and LA-ICPMS trace element analyses of the zircon rims and cores reveal that in two samples the zircon rims are enriched in rare earth elements (REE) compared to their cores, potentially pointing to a hydrothermal origin. Apatite has unusually high REE and Y concentrations (some total REE2O3 > 20 wt. % oxide and up to 8 wt. % oxide Y2O3), as does titanite, which allowed for the in situ analysis of Sm-Nd in apatite and titanite by LA-MC-ICP-MS. Initial Nd isotopic composition of both ore and host rock apatite and host rock titanite are consistent with published Adirondack initial Nd whole rock data, suggesting a local source for REE in these ores. EMPA and LA-ICPMS trace-element analyses of the major rock-forming minerals indicate that the feldspar have undergone Na-metasomatism and are depleted in REEs

  18. Laser-Assisted Atom Probe Tomography of Deformed Minerals: A Zircon Case Study.

    PubMed

    La Fontaine, Alexandre; Piazolo, Sandra; Trimby, Patrick; Yang, Limei; Cairney, Julie M

    2017-04-01

    The application of atom probe tomography to the study of minerals is a rapidly growing area. Picosecond-pulsed, ultraviolet laser (UV-355 nm) assisted atom probe tomography has been used to analyze trace element mobility within dislocations and low-angle boundaries in plastically deformed specimens of the nonconductive mineral zircon (ZrSiO4), a key material to date the earth's geological events. Here we discuss important experimental aspects inherent in the atom probe tomography investigation of this important mineral, providing insights into the challenges in atom probe tomography characterization of minerals as a whole. We studied the influence of atom probe tomography analysis parameters on features of the mass spectra, such as the thermal tail, as well as the overall data quality. Three zircon samples with different uranium and lead content were analyzed, and particular attention was paid to ion identification in the mass spectra and detection limits of the key trace elements, lead and uranium. We also discuss the correlative use of electron backscattered diffraction in a scanning electron microscope to map the deformation in the zircon grains, and the combined use of transmission Kikuchi diffraction and focused ion beam sample preparation to assist preparation of the final atom probe tip.

  19. Integrated Laser Ablation U/Pb and (U-Th)/He Dating of Detrital Accessory Minerals from the Naryani River, Central Nepal

    NASA Astrophysics Data System (ADS)

    Horne, A.; Hodges, K. V.; Van Soest, M. C.

    2015-12-01

    The newly developed 'laser ablation double dating' (LADD) technique, an integrated laser microprobe U/Pb and (U-Th)/He dating method, could be an exceptionally valuable tool in detrital thermochronology for identifying sedimentary provenance and evaluating the exhumation history of a source region. A recent proof-of-concept study has used LADD to successfully date both zircon and titanite crystals from the well-characterized Fish Canyon tuff, but we also believe that another accessory mineral, rutile, could be amenable to dating via the LADD technique. To continue the development of the method, we present an application of LADD to detrital zircon, titanite, and rutile from a sample collected on the lower Naryani River of central Nepal. Preliminary analyses of the sample have yielded zircon U/Pb dates ranging from 31.4 to 2405 Ma; zircon (U-Th)/He from 1.8 to 15.4 Ma; titanite U/Pb between 18 and 110 Ma; titanite (U-Th)/He between 1 and 16 Ma; rutile U/Pb from 6 to 45 Ma; and rutile (U-Th)/He from 2 to 25 Ma. In addition to the initial data, we can use Ti-in-zircon, Zr-in-titanite, and Zr-in-rutile thermometers to determine the range of possible long-term cooling rates from grains with U/Pb ages younger than collision. Thus far our results from zircon analyses imply a cooling rate of approximately 15°C/Myr; titanite analyses imply between 10 and 67°C/Myr; and rutile between 9 and 267°C/Myr. This spread in potential cooling rates, especially in the order of magnitude differences of cooling rates calculated from the rutile grains, suggests that the hinterland source regions of the Naryani river experienced dramatically different exhumation histories during Himalayan orogenisis. Ongoing analyses will expand the dataset such that we can more adequately characterize the range of possibilities represented in the sample.

  20. Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia

    NASA Astrophysics Data System (ADS)

    Rubatto, Daniela; Williams, Ian S.; Buick, Ian S.

    2001-01-01

    We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U-Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade, at ˜600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557-1587 Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750-800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U-Pb system in relatively large monazite crystals can exceed 750-800 °C.

  1. Zircon (Hf, O isotopes) as melt indicator: Melt infiltration and abundant new zircon growth within melt rich layers of granulite-facies lenses versus solid-state recrystallization in hosting amphibolite-facies gneisses (central Erzgebirge, Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Tichomirowa, Marion; Whitehouse, Martin; Gerdes, Axel; Schulz, Bernhard

    2018-03-01

    In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe-Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier Usbnd Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (Usbnd Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate

  2. Contrasting Cu-Au and Sn-W Granite Metallogeny through the Zircon Geochemical and Isotopic Record

    NASA Astrophysics Data System (ADS)

    Gardiner, Nicholas; Hawkesworth, Chris; Robb, Laurence; Whitehouse, Martin; Roberts, Nick; Kirkland, Chris

    2017-04-01

    Magmatic genesis and evolution - mediated by geodynamic setting - exert a primary control on the propensity of granites to be metal fertile. A revolution in our understanding of these petrogenetic processes has been made through a range of mineral-based tools, most notably the common accessory mineral zircon. There is consequently considerable interest in whether the geochemical and isotopic compositions of zircon can be applied to metallogenic problems. The paired magmatic belts of Myanmar have broadly contrasting metallogenic affinities (Sn-W versus Cu-Au), and are interpreted to have formed on the accretionary margin of the subducting Neo-Tethys Ocean. They therefore present the opportunity to geochemically compare and contrast the zircon compositions in two end-member types of granite-hosted mineral deposits generated in collisional settings. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset that fingerprint: (a) source; (b) redox conditions; and (c) degree of fractionation. These variables all impact on magma fertility, and our key question to address is whether they can be reliably traced and calibrated within the Myanmar zircon record. Granitoid-hosted zircons from the I-type copper arc have juvenile ɛHf (+7 to +12) and mantle-like δ18O (5.3 ‰), whereas zircons from the S-type tin belt have low ɛHf (-7 to -13) and heavier δ18O (6.2-7.7 ‰). Plotting Hf versus U/Yb reaffirms that the tin belt magmas contain greater crustal contributions than the copper arc rocks. Links between whole rock Rb/Sr and zircon Eu/Eu* highlights that the latter can be used to monitor magma fractionation in systems that crystallize plagioclase (low Sr/Y). Ce/Ce* and Eu/Eu* in zircon are thus sensitive to redox and fractionation respectively, and can be used to evaluate the sensitivity of zircons to the metallogenic affinity of their host rocks. Tin contents that exceed the solubility limit are required in order to make a magmatic

  3. Provenance of sediments from Sumatra, Indonesia - Insights from detrital U-Pb zircon geochronology, heavy mineral analyses and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Liebermann, C.; Hall, R.; Gough, A.

    2017-12-01

    The island of Sumatra is situated at the southwestern margin of the Indonesian archipelago. Although it is the sixth largest island in the world, the geology of the Sumatra sedimentary basins and their underlying basement is relatively poorly understood in terms of their provenance. This work is a multi-proxy provenance study utilizing U-Pb detrital zircon dating by LA-ICP-MS combined with optical and Raman spectroscopy-based heavy mineral analysis. It will help to unravel the stratigraphy of Sumatra, contribute to paleogeographic reconstruction of western SE Asia, and aid a wider understanding of Sumatran petroleum plays. Thin section analyses, heavy mineral assemblages, and >3500 concordant U-Pb zircon ages, from samples acquired during two fieldwork seasons indicate a mixed provenance for Cenozoic sedimentary formations, including both local igneous sources and mature basement rocks. Characteristic Precambrian zircon age spectra are found in all analysed Cenozoic sedimentary strata. These can be correlated with zircon age populations found in Sumatran basement rocks; Neoproterozoic and Mesoproterozoic age groups are dominant (c. 500-600 Ma, c. 850-1000 Ma, c. 1050-1200 Ma). Paleoproterozoic to Archaean zircons occur as minor populations. The Phanerozoic age spectra of the Cenozoic formations are characterised by distinct Carboniferous, Permo-Triassic, and Jurassic-Cretaceous zircon populations. Permo-Triassic zircons are interpreted to come from granitoids in the Malay peninsula or Sumatra itself. Eocene to Lower Miocene strata are characterised by ultrastable heavy minerals such as zircon, tourmaline, and rutile, which together with garnet, suggest the principal sources were igneous and metamorphic basement rocks. Cenozoic zircons appear only from the Middle Miocene onwards. This change is interpreted to indicate a new contribution from a local volcanic arc, and is supported by the occurrence of unstable heavy minerals such as apatite and clinopyroxene, and the

  4. Oxygen isotopes in garnet and accessory minerals to constrain fluids in subducted crust

    NASA Astrophysics Data System (ADS)

    Rubatto, Daniela; Gauthiez-Putallaz, Laure; Regis, Daniele; Rosa Scicchitano, Maria; Vho, Alice; Williams, Morgan

    2017-04-01

    Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. Garnet and U-Pb accessory minerals constitute some of the most robust and ubiquitous minerals in subducted crust and can preserve multiple growth zones that track the metamorphic evolution of the sample they are hosted in. Microbeam investigation of the chemical (major and trace elements) and isotopic composition (oxygen and U-Pb) of garnet and accessory minerals is used to track significant fluid-rock interaction at different stages of the subduction system. This approach requires consideration of the diffusivity of oxygen isotopes particularly in garnet, which has been investigated experimentally. The nature of the protolith and ocean floor alteration is preserved in relict accessory phases within eclogites that have been fully modified at HP conditions (e.g. Monviso and Dora Maira units in the Western Alps). Minerals in the lawsonite-blueschists of the Tavsanli zone in Turkey record pervasive fluid exchange between mafic and sedimentary blocks at the early stage of subduction. High pressure shear zones and lithological boundaries show evidence of intense fluid metasomatism at depth along discontinuities in Monviso and Corsica. In the UHP oceanic crust of the Zermatt-Saas Zone, garnet oxygen isotopes and tourmaline boron isotopes indicate multistage fluid infiltration during prograde metamorphism. Localized exchanges of aqueous fluids are also observed in the subducted continental crust of the Sesia-Lanzo Zone. In most cases analyses of distinct mineral zones enable identification of multiple pulses of fluids during the rock evolution.

  5. The Fast and the Slow, the High and the Low - Investigations of Pb and He Diffusion in Accessory Minerals and Implications for Geochronology (Invited)

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2009-12-01

    We have measured Pb diffusion in a range of accessory minerals over the past few decades, and have recently begun investigations of helium diffusion with a study of diffusion in apatite and zircon (Cherniak et al., 2009). In this work, we obtained the following Arrhenius relation for He diffusion in Durango fluorapatite: D = 2.10x10-6 exp( - 117 ± 6 kJ mol-1/RT) m2sec-1 In contrast to apatite, He diffusion in zircon exhibits marked anisotropy, with diffusion normal to c about two orders of magnitude slower than diffusion parallel to c. For He diffusion in zircon we determined these Arrhenius relations for diffusion normal and parallel to c: D⊥c = 2.3x10-7 exp(-146± 11 kJ mol-1/RT) 2sec-1 D∥c = 1.7x10-5 exp(-148± 17 kJ mol-1/RT)m2sec-1 As a continuation of these efforts, we have characterized diffusion of helium in natural monazite and titanite. Polished slabs of these minerals were implanted with 100 keV 3He at a dose of 5x1015 3He/cm2. Implanted monazite and titanite were annealed in Pt capsules in 1-atm furnaces for times ranging from 15 minutes to 6 weeks at temperatures from 252-600°C. 3He distributions in the minerals were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For diffusion normal to (100) we obtain the following Arrhenius relation for He diffusion in monazite: D = 1.6x10-7 exp(-150 ± 11 kJ mol-1/RT) m2sec-1. Over the investigated temperature range, diffusivities are similar to those measured by Boyce et al. (2005), and fall between the values measured by Farley (2007) for diffusion in synthetic CePO4, NdPO4, SmPO4, and GdPO4. He diffusion in monazite is similar to He diffusion in zircon normal to c, and about 4 orders of magnitude slower than He diffusion in apatite (Cherniak et al., 2009). For diffusion in titanite, we obtain the Arrhenius relation: D = 8.7x10-7 exp(-143 ± 7 kJ mol-1/RT) m2sec-1. He diffusivities for titanites from two different localities are comparable, and similar to those measured in the

  6. U, Th, Pb and REE abundances and Pb 207/Pb 206 ages of individual minerals in returned lunar material by ion microprobe mass analysis.

    NASA Technical Reports Server (NTRS)

    Andersen, C. A.; Hinthorne, J. R.

    1972-01-01

    Results of ion microprobe analyses of Apollo 11, 12 and 14 material, showing that U, Th, Pb and REE are concentrated in accessory minerals such as apatite, whitlockite, zircon, baddeleyite, zirkelite, and tranquillityite. Th/U ratios are found to vary by over a factor of 40 in these minerals. K, Ba, Rb and Sr have been localized in a K rich, U and Th poor glass phase that is commonly associated with the U and Th bearing accessory minerals. Li is observed to be fairly evenly distributed between the various accessory phases. The phosphates have been found to have REE abundance patterns (normalized to the chondrite abundances) that are fairly flat, while the Zr bearing minerals have patterns that rise steeply, by factors of ten or more, from La to Gd. All the accessory minerals have large negative Eu anomalies. Radiometric age dates (Pb 207/Pb 206) of the individual U and Th bearing minerals compare favorably with the Pb 207/Pb 206 age of the bulk rocks.

  7. Zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the Ivrea-Verbano and Strona-Ceneri Zones, NW Italy

    NASA Astrophysics Data System (ADS)

    Guergouz, Celia; Martin, Laure; Vanderhaeghe, Olivier; Thébaud, Nicolas; Fiorentini, Marco

    2018-05-01

    In order to improve the understanding of thermal-tectonic evolution of high-grade terranes, we conducted a systematic study of textures, REE content and U-Pb ages of zircon and monazite grains extracted from migmatitic metapelites across the amphibolite to granulite facies metamorphic gradient exposed in the Ivrea-Verbano and Strona-Ceneri Zones (Italy). This study documents the behaviour of these accessory minerals in the presence of melt. The absence of relict monazite grains in the metasediments and the gradual decrease in the size of inherited zircon grains from amphibolite to granulite facies cores indicate partial to total dissolution of accessory minerals during the prograde path and partial melting. The retrograde path is marked by (i) growth of new zircon rims (R1 and R2) around inherited cores in the mesosome, (ii) crystallisation of stubby zircon grains in the leucosome, especially at granulite facies, and (iii) crystallisation of new monazite in the mesosome. Stubby zircon grains have a distinctive fir-tree zoning and a constant Th/U ratio of 0.20. Together, these features reflect growth in the melt; conversely, the new zircon grains with R1 rims have dark prismatic habits and Th/U ratios < 0.1, pointing to growth in solid residues. U-Pb ages obtained on both types are similar, indicating contemporaneous growth of stubby zircon and rims around unresorbed zircon grains, reflecting the heterogeneous distribution of the melt at the grain scale. In the Ivrea-Verbano Zone the interquartile range (IQR) of U-Pb ages on zircon and monazite are interpreted to represent the length of zircon and monazite crystallisation in the presence of melt. Accordingly, they provide an indication on the minimum duration for high-temperature metamorphism and partial melting of the lower crust: 20 Ma and 30 Ma in amphibolite and granulite facies, respectively. In amphibolite facies, zircon crystallisation between 310 and 294 Ma (IQR) is interpreted to reflect metamorphic peak

  8. HAFNIAN ZIRCONS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    von Knorring, O.; Hornung, G.

    1961-06-17

    Two hafnia zircons were examined in detail, one from Mtoko in Southern Rhodesia, containing 21% HfO/sub 2/, and the other from Karibib in South-West Africa, with 31% HfO/sub 2/. In both cases the zircons are associated with the later tantalum-rich phase of mineralization. The Mtoko zircon forms small, mauve- colored, independent crystals in the albitic zone of the pegmatite. The zircon from Karibib occurs in larger reddish-brown masses, partly intergrown with minute manganotantalite crystals and set in a matrix of lithium-bearing mica, albite, quartz and kaolinized feldspar. Some crystals show dominant pyramid faces, with a suppressed prism. Both zircons exhibitmore » an intense golden-yellow fluorescence in UV light. The zircon from Karibib was found to be only weakly radioactive. Data are given concerning various properties of the two zircons. (P.C.H.)« less

  9. U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

    NASA Technical Reports Server (NTRS)

    Zhou, Q.; Zeigler, R. A.; Yin, Q. Z.; Korotev, R. L.; Joliff, B. L.; Amelin, Y.; Marti, K.; Wu, F. Y.; Li, X. H.; Li, Q. L.; hide

    2012-01-01

    Zircon U-Pb geochronology has made a great contribution to the timing of magmatism in the early Solar System [1-3]. Ca phosphates are another group of common accessory minerals in meteorites with great potential for U-Pb geochronology. Compared to zircons, the lower closure temperatures of the U-Pb system for apatite and merrillite (the most common phosphates in achondrites) makes them susceptible to resetting during thermal metamorphism. The different closure temperatures of the U-Pb system for zircon and apatite provide us an opportunity to discover the evolutionary history of meteoritic parent bodies, such as the crystallization ages of magmatism, as well as later impact events and thermal metamorphism. We have developed techniques using the Cameca IMS-1280 ion microprobe to date both zircon and phosphate grains in meteorites. Here we report U-Pb dating results for zircons and phosphates from lunar meteorites Dhofar 1442 and SaU 169. To test and verify the reliability of the newly developed phosphate dating technique, two additional meteorites, Acapulco, obtained from Acapulco consortium, and angrite NWA 4590 were also selected for this study as both have precisely known phosphate U-Pb ages by TIMS [4,5]. Both meteorites are from very fast cooled parent bodies with no sign of resetting [4,5], satisfying a necessity for precise dating.

  10. Zircon-pyrochlore ores of Proterozoic Gremyakha-Vyrmes polyphase massif, Kola Peninsula: source and evolution

    NASA Astrophysics Data System (ADS)

    Sorokhtina, Natalia; Belyatsky, Boris; Antonov, Anton; Kononkova, Natalia; Lepekhina, Elena; Kogarko, Lia

    2017-04-01

    The alkaline-ultrabasic Gremyakha-Vyrmes massif occurs within the Central Kola terrane in the northern part of the Fennoscandian Shield and consists of diverse rock complexes: basic-ultrabasic rocks, foidolites, alkaline metasomatic rocks and carbonatites, alkaline granites and granosyenites. Nb-Zr ore deposit is confined to alkaline metasomatic rocks developed over foidolites. The metasomatites are represented by albitites and aegirinites occur as submeridionally orientated zones extending up to 6-8 km and several hundred meters thickness. They are mainly composed of albite and aegirine, but amphibole, annite, microcline, fluorapatite, titanite, ilmenite, pyrochlore group minerals, zircon are present [Sorokhtina et al., 2016]. Carbonatites are developed sporadically and accessory zircon but not the pyrochlore is observed only in contact zones with albitites and aegerinites. In metasomatites, zircon and pyrochlore are main rare metal minerals, which are formed at the latest stages of crystallization. Ca-dominant fluorcalcio- and hydroxycalciopyrochlores are the most abundant, whereas U-dominant pyrochlore, oxyuranobetafite, zero-valent-dominant (Ba, Sr-dominant) pyrochlore, hydro- or kenopyrochlore are rare. The pyrochlore-group minerals form heterogeneous metacrystals containing inclusions of host rock minerals, calcite, ilmenite, zircon, sulfides, and graphite. While pyrochlore is replaced by Si-rich "pyrochlore" (SiO2 is up to 18 wt.%.), cation-deficient hydrated pyrochlore, Fe-Si-Nb, U-Si-Nb, and Al-Si-Nb phases along fracture zones and margins. The early generation zircon is represented by large heterogeneous metacrystals filled with inclusions of various host rock minerals, calcite, ilmenite, thorite, thorianite and sulfides, while the late zircons are empty of inclusions. Zircons are nearly stoichiometric in composition; but intermediate zones are enriched in Pb, Y and Th, and overgrowths are enriched Hf only. According to CL and ion-microprobe analysis

  11. Zircon U-Pb dating of eclogite from the Qiangtang terrane, north-central Tibet: a case of metamorphic zircon with magmatic geochemical features

    NASA Astrophysics Data System (ADS)

    Zhai, Qing-guo; Jahn, Bor-ming; Li, Xian-hua; Zhang, Ru-yuan; Li, Qiu-li; Yang, Ya-nan; Wang, Jun; Liu, Tong; Hu, Pei-yuan; Tang, Suo-han

    2017-06-01

    Zircon is probably the most important mineral used in the dating formation of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks. The origin of zircon, i.e., magmatic or metamorphic, is commonly assessed by its external morphology, internal structure, mineral inclusions, Th/U ratios and trace element composition. In this study, we present an unusual case of metamorphic zircon from the Qiangtang eclogite, north-central Tibet. The zircon grains contain numerous eclogite-facies mineral inclusions, including omphacite, phengite, garnet and rutile; hence, they are clearly of metamorphic origin. However, they display features similar to common magmatic zircon, including euhedral crystal habit, high Th/U ratios and enriched heavy rare earth elements pattern. We suggest that these zircon grains formed from a different reservoir from that for garnet where no trace elements was present and trace element equilibrium between zircon and garnet was achieved. U-Pb dating of zircon gave an age of 232-237 Ma for the eclogite, and that of rutile yielded a slightly younger age of ca. 217 Ma. These ages are consistent with the reported Lu-Hf mineral isochron and phengite Ar-Ar ages. The zircon U-Pb and mineral Lu-Hf isochron ages are interpreted as the time of the peak eclogite-facies metamorphism, whereas the rutile U-Pb and phengite Ar-Ar ages represent the time of exhumation to the middle crust. Thus, the distinction between metamorphic and magmatic zircons cannot be made using only Th/U ratios and heavy REE compositions for HP-UHP metamorphic rocks of oceanic derivation.

  12. Considerations for successful cosmogenic 3He dating in accessory phases

    NASA Astrophysics Data System (ADS)

    Amidon, W. H.; Farley, K. A.; Rood, D. H.

    2008-12-01

    apatite. In contrast the combination of high Li contents and a young closure age (0.6 My) in rhyolite from the Coso volcanic field leads to a large 3Hecn component (30%) and small 3Henuc component (5%) in zircon. Analysis of samples from a variety of lithologies shows that zircon and apatite tend to be low in Li (1-10 ppm), but are vulnerable to implantation of 3He from adjacent minerals due to their small grain size, especially from minerals like biotite and hornblende. This point is well illustrated by data from both the Sierra Nevada and Coso examples, in which there is a strong correlation between grain size and 3He concentration for zircons due to implantation. In contrast, very large zircons (150>125 um width) obtained from shielded samples of the Shoshone Falls rhyolite (SW Idaho) do not contain a significant implanted component. Thus, successful 3He dating of accessory phases requires low Li content (<10 ppm) in the target mineral and either 1) low Li in adjacent minerals, or 2) the use of large grain sizes (>100 um). In high-Li cases, the fraction of 3Henuc is minimized in samples with young helium closure ages or longer duration of exposure. However because the 3Hecn/3Hespall ratio is fixed for a given Li content, longer exposure will not reduce the fraction of 3Hecn.

  13. Peculiar Feldspar And Quartz Inclusions Within Zircons From Anorthosites, North Eastern Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Eliwa, H. A.; Dawoud, M. I.; Khalaf, I. M.; Negendank, J. F.; Itaya, T.

    2004-12-01

    Zircons from three anorthosite outcrops along Wadi Dib area, north Eastern Desert of Egypt contain abundant and conspicuous inclusions of quartz, feldspar, amphibole and apatite. These anorthosites, as (50-100m thick) layers, represent the top of mafic-ultramafic intrusions exhibiting rhythmic layering visible by reputation of melanocratic and leucocratic layers. Field and microscopic studies exhibit that these anorthosites were affected by the action of residual magmatic solutions associated with the late stage crystallization of the younger granites, which modified their mineralogical composition. They are composed totally of plagioclase with subordinate amount of clinoenstatite, augite, amphibole, biotite, K-feldspar, and quartz. Accessories are magnetite, ilmenite, apatite and zircon. The abundance and the mode of occurrence of K-feldspar, quartz, and biotite with apatite and zircon among the megacrysts suggest their formation is ascribed to the interaction with the residual solutions. The microprobe data exhibit difference between feldspar and amphiboles contained herein zircons and those as anorthosite mineral constituents. The genetic relationship between zircons and their inclusions suggests later growth of zircons than inclusions and most probably at the final stage of rock modification. Zircons are magmatic and found in the interstitial feldspar and quartz among plagioclase megacrysts in aggregates or as individual grains. The microscopic and SEM images investigation exhibit that most zircons are subhedral to euhedral equant and prismatic crystals. Most zircons have same range of crystal morphologies and internal growth structures with predominance of prism /{100/} and pyramid /{101/} and occasionally prism /{110/} and pyramid /{111/}. No evidences for poly-faceted grains, inherited cores or later overgrowths were detected. CL images distinguished zircons with visible core-rim structures and others with regular and continuous growth zones contained herein

  14. Advances and limitations on interpreting the erosional record from isotopic analysis of single detrital mineral grains

    NASA Astrophysics Data System (ADS)

    Parrish, Randall

    2010-05-01

    The analysis of provenance of clastic sediments is useful for reconstructing the characteristics and rates of exhumation of source areas, and sometimes placing minimum age constraints on depositional age. Due largely to increased availability and ease of access to LA-ICP-MS instrumentation, the analysis of provenance using single detrital accessory minerals has grown very rapidly over recent years. With this however is a culture of casual users who may not fully appreciate subtleties of measurement and isotope interpretation. The isotopic provenance literature is dominated by zircon-centric studies that use U-Pb dating and Hf isotope measurements of single zircons, but unfortunately an increasing number of these studies appear to lack sufficient understanding of U-Pb and Hf systematics; misleading interpretations are increasingly common. The inherent information contained in detrital accessory minerals is potentially immense, scientifically, but comprehensive interpretations attempting to reconstruct the geological make-up and evolution of sources require dating of multiple types of accessory minerals (i.e. zircon, titanite, monazite, garnet inclusions, micas, allanite, rutile, apatite) by various methods (U-Pb, fission track, Ar-Ar…) at times accompanied by isotope geochemical data (Lu-Hf, Sm-Nd, Rb-Sr) of phases where Sr, Hf, or REE comprise a major element (≥0.5%). Many approaches have been demonstrated but the mix of methodologies needs to be tailored to the problem, in view of the variable effort and expense needed to acquire good datasets. To date there are few comprehensive multi-mineral, multi-isotope system applications, and too many studies that follow a prescriptive cookbook that lacks innovation and fails to address a problem. The field needs to focus effort on the approaches that can solve a problem well rather than doing either just the easy methods or too many methods only moderately well. Zircon studies require strategies that reduce or

  15. Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

    NASA Astrophysics Data System (ADS)

    Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

    2018-02-01

    This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems <100>{010} and < 1 bar 10>{110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system <100>{001} and rotation axis [010]. The slip system < 1 bar 10>{110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the

  16. Deciphering the evolution of rapakivi magmas from mineral inclusions in alkali feldspar megacrysts and zircon

    NASA Astrophysics Data System (ADS)

    Heinonen, Aku; Mänttäri, Irmeli; Rämö, Tapani; Larjamo, Kirsi

    2017-04-01

    Rapakivi granites are ferroan (A-type) granites that are characterized by ovoid-shaped alkali feldspar megacrysts (diameter up to 15 cm) commonly mantled by plagioclase forming the namesake rapakivi texture. The 1.63 Ga Wiborg batholith in southeastern Finland is the type area of rapakivi granites. Recent studies into the chemistry and geochronology of the mineral inclusions within the Wiborg rapakivi granite ovoids have shown that the megacrysts may represent magmas that crystallized significantly earlier and either in different P/T conditions or from magmas with dissimilar compositions than the matrices of the respective granites. It is possible that the ovoids crystallized from magmas with more evolved geochemical characteristics than the matrices, including higher levels of REE and other incompatibe elements. All ovoids are perthitic and have concave and rod-shaped quartz, hypidiomorphic or slightly resorbed plagioclase (often with partial quartz rim), zircon, biotite, apatite, and ilmenite (and occasionally minor magnetite) inclusions. The ovoids of the mafic rapakivi granite types have also hornblende and sometimes olivine and clinopyroxene inclusions, whereas the more felsic types have abundant fluorite. In contrast to the ovoids, the groundmass feldspar grains have hardly any inclusions. Differences are also observed in the hornblende compositions between the ovoid inclusion (dominantly ferroedenitic) and matrix (ferropargasitic/hastingsitic) populations. As zircon is an almost ubiquitous inclusion phase, time-integrated trace element composition comparisons of not only ovoid inclusion and matrix populations but also between different morphological types have been possible. Also the zircon crystals themselves contain plenty of inclusions. Alkali feldspar (albite and potassic feldspar) and quartz constitute the bulk of the inclusions within zircon crystals but chloritized mafic minerals, and sometimes also fluorite and ilmenite are common. A detailed

  17. 238U/235U determinations of some commonly used reference materials and U-bearing accessory minerals (Invited)

    NASA Astrophysics Data System (ADS)

    Condon, D.; Noble, S.; McLean, N.; Bowring, S. A.

    2009-12-01

    We have determined 238U/235U ratios for a suite of commonly used natural (CRM 112a, SRM 950a, HU-1) and synthetic (IRMM 184 and CRM U500) uranium reference materials in addition to several U-bearing accessory phases (zircon and monazite) by thermal ionisation mass-spectrometry (TIMS) using the IRMM 3636 233U-236U double spike to accurately correct for mass fractionation. The 238U/235U values for the natural uranium reference materials differ, by up to 0.1%, from the widely used ‘consensus’ value (137.88) with all having 238U/235U values less than 137.88. Similarly, initial 238U/235U data from zircon and monazite yield 238U/235U values that are lower than the ‘consensus’ value. The data obtained from U-bearing minerals is used to assess how the uncertainty in the 238U/235U ratio contributes to the systematic discordance observed in 238U/206Pb and 235U/207Pb dates (Mattinson, 2000; Schoene et al., 2006) which has traditionally been wholly attributed to error in the U decay constants. The 238U/235U determinations made on the synthetic reference materials yield results that are considerably more precise and accurate than the certified values (0.02% vs. 0.1% for CRM U500). The calibration of isotopic tracers used for U-daughter geochronology that are partially based upon these reference materials, and the resultant age determinations, will benefit from increased accuracy and precision. Mattinson, J.M., 2000. Revising the “gold standard”—the uranium decay constants of Jaffey et al., 1971. Eos Trans. AGU, Spring Meet. Suppl., Abstract V61A-02. Schoene B., Crowley J.L., Condon D.C., Schmitz M.D., Bowring S.A., 2006, Reassessing the uranium decay constants for geochronology using ID-TIMS U-Pb data. Geochimica et Cosmochimica Acta 70: 426-445

  18. Origin of zircon-bearing mantle eclogites entrained in the V. Grib kimberlite (Arkhangelsk region, NW Russia): Evidence from mineral geochemistry and the U-Pb and Lu-Hf isotope compositions of zircon

    NASA Astrophysics Data System (ADS)

    Shchukina, Elena V.; Agashev, Alexey M.; Zedgenizov, Dmitry A.

    2018-05-01

    The concentrations of major and trace elements in minerals, reconstructed whole-rock compositions of zircon-bearing equigranular eclogites from the V. Grib kimberlite pipe located within the Arkhangelsk Diamondiferous Province (North-Western Russia), and results of the U-Pb and Lu-Hf isotope analyses of zircon grains from eclogites and granulite xenoliths are reported. These data suggest that the equigranular eclogites could represent the fragments of mid-ocean-ridge basalt that were metamorphosed during Paleoproterozoic subduction at 1.7-1.9 Ga. The Hf isotope compositions of the eclogitic zircon display uniformity and indicate corresponding Hf-depleted mantle model ages of 2.2-2.3 Ga. The formation of zircon in eclogites could have resulted from interactions with metasomatic/subduction-related fluids just prior to, but associated with, Paleoproterozoic eclogite formation. A link between eclogitic zircon formation and continental lower-crustal rocks can be excluded based on differences in the Hf isotope compositions of eclogitic and granulitic zircon grains. The U-Pb upper intercept age of granulitic zircon of 2716 ± 61 Ma provides a new minimum age constraint for zircon crystallisation and granulite formation. The U-Pb ages obtained from granulitic zircon show two stages of Pb loss at 2.2-2.6 Ga and 1.7-2.0 Ga. The late Paleoproterozoic stage of Pb loss recorded in granulitic zircon is due to the intensive reworking of basement crustal rocks, which was caused by a tectonic process/subduction event associated with equigranular eclogite formation. Our data, along with evidence previously obtained from the V. Grib pipe coarse-granular eclogites, show at least two main subduction events in the lithospheric mantle of the Arkhangelsk region: the Archean (2.8 Ga) and Paleoproterozoic (1.7-1.9 Ga) subductions, which correspond to major magmatic and metamorphic events in the Baltic Shield.

  19. Pre-Variscan evolution of the Western Tatra Mountains: new insights from U-Pb zircon dating.

    PubMed

    Burda, Jolanta; Klötzli, Urs

    In situ LA-MC-ICP-MS U-Pb zircon geochronology combined with cathodoluminescence imaging were carried out to determine protolith and metamorphic ages of orthogneisses from the Western Tatra Mountains (Central Western Carpathians). The metamorphic complex is subdivided into two units (the Lower Unit and the Upper Unit). Orthogneisses of the Lower Unit are mostly banded, fine- to medium-grained rocks while in the Upper Unit varieties with augen structures predominate. Orthogneisses show a dynamically recrystallised mineral assemblage of Qz + Pl + Bt ± Grt with accessory zircon and apatite. They are peraluminous (ASI = 1.20-1.27) and interpreted to belong to a high-K calc-alkaline suite of a VAG-type tectonic setting. LA-MC-ICP-MS U-Pb zircon data from samples from both units, from crystals with oscillatory zoning and Th/U > 0.1, yield similar concordia ages of ca. 534 Ma. This is interpreted to reflect the magmatic crystallization age of igneous precursors. These oldest meta-magmatics so far dated in the Western Tatra Mountains could be linked to the fragmentation of the northern margin of Gondwana. In zircons from a gneiss from the Upper Unit, cores with well-developed oscillatory zoning are surrounded by weakly luminescent, low contrast rims (Th/U < 0.1). These yield a concordia age of ca. 387 Ma corresponding to a subsequent, Eo-Variscan, high-grade metamorphic event, connected with the formation of crustal-scale nappe structures and collision-related magmatism.

  20. Transformations to granular zircon revealed: Twinning, reidite, and ZrO2 in shocked zircon from Meteor Crater (Arizona, USA)

    USGS Publications Warehouse

    Cavosie, Aaron; Timms, Nicholas E.; Erickson, Timmons M.; Hagerty, Justin J.; Hörz, Friedrich

    2016-01-01

    Granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis. Meteor Crater in Arizona (United States) contains abundant evidence of shock metamorphism, including shocked quartz, the high pressure polymorphs coesite and stishovite, diaplectic SiO2 glass, and lechatelierite (fused SiO2). Here we report the presence of granular zircon, a new shocked mineral discovery at Meteor Crater, that preserve critical orientation evidence of specific transformations that occurred during its formation at extreme impact conditions. The zircon grains occur as aggregates of sub-µm neoblasts in highly shocked Coconino Formation Sandstone (CFS) comprised of lechatelierite. Electron backscatter diffraction shows that each grain consists of multiple domains, some with boundaries disoriented by 65°, a known {112} shock-twin orientation. Other domains have crystallographic c-axes in alignment with {110} of neighboring domains, consistent with the former presence of the high pressure ZrSiO4 polymorph reidite. Additionally, nearly all zircon preserve ZrO2 + SiO2, providing evidence of partial dissociation. The genesis of CFS granular zircon started with detrital zircon that experienced shock-twinning and reidite formation from 20 to 30 GPa, ultimately yielding a phase that retained crystallographic memory; this phase subsequently recrystallized to systematically oriented zircon neoblasts, and in some areas partially dissociated to ZrO2. The lechatelierite matrix, experimentally constrained to form at >2000 °C, provided an ultra high-temperature environment for zircon dissociation (~1670 °C) and neoblast formation. The capacity of granular zircon to preserve a cumulative P-T record has not been recognized previously, and provides a new method for retrieving histories of impact-related mineral transformations in the crust at conditions far beyond which most rocks melt.

  1. Magma evolution as seen through zircon geochemistry: an example from the Southern Adamello Batholith, N. Italy

    NASA Astrophysics Data System (ADS)

    Broderick, C.; Schaltegger, U.; Gerdes, A.; Frick, D.; Guenther, D.; Brack, P.

    2012-04-01

    Zircon is an ubiquitous accessory mineral often used for U-Pb geochronology but is also an important recorder of geochemical information. The trace element and isotopic characteristics of zircon yield potential for tracking changes in an evolving magma through time. With recent advances in U-Pb zircon geochronology, 10-100 ka to Ma timescales are observed for incremental pluton construction (Michel et al., 2008, Schaltegger et al., 2009). In observed 100 ka timescales of zircon crystallization, can zircon record the processes that produce trace element variations in a magma? This study focuses on the Val Fredda Complex (VFC) in the southern tip of the 43 to 33 Ma Adamello batholith, N. Italy. The VFC displays complex relationships among mafic melts that were injected into solidifying felsic magmas. Single zircon crystals were dated using CA-ID-TIMS. With permil uncertainties on 206Pb/238U zircon dates, zircons reveal complexities within single populations. The mafic units crystallized potential autocrystic zircons over a duration of 100 - 150ka, whereas the felsic units record up to 200ka of zircon crystallization. In order to understand these complex zircon populations, we analyzed Hf isotopes and trace elements, on the same volume of zircon used for U-Pb dating, following the TIMS-TEA method (Schoene et al., 2010). This detailed zircon study will allow us to look at how magmas are evolving with time. Hf isotopes of VFC mafic zircons reveal distinct ɛHf values between the three mafic units and their ɛHf values remain consistent through time, whereas the VFC felsic units record more complexity in their ɛHf values. We observe changes such as increasing and slight decreases in ɛHf with time which suggest different processes are occurring to produce the different felsic units. Trace element ratios in zircon reveal differences which allow us to make distinctions between felsic and mafic units (e.g. Th/U, (Lu/Gd)N, REEs). The VFC records 200 ka of zircon

  2. Detrital shocked minerals: microstructural provenance indicators of impact craters

    NASA Astrophysics Data System (ADS)

    Cavosie, A. J.

    2014-12-01

    The study of detrital shocked minerals (DSMs) merges planetary science, sedimentology, mineralogy/crystallography, accessory mineral geochemistry, and geochronology, with the goal of identifying and determining provenance of shock metamorphosed sand grains. Diagnostic high-pressure impact-generated microstructures (planar fractures, planar deformation features) are readily identified on external grain surfaces using standard SEM imaging methods (BSE), and when found, unambiguously confirm an impact origin for a given sand grain. DSMs, including quartz, zircon, monazite, and apatite, have thus far been documented at the Vredefort Dome [1,2,3], Sudbury [4], Rock Elm [5], and Santa Fe [6,7] impact structures. DSMs have been identified in alluvium, colluvium, beach sand, and glacial deposits. Two main processes are recognized that imply the global siliciclastic record contains DSMs: they survive extreme distal transport, and they survive 'deep time' lithification. Distal transport: In South Africa, shocked minerals are preserved in alluvium from the Vaal River >750 km downstream from the Vredefort impact; SHRIMP U-Pb geochronology has confirmed the origin of detrital shocked zircon and monazite from shocked Vredefort bedrock [2]. Vredefort-derived shocked zircons have also been found at the mouth of the Orange River on the Atlantic coast, having travelled ~2000 km downriver from Vredefort [8]. Deep time preservation: Vredefort-derived shocked zircon and quartz has been documented in glacial diamictite from the 300 Myr-old Dwyka Group in South Africa. Shocked minerals were thus entrained and transported in Paleozoic ice sheets that passed over Vredefort [9]. An impact crater can thus be viewed as a unique 'point source', in some cases for billions of years [2,4]; DSMs thus have applications in studying eroded impact craters, sedimentary provenance, landscape evolution, and long-term sediment transport processes throughout the geologic record. This work was supported by

  3. Pan-Africa/Pan-Brazilian detrital zircons in Lower Palaeozoic schists of SW Norway - enigmatic detrital zircon U-Pb ages

    NASA Astrophysics Data System (ADS)

    Zimmermann, Udo; Bjørheim, Maren; Clark, Chris

    2013-04-01

    We present Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb zircon age data from metasedimentary rocks (schists and quartzites) located in the town of Stavanger (SW Norway). The metasedimentary sequence is composed of schists, medium grained quartz-rich metawackes and quartzites. Quartzites and meta-quartz-wackes exhibit a mylonitic fabric with newly grown fine-grained muscovite defining the fabric. Accessory minerals are zircon, allanite, detrital apatite, monazite, ilmenite, rutile and zircon. The schists are dark and dominated by quartz and feldspar in a fine chloritic and silica-rich matrix and represent the dominant lithology of the region. While quartzites and metawackes show typical geochemical characteristics for strongly reworked rocks, the schists have very low Zr/Sc and Th/Sc ratios below 0.9 and point together with other trace element ratios (La/Sc, Ti/Zr) to the strong influence of less fractionated, mafic, sources in the detritus, possibly arc derived. U-Pb ages of detrital zircon from quartzites range between 740 to 1800 Ma. There is a defined population at 1135 and 1010 Ma tentatively correlated with the Sveconorwegian orogeny. A second population at ~1450 Ma that can be related to a tectono-magmatic event during the Earliest Mesoproterozoic, also recorded in Oslo, southern Sweden and Bornholm, mapped along the proposed southern margin of Baltica. Other detrital zircons record ages between 1586 - 1664 Ma that are not related to the latter event. The oldest U-Pb detrital zircon grain age was 1796 Ma and is potentially associated with the terminal phase of the Svecofennian orogeny. Detrital zircons from the associated schists do show a similar abundance of main age clusters but the oldest found zircons dates to 2013 Ma while the maximum depositional age could be determined by grains of Cambrian to even Ordovician ages with a large 1 sigma error, as such that we rather propose a Cambrian maximum depositional age. It is possible to speculate that

  4. Detrital zircons and Earth system evolution

    NASA Astrophysics Data System (ADS)

    McKenzie, R.

    2016-12-01

    Zircon is a mineral commonly produced in silicic magmatism. Therefore, due to its resilience and exceedingly long residence times in the continental crust, detrital zircon records can be used to track processes associated with silicic magmatism throughout Earth history. In this contribution I will address the potential role of preservational biases in zircon record, and further discuss how zircon datasets can be used to help better understand the relationship between lithospheric and Earth system evolution. I will use large compilations of zircon data to trace the composition and weatherability of the continental crust, to evaluate temporal rates of crustal recycling, and finally to track spatiotemporal variation in continental arc magmatism and volcanic CO2 outgassing throughout Earth history. These records demonstrate that secular changes in plate tectonic regimes played a prominent role in modulating conditions of the ocean+atmosphere system and long-term climate state for the last 3 billion years.

  5. Interpreting U-Pb data from primary and secondary features in lunar zircon

    NASA Astrophysics Data System (ADS)

    Grange, M. L.; Pidgeon, R. T.; Nemchin, A. A.; Timms, N. E.; Meyer, C.

    2013-01-01

    In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U-Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th-U-Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal-plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U-Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal-plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U-Pb isotopic systems.

  6. Complete zircon and chromite digestion by sintering of granite, rhyolite, andesite and harzburgite rock reference materials for geochronological purposes

    NASA Astrophysics Data System (ADS)

    Bokhari, Syed Nadeem H.; Meisel, Thomas

    2014-05-01

    Zircon (ZrSiO4) is a common accessory mineral in nature that occurs in a wide variety of sedimentary, igneous, and metamorphic rocks. Zircon has the ability to retain substantial chemical and isotopic information that are used in range of geochemical and geo- chronological investigations. Sample digestion of such rock types is a limiting factor due to the chemical inertness of zircon (ZrSiO4) tourmaline, chromite, barite, monazite, sphene, xenotime etc. as the accuracy of results relies mainly on recovery of analytes from these minerals. Dissolution by wet acid digestions are often incomplete and high blank and total dissolved solids (TDS) contents with alkali fusions lead to an underestimation of analyte concentrations. Hence an effective analytical procedure, that successfully dissolves refractory minerals such as zircon is needed to be employed for reliable analytical results. Na2O2 digestion [1] was applied in characterisation of granite (G-3), rhyolite (MRH), andesite (MGL-AND) and harzburgite (MUH-1) powdered reference material with solution based ICP-MS analysis. In this study we undertake a systematic evaluation of decomposition time and sample:Na2O2 ratio and test portion size after minimising effect of all other constraints that makes homogeneity ambiguous. In recovering zircon and chromite 100 mg test portion was mixed with different amounts of Na2O2 i.e. 100-600 mg. Impact of decomposition time was observed by systematically increasing heating time from 30-45 minutes to 90-120 minutes at 480°C. Different test portion sizes 100-500 mg of samples were digested to control variance of inhomogeneity. An improved recovery of zirconium in zircon in granite (G-3), rhyolite MRH), andesite (MGL-AND) and chromite in harzburgite (MUH-1) was obtained by increasing heating time (2h) at 480°C and by keeping (1:6) ratio of sample:Na2O2. Through this work it has been established that due to presence of zircon and chromite, decomposition time and sample:Na2O2 ratio has

  7. Paragneiss zircon geochronology and trace element geochemistry, North Qaidam HP/UHP terrane, western China

    USGS Publications Warehouse

    Mattinson, C.G.; Wooden, J.L.; Zhang, J.X.; Bird, D.K.

    2009-01-01

    In the southeastern part of the North Qaidam terrane, near Dulan, paragneiss hosts minor peridotite and UHP eclogite. Zircon geochronology and trace element geochemistry of three paragneiss samples (located within a ???3 km transect) indicates that eclogite-facies metamorphism resulted in variable degrees of zircon growth and recrystallization in the three samples. Inherited zircon core age groups at 1.8 and 2.5 Ga suggest that the protoliths of these rocks may have received sediments from the Yangtze or North China cratons. Mineral inclusions, depletion in HREE, and absence of negative Eu anomalies indicate that zircon U-Pb ages of 431 ?? 5 Ma and 426 ?? 4 Ma reflect eclogite-facies zircon growth in two of the samples. Ti-in-zircon thermometry results are tightly grouped at ???660 and ???600 ??C, respectively. Inclusions of metamorphic minerals, scarcity of inherited cores, and lack of isotopic or trace element inheritance demonstrate that significant new metamorphic zircon growth must have occurred. In contrast, zircon in the third sample is dominated by inherited grains, and rims show isotopic and trace element inheritance, suggesting solid-state recrystallization of detrital zircon with only minor new growth. ?? 2009 Elsevier Ltd.

  8. Geochemical and textural characterization of phosphate accessory phases in the vein assemblage and metasomatically altered Llallagua tin porphyry

    NASA Astrophysics Data System (ADS)

    Betkowski, Wladyslaw B.; Rakovan, John; Harlov, Daniel E.

    2017-09-01

    Petrographic and geochemical characterization of phosphate accessory minerals represents a powerful tool in understanding the mineralization and metasomatic history of one of the world's biggest tin deposits, the Siglo XX mine, Salvadora stock, Llallagua, Bolivia. The Llallagua tin deposit lies in a hydrothermally altered porphyry stock that is part of the subduction-related Bolivian tin belt. Despite numerous studies, there is still a debate over the timing and characteristics of mineralization history of the deposit. Primary igneous fluorapatite and monazite (for the first time) were recognized in the altered porphyry. The igneous monazite is enriched in Th, unlike the hydrothermal monazite that is recognized for its low Th concentration. Fluorapatite, monazite, and xenotime also coexist with cassiterite within the hydrothermal vein assemblage. Fluorapatite and xenotime are essentially pristine. Monazite, however, shows various degrees of alteration in the form of regenerative mineral replacement (RMR). This exemplifies differential reactivity and selective mineral replacement/alteration of three accessory phosphate minerals, that are all important geochemical tracers of magmatic and hydrothermal processes, and which can all be used as geochronometers. Mineral textures and composition in the altered porphyry and vein assemblages have been evaluated. Monazite-xenotime geothermometry indicates monazite crystallization beginning around 550 °C. Monazite continues to grow as temperatures gradually decrease to about 300 °C, when most of cassiterite precipitation occurred in the samples studied. The primary mechanism of phosphate alteration has been identified as a coupled dissolution-reprecipitation process, which led to REE exchange in the igneous fluorapatite and hydrothermal monazite. In Type I local alteration, La and Pr-Nd show continuity across the pre- and post- alteration concentric zones indicating that they were not affected by alteration. This is an

  9. Ti-in-Zircon Thermometer: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Fu, B.; Cavosie, A. J.; Clechenko, C. C.; Fournelle, J.; Kita, N. T.; Lackey, J.; Page, F.; Wilde, S. A.; Valley, J. W.

    2005-12-01

    The titanium in zircon thermometer has been applied to 167 zircons from diverse rock types. These rocks include metamorphosed anorthosite and gabbro (1.15 Ga, intrusion age), and unmetamorphosed granitic pegmatite (0.9 Ga) from the Adirondack Highlands; metaluminous and peraluminous granites (114-90 Ma) of the Sierra Nevada Batholith; megacrysts from kimberlite pipes in southern Africa, Brazil, and Siberia; and detrital zircons (4.4-3.9 Ga) of metaconglomerate from Jack Hills, Western Australia. Titanium concentration in zircon was analysed using a CAMECA IMS-1280 ion microprobe (see Page et al., this volume). Spot analyses were correlated to U-Pb SHRIMP pits especially for Adirondack and Jack Hills zircons. The majority of zircons have Ti-content less than 10 ppm. Variability, in excess of analytical precision, within individual zircons is observed in about one-third of crystals. In general, there is no systematic change in Ti from core to rim (identified by cathodoluminescence) of zircons, or with regard to age, U content, Th/U ratio, or U-Pb age concordance for these non-metamict grains. The average temperatures for zircon crystallization in different rock suites using the experimental/empirical calibration of Watson and Harrison (W&H, 2005, Science 308:841), assuming the presence of rutile and quartz, are estimated to be: anorthosite 735±41°C (1SD, n=24; Ti = 10±5 ppm); metagabbro 714±31°C (n=19; Ti = 8±4 ppm); Adirondack pegmatite 500±16°C (n=5; Ti = 0.3±0.1 ppm); metaluminous and peraluminous granites from Sierra Nevada 681±67°C (n=53; Ti = 6±5 ppm) and 613±75°C (n=68; Ti = 3±3 ppm); kimberlite megacrysts 740±64°C (n=169; Ti = 14±13 ppm) (Page et al., this volume); and detrital zircons from Jack Hills metaconglomerate 718±63°C (n=64; Ti = 10±9 ppm). Most of the host rocks contain ilmenite or titanite suggesting that α(TiO2)>0.5, but rutile activity is unknown for megacrysts and detrital zircons. Pegmatite contains no Ti-rich minerals

  10. Selective zircon accumulation in a new benthic foraminifer, Psammophaga zirconia, sp. nov.

    NASA Astrophysics Data System (ADS)

    Sabbatini, Anna; Negri, Alessandra; Bartolini, Annachiara; Morigi, Caterina; Boudouma, Omar; Dinelli, Enrico; Florindo, Fabio; Galeazzi, Roberta; Holzmann, Maria; Lurcock, Pontus C.; Massaccesi, Luca; Pawlowski, Jan W.; Rocchi, Sergio

    2017-04-01

    Benthic foraminifera are single-celled eukaryotes that make a protective organic, agglutinated or calcareous test. Some agglutinated, single-chambered taxa, including Psammophaga Arnold, 1982, retain mineral particles in their cytoplasm, but the selective mechanism of accumulation is not clear. Here, we report the ability of a foraminiferal species to select and accumulate zircons and other heavy minerals in their cytoplasm. In particular, the use of Scanning Electron Microscope coupled with an Energy Dispersive X-ray microanalysis system (SEM-EDS) enabled a representative overview of the mineral diversity and showed that the analysed Psammophaga zirconia sp. nov. individuals contained dominantly crystals of zircon (51%), titanium oxides (27%), and ilmenite (11%) along with minor magnetite and other minerals. The studied specimens occur in the shallow central Adriatic Sea where the sediment has a content of zircon below 1% and of other heavy minerals below 4%. For that reason, we suggest that: (i) P. zirconia may be able to chemically select minerals, specifically zircon and rutile; (ii) the chemical mechanism allowing the selection is based on electrostatic interaction, and it could work also for agglutinated foraminifera. In particular, this aptitude for high preferential uptake and differential ingestion or retention of zircon is reported here for the first time, together with the selection of other heavy minerals already described in members of the genus Psammophaga. They are generally counted among early foraminifera, constructing a morphologically simple test with a single chamber. Our molecular phylogenetic study confirms that P. zirconia is a new species, genetically distinctive from other Psammophaga, and occurs in the Adriatic as well as in the Black Sea. Finally, the presence of eukaryotic soft-walled monothalamous microfossils, capable of building a fine aluminosilicate case, in the Precambrian geological record, makes them useful as a valuable record

  11. Zircon evidence for incorporation of terrigenous sediments into the magma source of continental basalts.

    PubMed

    Xu, Zheng; Zheng, Yong-Fei; Zhao, Zi-Fu

    2018-01-09

    Crustal components may be incorporated into continental basalts by either shallow contamination or deep mixing. While the former proceeds at crustal depths with common preservation of refractory minerals, the latter occurs at mantle depths with rare survival of relict minerals. Discrimination between the two mechanisms has great bearing to subcontinental mantle geochemistry. Here we report the occurrence of relict zircons in Cenozoic continental basalts from eastern China. A combined study of zircon U-Pb ages and geochemistry indicates that detrital zircons were carried by terrigenous sediments into a subcontinental subduction zone, where the zircon were transferred by fluids into the magma sources of continental basalts. The basalts were sampled from three petrotectonic units with distinct differences in their magmatic and metamorphic ages, making the crustal contamination discernible. The terrigenous sediments were carried by the subducting oceanic crust into the asthenospheric mantle, producing both soluble and insoluble materials at the slab-mantle interface. These materials were served as metasomatic agents to react with the overlying mantle wedge peridotite, generating a kind of ultramafic metasomatites that contain the relict zircons. Therefore, the occurrence of relict zircons in continental basalts indicates that this refractory mineral can survive extreme temperature-pressure conditions in the asthenospheric mantle.

  12. Zircon growth in shear zones

    NASA Astrophysics Data System (ADS)

    Kaulina, Tatiana

    2013-04-01

    The possibility of direct dating of the deformation process is critical for understanding of orogenic belts evolution. Establishing the age of deformation by isotopic methods is indispensable in the case of uneven deformation overlapping, when later deformation inherits the structural plan of the early strains, and to distinguish them on the basis of the structural data only is impossible. A good example of zircon from the shear zones is zircon formed under the eclogite facies conditions. On the one hand, the composition of zircon speaks about its formation simultaneously to eclogitic paragenesis (Rubatto, Herman, 1999; Rubatto et al., 2003). On the other hand, geological studies show that mineral reactions of eclogitization are often held only in areas of shear deformations, which provides access of fluid to the rocks (Austrheim, 1987; Jamtveit et al., 2000; Bingen et al., 2004). Zircons from mafic and ultramafic rocks of the Tanaelv and Kolvitsa belts (Kola Peninsula, the Baltic Shield) have showed that the metamorphic zircon growth is probably controlled by the metamorphic fluid regime, as evidenced by an increase of zircon quantity with the degree of shearing. The internal structure of zircon crystals can provide an evidence of zircon growth synchronous with shearing. The studied crystals have a sector zoning and often specific "patchy" zoning (Fig. 1), which speaks about rapid change of growth conditions. Such internal structure can be compared with the "snowball" garnet structure reflecting the rotation of crystals during their growth under a shift. Rapidly changing crystallization conditions can also be associated with a small amount of fluid, where supersaturation is changing even at a constant temperature. Thus, the growth of metamorphic zircon in shear zones is more likely to occur in the fluid flow synchronous with deformation. A distinctive feature of zircons in these conditions is isometric shape and sector "patchy" zoning. The work was supported by

  13. Effective LA-ICP-MS dating of common-Pb bearing accessory minerals with new data reduction schemes in Iolite

    NASA Astrophysics Data System (ADS)

    Kamber, Balz S.; Chew, David M.; Petrus, Joseph A.

    2014-05-01

    Compared to non-destructive geochemical analyses, LA-ICP-MS consumes ca. 0.1 μm of material per ablation pulse. It is therefore to be expected that the combined analyses of ca. 200 pulses will encounter geochemical and isotopic complexities in all but the most perfect minerals. Experienced LA-ICP-MS analysts spot down-hole complexities and choose signal integration areas accordingly. In U-Pb geochronology, the task of signal integration choice is complex as the analyst wants to avoid areas of common Pb and Pb-loss and separate true (concordant) age complexity. Petrus and Kamber (2012) developed VizualAge as a tool for reducing and visualising, in real time, U-Pb geochronology data obtained by LA-ICP-MS as an add-on for the freely available U-Pb geochronology data reduction scheme of Paton et al. (2010) in Iolite. The most important feature of VizualAge is its ability to display a live concordia diagram, allowing users to inspect the data of a signal on a concordia diagram as the integration area it is being adjusted, thus providing immediate visual feedback regarding discordance, uncertainty, and common lead for different regions of the signal. It can also be used to construct histograms and probability distributions, standard and Tera-Wasserburg style concordia diagrams, as well as 3D U-Th-Pb and total U-Pb concordia diagrams. More recently, Chew et al. (2014) presented a new data reduction scheme (VizualAge_UcomPbine) with much improved common Pb correction functionality. Common Pb is a problem for many U-bearing accessory minerals and an under-appreciated difficulty is the potential presence of (possibly unevenly distributed) common Pb in calibration standards, introducing systematic inaccuracy into entire datasets. One key feature of the new method is that it can correct for variable amounts of common Pb in any U-Pb accessory mineral standard as long as the standard is concordant in the U/Pb (and Th/Pb) systems after common Pb correction. Common Pb correction

  14. Preliminary summary review of thorium-bearing mineral occurrences in Alaska

    USGS Publications Warehouse

    Bates, Robert G.; Wedow, Helmuth

    1952-01-01

    Thorium-bearing minerals are known at 47 localities in Alaska. At these localities the thorium occurs as a major constituent or in minor amounts as an impurity in one or more of the following 12 minerals: allanite, columbite, ellsworthite, eschynite, gummite, monazite, orangite, parisite, thorianite, thorite, xenotime, and zircon. In addition other minerals, such as biotite and sphene, are radioactive and may contain thorium. Several unidentified columbate minerals with uranium or thorium and uranium as major constituents have been recognized at some localities. The distribution, by type of deposit, of the 57 thorium occurrences is as follows: lode - 3, lode and placer - 1, granitic rock - 3, granitic rock and related placer - 14, and placer - 26. Of the four lode occurrences only the radioactive veins at Salmon Bay in southeastern Alaska and the contact metamorphic deposit in the Nixon Fork area of central Alaska warrant further consideration, although insufficient data are available to determine whether these two deposits have commercial possibilities. The remaining occurrences of thorium-bearing minerals in Alaska are limited to placer deposits and disseminations of accessory minerals in granitic rocks. In most of these occurrences the thorium-bearing minerals occur in only trace amounts and consequently warrent little further consideration. More data are needed to determine the possibilities of byproduct recovery of thorium-bearing minerals from several of the gold and tin placers.

  15. Les minéraux accessoires des granitoïdes de la suite taourirt, Hoggar (Algérie): conséquences pétrogénétiques

    NASA Astrophysics Data System (ADS)

    Azzouni-Sekkal, Abla; Bonin, Bernard

    1998-01-01

    The post-Pan-African 'taourirt' suite of Hoggar (Algeria) is made up by themagmatic suite: G I monzogranite, G IIa monzogranite+syenogranite, G IIb subsolvus alkali feldspar granite (alaskite), GIII hypersolvus alkali feldspar syenite + granite. Silicates (zircon, thorite, allanite, chevkinite, titanite), oxides (magnetite, ilmenite, fergusonite) and phosphates (apatite, monazite), often abundant, constitute various accessory mineral associations. Crystal morphology, place in the sequence of crystallisation and mineral chemistry change as a function of parageneses. The constant titanite + magnetite + ilmenite assemblage in G I and G II rocks illustrates more oxidising conditions than in G III group, where hedenbergite + magnetite + ilmenite coexist. Two groups of accessory minerals are distinguished: (1) LREE rich (3×10 4 to 3×10 5 × chondrites) and Y rich (50 to 10 4 × chondrites), such as allanite, chevkinite and monazite, (2) LREE poor (100 to 10 4 × chondrites) and Y rich (1000 to 10 5 × chondrites), such as zircon, thorite, titanite and fergusonite. Shapes of chondrite-normalised patterns and evolutionary trends of REE, as well as of other HFSE, such as Nb, Zr, U and Th, in bulk rocks are dependent on relative abundances of the different accessory minerals.

  16. Geochemistry and Temperatures Recorded by Zircon During the Final Stages of the Youngest Toba Tuff Magma Chamber, Sumatra, Indonesia

    NASA Astrophysics Data System (ADS)

    Gaither, T.; Reid, M. R.; Vazquez, J. A.

    2009-12-01

    The ~74 ka eruption of the Youngest Toba Tuff (YTT) in Sumatra, Indonesia, was one of the largest single volcanic eruptions in geologic history, on par with other voluminous silicic eruptions such as the Huckleberry Ridge Tuff of Yellowstone and the Bishop Tuff of Long Valley, California. We are exploring how zircon and other accessory mineral phases record compositional and thermal changes that occurred in the YTT magma, and the important clues these crystal scale records hold for magma chamber dynamics and processes that lead up to supervolcano eruptions. In this study, we report trace element (REE, U, Th, Ti, and Hf) characteristics, Ti-in-zircon crystallization temperatures, and apparent REE partition coefficients obtained for YTT zircon rims. Twenty-nine zircons from pumices with a compositional range of 70-76 wt% SiO2 were analyzed on the UCLA Cameca ims 1270 ion microprobe. The grains were mounted so that only the outermost ~1.5 microns of the crystals were analyzed. Median Zr/Hf ratios of 34 to 38 characterize zircons from the pumices; the high silica rhyolite grains have lower Zr/Hf. Chondrite-normalized REE patterns are strongly LREE-depleted. Positive Ce anomalies are large (Ce/Ce* ranges up to 88) and Eu/Eu* varies by a factor of four (0.05 to 0.21). Eu/Eu*, Nd/Yb, and Th/U decrease with decreasing Zr/Hf, showing that the variation in zircon rim compositions may be related by co-precipitation of feldspar and allanite along with zircon. Titanium contents also decrease with decreasing Zr/Hf, suggesting that the chemical differences could be related to temperature changes. REE partition coefficients calculated from zircon rim compositions and pumice glass compositions give a good fit to a lattice strain model. They are also quite similar to the partition coefficients of Sano et al. (2002) which have been shown to be successful at reproducing melt compositions in other settings. Temperatures of crystallization calculated using the Ti-in-zircon

  17. Provenance and metamorphic PT conditions of Cryogenian-Ediacaran metasediments from the Kid metamorphic complex, Sinai, NE Arabian-Nubian Shield: Insights from detrital zircon geochemistry and mineral chemistry

    NASA Astrophysics Data System (ADS)

    El-Bialy, Mohammed Z.; Ali, Kamal A.; Abu El-Enen, Mahrous M.; Ahmed, Ahmed H.

    2015-12-01

    The Malhaq and Um Zariq formations occupy the northern part of the Neoproterozoic Kid metamorphic complex of SE Sinai, NE Arabian-Nubian Shield. This study presents new mineral chemistry data and LA-ICP-MS analyses of the trace element concentrations on zircons separated from metapelites from these formations. The detrital zircons of Um Zariq Formation are more enriched in ΣREE, whereas Malhaq Formation zircons are markedly HREE-enriched with strongly fractionated HREE patterns. The quite differences in the overall slope and size of the Eu and Ce anomalies between REE patterns of the two zircon suites provide a robust indication of different sources. The Ti-in-zircon thermometer has revealed that the zircons separated from Malhaq Formation were crystallized within the 916-1018 °C range, while those from Um Zariq Formation exhibit higher range of crystallization temperatures (1084-1154 °C). The detrital zircons of Malhaq Formation were derived mainly from mafic source rocks (basalt and dolerite), whereas Um Zariq Formation zircons have varied and more evolved parent rocks. Most of the investigated zircons from both formations are concluded to be unaltered magmatic that were lately crystallized from a high LREE/HREE melt. All the studied detrital zircon grains show typical trace elements features of crustal-derived zircons. All of the Um Zariq Formation and most of Malhaq Formation detrital zircons are geochemically discriminated as continental zircons. Both formation metapelites record similar, overlapping peak metamorphic temperatures (537-602 °C and 550-579 °C, respectively), and pressures (3.83-4.93 kbar and 3.69-4.07 kbar, respectively). The geothermal gradient, at the peak metamorphic conditions, was quite high (37-41 °C/km) corresponding to metamorphism at burial depth of 14-16 km. The peak regional metamorphism of Um Zariq and Malhaq formations is concluded to be generated during extensional regime and thinning of the lithosphere in an island arc

  18. High Pressure Behavior of Zircon at Room Temperature

    NASA Astrophysics Data System (ADS)

    Reichmann, H. J.; Rocholl, A.

    2016-12-01

    Zircon, ZrSiO4, is an ubiquitous mineral in the Earth's crust, forming under a wide range of metamorphic and igneous conditions. Its high content in certain trace elements (REE, Hf, Th, U) and due to its isotopic information, together with its chemical and physical robustness makes zircon an unique geochemical tool and geochronometer. Despite its geological importance there is a disagreement regarding the responds of zircon to elevated pressure, especially about the commencement of a pressure - induced structural phase transition. At elevated pressure zircon (I41/amd) undergoes a pressure induced phase transition to the scheelite structure (I41/a) . In the low pressure and high pressure phase, the (SiO4)4- tetrahedral units are present. However, the onset of the phase transition at room temperature is not well defined: zircon - scheelite transitions have been reported in a pressure regime ranging from 20 to 30 GPa (e.g. Ono et al., 2004). To clarify this issue, we performed Raman spectroscopy measurement up to 60 GPa on a non-metamict single crystal zircon sample (reference material 91500; Wiedenbeck et al., 1995; Wiedenbeck et al., 2004). A closer look at the external lattice modes at 201 cm-1 shows a decreasing of the wavenumbers with increasing pressure up to 21 GPa followed by a steep increase. The lattice modes at 213 and 224 cm-1 also exhibit a subtle kink in this pressure range. This pressure coincides with that one reported for the zircon - scheelite transition (van Westrenen et al., 2004). Another interesting issue is the behavior of the internal modes at higher pressures. The ν3 stretching modes at about 1000 cm-1show distinct discontinuities at 31 GPa accompanied by the emerging of new features in the Raman spectrum suggesting another, pressure triggered modification in the zircon structure. References: Ono, Funakoshi, Nakajima, Tange, and Katsura (2004) Contr. Mineral. Petrol., 147, 505-509. Van Westrenen, Frank, Hanchar, Fei, Finch, and Zha (2004

  19. Determination of zircon/melt trace element partition coefficients from SIMS analysis of melt inclusions in zircon

    NASA Astrophysics Data System (ADS)

    Thomas, J. B.; Bodnar, R. J.; Shimizu, N.; Sinha, A. K.

    2002-09-01

    Partition coefficients ( zircon/meltD M) for rare earth elements (REE) (La, Ce, Nd, Sm, Dy, Er and Yb) and other trace elements (Ba, Rb, B, Sr, Ti, Y and Nb) between zircon and melt have been calculated from secondary ion mass spectrometric (SIMS) analyses of zircon/melt inclusion pairs. The melt inclusion-mineral (MIM) technique shows that D REE increase in compatibility with increasing atomic number, similar to results of previous studies. However, D REE determined using the MIM technique are, in general, lower than previously reported values. Calculated D REE indicate that light REE with atomic numbers less than Sm are incompatible in zircon and become more incompatible with decreasing atomic number. This behavior is in contrast to most previously published results which indicate D > 1 and define a flat partitioning pattern for elements from La through Sm. The partition coefficients for the heavy REE determined using the MIM technique are lower than previously published results by factors of ≈15 to 20 but follow a similar trend. These differences are thought to reflect the effects of mineral and/or glass contaminants in samples from earlier studies which employed bulk analysis techniques. D REE determined using the MIM technique agree well with values predicted using the equations of Brice (1975), which are based on the size and elasticity of crystallographic sites. The presence of Ce 4+ in the melt results in elevated D Ce compared to neighboring REE due to the similar valence and size of Ce 4+ and Zr 4+. Predicted zircon/meltD values for Ce 4+ and Ce 3+ indicate that the Ce 4+/Ce 3+ ratios of the melt ranged from about 10 -3 to 10 -2. Partition coefficients for other trace elements determined in this study increase in compatibility in the order Ba < Rb < B < Sr < Ti < Y < Nb, with Ba, Rb, B and Sr showing incompatible behavior (D M < 1.0), and Ti, Y and Nb showing compatible behavior (D M > 1.0). The effect of partition coefficients on melt evolution during

  20. Mineral Dissolution and Precipitation due to Carbon Dioxide-Water-Rock Interactions: The Significance of Accessory Minerals in Carbonate Reservoirs (Invited)

    NASA Astrophysics Data System (ADS)

    Kaszuba, J. P.; Marcon, V.; Chopping, C.

    2013-12-01

    Accessory minerals in carbonate reservoirs, and in the caprocks that seal these reservoirs, can provide insight into multiphase fluid (CO2 + H2O)-rock interactions and the behavior of CO2 that resides in these water-rock systems. Our program integrates field data, hydrothermal experiments, and geochemical modeling to evaluate CO2-water-rock reactions and processes in a variety of carbonate reservoirs in the Rocky Mountain region of the US. These studies provide insights into a wide range of geologic environments, including natural CO2 reservoirs, geologic carbon sequestration, engineered geothermal systems, enhanced oil and gas recovery, and unconventional hydrocarbon resources. One suite of experiments evaluates the Madison Limestone on the Moxa Arch, Southwest Wyoming, a sulfur-rich natural CO2 reservoir. Mineral textures and geochemical features developed in the experiments suggest that carbonate minerals which constitute the natural reservoir will initially dissolve in response to emplacement of CO2. Euhedral, bladed anhydrite concomitantly precipitates in response to injected CO2. Analogous anhydrite is observed in drill core, suggesting that secondary anhydrite in the natural reservoir may be related to emplacement of CO2 into the Madison Limestone. Carbonate minerals ultimately re-precipitate, and anhydrite dissolves, as the rock buffers the acidity and reasserts geochemical control. Another suite of experiments emulates injection of CO2 for enhanced oil recovery in the Desert Creek Limestone (Paradox Formation), Paradox Basin, Southeast Utah. Euhedral iron oxyhydroxides (hematite) precipitate at pH 4.5 to 5 and low Eh (approximately -0.1 V) as a consequence of water-rock reaction. Injection of CO2 decreases pH to approximately 3.5 and increases Eh by approximately 0.1 V, yielding secondary mineralization of euhedral pyrite instead of iron oxyhydroxides. Carbonate minerals also dissolve and ultimately re-precipitate, as determined by experiments in the

  1. U-Pb Ages of Lunar Apatites

    NASA Technical Reports Server (NTRS)

    Vaughan, J.; Nemchin, A. A.; Pidgeon, R. T.; Meyer, Charles

    2006-01-01

    Apatite is one of the minerals that is rarely utilized in U-Pb geochronology, compared to some other U-rich accessory phases. Relatively low U concentration, commonly high proportion of common Pb and low closure temperature of U-Pb system of apatite inhibit its application as geochronological tool when other minerals such as zircon are widely available. However, zircon appear to be restricted to certain type of lunar rocks, carrying so called KREEP signature, whereas apatite (and whitlockite) is a common accessory mineral in the lunar samples. Therefore, utilizing apatite for lunar chronology may increase the pool of rocks that are available for U-Pb dating. The low stability of U-Pb systematics of apatite may also result in the resetting of the system during meteoritic bombardment, in which case apatite may provide an additional tool for the study of the impact history of the Moon. In order to investigate these possibilities, we have analysed apatites and zircons from two breccia samples collected during the Apollo 14 mission. Both samples were collected within the Fra Mauro formation, which is interpreted as a material ejected during the impact that formed the Imbrium Basin.

  2. Paleomagnetism of Hadean and Archean Detrital Zircons from the Jack Hills, Western Australia

    NASA Astrophysics Data System (ADS)

    Weiss, B. P.; Lima, E. A.; Alexander, E.; Bell, E. A.; Boehnke, P.; Wielicki, M. M.; Harrison, M.; Fu, R. R.; Kehayias, P.; Glenn, D. R.; Walsworth, R. L.; Araujo, J. F. D.; Einsle, J. F.; Harrison, R.; Trail, D.; Watson, E. B.

    2016-12-01

    Determining the history of Earth's dynamo prior to the oldest known well-preserved rock record is one of the ultimate challenges in the field of paleomagnetism. The dynamo's early history has major implications for the evolution of the core, the initiation of plate tectonics, the physics of magnetic field generation, and the habitability of the early Earth. The only known minerals that might retain paleomagnetic records from well before 3.5 billion years ago (Ga) are detrital zircon crystals found in sedimentary rocks in Western Australia. Ranging up to 4.38 Ga in age, they are the oldest known terrestrial minerals. Tarduno et al. (2015) argued that detrital zircons contain records of an active dynamo dating back to 4.2 Ga. However, it has not been demonstrated that the zircons have escaped remagnetization during the intervening time since their formation (Weiss et al. 2016). Therefore, the age of magnetization in the Jack Hills zircons and the existence of a dynamo prior to 3.5 Ga have yet to be established. To address this issue, we have been studying the magnetism and thermal and aqueous alteration histories of single Archean and Hadean Jack Hills zircon crystals. Peak unblocking temperatures combined with electron backscatter diffraction indicate that the zircons contain inclusions of magnetite and hematite. Electron microscopy, X-ray tomography, and quantum diamond magnetometry indicate that much of the iron oxides in the zircons are associated with cracks and are therefore likely secondary. However, our newly developed Li-in-zircon geospeedometry technique shows for the first time that a small fraction of Hadean zircons retain sharp gradients in Li concentration (see figure), indicating they likely have never heated above the magnetite Curie temperature since their formation at >4 Ga. We describe thermal demagnetization and Thellier-Thellier paleointensity studies of these zircons and implications for the existence of a Hadean dynamo.

  3. Geochronology and geochemistry of the granites from the Zhuxi W-Cu ore deposit in South China: Implication for petrogenesis, geodynamical setting and mineralization

    NASA Astrophysics Data System (ADS)

    Pan, Xiaofei; Hou, Zengqian; Zhao, Miao; Chen, Guohua; Rao, Jianfeng; Li, Yan; Wei, Jin; Ouyang, Yongpeng

    2018-04-01

    The giant Zhuxi tungsten deposit is located in the Taqian-Fuchun Ore Belt in northeastern Jiangxi province, and genetically associated with the Zhuxi granitic stocks and dykes. Three mineralization-related granites including granite porphyry dykes (GP), biotite granitic stocks (BG), and white granitic dykes (WG), were identified in the Zhuxi deposit. SHRIMP zircon U-Pb analysis for the three granitic rocks present ages ranging from 153.5 ± 1.0 Ma to 150.4 ± 1.0 Ma. The BG mainly contains quartz, microcline, albite, biotite and muscovite with minor accessory minerals including zircon, apatite, monazite, Ti/Fe oxides, and dolerite. However, the WG is mainly composed of quartz, microcline and albite with minor muscovite and accessory minerals. The GP is a medium-grained porphyritic granite and its phenocrysts include quartz, alkali feldspar, muscovite and plagioclase. All the Zhuxi granites have high SiO2 content (71.97 wt%-81.19 wt%) and total alkali (3.25 wt%-9.42 wt%), and their valid aluminum saturation index (ASI) values show a wide range of 1.03 to 2.49. High Rb/Sr ratios, low Sr content (<50 ppm) and markedly negative Eu anomalies of GP, WG and BG demonstrated that the Zhuxi granites are highly fractioned and intensive crystal differentiated. Because they display the features of both I- and S-types granites, they were confirmed to be I-S transform-type granites. Whole rock εNd(t) and zircon εHf(t) values fall into the ranges of -6.98 to -11.97, and -3.1 to -11.5, and the Nd (TDM2) and Hf two-stage model ages (TDMc) are 1.51-1.92 Ga and 1.42-2.01 Ga, respectively. Geochemical and isotopic data suggest that these highly fractionated I-S transform-type granites were originated from magmas which showed affinity with the Proterozoic continent and the Shuangqiaoshan Group and little mantle contribution was involved during the generation of Zhuxi granitic rocks. Extreme fractional crystallization resulted in further enrichment of tungsten in the evolved granitic

  4. Hydrogen diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Ingrin, Jannick; Zhang, Peipei

    2016-04-01

    Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ° C to 1150 ° C. FTIR analyses were performed on oriented slices before and after each annealing run. H diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001] follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy and slower diffusivity than other NAMs below 1150 ° C even iron-poor garnets which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al. 2005). During H-D exchange zircon incorporates also deuterium. This hydration reaction involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic bands in the near infrared region during annealing. It is the first time that a hydration reaction U5+ + OH- = U4+ + O2- + 1/2H2, is experimentally reported. The kinetics of deuterium incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures. At 500 ° C, a zircon with a radius of 300 μm would retain its H isotopic signature over more than a million years. However, a zircon is unable to retain this information for geologically significant times under high-grade metamorphism unless the grain size is large enough. Refrences Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics and Chemistry of Minerals, 31, 593-605. Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and deuteration in

  5. Crystallization process of zircon and fergusonite during hydrothermal alteration in Nechalacho REE deposit, Thor Lake, Canada

    NASA Astrophysics Data System (ADS)

    Hoshino, M.; Watanabe, Y.; Murakami, H.; Kon, Y.; Tsunematsu, M.

    2012-04-01

    The core samples of two drill holes, which penetrate sub-horizontal mineralized horizons at Nechalacho REE deposit in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify magmatic and hydrothermal processes that enriched HFSE (e.g. Zr, Nb, Y and REE). Zircon is the most common REE minerals in Nechalacho REE deposit. The zircon is divided into five types as follows: Type-1 zircon occurs as single grain in phlogopite and the chondrite-normalized REE pattern is characterized by a steeply-rising slope from the LREE to the HREE with a positive Ce-anomaly and negative Eu-anomaly. This chemical characteristic is similar to that of igneous zircon. Type-2 zircon consists of HREE-rich magmatic porous core and LREE-Nb-F-rich hydrothermal rim. This type zircon is mostly included in phlogopite and fluorite, and occasionally in microcline. Type-3 zircon is characterized by euhedral to anhedral crystal, occurring in a complex intergrowth with REE fluorocarbonates. Type-3 zircons have high contents of REE, Nb and fluorine. Type-4 zircon consists of porous-core and -rim zones, but their chemical compositions are similar to each other. This type zircon is a subhedral crystal rimmed by fergusonite. Type-5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircons are filled by fergusonite. Type-4 and -5 zircons show low REE and Nb contents. Occurrences of these five types of zircon are different according to the depth and degree of the alteration by hydrothermal solutions rich in F- and CO3 of the two drill holes, which permit a model for evolution of the zircon crystallization in Nechalacho REE deposit as follows: (1) type-1 (single magmatic zircon) is formed in miaskitic syenite. (2) LREE-Nb-F-rich hydrothermal zircon formed around HREE-rich magmatic zircon (type-2 zircon); (3) type-3 zircon crystallized thorough F and CO3-rich hydrothermal alteration of type-2 zircon which formed the complex

  6. Ti-in-zircon thermometry: applications and limitations

    NASA Astrophysics Data System (ADS)

    Fu, Bin; Page, F. Zeb; Cavosie, Aaron J.; Fournelle, John; Kita, Noriko T.; Lackey, Jade Star; Wilde, Simon A.; Valley, John W.

    2008-08-01

    The titanium concentrations of 484 zircons with U-Pb ages of ˜1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zircons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413-433) without making corrections for reduced oxide activities (e.g., TiO2 or SiO2), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500° to 850°C, and are lower than either zircon saturation temperatures (for granitic rocks) or predicted crystallization temperatures of evolved melts (˜15% melt residue for mafic rocks). Temperatures average: 653 ± 124°C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 ± 111°C (261 zircons) for mafic rocks, and 758 ± 98°C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced a_{TiO2} or a_{SiO2}, variable pressure, deviations from Henry’s Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystallization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with significantly lower crystallization temperature for the last 10-15% melt residue than that of the main rock. While some magmatic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti

  7. Fatigue properties for the fracture strength of columnar accessory minerals embedded within metamorphic tectonites: implications for stress magnitude in continental crust at the depth of the brittle-plastic transition zone

    NASA Astrophysics Data System (ADS)

    Kimura, N.; Iwashita, N.; Masuda, T.

    2009-04-01

    1. Introduction Previous studies have compiled yield-strength profiles of continental lithosphere based on the results of laboratory measurements and numerical calculations; however, yield-strength values remain poorly constrained, especially at depths below the brittle-plastic transition zone. Recent studies by the authors have refined the microboudin technique for estimating palaeostress magnitude in the deep crust (> 10 km depth). This technique has the potential to provide important information on stress levels in the deep continental crust, an environment to which available in situ stress measurements and palaeopiezometric methods cannot be applied. In applying the microboudinage technique, obtaining an estimate of the palaeostress magnitude requires knowledge of the fracture strength of columnar accessory minerals (e.g., tourmaline, amphibole, and epidote) that are subjected to brittle fracturing during plastic deformation of the surrounding matrix minerals. The absolute magnitude of fracture strength is known to show a marked reduction in the case of fatigue fracture. Fatigue fracture falls into two categories: static fatigue and cyclic fatigue. In the field of experimental rock deformation, stress corrosion by water molecules (static fatigue) is commonly invoked as the mechanism of fatigue fracture; however, evidence of both static and cyclic fatigue has been reported from studies of natural geological samples. The present study focused on the fatigue properties of columnar accessory minerals at high temperatures, with the aim of improving the accuracy of estimates of natural palaeostress magnitude at depth in the crust. 2. Constant stress-rate test A constant stress-rate test was performed to determine the influence of static fatigue on the strength of columnar accessory minerals. The test was conducted under three-point bending with a span distance of 10 mm. Temperature conditions and the crosshead speed were set in the ranges of ambient to 600°C, and 0

  8. Mineral inclusions and SHRIMP U-Pb dating of zircons from the Alamas nephrite and granodiorite: Implications for the genesis of a magnesian skarn deposit

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Zhang, Rongqing; Zhang, Zhiyu; Shi, Guanghai; Zhang, Qichao; Abuduwayiti, Maituohuti; Liu, Jianhui

    2015-01-01

    Extending approximately 1300 km and located in the Western Kunlun Mountains, the Hetian nephrite belt is the largest nephrite belt in the world and contains approximately 11 major deposits and more than 20 orebodies including the Alamas deposit. Hetian nephrite deposits can be classified as Mg-skarn deposits with Precambrian dolomitic marble host rock and green, green-white and white nephrite zones are distributed gradually in the zone of a granodiorite pluton. The green nephrite is mainly predominately composed of tremolite with generally minor to trace constituents of diopside, grossularitic garnet, actinolite and other minerals. Also green nephrite has higher content of TFe2O3, than green-white and white nephrites have. We subdivided the zircons from the green nephrites into four types, depending on their internal textures, mineral inclusions, and SHRIMP U-Pb ages. Type I zircons are round instead of idiomorphic in shape and lack obvious zoning. Type II and IV zircons have broad, clear oscillatory zoning and are hypidiomorphic or idiomorphic in shape; they contain inclusions of diopside, tremolite, chlorite and calcite. Most Type III zircons are narrow rims (< 10 μm) surrounding Type II and Type I zircons with highly luminous brightness and no zoning. Both Type I and Type II zircons have individual ages of 411 to 445 Ma and Type IV zircons have younger ages (388 to 406 Ma). Among the concordant ages, 425.7 ± 5.8 Ma and 420.0 ± 9.9 Ma for the QYZr1 and QYZr2 are consistent within error, with the 418.5 ± 2.8 Ma of the Alamas granodiorite formation age and the maximum age of the Alamas nephrite deposit. The partially recrystallization of zircons during skarn formation possibly lead to some younger individual ages (406.5 to 308 Ma). In the Western Kunlun Mountain, both Buya granite and Alamas grandiorite are high Ba-Sr granites and crystallized in Western Kunlun Orogen. The Buya granite formed at about 430 Ma in a post-orogenic tectonic environment. Considering

  9. Timing of metasomatism in a subcontinental mantle: evidence from zircon at Finero (Italy)

    NASA Astrophysics Data System (ADS)

    Badanina, I. Yu.; Malitch, K. N.

    2012-04-01

    The Finero phlogopite-peridotite represents a metasomatized residual mantle harzburgite, exposed at the base of the lower-crust section in the Ivrea Zone, Western Alps (Hartmann and Wedepohl 1993). It forms the core of a concentrically zoned sequence of internal layered gabbro, amphibole-rich peridotite and external gabbro. The phlogopite peridotite contains small-size chromitite bodies, with a suite of accessory minerals such as phlogopite, apatite, Ca-Mg carbonates, zirconolite, zircon, thorianite and uraninite, proposed to form during alkaline-carbonatitic metasomatism process within the mantle (Zaccarini et al. 2004). In this study, the combined application of a non-destructive technique to separate zircon from their host rocks (see details at http://www.natires.com) and in-situ analytical technique for compositional and isotopic analysis (SHRIMP-II at Russian Geological Research Institute, St. Petersburg) has provided new more detailed age constraints on the formation of chromitite and related metasomatic events within a mantle tectonite at Finero. Chromitite samples derived from the dump in the prospecting trenches of Rio Creves. In thin sections, zircon occurs as relatively large (up to 200 μm) grains characterized by subhedral to euhedral shapes. Separated grains of zircon form two distinct populations. Dominant zircon population is pale pink and characterized by different shapes (subhedral, subrounded or elongated). In cathodoluminescense, the main set of population is represented by complex grains, which show development of core-rim relationship (most likely recrystallized rim on a preserved core). Subordinate zircon grains are colourless. They are characterized by a smoky cathodoluminescense, with almost no internal pattern. Three main U-Pb age clusters have been recognized. The youngest age cluster, typical for subordinate colourless zircon population and rims in complex grains of dominant pale pink population, show two concordant 206Pb/238U ages (e

  10. Constraints on the timing of multiple thermal events and re-equilibration recorded by high-U zircon and xenotime: Case study of pegmatite from Piława Górna (Góry Sowie Block, SW Poland)

    NASA Astrophysics Data System (ADS)

    Budzyń, Bartosz; Sláma, Jiří; Kozub-Budzyń, Gabriela A.; Konečný, Patrik; Holický, Ivan; Rzepa, Grzegorz; Jastrzębski, Mirosław

    2018-06-01

    demonstrates the importance of the careful examination of compositional, microtextural and geochronological data obtained using microanalytical techniques to reconstruct the complex thermal histories recorded by accessory minerals.

  11. Ancient and modern rhyolite: Using zircon trace element compositions to examine the origin of volcanic rocks

    NASA Astrophysics Data System (ADS)

    Klemetti, E. W.; Lackey, J.; Starnes, J.; Wooden, J. L.

    2011-12-01

    Volcanic rocks are an important marker for magmatism in the Earth's past and may be all that remains (or is exposed) to elucidate on magmagenesis in ancient terranes. Unlike plutonic rocks, which are likely aggregates of many pulses of magmatism over 104 to 106 year timescales, volcanic rocks are snapshots into specific moments in the development of a magmatic system, and in a larger sense, the tectonic setting in which the volcanoes reside. However, volcanic rocks from the rock record are commonly altered, preventing straightforward petrogenetic interpretation. In contrast, studies of refractory trace minerals such as zircon allow original petrogenesis to be recovered. In the south central Sierra Nevada batholith, Triassic to Cretaceous meta-rhyolites of the Mineral King roof pendant record snapshots of rhyolitic volcanism from key intervals of magmatism in the Sierra arc, however these rhyolites are highly altered and deformed, so little can be deduced about the original magmas or their tectonic settings. To resolve this, we recovered zircon from the four principle rhyolite units to date via SHRIMP-RG. Ages on rhyolites at Mineral King range from ˜196 Ma to 134 Ma, with three of the rhyolites being between 134 and 136 Ma. We also measured trace element composition (REE, Hf, Y and others) to explore the origins of the rhyolites. We can examine the processes at work in the development of these rhyolites along the western margin of North America during the Jurassic and Cretaceous by comparing them with modern volcanic arcs that produce abundant rhyolite eruptions, such as the Okataina Caldera Complex, New Zealand. Compared to zircon from the Okataina rhyolites, Mineral King rhyolites show a much more fractionation-dominated pattern of high Eu/Eu* (0.30-0.50) to low (<0.10) Eu/Eu* relative to increasing Hf, suggesting systems dominated by crystal fractionation or derived from a feldspar-rich source, unlike Okataina zircon that suggest abundance crystal recycling

  12. Petrology of Zircon-Bearing Diogenite Northwest Africa 10666

    NASA Technical Reports Server (NTRS)

    Tanner, T. B.; Jeffcoat, C. R.; Righter, M.; Berger, E. L.; Lapen, T. J.; Irving, A. J.; Kuehner, S. M.; Fujihara, G.

    2017-01-01

    The howardite, eucrite, and diogenite (HED) meteorites are a group of achondrites thought to be derived from the asteroid 4 Vesta, though there is active debate as to whether all diogenites are part of the HED suite. Petrologic investigation of the HED meteorite group provides a means of understanding early planetary differentiation processes and early evolution of planets in our solar system. Diogenites are predominantly coarse grained ortho-pyroxenites with some samples containing appreciable amounts of clinopyroxene, olivine, chromite, and plagioclase. Accessory metal, troilite, and apatite are common. Many diogenites are brecciated, however, there are few poorly to unbrecciated samples. Diogenites are important because they may represent the lower crust of 4 Vesta. Although Mg isotope data indicates that the sources of diogenites are ancient, their crystallization ages are difficult to constrain due to their protracted thermal histories. The limited chronologic data for diogenites also limits the ability to test petrogenetic connections with eucrites and even parent body. A reliable and high closure-temperature isotope system, such as U-Pb in zircon, is needed to address the timing of diogenite igneous crystallization. Description of the textures and mineralogy of diogenites are essential to their classification and understanding their formation, in particular, whether all phases are petrogenetically related. Here, we present detailed petrographic data from a rare zircon-bearing feldspathic diogenite, Northwest Africa (NWA) 10666 and provide textural evidence for igneous crystallization of the zircon.

  13. Resolving the age of Wilson Creek Formation tephras and the Mono Lake excursion using high-resolution SIMS dating of allanite and zircon rims

    NASA Astrophysics Data System (ADS)

    Vazquez, J. A.; Lidzbarski, M. I.

    2012-12-01

    the recorded event is instead the Laschamp excursion. The results are consistent with a depositional chronology from correlation of relative paleointensity (Zimmerman et al., 2006) that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation. Moreover, the results demonstrate that high-spatial resolution SIMS dating of accessory mineral rims is an alternative and promising approach for resolving the depositional ages of silicic tephras containing minerals that crystallized over protracted intervals or that are plagued by incorporation of xenocrysts and/or antecrysts. References: Lajoie, K., 1968, PhD Dissertation, UC Berkeley; Zimmerman et al., 2006, EPSL 252: 94-106.

  14. Geochemistry, mineralogy, and zircon U-Pb-Hf isotopes in peraluminous A-type granite xenoliths in Pliocene-Pleistocene basalts of northern Pannonian Basin (Slovakia)

    NASA Astrophysics Data System (ADS)

    Huraiová, Monika; Paquette, Jean-Louis; Konečný, Patrik; Gannoun, Abdel-Mouhcine; Hurai, Vratislav

    2017-08-01

    Anorogenic granite xenoliths occur in alkali basalts coeval with the Pliocene-Pleistocene continental rifting of the Pannonian Basin. Observed granite varieties include peraluminous, calcic to peralkalic, magnesian to ferroan types. Quartz and feldspars are dominant rock-forming minerals, accompanied by minor early ilmenite and late magnetite-ulvöspinel. Zircon and Nb-U-REE minerals (oxycalciopyrochlore, fergusonite, columbite) are locally abundant accessory phases in calc-alkalic types. Absence of OH-bearing Fe, Mg-silicates and presence of single homogeneous feldspars (plagioclase in calcic types, anorthoclase in calc-alkalic types, ferrian Na-sanidine to anorthoclase in alkalic types) indicate water-deficient, hypersolvus crystallization conditions. Variable volumes of interstitial glass, absence of exsolutions, and lacking deuteric hydrothermal alteration and/or metamorphic/metasomatic overprint are diagnostic of rapid quenching from hypersolidus temperatures. U-Pb zircon ages determined in calcic and calc-alkalic granite xenoliths correspond to a time interval between 5.7 and 5.2 Ma. Positive ɛHf values (14.2 ± 3.9) in zircons from a 5.2-Ma-old calc-alkalic granite xenolith indicate mantle-derived magmas largely unaffected by the assimilation of crustal material. This is in accordance with abundances of diagnostic trace elements (Rb, Y, Nb, Ta), indicating A1-type, OIB-like source magmas. Increased accumulations of Nb-U-REE minerals in these granites indicate higher degree of the magmatic differentiation reflected in Rb-enrichment, contrasting with Ba-enrichment in barren xenoliths. Incipient charnockitization, i.e. orthopyroxene and ilmenite crystallization from interstitial silicate melt, was observed in many granite xenoliths. Thermodynamic modeling using pseudosections showed that the orthopyroxene growth may have been triggered by water exsolution from the melt during ascent of xenoliths in basaltic magma. Euhedral-to-skeletal orthopyroxene growth

  15. Uranium-lead dating of hydrothermal zircon and monazite from the Sin Quyen Fe-Cu-REE-Au-(U) deposit, northwestern Vietnam

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Chun; Zhou, Mei-Fu; Chen, Wei Terry; Zhao, Xin-Fu; Tran, MyDung

    2018-03-01

    The Sin Quyen deposit in northwestern Vietnam contains economic concentrations of Cu, Au and LREE, and sub-economic concentration of U. In this deposit, massive and banded replacement ores are hosted in Neoproterozoic metapelite. The paragenetic sequence includes sodic alteration (stage I), calcic-potassic alteration and associated Fe-REE-(U) mineralization (stage II), Cu-Au mineralization (stage III), and sulfide-(quartz-carbonate) veins (stage IV). The Sin Quyen deposit experienced an extensive post-ore metamorphic overprint, which makes it difficult to precisely determine the mineralization age. In this study, zircon and monazite U-Pb geochronometers and the Rb-Sr isochron method are used to constrain the timing of mineralization. Zircon grains in the ore are closely intergrown or texturally associated with hydrothermal minerals of stage II (e.g., garnet, allanite, and hedenbergite). They may contain primary fluid inclusions and display irregular zoning in cathodoluminescence (CL) images. Zircon grains are rich in U (688 to 2902 ppm) and poor in Th (0.2 to 2.9 ppm). Their δ18OV-SMOW values range from 11.9 to 14.0‰, higher than those of typical magmatic zircon. These textural and compositional features imply that zircon precipitated from 18O- and U-rich hydrothermal fluids, coeval with the minerals of stage II. Monazite occurs in close association with stage II magnetite and allanite and has low contents of Th (<2700 ppm), indicative of a hydrothermal origin. Hydrothermal zircon and monazite have indistinguishable U-Pb ages of 841 ± 12 and 836 ± 18 Ma, respectively, representing the timing of Fe-REE mineralization. There is no direct isotopic constraint on the timing of the Cu-Au mineralization, but geological observations suggest that the Cu-Au and Fe-REE ores most likely formed within a single evolved hydrothermal process. In the plot of 87Rb/86Sr vs. 87Sr/86Sr, the composition of bulk-ore and biotite separates from ore lie along a reference line for 30 Ma

  16. Preliminary study on multi-element profile mapping of crustal and mantle zircons by using Synchrotron Radiation X-ray Fluorescence (SR-XRF)

    NASA Astrophysics Data System (ADS)

    Hasözbek, Altug; Shyam, Badri; Siebel, Wolfgang; Schmitt, Axel; Akay, Erhan; Skinner, Lawrie

    2013-04-01

    Zircon (ZrSiO4) is a mineral of singular importance in the geosciences. Zircon microanalysis has greatly contributed to our understanding of key events in earth's history as certain radioactive heavy elements and their daughter products are well-preserved within the exceptionally stable inorganic matrix of the mineral. A prevailing notion in this field is that zircon, as a mineral, is predominantly a crustal mineral; this has been contested in the last few years with more reports of mantle-derived zircons (Siebel et al., 2009). Zircons enriched from different parts of the upper mantle to lower crust from Turkey (Hasozbek et al. 2010) and Germany (Siebel et al., 2009) will be presented in this study using SR-XRF mapping carried out at beamline 2-IDE at the Advanced Photon Source synchrotron facility (Argonne National Laboratory, USA). The high-resolution (5-10 µm) elemental maps were obtained with collimated and linearly polarized synchrotron radiation (10 to 17 keV) and possess the advantage of being a completely non-destructive technique. Elemental maps of various trace and rare-earth elements along the cross-section of the zircons reveal a zonation-related distribution, which may be used to reveal factors affecting the growth history and dynamics of the crystal formation. Further, abrupt changes in elemental distribution or concentration were found to correspond to faults or inclusions within the zircon crystal. If such observations are found to be applicable for a wide range of samples, elemental mapping with this technique may serve as an important qualitative diagnostic to locating µ-meter inclusions that may be challenging to identify using other techniques (ICP-MS LA, SHRIMP,…) Through these preliminary elemental profile mapping studies of crustal and mantle zircons using SR-XRF methods, we aim to highlight a relatively quick and promising analytical method that may be used to study various geological problems.

  17. The plutonic-volcanic connection in porphyry copper deposits: Evidence from zircon geochemistry and high-precision CA-ID-TIMS geochronology

    NASA Astrophysics Data System (ADS)

    Buret, Y.; Von Quadt, A.; Wotzlaw, J. F.; Heinrich, C. A.

    2016-12-01

    Porphyry Cu deposits represent the interface between plutonic and volcanic domains of upper crustal magmatic systems. These deposits are typically composed of multiple porphyritic intrusions which constrain the duration of ore formation to a maximum of several 104 years [1] and are commonly intruded into the base of volcanoes. The relationship between volcanic activity and porphyry stocks is often difficult to establish, as they are rarely exposed together unless later faulting and/or tilting occurred [2]. In order to investigate the relationships between extrusive magmatism and porphyry Cu formation we compare zircon petrochronology from late stage volcanic units with the nearby world class Bajo de la Alumbrera porphyry Cu deposit, from the Late Miocene Farallón Negro Volcanic Complex (FNVC) in Northwest Argentina. In this study we texturally characterise zircon crystals by CL-imaging prior to obtaining in-situ geochemical and geochronological information by LA-ICP-MS. Analysed zircon grains were then extracted and analysed by high precision CA-ID-TIMS. This approach has the two-fold benefit of screening for inherited cores, and obtaining texturally defined geochemical information, prior to dissolution of the zircon crystal for CA-ID-TIMS analysis. We use this information to establish temporal and geochemical links between studied volcanic and porphyry units in the FNVC. The results of this study suggest a close temporal and genetic link between the Bajo de la Alumbrera porphyry Cu deposit and the late stage volcanism at the FNVC. Voluminous explosive volcanism immediately following porphyry formation has important implications for the thermal and rheological state of the magma that is parental to the porphyries and fed the eruption. Further work investigating the geochemistry of other accessory and major minerals could shed further light on the evolution of the magmatic body prior to eruption/ emplacement. References: [1] Buret et al. (2016) EPSL 450:120-131; [2

  18. Applications of primary and secondary inclusion assemblages for zircon petrogenesis and alteration

    NASA Astrophysics Data System (ADS)

    Bell, E. A.

    2017-12-01

    Igneous zircon often contains abundant mineral inclusions which represent a mixture of primary phases captured during crystallization in magma and secondary phases formed either during late-stage deuteric alteration of a solidifying pluton, during later metamorphism, or during detrital transport and diagenesis in groundwater. Microstructural examination of zircon from both magmatic and metamorphic rocks reveals varying abundances of clearly secondary phases filling cracks and potentially secondary phases in contact with cracks or in disturbed regions of the host zircon. We used EDS and WDS X-ray spectroscopy to examine crack-isolated, crack-intersecting, and crack-filling phases in zircon from Phanerozoic magmatic rocks (USA, Victoria), several Grenville (Blue Ridge, VA) orthogneisses, and detrital zircons in metasediments from Jack Hills, Mt. Narryer (Western Australia) and the Nuvvuagittuq supracrustal belt (northern Quebec). Orthogneiss and detrital zircon appear to retain primary inclusion compositions away from contact with cracks or disturbed regions of zircon (as distinguished by U-Pb). Characteristic trace element patterns associated with chemical alteration of zircon match well with the apparently dominant secondary phases in metasedimentary detrital zircons and magmatic zircon subjected to deuteric alteration. Additionally, high spatial resolution Pb isotopic analyses of secondary phosphates using the CAMECA ims1290 ion microprobe reveal preservation of multiple generations of metamorphic phosphate, in some cases juxtaposed within a single inclusion on the 5-10 micron scale. Zircon can therefore in many cases preserve the compositions of its primary inclusion cargo through later metamorphism. Zircon can also preserve information about individual hydrothermal or metamorphic events during the grain's residence in the crust.

  19. Zirconium and hafnium in the southeastern Atlantic States

    USGS Publications Warehouse

    Mertie, J.B.

    1958-01-01

    The principal source of zirconium and hafnium is zircon, though a minor source is baddeleyite, mined only in Brazil. Zircon is an accessory mineral in igneous, metamorphic, and sedimentary rocks, but rarely occurs in hardrock in minable quantities. The principal sources of zircon are therefore alluvial deposits, which are mined in many countries of five continents. The principal commercial deposits in the United States are in Florida, though others exist elsewhere in the southeastern Coastal Plain. The evidence indicates that conditions for the accumulation of workable deposits of heavy minerals were more favorable during the interglacial stages of the Pleistocene epoch than during Recent time. Therefore detrital ores of large volume and high tenor are more likely to be found in the terrace deposits than along the present beaches. Other concentrations of heavy minerals, however, are possible at favored sites close to the Fall Line where the Tuscaloosa formation rests upon the crystalline rocks of the Piedmont province. A score of heavy and semiheavy minerals occur in the detrital deposits of Florida, but the principal salable minerals are ilmenite, leucoxene, rutile, and zircon, though monazite and staurolite are saved at some mining plants. Commercial deposits of heavy minerals are generally required to have a tenor of 4 percent, though ores with a lower tenor can be mined at a profit if the content of monazite is notably high. The percentages of zircon in the concentrates ranges from 10 to 16 percent, and in eastern Florida from 13 to 15 percent. Thus the tenor in zircon of the ore-bearing sands ranges from 0.4 to 0.6 percent. The content of hafnium in zircon is immaterial for many uses, but for some purposes very high or very low tenors in hafnium are required. Alluvial zircon cannot be separated into such varieties, which, if needed, must be obtained from sources in bedrock. It thus becomes necessary to determine the Hf : Zr ratios in zircon from many kinds of

  20. A 4.43 Ga Transition from Mega-impact to Habitability Deduced from Microstructural Geochronology of Martian Zircon and Baddeleyite

    NASA Astrophysics Data System (ADS)

    Moser, D.; Reinhard, D. A.; Larson, D. J.; McCubbin, F. M.; Darling, J.; White, L. F.; Arcuri, G.; Irving, A. J.; Tait, K.; Barker, I.

    2017-12-01

    The rates at which early planetary surfaces like those of Mars and Earth transitioned to stability within the heavy bombardment epoch are poorly constrained. Here we show through analysis of the shock history of the earliest mineral remnants of Mars crust, specifically the accessory and highly refractory phases zircon and baddeleyite in martian meteorites, that the transition for Mars was relatively rapid and early. The Moon-sized impactor widely believed to have generated the martian hemispheric dichotomy, would have caused catastrophic heating, impact metamorphism and global re-surfacing by magma.This process would either destroy any primordial accessory phases through melting and vaporization, or impart micro- or nano-structural signatures of ultra-high temperature and/or pressure metamorphism on survivor crystals. We have conducted atom probe and/or correlative electron microscopy on intensely shocked and heated zircon and baddeleyite reference samples from Earth and the Moon, as well as from 4.43 Ga grains occurring as crystals and in lithic clasts in six polished surfaces of the Rabt Sbayta suite of martian polymict regolith breccias (NWA 7475, NWA 7034, NWA 7906, Rabt Sbayta 003). The martian population (n=68) shows no micro- or nano-signatures of ultra high temperature or pressure metamorphism. Instead, it exhibits mostly low-grade shock and thermal features consistent with regolith formation at 1.5 Ga and recent low pressure ( 5GPa) launch to Earth. Taken together with the time for decay of the mega-impact heat effects, as well as the 4.50 Ga age estimate for martian mantle solidification (modelled by other workers) our results indicate an early, 70 million year long transition from initiation of the hemispheric dichotomy to establishment of at least one domain of persistently stable and potentially habitable crust. The accelerated deep mantle convection prompted by mega-impact may have also increased the transport rate of volatiles to the Martian exterior

  1. U-Pb-Th geochronology of monazite and zircon in albitite metasomatites of the Rožňava-Nadabula ore field (Western Carpathians, Slovakia): implications for the origin of hydrothermal polymetallic siderite veins

    NASA Astrophysics Data System (ADS)

    Hurai, V.; Paquette, J.-L.; Lexa, O.; Konečný, P.; Dianiška, I.

    2015-10-01

    Sodic metasomatites (albitites) occur around and within siderite veins in the southern part of the Gemeric tectonic unit of the Western Carpathians. Accessory minerals of the metasomatites represented by monazite, zircon, apatite, rutile, tourmaline and siderite are basically identical with the quartz-tourmaline stage of other siderite and stibnite veins of the tectonic unit. Statistical analysis of chemical Th-U(total)-Pb isochron method (CHIME) of monazite dating yielded Jurassic-Cretaceous ages subdivided into 3-4 modes, spreading over time interval between 78 and 185 Ma. In contrast, LA-ICPMS 206Pb/238U dating carried out on the same monazite grains revealed a narrow crystallization interval, showing ages of Th-poor cores with phengite inclusions identical within the error limit with Th-rich rims with cauliflower-like structure. The determined lower intercept at 139 ± 1 Ma overlapped the Vallanginian-Berriasian boundary, thus corroborating the model of formation of hydrothermal vein structures within an arcuate deformation front built up in the Variscan basement as a response to Early Cretaceous compression, folding and thrusting. In contrast, associated zircons are considerably older than the surrounding Early-Palaeozoic volcano-sedimentary rocks, showing Neoproterozoic ages. The zircon grains in albitite metasomatites are thus interpreted as fragments of Pan-African magmatic detritus incorporated in the vein structures by buoyant hydrothermal fluids.

  2. Radiation damage-He diffusivity models applied to deep-time thermochronology: Zircon and titanite (U-Th)/He datasets from cratonic settings

    NASA Astrophysics Data System (ADS)

    Guenthner, W.; DeLucia, M. S.; Marshak, S.; Reiners, P. W.; Drake, H.; Thomson, S.; Ault, A. K.; Tillberg, M.

    2017-12-01

    Advances in understanding the effects of radiation damage on He diffusion in uranium-bearing accessory minerals have shown the utility of damage-diffusivity models for interpreting datasets from geologic settings with long-term, low-temperature thermal histories. Craton interiors preserve a billion-year record of long-term, long-wavelength vertical motions of the lithosphere. Prior thermochronologic work in these settings has focused on radiation damage models used in conjunction with apatite (U-Th)/He dates to constrain Phanerozoic thermal histories. Owing to the more complex damage-diffusivity relationship in zircon, the zircon (U-Th)/He system yields both higher and, in some cases, lower temperature sensitivities than the apatite system, and this greater range in turn allows researchers to access deeper time (i.e., Proterozoic) segments of craton time-temperature histories. Here, we show two examples of this approach by focusing on zircon (U-Th)/He datasets from 1.8 Ga granitoids of the Fennoscandian Shield in southeastern Sweden, and 1.4 Ga granites and rhyolites of the Ozark Plateau in southeastern Missouri. In the Ozark dataset, the zircon (U-Th)/He data, combined with a damage-diffusivity model, predict negative correlations between date and effective uranium (eU) concentration (a measurement proportional to radiation damage) from thermal histories that include an episode of Proterozoic cooling (interpreted as exhumation) following reheating (interpreted as burial) to temperature of 260°C at 850-680 Ma. In the Fennoscandian Shield, a similar damage model-based approach yields time-temperature constraints with burial to 217°C between 944 Ma and 851 Ma, followed by exhumation from 850 to 500 Ma, and burial to 154°C between 366 Ma and 224 Ma. Our Fennoscandian Shield samples also include titanite (U-Th)/He dates that span a wide range (945-160 Ma) and are negatively correlated with eU concentration, analogous to our zircon He dataset. These results support

  3. Is Myanmar jadeitite of Jurassic age? A result from incompletely recrystallized inherited zircon

    NASA Astrophysics Data System (ADS)

    Yui, Tzen-Fu; Fukoyama, Mayuko; Iizuka, Yoshiyuki; Wu, Chao-Ming; Wu, Tsai-Way; Liou, J. G.; Grove, Marty

    2013-02-01

    Zircons from two Myanmar jadeitite samples were separated for texture, mineral inclusion, U-Pb dating and trace element composition analyses. Three types of zircons, with respect to U-Pb isotope system, were recognized. Type I zircons are inherited ones, yielding an igneous protolith age of 160 ± 1 Ma; Type II zircons are metasomatic/hydrothermal ones, giving a (minimum) jadeitite formation age of 77 ± 3 Ma; and Type III zircons are incompletely recrystallized ones, with non-coherent and geologically meaningless ages from 153 to 105 Ma. These Myanmar jadeitites would therefore have formed through whole-sale metasomatic replacement processes. Compared with Type I zircons, Type II zircons show typical metasomatic/hydrothermal geochemical signatures, with low Th/U ratio (< 0.1), small Ce anomaly (Ce/Ce* = < 5) and low ΣREE content (40-115 ppm). Type III zircons, however, commonly have the above geochemical signatures straddle in between Type I and Type II zircons. It is shown that the resetting rates of various trace element compositions and U-Pb isotope system of inherited zircons are not coupled "in phase" in response to zircon recrystallization during jadeitite formation. The observed abnormally low Th/U ratio and small Ce anomaly of some Type I zircons, as well as the lack of negative Eu anomaly of all Type I zircons, should be suspected to be of secondary origin. In extreme cases, incompletely recrystallized zircons may show typical metasomatic/hydrothermal geochemical signatures, but leave U-Pb isotope system partially reset or even largely unchanged. Such zircons easily lead to incorrect age interpretation, and hence erroneous geological implication. The Myanmar jadeitites, based on the present study, might have formed during the Late Cretaceous subduction before the beginning of India-Asia continental collision at Paleocene. Previously proposed Late Jurassic ages for Myanmar jadeitites are suggested as results rooted on data retrieved from incompletely

  4. Fission-track dating applied to mineral exploration

    USGS Publications Warehouse

    Naeser, C.W.

    1984-01-01

    The partial to total resetting of fission-track ages of minerals in country rock near a mineralized area can be used to (1) locate a thermal anomaly, and (2) date the mineralizing event. Two mining districts in Colorado have been studied - Rico and Gilman. Rico is a precious- and base-metal mining district. Initial fission-track dating of a sill located about 6 km from the center of the district gave ages of 20 Myr and 65 Myr for apatite and zircon, respectively. The Eagle Mine in the Gilman District is the largest producer of zinc in the state of Colorado. Fission-track dating of zircon from a 70 Myr-old sill shows partial resetting of the zircon (45 Myr). The thermal anomaly identified by fission-track dating is seen in both districts far outside the area affected by obvious alteration. Based on the results of these two pilot studies, fission-track dating can be a useful exploration method for thermal anomalies associated with buried or otherwise poorly expressed mineral deposits.

  5. Tiny twists in time; exploring angular resolution of in situ EBSD orientation microstructures in solar system zircon

    NASA Astrophysics Data System (ADS)

    Moser, D. E.

    2012-12-01

    Kikuchi discovered electron diffraction in samples of calcite in the 1920's, and orientation of lattice planes by Electron Backscatter Diffraction (EBSD) is now routinely measured by automated camera systems at a spatial resolution of tens of nanometers using Field Emission Gun SEM. The current methodology is proving particularly powerful when measuring lattice orientation microstructure in U-Pb geochronology minerals such as zircon and baddeleyite that have experienced high temperature deformation or shock metamorphism. These are among the oldest preserved mineral phases in inner solar system materials, and we have been applying EBSD to rare samples of the Early Earth and grains from extraterrestrial environments such as the Moon and Mars. In these cases the EBSD orientation data are useful for identifying high diffusivity pathways that may have afforded isotopic and trace element disturbance, microstructural proxies for shock metamorphic pressures, as well as resolving glide plane systems in ductile zircon and shear twin mechanisms. Blanket estimates of angular resolution for automated EBSD misorientation measurements are often in the range of 0.5 degrees. In some cases strain giving rise to only a few degrees of lattice misorientation has facilitated 100% Pb-loss. In some cases, however, there is a spatial correlation between trace element or cathodoluminescence zoning in zircon and what appears to be low magnitudes misorientation close to the limits of resolution. Given the proven value of performing EBSD analysis on geochronology minerals, a more thorough exploration of the precision and accuracy of EBSD lattice misorientation measurements is warranted. In this talk the relative weighting of the factors that limit EBSD angular resolution will be investigated, focusing on U-Pb dating minerals such as zircon. These factors include; sample surface preparation, phase symmetry, pseudo-symmetry effects, degree of crystallinity, Kikuchi band contrast and indexing

  6. Cenozoic exhumation and tectonic evolution of the Qimen Tagh Range, northern Tibetan Plateau: Insights from the heavy mineral compositions, detrital zircon U-Pb ages and seismic interpretations

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Wu, C.; Wang, J.; Zhou, T.; Zhang, C.; Li, J.

    2017-12-01

    The Qaidam Basin is the largest intermountain basin within the Tibetan Plateau. The Cenozoic sedimentary flling characteristics of the basin was significantly influenced by the surrounding tectonic belt, such as the Altyn Tagh Range to the north-west and Qimen Tagh Range to the south. The tectonic evolution of the Qimen Tagh Range and the structural relationship between the Qaidam Basin and Qimen Tagh Range remain controversial. To address these issues, we analyzed thousands of heavy mineral data, 720 detrital zircon ages and seismic data of the Qaidam Basin. Based on the regional geological framework and our kinematic analyses, the Cenozoic tectonic evolution of the Qimen Tagh Range can be divided into two stages. From the Early Eocene to the Middle Miocene, the Devonian (400-360 Ma) and Permian to Triassic (300-200 Ma) zircons which were sourced from the Qimen Tagh Range and the heavy mineral assemblage of zircon-leucoxene-garnet-sphene on the north flank of the Qimen Tagh Range indicated that the Qimen Tagh Range has been exhumed before the Eocene and acted as the primary provenance of the Qaidam Basin. The Kunbei fault system (i.e. the Kunbei, Arlar and Hongliuquan faults) in the southwest of the Qaidam Basin, which can be seen as a natural study window of the Qimen Tagh Range, was characterized by left-lateral strike-slip faults and weak south-dipping thrust faults based on the seismic sections. This strike-slip motion was generated by the uplift of the Tibetan Plateau caused by the onset of the Indian-Eurasian collision. Since the Middle Miocene, the primary mineral assemblages along the northern flank of the Qimen Tagh Range changed from the zircon-leucoxene-garnet-sphene assemblage to the epidote-hornblende-garnet-leucoxene assemblage. Simultaneously, the Kunbei fault system underwent intense south-dipping thrusting, and a nearly 2.2-km uplift can be observed in the hanging wall of the Arlar fault. We attributed these variations to the rapid uplift event of

  7. What can zircon ages from the Jack Hills detrital zircon suite really tell us about Hadean geodynamics?

    NASA Astrophysics Data System (ADS)

    Whitehouse, Martin; Nemchin, Alexander

    2015-04-01

    As the only direct sample of the Hadean Earth, detrital zircon grains from the Jack Hills, Western Australia, have been the subject of intense investigation over the almost three decades since their discovery. A wide variety of geochemical and isotopic analyses of these grains, as well as their mineral inclusions, have been used variously to support two fundamentally different models for Hadean geodynamics: (i) Some form of (not necessarily modern-style) plate recycling generating felsic (continental-type?) crust at the boundaries [1, 2], or conversely (ii) the persistence of a long-lived, stagnant basaltic lid within which magmatism occurred as a result of internal temperature perturbations and/or impacts [3, 4], a model also generally consistent with a wide range of observations from post-Hadean geochemical reservoirs. Despite the considerable time and resources expended, the majority of these studies uncritically accept the individual U-Pb zircon ages, even though their veracity is key to many of the interpretations [5, 6]. We report here the results of an in-depth evaluation of all published (and new) U-Pb ages from the Jack Hills zircon suite in order to define age populations that can be used with a high degree of confidence in geodynamic interpretations. A notable problem in the interpretation of U-Pb data from ancient zircon grains (including those as young as the Neoarchean) is that disturbance of the systematics even several 100 Ma after crystallization causes data to spread along the concordia curve without becoming discernably discordant within the relatively large error bounds associated with U/Pb ages from in situ dating methods (e.g. SIMS). While 207Pb/206Pb ages are typically more precise, individually they provide no means to detect Pb-loss-induced younging. However, if two or preferably more analyses have been made in the same zircon growth zone, a reasonable evaluation of the possibility of Pb-loss can be made. In the available Jack Hills zircon

  8. Impact-shocked zircons: discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

    USGS Publications Warehouse

    Bohor, B.F.; Betterton, W.J.; Krogh, T.E.

    1993-01-01

    Textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously. However, planar deformation features (PDF) due to shock metamorphism are well documented in quartz and other mineral grains from these same environments. An etching technique was developed that allows SEM visualization of PDF and other probable shock-induced textural features, such as granular (polycrystalline) texture, in zircons from a variety of impact shock environments. These textural features in shocked zircons from K/T boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the UPb isotopic system. ?? 1993.

  9. Impact-shocked zircons: Discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

    NASA Technical Reports Server (NTRS)

    Bohor, B. F.; Betterton, W. J.; Krogh, T. E.

    1993-01-01

    Textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously. However, planar deformation features (PDF) due to shock metamorphism are well documented in quartz and other mineral grains from these same environments. An etching technique was developed that allows scanning electron microscope (SEM) visualization of PDF and other probable shock-induced textural features, such as granular (polycrystalline) texture, in zircons from a variety of impact shock environments. These textural features in shocked zircons from K/T boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the U-Pb isotopic system.

  10. Empirical constraints on the effects of radiation damage on helium diffusion in zircon

    NASA Astrophysics Data System (ADS)

    Anderson, Alyssa J.; Hodges, Kip V.; van Soest, Matthijs C.

    2017-12-01

    In this study, we empirically evaluate the impact of radiation damage on zircon (U-Th)/He closure temperatures for a suite of zircon crystals from the slowly cooled McClure Mountain syenite of south-central Colorado, USA. We present new zircon, titanite, and apatite conventional (U-Th)/He dates, zircon laser ablation (U-Th)/He and U-Pb dates, and zircon Raman spectra for crystals from the syenite. Titanite and apatite (U-Th)/He dates range from 447 to 523 Ma and 88.0 to 138.9 Ma, respectively, and display no clear correlation between (U-Th)/He date and effective uranium concentration. Conventional zircon (U-Th)/He dates range from 230.3 to 474 Ma, while laser ablation zircon (U-Th)/He dates show even greater dispersion, ranging from 5.31 to 520 Ma. Dates from both zircon (U-Th)/He datasets decrease with increasing alpha dose, indicating that most of the dispersion can be attributed to radiation damage. Alpha dose values for the dated zircon crystals range from effectively zero to 2.15 × 1019 α /g, spanning the complete damage spectrum. We use an independently constrained thermal model to empirically assign a closure temperature to each dated zircon grain. If we assume that this thermal model is robust, the zircon radiation damage accumulation and annealing model of Guenthner et al. (2013) does not accurately predict closure temperatures for many of the analyzed zircon crystals. Raman maps of the zircons dated by laser ablation document complex radiation damage zoning, sometimes revealing crystalline zones in grains with alpha dose values suggestive of amorphous material. Such zoning likely resulted in heterogeneous intra-crystalline helium diffusion and may help explain some of the discrepancies between our empirical findings and the Guenthner et al. (2013) model predictions. Because U-Th zoning is a common feature in zircon, radiation damage zoning is likely to be a concern for most ancient, slowly cooled zircon (U-Th)/He datasets. Whenever possible, multiple

  11. Effect of pressure on Zircon's (ZrSiO4) Raman active modes: a first-principles study

    NASA Astrophysics Data System (ADS)

    Sheremetyeva, Natalya; Cherniak, Daniele; Watson, Bruce; Meunier, Vincent

    Zircon is a mineral commonly found in the Earth crust. Its remarkable properties have given rise to considerable attention. This includes possible inclusion of radioactive elements in natural samples, which allows for geochronological investigations. Subsequently, Zircon was proposed as possible host material for radioactive waste management. Internal radiation damage in zircon leads to the destruction of its crystal structure (an effect known as metamictization) which is subject to ongoing research. Recently, the effect of pressure and temperature on synthetic zircon has been analyzed experimentally using Raman spectroscopy which led to the calibration of zircon as a pressure sensor in diamond-anvil cell experiments. While there have been a number of theoretical studies, the effect of pressure on the Raman active modes of zircon has not been investigated theoretically. Here we present a first-principles pressure calibration of the Raman active modes in Zircon employing density-functional theory (DFT). We find excellent quantitative agreement of the slopes ∂ω / ∂P with the experimental ones and are able to rationalize the ω vs. P behavior based on the details of the vibrational modes.

  12. Opening the closed box: lattice diffusion in zircon?

    NASA Astrophysics Data System (ADS)

    Wheeler, J.; MacDonald, J.; Goodenough, K. M.; Crowley, Q.; Harley, S.; Mariani, E.

    2015-12-01

    In principle, any radiogenic parent or daughter element can diffuse through any crystalline lattice. Given improved analytic techniques and mathematical models, geochronology is beginning to take such diffusion into account in a quantitative fashion. Whilst lattice diffusion compromises simple interpretation of radiometric data, it can, when combined with spatially resolved data, provide more detailed insight into thermal histories. In regions that have experienced particularly high temperatures diffusion may become significant in minerals normally thought to be reliably closed. We have modelled Pb diffusion in zircon, building on earlier work on Ar diffusion in micas - the mathematics being basically the same. We are motivated by some challenging isotope data from zircon in the Lewisian Complex of NW Scotland (a TTG region with a long Archaean and Proterozoic history). For example we have grains with old rims and younger cores. Whilst other explanations are possible, we show how lattice diffusion of Pb is plausible, using experimental diffusion data together with estimates of ultra-high temperatures from the region. We have modified a previous model for Ar diffusion ("Diffarg") to include variations in parent isotope concentration, so we can understand the consequences of U zonation within zircon grains during prolonged thermal histories. This is also relevant to asking why Pb has apparently not diffused in zircon from other UHT regions - or has it?

  13. Do Hf isotopes in magmatic zircons represent those of their host rocks?

    NASA Astrophysics Data System (ADS)

    Wang, Di; Wang, Xiao-Lei; Cai, Yue; Goldstein, Steven L.; Yang, Tao

    2018-04-01

    Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from ∼630 °C to ∼900 °C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.

  14. International strategic minerals inventory summary report; zirconium

    USGS Publications Warehouse

    Towner, R.R.

    1992-01-01

    Zircon, a zirconium silicate, is currently the most important commercial zirconium-bearing mineral. Baddeleyite, a natural form of zirconia, is less important but has some specific end uses. Both zircon and baddeleyite occur in hard-rock and placer deposits, but at present all zircon production is from placer deposits. Most baddeleyite production is from hard-rock deposits, principally as a byproduct of copper and phosphate-rock mining. World zirconium resources in identified, economically exploitable deposits are about 46 times current production rates. Of these resources, some 71 percent are in South Africa, Australia, and the United States. The principal end uses of zirconium minerals are in ceramic applications and as refractories, abrasives, and mold linings in foundries. A minor amount, mainly of zircon, is used for the production of hafnium-free zirconium metal, which is used principally for sheathing fuel elements in nuclear reactors and in the chemical-processing industry, aerospace engineering, and electronics. Australia and South Africa are the largest zircon producers and account for more than 70 percent of world output; the United States and the Soviet Union account for another 20 percent. South Africa accounts for almost all the world's production of baddeleyite, which is about 2 percent of world production of contained zirconia. Australia and South Africa are the largest exporters of zircon. Unless major new deposits are developed in countries that have not traditionally produced zircon, the pattern of world production is unlikely to change by 2020. The proportions, however, of production that come from existing producing countries may change somewhat.

  15. Finding the "true" age: ways to read high-precision U-Pb zircon dates

    NASA Astrophysics Data System (ADS)

    Schaltegger, U.; Schoene, B.; Ovtcharova, M.; Sell, B. K.; Broderick, C. A.; Wotzlaw, J.

    2011-12-01

    rheological lockup by the crystals. Last crystallizing zircons in the interstitial melt may therefore postdate emplacement of the magma. The range of 206Pb/238U ages may yield a time frame for the cooling of a given magma batch, which could be added to quantitative thermal models of magma emplacement and cooling. Hf isotopes and trace elements of the dated zircon are used to trace the nature of the dated grains [4], specifically for identification of crystals that form earlier at lower crustal levels (antecrysts). Autocrystic zircons typically show, e.g., distinctly different (higher or lower) Th/U ratios. Cautiously interpreted high-precision U-Pb data of chemically abraded zircons may resolve the evolution of a magmatic system from its roots to final emplacement or eruption, trace fractional crystallization of zircon and other accessory and major phases in a magma batch, and add quantitative temporal constraints to thermal models. The proposed interpretation scheme thus adds significant information compared to conventional statistics. [1] Mattinson J., 2005, Chem. Geol. 200, 47-66; ; [2] Slama et al., 2008, Chem. Geol. 249, 1-35; [3] Miller et al., 2007, J. Volc. Geotherm. Res. 167, 282-299; [4] Schoene et al., 2010, Geochim. Cosmochim. Acta 74, 7144-7159

  16. Trace element determination of zircons from adakites and granitoids: implications for petrogenetic processes

    NASA Astrophysics Data System (ADS)

    Chen, T. W.; Chu, M. F.; Chung, S. L.; Iizuka, Y.

    2017-12-01

    Zircon has long been proposed as a time capsule of crustal formation. Concerning of its high capacity of lithophile elements, the dramatic change of crustal chemical composition in late Archean, i.e. from TTG suites to granitoids, may be recorded in zircon remnants. In this study, major- and trace element contents of zircons from adakites, a modern analogue of TTG suites, in southern Tibet were determined by EPMA and LA-ICPMS, respectively, and compared with those in Gangdese granitoids and Sumatra high/low ΣREE granitoids in order to examine the hypothesis. The REE patterns of zircons in this study show little inter-sample discrepancy though there is significant difference in whole-rock HREE contents between adakites and granitoids. Since none of geochemical feature, including REE contents, of zircons correlates with SiO2 content or ASI of corresponding host rocks, fractional crystallization shows insignificant impact on the compositional variation in zircons. In addition to the influence of lattice strain and charge balance requirements, zircons in these rock samples are proposed to crystallize from the magma mush, so they record the composition with least composition difference, not that of the bulk melt. More specifically, the pre-/co-existing mineral phases, e.g. apatite, play a critical role in preferentially taking the LREE and MREE from melt, and eliminating the HREE depletion in residual melt and thus zircons of Gangdese adakites. With the aim of objectively identifying geochemical discriminants of zircons from adakites and granitoids, statistical analysis was used and then 8 parameters were selected, i.e. Ti, V, Yb, Hf, Sc/Yb, U/Yb, Eu/Eu*, ΣHREE. Despite the zircon populations of adakites- and granitoids-origins overlapping in any bivariate plot, the linear combination of discriminants provides a potential way to distinguish zircons from these two groups.

  17. Alteration and chemical U-Th-total Pb dating of heterogeneous high-uranium zircon from a pegmatite from the Aduiskii massif, middle Urals, Russia

    NASA Astrophysics Data System (ADS)

    Zamyatin, Dmitry A.; Shchapova, Yuliya V.; Votyakov, Sergey L.; Nasdala, Lutz; Lenz, Christoph

    2017-09-01

    The U-Th-Pb isotope system in the accessory mineral zircon may be disturbed, as for instance by the secondary loss of radiogenic lead. The recognition of such alteration is crucial for the sound interpretation of geochronology results, in particular for chemical dating by means of an electron probe micro-analyser (EPMA). Here we present the example of high-U zircon samples from a granite pegmatite from the Aduiskii Massif, Middle Urals, Russia. The structural and chemical heterogeneity of samples was characterised by EPMA, including joint probability distribution (JPD) analysis of back-scattered electrons (BSE), cathodoluminescence (CL) and U M β images, and by Raman and photoluminescence (PL) spectroscopy. We found a high-U interior region (U up to 11.4 wt%) without any obvious indication of alteration. This domain has stoichiometric composition, and its Raman spectrum is similar to that of amorphous ZrSiO4. In addition, altered lower-U regions are present that are non-stoichiometric and contain non-formula elements such as Ca, Al, Fe, and water up to several wt%. Their Raman spectra yielded a band near 760-810 cm-1 which is not related to any ZrSiO4 vibration; we assign it tentatively to the symmetric stretching of (UO2)2+ groups. This assignment is supported by the observation of a fairly intense PL phenomenon whose spectral position and vibrational-coupling structure strongly indicates a uranyl-related emission. Altered zones were formed by both fluid-driven diffusion reaction and coupled dissolution-reprecipitation processes. The variation of BSE and CL intensities in amorphous high-U zircon is controlled by its chemical composition and the presence of water and uranyl groups. We have determined a weighted mean EPMA age of 246 ± 2 Ma, which agrees reasonably well with previous dating results for the Aduiskii Massif.

  18. Rock-magnetic properties of single zircon crystals sampled from the Tanzawa tonalitic pluton, central Japan

    NASA Astrophysics Data System (ADS)

    Sato, Masahiko; Yamamoto, Shinji; Yamamoto, Yuhji; Okada, Yoshihiro; Ohno, Masao; Tsunakawa, Hideo; Maruyama, Shigenori

    2015-09-01

    This paper reports on the rock-magnetic properties of single zircon crystals, which are essential for future work establishing the reliable paleointensity method using single zircon crystals. Zircon crystals used in this study were sampled from the Nakagawa River, which crosses the Tanzawa tonalitic pluton in central Japan. Rock-magnetic measurements were conducted on 1037 grains of zircons, but many of these measurements are below the limits of the sensitivity of the magnetometers employed. Isothermal remanent magnetizations (IRMs) of 876 zircon crystal are below the practical resolution of this study; we infer that these crystals contain no or only minute quantities of ferromagnetic minerals. The other zircon crystals contain enough magnetic minerals to be measured in the DC SQUID magnetometer. For 81 zircon crystals, IRM intensities ( M IRM) are larger than 4 × 10-12 Am2, while natural remanent magnetization (NRM) intensities ( M NRM) are below 4 × 10-12 Am2, indicating that these crystals are inappropriate for the paleomagnetic study. For the samples that had values of M NRM ≥ 4 × 10-12 Am2 and M IRM ≥ 4 × 10-12 Am2 (80 zircons), combining the rock-magnetic parameter, we proposed the sample-selection criteria for future study of paleointensity experiments using single zircon crystals. In the case that the samples had high coercivity ( B c) values (>10 mT) or high M NRM/ M IRM values (>~0.1), main remanence carriers are probably pyrrhotite and these samples are inappropriate for the paleointensity study. In the case that the samples had low B c values (<10 mT) and low M NRM/ M IRM values (<~0.1), main remanence carriers seem to be nearly pure magnetite with pseudo-single-domain grain sizes, and these samples are expected to appropriate for the paleointensity study. Total thermoremanent magnetization (TRM) acquisition experiments were also carried out for 12 samples satisfying the above criteria. The TRM intensity was comparable with that of NRM, and a

  19. Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon

    USGS Publications Warehouse

    Tourrette, T.Z.L.; Burnett, D.S.; Bacon, C.R.

    1991-01-01

    Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO2), are interpreted to be portions of the magma chamber walls that were torn off during eruption. The glass is clear and well homogenized for all measured elements except Zr. Results for Fe-Ti oxides give DUoxide/liq ??? 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are moderately well equilibrated with the melt for many of the minor elements, while those that are inclusions in relict plagioclase are not. Uranium and ytterbium inhomogeneities in zircons indicate that the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons faster than the zircons were dissolving. Minimum U, Y, and P concentrations in zircons give maximum DUzrc/liq = 13,DYzrc/liq = 23, and DPzrc/liq = 1, but these are considerably lower than reported by other workers for U and Y. Based on our measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractionation during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in our samples. This demonstrates an actual case of non-equilibrium source retention of accessory phases, which in general could be an important trace-element fractionation mechanism. Our results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites. Rough calculations based on Zr gradients in the glass indicate that the samples could have been partially molten for 800 to 8000 years. ?? 1991.

  20. Surface chemistry and flotation behavior of monazite, apatite, ilmenite, quartz, rutile, and zircon using octanohydroxamic acid collector

    NASA Astrophysics Data System (ADS)

    Nduwa Mushidi, Josue

    Global increase in rare earth demand and consumption has led to further understanding their beneficiation and recovery. Monazite is the second most important rare earth mineral that can be further exploited. In this study, the surface chemistry of monazite in terms of zeta potential, adsorption density, and flotation response by microflotation using octanohydroxamic acid is determined. Apatite, ilmenite, quartz, rutile, and zircon are minerals that frequently occur with monazite among other minerals. Hence they were chosen as gangue minerals in this study. The Iso Electric Point (IEP) of monazite, apatite, ilmenite, quartz, rutile, and zircon are 5.3, 8.7, 3.8, 3.4, 6.3, and 5.1 respectively. The thermodynamic parameters of adsorption were also evaluated. Ilmenite, rutile and zircon have high driving forces for adsorption with DeltaGads. = 20.48, 22.10, and 22.4 kJ/mol respectively. The free energy of adsorption is 14.87 kJ/mol for monazite. Adsorption density testing shows that octanohydroxamic acid adsorbs on negatively charged surfaces of monazite and its gangue minerals which indicates chemisorption. This observation was further confirmed by microflotation experiments. Increasing the temperature to 80°C raises the adsorption and flotability of monazite and gangue minerals. This does not allow for effective separation. Sodium silicate appeared to be most effective to depress associated gangue minerals. Finally, the fundamentals learned were applied to the flotation of monazite ore from Mt. Weld. However, these results showed no selectivity due to the presence of goethite as fine particles and due to a low degree of liberation of monazite in the ore sample.

  1. Trace element chemistry of zircons from oceanic crust: A method for distinguishing detrital zircon provenance

    USGS Publications Warehouse

    Grimes, Craig B.; John, Barbara E.; Kelemen, P.B.; Mazdab, F.K.; Wooden, J.L.; Cheadle, Michael J.; Hanghoj, K.; Schwartz, J.J.

    2007-01-01

    We present newly acquired trace element compositions for more than 300 zircon grains in 36 gabbros formed at the slow-spreading Mid-Atlantic and Southwest Indian Ridges. Rare earth element patterns for zircon from modern oceanic crust completely overlap with those for zircon crystallized in continental granitoids. However, plots of U versus Yb and U/Yb versus Hf or Y discriminate zircons crystallized in oceanic crust from continental zircon, and provide a relatively robust method for distinguishing zircons from these environments. Approximately 80% of the modern ocean crust zircons are distinct from the field defined by more than 1700 continental zircons from Archean and Phanerozoic samples. These discrimination diagrams provide a new tool for fingerprinting ocean crust zircons derived from reservoirs like that of modern mid-ocean ridge basalt (MORB) in both modern and ancient detrital zircon populations. Hadean detrital zircons previously reported from the Acasta Gneiss, Canada, and the Narryer Gneiss terrane, Western Australia, plot in the continental granitoid field, supporting hypotheses that at least some Hadean detrital zircons crystallized in continental crust forming magmas and not from a reservoir like modern MORB. ?? 2007 The Geological Society of America.

  2. Magmatic Longevity Constrained by ID-TIMS U-Pb Dating of Zircon and Titanite

    NASA Astrophysics Data System (ADS)

    Szymanowski, D.; Wotzlaw, J. F.; Ellis, B. S.; Bachmann, O.; Von Quadt, A.

    2016-12-01

    Clues about the timescales and thermal conditions associated with the growth and evacuation of large silicic magma reservoirs are frequently drawn from radiometric dating, diffusion modelling, or thermomechanical modelling. A growing amount of petrological and geochronological evidence, supported by thermal modelling, suggests that many silicic magma reservoirs may exist for some 104-106 years in the form of high-crystallinity mushes at relatively low temperatures ( 700-750°C; [1-3]). Geochronological studies addressing this issue typically utilise the U-Pb system in zircon capable of recording extended periods of crystallisation, particularly in evolved calc-alkaline systems that spend most of their lifetime zircon-saturated. In this study, we integrate U-Pb dating of zircon and titanite to investigate the longevity of the magma reservoir that produced the Kneeling Nun Tuff, a 35 Ma, >900 km3 crystal-rich rhyolitic super-eruption from the Mogollon-Datil volcanic field in New Mexico (USA). High-precision ID-TIMS U-Pb dates of single crystals of both zircon and titanite independently record a continuous crystallisation history over >400,000 years. We combine the dating of both accessory phases with textural, major, trace element and isotopic studies of single crystals, placing tight constraints on the thermal conditions of magma accumulation and storage while recording differentiation and rejuvenation processes within the magma reservoir. The results suggest a protracted `cool' upper-crustal storage of magma prior to the Kneeling Nun Tuff eruption followed by a melting event which reduced the magma crystallinity and conditioned it for eruption. [1] Bachmann & Bergantz (2004), J. Petrol. 45, 1565-1582. [2] Gelman et al. (2013), Geology 41, 759-762. [3] Cooper & Kent (2014), Nature 506, 480-483.

  3. Petrogenesis of Cretaceous volcanic-intrusive complex from the giant Yanbei tin deposit, South China: Implication for multiple magma sources, tin mineralization, and geodynamic setting

    NASA Astrophysics Data System (ADS)

    Li, Qian; Zhao, Kui-Dong; Lai, Pan-Chen; Jiang, Shao-Yong; Chen, Wei

    2018-01-01

    The giant Yanbei tin ore deposit is the largest porphyry-type tin deposit in South China. The orebodies are hosted by the granite porphyry in the central part of the Yanbei volcanic basin in southern Jiangxi Province. The Yanbei volcanic-intrusive complex mainly consists of dacitic-rhyolitic volcanic rocks, granite, granite porphyry and diabase dikes. In previous papers, the granite porphyry was considered as subvolcanic rocks, which came from the same single magma chamber with the volcanic rocks. In this study, zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemical and Sr-Nd isotopic compositions of different magmatic units in the Yanbei complex are reported. Geochronologic results show that various magmatic units have different formation ages. The dacite yielded a zircon U-Pb age of 143 ± 1 Ma, and the granite porphyry has the emplacement age of 138 ± 1 Ma. Diabase dikes which represented the final stage of magmatism, yielded a zircon U-Pb age of 128 ± 1 Ma. Distinctive whole rock Sr-Nd and zircon Hf isotopic compositions suggest that these magmatic units were derived from different magma sources. The volcanic rocks were mainly derived from the partial melting of Paleoproterozoic metasedimentary rocks without additions of mantle-derived magma. The granite porphyry has an A-type geochemical affinity, and was derived from remelting of Paleo-Mesoproterozoic crustal source with involvement of a subordinate mantle-derived magma. The granite porphyry is also a typical stanniferous granite with high F (4070-6090 ppm) and Sn (7-39 ppm) contents. It underwent strongly crystal fractionation of plagioclase, K-feldspar, and accessory minerals (like apatite, Fe-Ti oxides), which may contribute to the tin mineralization. The diabase was derived by partial melting of enriched lithospheric mantle which had been metasomatised by slab-derived fluids. The change of magmatic sources reflected an increasing extensional tectonic environment, perhaps induced by slab

  4. U-Pb Detrital Zircon Ages from Sarawak: Changes in Provenance Reflecting the Tectonic Evolution of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Breitfeld, H. T.; Galin, T.; Hall, R.

    2014-12-01

    Sarawak is located on the northern edge of Sundaland in NW Borneo. Five sedimentary basins are distinguished with ages from Triassic to Cenozoic. New light mineral, heavy mineral and U-Pb detrital zircon ages show differences in provenance reflecting the tectonic evolution of the region. The oldest clastic sediments are Triassic of the Sadong-Kuching Basin and were sourced by a Carnian to Norian volcanic arc and erosion of Cathaysian rocks containing zircons of Paleoproterozoic age. Sandstones of the Upper Jurassic to Cretaceous Bau-Pedawan Basin have distinctive zircon populations indicating a major change of tectonic setting, including initiation of subduction below present-day West Sarawak in the Late Jurassic. A wide range of inherited zircon ages indicates various Cathaysian fragments as major source areas and the arrival of the SW Borneo Block following subduction beneath the Schwaner Mountains in the early Late Cretaceous. After collision of the SW Borneo Block and the microcontinental fragments with Sundaland in the early Late Cretaceous, deep marine sedimentation (Pedawan Formation) ceased, and there was uplift forming the regional Pedawan-Kayan unconformity. Two episodes of extension were responsible for basin development on land from the latest Cretaceous onwards, probably in a strike-slip setting. The first episode formed the Kayan Basin in the Latest Cretaceous (Maastrichtian) to Early Paleocene, and the second formed the Ketungau Basin and the Penrissen Sandstone in the Middle to Late Eocene. Zircons indicate nearby volcanic activity throughout the Early Cenozoic in NW Borneo. Inherited zircon ages indicate an alternation between Borneo and Tin Belt source rocks. A large deep marine basin, the Rajang Basin, formed north of the Lupar Line fault. Zircons from sediments of the Rajang Basin indicate they are of similar age and provenance as the contemporaneous terrestrial sediments to the south suggesting a narrow steep continental Sundaland margin at the

  5. Experimental shock deformation in zircon: a transmission electron microscopic study

    NASA Astrophysics Data System (ADS)

    Leroux, H.; Reimold, W. U.; Koeberl, C.; Hornemann, U.; Doukhan, J.-C.

    1999-06-01

    In recent years, apparently shock-induced and, thus, impact-characteristic microdeformations, in the form of planar microdeformation features and so-called strawberry (granular) texture, have been observed in zircons in rocks from confirmed impact structures and from the K/ T boundary. The nature of the planar microdeformations in this mineral is, however, still unknown, and critical information is needed regarding the shock pressure range in which these deformation effects are produced. We experimentally shock deformed two series of thin zircon (ZrSiO 4) target plates, cut perpendicular to the c-axis, at shock pressures of 20, 40, and 60 GPa. The recovered samples were characterized by optical and scanning electron microscopy. In addition, one sample series was studied by transmission electron microscopy (TEM). Microdeformation effects observed at 20 GPa include pervasive micro-cleavage and dislocation patterns. Plastic deformation is indicated by a high density of straight dislocations in glide configuration. The dominant glide systems are <100>{010}. Micro-cleavages, induced by shear stresses during the compression stage, occur mostly in the {100} planes. The large density of dislocations at crack tips shows that plastic deformation was initiated by the micro-cracking processs. At 40 GPa, the sample was partly transformed from the zircon (z) to a scheelite (CaWO 4)-type (s) structure. Planar deformation features (PDFs) containing an amorphous phase of zircon composition are present in the not yet transformed zircon relics. The phase with scheelite structure, initiated in the {100} planes of zircon, consists of thin (0.1 to several μm) bands that crosscut the zircon matrix. The phase transformation is displacive (martensitic) and can be related by {100} z // {112} s and [001] z // <110> s. The scheelite structure phase is densely twinned, with twins in the (112) plane. The 60-GPa sample consists completely of the scheelite structure phase. Crosscutting and

  6. Complicated secondary textures in zircon record evolution of the host granitic rocks: Studies from Western Tauern Window and Ötztal-Stubai Crystalline Complex (Eastern Alps, Western Austria)

    NASA Astrophysics Data System (ADS)

    Kovaleva, Elizaveta; Harlov, Daniel; Klötzli, Urs

    2017-07-01

    Samples of metamorphosed and deformed granitic rocks were collected from two Alpine complexes with well-constrained metamorphic history: Western Tauern Window and Ötztal-Stubai Crystalline Complex. Zircon grains from these samples were investigated in situ by a combination of scanning electron microscope techniques, cathodoluminescence (CL) imaging and Raman spectroscopy. The aims were: to describe and interpret complicated secondary textures and microstructures in zircon; based on cross-cutting relationships between secondary microstructures, reconstruct the sequence of processes, affecting zircon crystals; link the evolution of zircon with the history of the host rocks. The results indicate that zircon in the sampled granitic rocks forms growth twins and multi-grain aggregates, which are unusual for this mineral. Moreover, various secondary textures have been found in the sampled zircon, often cross-cutting each other in a single crystal. These include: distorted oscillatory CL zoning with inner zones forming inward-penetrating, CL-bright embayments, which are the evidence of dry recrystallization via annealing/lattice recovery; CL mosaicism with no preservation of growth zoning, but abundant nano- and micro-scale pores and mineral inclusions, which are the evidence of recrystallization by coupled dissolution-reprecipitation and/or leaching; embayed zircon boundaries filled with apatite, monazite, epidote and mylonitic matrix, indicating mineral-fluid reactions resulting in zircon dissolution and fragmentation; overgrowth CL-dark rims, which contain nano-pores and point to transport and precipitation of dissolved zircon matter. We conclude that zircon in our meta-granites is sensitive to metamorphism/deformation events, and was reactive with metamorphic fluids. Additionally, we have found evidence of crystal-plastic deformation in the form of low angle boundaries and bent grain tips, which is a result of shearing and ductile deformation of the host rock. We

  7. Mineral dissolution in the Cape Cod aquifer, Massachusetts, USA: I . Reaction stoichiometry and impact of accessory feldspar and glauconite on strontium isotopes, solute concentrations, and REY distribution

    USGS Publications Warehouse

    Bau, Michael; Alexander, Brian; Chesley, John T.; Dulski, Peter; Brantley, Susan L.

    2004-01-01

    To compare relative reaction rates of mineral dissolution in a mineralogically simple groundwater aquifer, we studied the controls on solute concentrations, Sr isotopes, and rare earth element and yttrium (REY) systematics in the Cape Cod aquifer. This aquifer comprises mostly carbonate-free Pleistocene sediments that are about 90% quartz with minor K-feldspar, plagioclase, glauconite, and Fe-oxides. Silica concentrations and pH in the groundwater increase systematically with increasing depth, while Sr isotopic ratios decrease. No clear relationship between 87Sr/86Sr and Sr concentration is observed. At all depths, the 87Sr/86Sr ratio of the groundwater is considerably lower than the Sr isotopic ratio of the bulk sediment or its K-feldspar component, but similar to that of a plagioclase-rich accessory separate obtained from the sediment. The Si-87Sr/86Sr-depth relationships are consistent with dissolution of accessory plagioclase. In addition, solutes such as Sr, Ca, and particularly K show concentration spikes superimposed on their respective general trends. The K-Sr-87Sr/86Sr systematics suggests that accessory glauconite is another major solute source to Cape Cod groundwater. Although the authigenic glauconite in the Cape Cod sediment is rich in Rb, it is low in in-grown radiogenic 87Sr because of its young Pleistocene age. The low 87Sr/86Sr ratios are consistent with equilibration of glauconite with seawater. The impact of glauconite is inferred to vary due to its variable abundance in the sediments. In the Cape Cod groundwater, the variation of REY concentrations with sampling depth resembles that of K and Rb, but differs from that of Ca and Sr. Shale-normalized REY patterns are light REY depleted, show negative Ce anomalies and super-chondritic Y/Ho ratios, but no Eu anomalies. REY input from feldspar, therefore, is insignificant compared to input from a K-Rb-bearing phase, inferred to be glauconite. These results emphasize that interpretation of groundwater

  8. Theoretical modeling of zircon's crystal morphology according to data of atomistic calculations

    NASA Astrophysics Data System (ADS)

    Gromalova, Natalia; Nikishaeva, Nadezhda; Eremin, Nikolay

    2017-04-01

    Zircon is an essential mineral that is used in the U-Pb dating. Moreover, zircon is highly resistant to radioactive exposure. It is of great interest in solving both fundamental and applied problems associated with the isolation of high-level radioactive waste. There is significant progress in forecasting of the most energetically favorable crystal structures at the present time. Unfortunately, the theoretical forecast of crystal morphology at high technological level is under-explored nowadays, though the estimation of crystal equilibrium habit is extremely important in studying the physical and chemical properties of new materials. For the first time, the thesis about relation of the equilibrium shape of a crystal with its crystal structure was put forward in the works by O.Brave. According to it, the idealized habit is determined in the simplest case by a correspondence with the reticular densities Rhkl of individual faces. This approach, along with all subsequent corrections, does not take into account the nature of atoms and the specific features of the chemical bond in crystals. The atomistic calculations of crystal surfaces are commonly performed using the energetic characteristics of faces, namely, the surface energy (Esurf), which is a measure of the thermodynamic stability of the crystal face. The stable crystal faces are characterized by small positive values of Esurf. As we know from our previous research (Gromalova et al.,2015) one of the constitutive factors affecting the value of the surface energy in calculations is a choice of potentials model. In this regard, we studied several sets of parameters of atomistic interatomic potentials optimized previously. As the first test model («Zircon 1») were used sets of interatomic potentials of interaction Zr-O, Si-O and O-O in the form of Buckingham potentials. To improve playback properties of zircon additionally used Morse potential for a couple of Zr-Si, as well as the three-particle angular harmonic

  9. Mass-spectrometric mining of Hadean zircons by automated SHRIMP multi-collector and single-collector U/Pb zircon age dating: The first 100,000 grains

    NASA Astrophysics Data System (ADS)

    Holden, Peter; Lanc, Peter; Ireland, Trevor R.; Harrison, T. Mark; Foster, John J.; Bruce, Zane

    2009-09-01

    significant numbers of zircons for statistically limited studies including correlations between age and morphology, mineral-inclusion paragenesis, as well as isotopic studies including Hf and O isotopic compositions, Pu-Xe, and Sm-Nd isotopes.

  10. Tectono-magmatic evolution of the Chihuahua-Sinaloa border region in northern Mexico: Insights from zircon-apatite U-Pb geochronology, zircon Hf isotope composition and geochemistry of granodiorite intrusions

    NASA Astrophysics Data System (ADS)

    Mahar, Munazzam Ali; Goodell, Philip C.; Feinstein, Michael Nicholas

    2016-11-01

    melting of a felsic older crust, neither evolved North American Proterozoic basement nor Jurassic metasedimentary rocks of the Guerrero terrane. Instead, the magma was primarily derived from partial melting of mantle related sources, possibly in the subcontinental mantle wedge above the Farallon plate. Our younger U-Pb zircon-apatite ages are well correlated with the late-stage cogenetic porphyry Cu-Au mineralization at 57 to 59 Ma. If the origin of ore mineralization is related to the magma sources of host batholiths, then a minimal input from crustal melt is suggested in the genesis of Cu-Au porphyry system.

  11. Mineral evolution and Earth history

    USGS Publications Warehouse

    Bradley, Dwight C.

    2015-01-01

    The field of mineral evolution—a merger of mineralogy and Earth history—coalesced in 2008 with the first of several global syntheses by Robert Hazen and coworkers in the American Mineralogist. They showed that the cumulative abundance of mineral species has a stepwise trend with first appearances tied to various transitions in Earth history such as the end of planetary accretion at ca. 4.55 Ga and the onset of bio-mediated mineralogy at ca. >2.5 Ga. A global age distribution is best established for zircon. Observed abundance of zircon fluctuates through more than an order of magnitude during successive supercontinent cycles. The pulse of the Earth is also recorded, albeit imperfectly, by the 87Sr/86Sr composition of marine biogenic calcite; the Sr-isotopic ratio of this mineral reflects the balance of inputs of primitive strontium at mid-ocean ridges and evolved strontium that drains off the continents. A global mineral evolution database, currently in the works, will greatly facilitate the compilation and analysis of extant data and the expansion of research in mineralogy outside its traditional bounds and into more interdisciplinary realms.

  12. Tracing the depositional history of Kalimantan diamonds by zircon provenance and diamond morphology studies

    NASA Astrophysics Data System (ADS)

    Kueter, Nico; Soesilo, Joko; Fedortchouk, Yana; Nestola, Fabrizio; Belluco, Lorenzo; Troch, Juliana; Wälle, Markus; Guillong, Marcel; Von Quadt, Albrecht; Driesner, Thomas

    2016-11-01

    Diamonds in alluvial deposits in Southeast Asia are not accompanied by indicator minerals suggesting primary kimberlite or lamproite sources. The Meratus Mountains in Southeast Borneo (Province Kalimantan Selatan, Indonesia) provide the largest known deposit of these so-called "headless" diamond deposits. Proposals for the origin of Kalimantan diamonds include the adjacent Meratus ophiolite complex, ultra-high pressure (UHP) metamorphic terranes, obducted subcontinental lithospheric mantle and undiscovered kimberlite-type sources. Here we report results from detailed sediment provenance analysis of diamond-bearing Quaternary river channel material and from representative outcrops of the oldest known formations within the Alino Group, including the diamond-bearing Campanian-Maastrichtian Manunggul Formation. Optical examination of surfaces of diamonds collected from artisanal miners in the Meratus area (247 stones) and in West Borneo (Sanggau Area, Province Kalimantan Barat; 85 stones) points toward a classical kimberlite-type source for the majority of these diamonds. Some of the diamonds host mineral inclusions suitable for deep single-crystal X-ray diffraction investigation. We determined the depth of formation of two olivines, one coesite and one peridotitic garnet inclusion. Pressure of formation estimates for the peridotitic garnet at independently derived temperatures of 930-1250 °C are between 4.8 and 6.0 GPa. Sediment provenance analysis includes petrography coupled to analyses of detrital garnet and glaucophane. The compositions of these key minerals do not indicate kimberlite-derived material. By analyzing almost 1400 zircons for trace element concentrations with laser ablation ICP-MS (LA-ICP-MS) we tested the mineral's potential as an alternative kimberlite indicator. The screening ultimately resulted in a small subset of ten zircons with a kimberlitic affinity. Subsequent U-Pb dating resulting in Cretaceous ages plus a detailed chemical reflection make

  13. 238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas

    USGS Publications Warehouse

    Vazquez, Jorge A.; Velasco, Noel O.; Schmitt, Axel K.; Bleick, Heather A.; Stelten, Mark E.

    2014-01-01

    Application of 238U-230Th disequilibrium dating of accessory minerals with contrasting stabilities and compositions can provide a unique perspective on magmatic evolution by placing the thermochemical evolution of magma within the framework of absolute time. Chevkinite, a Th-rich accessory mineral that occurs in peralkaline and metaluminous rhyolites, may be particularly useful as a chronometer of crystallization and differentiation because its composition may reflect the chemical changes of its host melt. Ion microprobe 128U-230Th dating of single chevkinite microphenocrysts from pre- and post-caldera La Primavera, Mexico, rhyolites yields model crystallization ages that are within 10's of k.y. of their corresponding K-Ar ages of ca. 125 ka to 85 ka, while chevkinite microphenocrysts from a post-caldera Yellowstone, USA, rhyolite yield a range of ages from ca. 110 ka to 250 ka, which is indistinguishable from the age distribution of coexisting zircon. Internal chevkinite-zircon isochrons from La Primavera yield Pleistocene ages with ~5% precision due to the nearly two order difference in Th/U between both minerals. Coupling chevkinite 238U-230Th ages and compositional analyses reveals a secular trend of Th/U and rare earth elements recorded in Yellowstone rhyolite, likely reflecting progressive compositional evolution of host magma. The relatively short timescale between chevkinite-zircon crystallization and eruption suggests that crystal-poor rhyolites at La Primavera were erupted shortly after differentiation and/or reheating. These results indicate that 238U-230Th dating of chevkinite via ion microprobe analysis may be used to date crystallization and chemical evolution of silicic magmas.

  14. Magmatic-hydrothermal fluid interaction and mineralization in alkali-syenite nodules from the Breccia Museo pyroclastic deposit, Naples, Italy: Chapter 7 in Volcanism in the Campania Plain — Vesuvius, Campi Flegrei and Ignimbrites

    USGS Publications Warehouse

    Fedele, Luca; Tarzia, Maurizio; Belkin, Harvey E.; De Vivo, Benedetto; Lima, Annamaria; Lowenstern, Jacob

    2007-01-01

    The Breccia Museo, a pyroclastic flow that crops out in the Campi Flegrei volcanic complex (Naples, Italy), contains alkali-syenite (trachyte) nodules with enrichment in Cl and incompatible elements (e.g., U, Zr, Th, and rare-earth elements). Zircon was dated at ≈52 ka, by U-Th isotope systematics using a SHRIMP. Scanning electron microscope and electron microprobe analysis of the constituent phases have documented the mineralogical and textural evolution of the nodules of feldspar and mafic accumulations on the magma chamber margins. Detailed electron microprobe data are given for alkali and plagioclase feldspar, salite to ferrosalite clinopyroxene, pargasite, ferrogargasite, magnesio-hastingsite hornblende amphibole, biotite mica, Cl-rich scapolite, and a member (probable davyne-type) of the cancrinite group. Detailed whole rock, major and minor element data are also presented for selected nodules. A wide variety of common and uncommon accessory minerals were identified such as zircon, baddeleyite, zirconolite, pollucite, sodalite, titanite, monazite, cheralite, apatite, titanomagnetite and its alteration products, scheelite, ferberite, uraninite/thorianite, uranpyrochlore, thorite, pyrite, chalcopyrite, and galena. Scanning electron microscope analysis of opened fluid inclusions identified halite, sylvite, anhydrite, tungstates, carbonates, silicates, sulfides, and phosphates; most are probably daughter minerals. Microthermometric determinations on secondary fluid inclusions hosted by alkali feldspar define a temperature regime dominated by hypersaline aqueous fluids. Fluid-inclusion temperature data and mineral-pair geothermometers for coexisting feldspars and hornblende and plagioclase were used to construct a pressure-temperature scenario for the development and evolution of the nodules. We have compared the environment of porphyry copper formation and the petrogenetic environment constructed for the studied nodules. The suite of ore minerals observed in

  15. The age of unusual xenogenic zircons from Yakutian kimberlites

    NASA Astrophysics Data System (ADS)

    Vladykin, N. V.; Lepekhina, E. A.

    2009-12-01

    Several spindle-shaped grains of zircon, which have a small size (<0.25 mm) and a distinct purplish pink coloration were found in the crushed samples of kimberlites from the Aykhal, Komsomolskaya-Magnitnaya, Botuobinskaya (Siberian platform), and Nyurbinskaya (Yakutia) pipes and olivine lamproites of the Khani massif (West Aldan). U-Pb SHRIMP II zircon dating performed at the VSEGEI Center for Isotopic Research yielded the ages of 1870-1890 Ma for the pipes of the Western province (Aykhal and Komsomolskaya) and 2200-2750 Ma for the pipes of the eastern province (Nyurbinskaya and Botuobinskaya), which allowed us to consider these zircons to be xenogenic to kimberlites. Although these zircons resemble in their age and color those from the granulite xenoliths in the Udachnaya pipe [2], no other granulite minerals are found there. Thus, major geological events in the mantle and lower crust, which led to the formation of zircon-bearing rocks, happened at 1800-1900 Ma in the northern part of the kimberlite province, whereas in the Eastern part of the province (Nakyn field) these events were much older (2220-2700 Ma). It is known that the period of 1800-1900 Ma in the Earth’s history was accompanied by intense tectonic movements and widespread alkaline-carbonatite magmatism. This magmatism was related to plume activity responsible for overheating the large portions of the mantle to the temperatures at which some diamonds in mantle rocks would burn (northern part of the kimberlite province). In the Nakyn area, the mantle underwent few or no geological processes at that time, and perhaps for this reason this area hosts more diamondiferous kimberlites. The age of olivine lamproites from the Khani massif is 2672-2732 Ma. Thus, these are some of the world’s oldest known K-alkaline rocks.

  16. Elemental and Isotopic Tomography at Single-Atom-Scale in 4.0 and 2.4 Ga Zircons

    NASA Astrophysics Data System (ADS)

    Valley, J. W.; Reinhard, D. A.; Snoeyenbos, D.; Lawrence, D.; Martin, I.; Kelly, T. F.; Ushikubo, T.; Strickland, A.; Cavosie, A. J.

    2012-12-01

    Atom probe tomography can determine identity (mass/charge ratio) and 3-D position of individual atoms in minerals such as zircon. These data provide unique information for understanding the thermal history and mechanisms of mineral reaction and exchange, including radiation damage. Nine needle-shaped specimens ~100 nm in diameter (at the apex) were sampled from 2 zircons by FIB and analyzed with a local-electrode atom probe (LEAP), CAMECA LEAP 4000X HR. The LEAP uses pulsed-laser heating to field evaporate the tip of a zircon needle and accelerates the ions into a position-sensitive TOF-MS. With due care for complex isobaric interferences (molecules, multiple ionizations) and background correction, it is possible to individually identify up to 10E8 atoms/needle (36% detection efficiency) by mass/charge (MRP ~ 1000@ m/n=16Da) and position (X-Y-Z coordinates on 0.2 nm scale) (Kelly & Larson 2012). The 3-D distribution of Pb and Y differ at atom-scale in the 2 zircons. Zircon #1 (4007 Ma, Jack Hills, W. Australia, Cavosie 2005, Ushikubo et al. 2008, Bouvier et al. 2011) is homogeneous in Pb and Y. In contrast, incompatible elements, including Pb and Y, are concentrated in equant 5-10 nm dia. domains, spaced ~50 nm apart in zircon #2 (2438 Ma, Albion-Raft R-Grouse Ck core complex, Utah, Strickland et al. 2011). U is homogeneously distributed in both zircons. The analyzed domains suffered 4-8 x 10E15 α-decay events/mg due to U and Th decay and yet both zircons yield >97% concordant U-Pb ages by SIMS, suggesting annealing of radiation damage during the life of the zircons. The 207-Pb/206-Pb ratios for these nm-scale domains, as measured by LEAP, average 0.17 for the 2.4 Ga Zrc2 (3 needles) and 0.43 for the 4.0 Ga Zrc1 (5 needles). These ratios are less precise (±40% 2σ) due to ultra-small sample size, but are in excellent agreement with values measured by SIMS, 0.1684 and 0.4269, respectively. Thus Pb in both zircons is radiogenic. The Pb-Y-rich domains and lack of

  17. Low heat flow inferred from >4 Gyr zircons suggests Hadean plate boundary interactions.

    PubMed

    Hopkins, Michelle; Harrison, T Mark; Manning, Craig E

    2008-11-27

    The first approximately 600 million years of Earth history (the 'Hadean' eon) remain poorly understood, largely because there is no rock record dating from that era. Detrital Hadean igneous zircons from the Jack Hills, Western Australia, however, can potentially provide insights into the conditions extant on our planet at that time. Results of geochemical investigations using these ancient grains have been interpreted to suggest the presence of a hydrosphere and continental crust before 4 Gyr. An underexploited characteristic of the >4 Gyr zircons is their diverse assemblage of mineral inclusions. Here we present an examination of over 400 Hadean zircons from Jack Hills, which shows that some inclusion assemblages are conducive to thermobarometry. Our thermobarometric analyses of 4.02-4.19-Gyr-old inclusion-bearing zircons constrain their magmatic formation conditions to about 700 degrees C and 7 kbar. This result implies a near-surface heat flow of approximately 75 mW m(-2), about three to five times lower than estimates of Hadean global heat flow. As the only site of magmatism on modern Earth that is characterized by heat flow of about one-quarter of the global average is above subduction zones, we suggest that the magmas from which the Jack Hills Hadean zircons crystallized were formed largely in an underthrust environment, perhaps similar to modern convergent margins.

  18. Annealing effects on cathodoluminescence of zircon

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Y.; Nishido, H.; Noumi, Y.

    2011-12-01

    U-Pb zircon dating (e. g., SHRIMP) is an important tool to interpret a history of the minerals at a micrometer-scale, where cathodoluminescence (CL) imaging allows us to recognize internal zones and domains with different chemical compositions and structural disorder at high spatial resolution. The CL of zircon is attributed by various types of emission centers, which are extrinsic ones such as REE impurities and intrinsic ones such as structural defects. Metamictization resulted from radiation damage to the lattice by alpha particles from the decay of U and Th mostly causes an effect on the CL features of zircon as a defect center. However, slightly radiation-damaged zircon, which is almost nondetectable by XRD, has not been characterized using CL method. In this study, annealing effects on CL of zircon has been investigated to clarify a recovery process of the damaged lattice at low radiation dose. A single crystal of zircon from Malawi was selected for CL measurements. It contains HfO2: 2.30 w.t %, U: 241 ppm and Th: 177 ppm. Two plate samples perpendicular to c and a axes were prepared for annealing experiments during 12 hours from room temperature to 1400 degree C. Color CL images were captured using a cold-cathode microscope (Luminoscope: Nuclide ELM-3R). CL spectral measurements were conducted using an SEM (JEOL: JSM-5410) combined with a grating monochromator (Oxford: Mono CL2) to measure CL spectra ranging from 300 to 800 nm in 1 nm steps with a temperature controlled stage. The dispersed CL was collected by a photoncounting method using a photomultiplier tube (Hamamatsu: R2228) and converted to digital data. All CL spectra were corrected for the total instrumental response. Spectral analysis reveals an anisotropy of the CL emission bands related to intrinsic defect center in blue region, radiation-induced defect center from 500 to 700 nm, and trivalent Dy impurity center at 480 and 580 nm, but their relative intensities are almost constant. CL on the

  19. Provenance analysis and detrital zircon geochronology on the onshore Makran accretionary wedge, SE Iran: implication for the geodynamic setting

    NASA Astrophysics Data System (ADS)

    Mohammadi, Ali; Burg, Jean-Pierre; Winkler, Wilfried; Ruh, Jonas

    2014-05-01

    juvenile magma sources, which are common in continental arc environments. Point counts of 32 sandstone thin sections were performed following the Gazzi-Dikinson method. 300-400 points were counted in each thin section. The sandstones are feldspathic litharenites and litharenites. Feldspar is dominantly plagioclase (> 90%) with minor amounts of K-feldspar. Most of the quartz grains (75%) are mono-crystalline but poly-crystalline ones (maximum 25%) also occur. Rock fragments are represented by sedimentary, volcanic and metamorphic grains. Volcanic rock-fragments mostly are andesites and volcanic chert. Sedimentary lithic grains comprise mostly sandstone, siltstone, limestone and dolomite. Metamorphic lithic grains generally are low-grade schists and phyllites. In various compositional ternary diagrams, the sources of the sandstones plot in the transitional to dissected arc and recycled orogenic fields. We selected 26 samples for heavy mineral study. 200-300 grain were identified and counted in each sample. Heavy mineral suites show a highly variable composition including (1) a group of ultra-stable minerals (zircon, monazite, tourmaline, rutile, brookite, anatase and sphene) derived from a granitic continental crust sources, (2) metastable minerals delivered from variable metamorphic-grade source rocks (epidote group, garnet, staurolite, chloritoid, kyanite, andalusite, glaucophane), (3) chromian spinel from ultrabasic rocks, (4) common hornblende either supplied from metamorphic or basic igneous series, and (5) a local pyroxene-rich source in the pyroclastic sandstone formation overlying pillow lavas. Glaucophane (5-20%) occurs in several samples, which indicates high-pressure/low-temperature metamorphic rocks in the detrital source areas for Eocene and Miocene sandstones. Earlier work in the Pakistani Makran suggested that pre-Miocene sediments were supplied from the Himalaya, whereas Miocene to Recent deposits were reworked older sediments of the accretionary wedge. Our

  20. SHRIMP U-Pb zircon dating from eclogite lenses in marble, Dabie-Sulu UHP terrane: restriction on the prograde, UHP and retrograde metamorphic ages

    NASA Astrophysics Data System (ADS)

    Liu, F.; Gerdes, A.; Xue, H.; Liang, F.

    2006-12-01

    Eclogite as lenses in impure marbles from Dabie-Sulu UHP terrane, represent parts of deeply subducted meta- sedimentary rocks. To constrain the age of metamorphism during subduction and exhumation, zircons from 2 eclogite samples in Dabie-Sulu impure marbles have been investigated. Beside Inherited (detrital) grains, 3 different metamorphic zircon domains have been identified based on distribution of mineral inclusion, trace elements and cathodoluminescence (CL) imaging: 1. Dark-luminescent rounded cores with quartz eclogite- facies mineral inclusions suggest formation at high-pressure (HP) metamorphic conditions. 2. White- luminescent zircon, either surrounding domain 1 or as rounded to spindly cores with index coesite eclogite- facies mineral inclusions indicates formation at UHP conditions. 3. Grey-luminescent rims around domain 2 with low-pressure mineral inclusions suggest formation during late regional amphibolite-facies retrogression. The three distinct zircon domains were dated by SHRIMP and yielded three discrete and meaningful age groups: 245±4 Ma for prograde HP metamorphism, 235±3 Ma for UHP metamorphism and 215±6 Ma for late amphibolite-facies retrogression from Dabie-Sulu eclogite. This data suggests that subduction and exhumation took place in about 10-11 Myr and 19-20 Myr, respectively. Continental materials was subducted from surface to the deep mantle depth at rates of 10 km/Myr, and subsequently exhumed from the mantle to the base of the crust at rates of 7 km/Myr. Ultrafast exhumation of the Dabie-Sulu UHP terrane from depth of 160 to 30 km was probably driven by buoyancy forces after UHP slab break-off at deep mantle depths.

  1. The role of detrital zircons in Hadean crustal research

    NASA Astrophysics Data System (ADS)

    Nebel, Oliver; Rapp, Robert P.; Yaxley, Gregory M.

    2014-03-01

    Meso-Archean sedimentary sequences at Mt. Narryer and the Jack Hills of the Narryer Terrane in Western Australia's Yilgarn Craton contain detrital zircon grains with ages as old as 4.37 Ga, the oldest preserved terrestrial matter. These grains are rare remnants of Hadean (4.5-4.0 Ga) terrestrial crust and their survival stems from the crystallographic properties of zircon during crustal reworking: they are resistant to physical and chemical weathering. Zircons are further suitable for single grain, precise age determinations making them a unique archive of the crustal past. Only a small proportion of all detrital zircons from the Narryer Terrane show Hadean age spectra and younger overgrowth rims on all 'Hadean' grains indicate multiple recycling events. Numerous studies that applied a spectacular range of analytical tools and proxies have been undertaken to decipher the geochemical nature of these zircons' host rocks, in order to place constraints on Hadean geodynamics and the processes responsible for creating the earliest terrestrial crust. Their elemental and isotope budget and mineral inclusions have helped to develop an emerging picture of a water-rich, evolved Hadean crust. However, subsequent studies have challenged this view and it seems that each piece of new evidence indicative of an early, evolved continental crust has non-unique interpretations also permissive of mafic to ultra-mafic crust. In this review we examine these disparate interpretations and their possible implications and conclude that at least parts of the earliest terrestrial crust were hydrated. However, to date there is no conclusive evidence for preserved granitic, continental crust. The protoliths of the Hadean detrital zircons were likely acidic in nature, yet the composition of the greater terrane from which these melts were derived was probably mafic. It remains unclear if the zircons formed in a geodynamic environment that includes Hadean subduction. We suspect that the Hadean

  2. Implications of Bishop Tuff zircon U-Pb ages for rates of zircon growth and magma accumulation

    NASA Astrophysics Data System (ADS)

    Reid, M. R.; Schmitt, A. K.

    2012-12-01

    Rates of geologic processes obtained from natural studies rely on accurate geochronologic information. An important benchmark in geochronology as well as a valuable source of insights into the evolution of voluminous explosive eruptions is the >600 km3 Bishop Tuff (BT). A recently determined weighted mean 206Pb/238U date of 767.1±0.9 ka for a BT zircon population [1] is indistinguishable from the recalibrated 40Ar/39Ar sanidine date of 767.4±2.2 ka [2], potentially providing a key intercalibration point between astronomical and radio-isotopic dating approaches. Consequences of these results are linear zircon growth rates of >1×10-14 cm/sec and magma accumulation rates of >200 km3/ka. In contrast, spatially selective SIMS U-Pb dating of BT zircons yielded mean pre-eruption ages of 850 ka [3], a difference that raises questions about the validity of intercalibration between U-Pb and K-Ar dating methods and the history of magma accumulation. We obtained new SIMS analyses of the BT zircons using more spatially and analytically sensitive methods and verifying our accuracy against the TIMS dated Quaternary zircon 61.308A (2.488±0.002 Ma). Analyses were performed on zircon rims and on oriented cross-sections exposed during optical interferometry-calibrated serial sectioning removing the outermost ~31 μm. Sputtering by a 100 nA ion beam versus the normally employed 10-12 nA beam resulted in enhanced radiogenic Pb yields and analytical uncertainties for Quaternary zircon approaching the U-Pb age reproducibility of the primary zircon standard (~1-2 % for AS3). Ages obtained at ~31 μm depth (representing <5% of crystal growth in most cases) average 892±26ka (MSWD=0.29), corroborating previous evidence for residence times of several tens of ka. Rim ages average 781±22 ka (MSWD=0.61), overlapping Ar/Ar determinations of eruption age and corroborating the importance of near-eruption aged zircon growth. Our results confirm the presence of BT zircon domains that predate

  3. Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea-Verbano Zone, northern Italy: two-stage decomposition of Fe-Ti oxides

    NASA Astrophysics Data System (ADS)

    Kovaleva, Elizaveta; Austrheim, Håkon O.; Klötzli, Urs S.

    2017-07-01

    In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the Ivrea-Verbano Zone. Unusual zircon textures are spatially associated with Fe-Ti oxides and occur as (1) vermicular-shaped aggregates 50-200 µm long and 5-20 µm thick and as (2) zircon coronae and fine-grained chains, hundreds of micrometers long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1) decomposition of Zr-rich ilmenite to Zr-bearing rutile, and formation of the vermicular-shaped zircon during retrograde metamorphism and hydration; and (2) recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz, and precipitation of the submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2). Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically and cataclastically deformed. Formation of thin zircon coronae (2) was coeval with, or immediately after, brittle deformation as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon coronae textures indicate metamorphic reactions in the host rock and establish the direction of the reaction front.

  4. Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Crow, Carolyn A.; McKeegan, Kevin D.; Moser, Desmond E.

    Here, we present the results of a coordinated SIMS U–Pb, trace element, Ti-in-zircon thermometry, and microstructural study of 155 lunar zircons separated from Apollo 14, 15, and 17 breccia and soil samples that help resolve discrepancies between the zircon data, the lunar whole rock history and lunar magma ocean crystallization models. The majority of lunar grains are detrital fragments, some nearly 1 mm in length, of large parent crystals suggesting that they crystallized in highly enriched KREEP magmas. The zircon age distributions for all three landing sites exhibit an abundance of ages at ~4.33 Ga, however they differ in thatmore » only Apollo 14 samples have a population of zircons with ages between 4.1 and 3.9 Ga. These younger grains comprise only 10% of all dated lunar zircons and are usually small and highly shocked making them more susceptible to Pb-loss. These observations suggest that the majority of zircons crystallized before 4.1 Ga and that KREEP magmatism had predominantly ceased by this time. We also observed that trace element analyses are easily affected by contributions from inclusions (typically injected impact melt) within SIMS analyses spots. After filtering for these effects, rare-earth element (REE) abundances of pristine zircon are consistent with one pattern characterized by a negative Eu anomaly and no positive Ce anomaly, implying that the zircons formed in a reducing environment. This inference is consistent with crystallization temperatures based on measured Ti concentrations and new estimates of oxide activities which imply temperatures ranging between 958 ± 57 and 1321 ± 100 °C, suggesting that zircon parent magmas were anhydrous. Together, the lunar zircon ages and trace elements are consistent with a ≤300 My duration of KREEP magmatism under anhydrous, reducing conditions. We also report two granular texture zircons that contain baddeleyite cores, which both yield 207Pb– 206Pb ages of 4.33 Ga. These grains are our best

  5. Coordinated U-Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons

    NASA Astrophysics Data System (ADS)

    Crow, Carolyn A.; McKeegan, Kevin D.; Moser, Desmond E.

    2017-04-01

    We present the results of a coordinated SIMS U-Pb, trace element, Ti-in-zircon thermometry, and microstructural study of 155 lunar zircons separated from Apollo 14, 15, and 17 breccia and soil samples that help resolve discrepancies between the zircon data, the lunar whole rock history and lunar magma ocean crystallization models. The majority of lunar grains are detrital fragments, some nearly 1 mm in length, of large parent crystals suggesting that they crystallized in highly enriched KREEP magmas. The zircon age distributions for all three landing sites exhibit an abundance of ages at ∼4.33 Ga, however they differ in that only Apollo 14 samples have a population of zircons with ages between 4.1 and 3.9 Ga. These younger grains comprise only 10% of all dated lunar zircons and are usually small and highly shocked making them more susceptible to Pb-loss. These observations suggest that the majority of zircons crystallized before 4.1 Ga and that KREEP magmatism had predominantly ceased by this time. We also observed that trace element analyses are easily affected by contributions from inclusions (typically injected impact melt) within SIMS analyses spots. After filtering for these effects, rare-earth element (REE) abundances of pristine zircon are consistent with one pattern characterized by a negative Eu anomaly and no positive Ce anomaly, implying that the zircons formed in a reducing environment. This inference is consistent with crystallization temperatures based on measured Ti concentrations and new estimates of oxide activities which imply temperatures ranging between 958 ± 57 and 1321 ± 100 °C, suggesting that zircon parent magmas were anhydrous. Together, the lunar zircon ages and trace elements are consistent with a ⩽300 My duration of KREEP magmatism under anhydrous, reducing conditions. We also report two granular texture zircons that contain baddeleyite cores, which both yield 207Pb-206Pb ages of 4.33 Ga. These grains are our best constraints on

  6. Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons

    DOE PAGES

    Crow, Carolyn A.; McKeegan, Kevin D.; Moser, Desmond E.

    2016-12-28

    Here, we present the results of a coordinated SIMS U–Pb, trace element, Ti-in-zircon thermometry, and microstructural study of 155 lunar zircons separated from Apollo 14, 15, and 17 breccia and soil samples that help resolve discrepancies between the zircon data, the lunar whole rock history and lunar magma ocean crystallization models. The majority of lunar grains are detrital fragments, some nearly 1 mm in length, of large parent crystals suggesting that they crystallized in highly enriched KREEP magmas. The zircon age distributions for all three landing sites exhibit an abundance of ages at ~4.33 Ga, however they differ in thatmore » only Apollo 14 samples have a population of zircons with ages between 4.1 and 3.9 Ga. These younger grains comprise only 10% of all dated lunar zircons and are usually small and highly shocked making them more susceptible to Pb-loss. These observations suggest that the majority of zircons crystallized before 4.1 Ga and that KREEP magmatism had predominantly ceased by this time. We also observed that trace element analyses are easily affected by contributions from inclusions (typically injected impact melt) within SIMS analyses spots. After filtering for these effects, rare-earth element (REE) abundances of pristine zircon are consistent with one pattern characterized by a negative Eu anomaly and no positive Ce anomaly, implying that the zircons formed in a reducing environment. This inference is consistent with crystallization temperatures based on measured Ti concentrations and new estimates of oxide activities which imply temperatures ranging between 958 ± 57 and 1321 ± 100 °C, suggesting that zircon parent magmas were anhydrous. Together, the lunar zircon ages and trace elements are consistent with a ≤300 My duration of KREEP magmatism under anhydrous, reducing conditions. We also report two granular texture zircons that contain baddeleyite cores, which both yield 207Pb– 206Pb ages of 4.33 Ga. These grains are our best

  7. Flow Chart for Mineral Separation from Granitic Rocks.

    ERIC Educational Resources Information Center

    Mursky, Gregory

    1987-01-01

    Provided is a flow chart for the separation and purification of major, minor, and accessory minerals from granitic rocks. With careful use of heavy liquids, and a Franz Isodynamic Magnetic Separator, it is possible to obtain mineral concentrates with a purity of 95 percent or better. (Author/RH)

  8. U-Th-Pb zircon dating of the 13.8-Ma dacite volcanic dome at Cerro Rico de Potosi, Bolivia

    USGS Publications Warehouse

    Zartman, R.E.; Cunningham, C.G.

    1995-01-01

    The temporal relationship between the extrusion of the Miocene dacite volcanic dome at Cerro Rico de Potasi, Bolivia, and the associated Ag-Sn mineralization has an important bearing on the heat and metal sources for this world class mineral deposit. The present study uses U-Th-Pb dating of sparse zircon contained in the dacite to demonstrate that, at most, only several hundred thousand years separate dome emplacement from main stage mineralization. -from Authors

  9. Recovering the primary geochemistry of Jack Hills zircons through quantitative estimates of chemical alteration

    NASA Astrophysics Data System (ADS)

    Bell, Elizabeth A.; Boehnke, Patrick; Harrison, T. Mark

    2016-10-01

    Despite the robust nature of zircon in most crustal and surface environments, chemical alteration, especially associated with radiation damaged regions, can affect its geochemistry. This consideration is especially important when drawing inferences from the detrital record where the original rock context is missing. Typically, alteration is qualitatively diagnosed through inspection of zircon REE patterns and the style of zoning shown by cathodoluminescence imaging, since fluid-mediated alteration often causes a flat, high LREE pattern. Due to the much lower abundance of LREE in zircon relative both to other crustal materials and to the other REE, disturbance to the LREE pattern is the most likely first sign of disruption to zircon trace element contents. Using a database of 378 (148 new) trace element and 801 (201 new) oxygen isotope measurements on zircons from Jack Hills, Western Australia, we propose a quantitative framework for assessing chemical contamination and exchange with fluids in this population. The Light Rare Earth Element Index is scaled on the relative abundance of light to middle REE, or LREE-I = (Dy/Nd) + (Dy/Sm). LREE-I values vary systematically with other known contaminants (e.g., Fe, P) more faithfully than other suggested proxies for zircon alteration (Sm/La, various absolute concentrations of LREEs) and can be used to distinguish primary compositions when textural evidence for alteration is ambiguous. We find that zircon oxygen isotopes do not vary systematically with placement on or off cracks or with degree of LREE-related chemical alteration, suggesting an essentially primary signature. By omitting zircons affected by LREE-related alteration or contamination by mineral inclusions, we present the best estimate for the primary igneous geochemistry of the Jack Hills zircons. This approach increases the available dataset by allowing for discrimination of on-crack analyses (and analyses with ambiguous or no information on spot placement or

  10. U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite melange, southwest Japan: insights into the timing of serpentinization

    USGS Publications Warehouse

    Tsujimori, T.; Liou, J.G.; Wooden, J.; Miyamoto, T.

    2005-01-01

    Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite mélange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P > 1.2 GPa at T > 350°C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ± 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization.

  11. The Laser Accessory Market

    NASA Astrophysics Data System (ADS)

    Desai, Ashvin

    1988-09-01

    Wandering through the exhibit hall yesterday, I noticed that if you look at the laser companies and if you look at the accessory companies, there are pretty much the same number of accessory booths as well as the laser companies. There was one difference. Laser company booths are all sexy looking, very flashy, big booths. Whereas if you look at the accessories booths, they were small, not so prominent.

  12. Impact of mineral fertility and bedrock erosion on single-mineral detrital studies: insights from trace-element and Nd-isotope systematics of detrital apatite from the Po River catchment

    NASA Astrophysics Data System (ADS)

    Malusa', Marco Giovanni; Wang, Jiangang; Garzanti, Eduardo; Villa, Igor M.; Wittman, Hella

    2017-04-01

    The detrital record provides an archive of mountain erosion that preserves key information for paleotectonic and paleoclimatic reconstructions. Detrital studies are often based on single-mineral analyses (e.g., geo/thermochronologic analyses on apatite and zircon). Their geologic interpretation can be challenging, because the impact of each eroding source on the detrital record is controlled by a range of factors including the rate of erosion and the fertility of chosen minerals in eroded bedrock. Here, we combine (i) a state-of-the art dataset of trace element and Nd isotope fingerprints of detrital apatite, (ii) a comprehensive dataset of apatite-fertility measurements (Malusà et al. 2016), (iii) fission-track data, and (iv) cosmogenic-derived erosion rates from the Po River catchment (Wittmann et al. 2016), to test the impact of mineral fertility and bedrock erosion on the single-mineral detrital signal preserved in the final sediment sink. Our results show that the information provided by accessory minerals, when complemented with accurate mineral fertility measurements, are fully consistent with information provided by the analysis of more abundant framework minerals. We found that trace element and Nd isotope analyses provide a reliable tool to disentangle the complex single-mineral record of orogenic erosion, and demonstrate that such a record is largely determined by high-fertility source rocks exposed within the drainage. Detrital thermochronology studies based on the lag-time approach should thus preferably include independent provenance discriminations and a full mineral fertility characterization of the potential source areas, in order to ensure a correct identification of the sediment sources and of the exogenic and endogenic processes monitored in the stratigraphic archive. Malusà M.G., Resentini A., Garzanti E., 2016. Hydraulic sorting and mineral fertility bias in detrital geochronology. Gondwana Res., 31, 1-19 Wittmann H., Malusà M.G., Resentini

  13. 14 CFR 23.1163 - Powerplant accessories.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... section, be sealed to prevent contamination of the engine oil system and the accessory system. (b... engine is hazardous when malfunctioning occurs, a means to prevent rotation without interfering with the... Controls and Accessories § 23.1163 Powerplant accessories. (a) Each engine mounted accessory must— (1) Be...

  14. 14 CFR 23.1163 - Powerplant accessories.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... section, be sealed to prevent contamination of the engine oil system and the accessory system. (b... engine is hazardous when malfunctioning occurs, a means to prevent rotation without interfering with the... Controls and Accessories § 23.1163 Powerplant accessories. (a) Each engine mounted accessory must— (1) Be...

  15. 14 CFR 23.1163 - Powerplant accessories.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... section, be sealed to prevent contamination of the engine oil system and the accessory system. (b... engine is hazardous when malfunctioning occurs, a means to prevent rotation without interfering with the... Controls and Accessories § 23.1163 Powerplant accessories. (a) Each engine mounted accessory must— (1) Be...

  16. 14 CFR 23.1163 - Powerplant accessories.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... section, be sealed to prevent contamination of the engine oil system and the accessory system. (b... engine is hazardous when malfunctioning occurs, a means to prevent rotation without interfering with the... Controls and Accessories § 23.1163 Powerplant accessories. (a) Each engine mounted accessory must— (1) Be...

  17. U-Pb ages and Hf isotopic composition of zircons in Austrian last glacial loess: constraints on heavy mineral sources and sediment transport pathways

    NASA Astrophysics Data System (ADS)

    Újvári, Gábor; Klötzli, Urs

    2015-07-01

    Loess sediments in Austria deposited ca. 30-20 ka ago yield different zircon age signatures for samples collected around Krems (SE Bohemian Massif; samples K23 and S1) and Wels (halfway between the Bohemian Massif and the Eastern Alps; sample A16). Cathodoluminescence (CL) imaging reveals both old, multistage zircons with complex growth histories and inherited cores, and young, first-cycle magmatic zircons. Paleoproterozoic ages between 2,200 and 1,800 Ma (K23 and S1), an age gap of 1,800-1,000 Ma for S1 and abundant Cadomian grains, indicate NW African/North Gondwanan derivation of these zircons. Also, A16 yields ages between 630 and 600 Ma that can be attributed to "Pan-African" orogenic processes. Significant differences are seen for the <500 Ma part of the age spectra with major age peaks at 493-494 and 344-335 Ma (K23 and S1), and 477 and 287 Ma (A16). All three samples show negative initial ɛHf signatures (-25 to -10, except one grain with +9.4) implying zircon crystallization from magmas derived by recycling of older continental crust. Hf isotopic compositions of 330- to 320-Ma-old zircons from S1 and K23 preclude a derivation from Bavarian Forest granites and intermediate granitoids. Rather, all the data suggest strong contributions of eroded local rocks (South Bohemian pluton, Gföhl unit) to loess material at the SE edge of the Bohemian Massif (K23 and S1) and sourcing of zircons from sediment donor regions in the Eastern Alps for loess at Wels (A16). We tentatively infer primary fluvial transport and secondary eolian reworking and re-deposition of detritus from western/southwestern directions. Finally, our data highlight that loess zircon ages are fundamentally influenced by fluvial transport, its directions, the interplay of sediment donor regions through the mixing of detritus and zircon fertility of rocks, rather than Paleowind directions.

  18. Geology, zircon geochronology, and petrogenesis of Sabalan volcano (northwestern Iran)

    NASA Astrophysics Data System (ADS)

    Ghalamghash, J.; Mousavi, S. Z.; Hassanzadeh, J.; Schmitt, A. K.

    2016-11-01

    Sabalan Volcano (NW Iran) is an isolated voluminous (4821 m elevation; > 800 km2) composite volcano that is located within the Arabia-Eurasia collision zone. Its edifice was assembled by recurrent eruptions of trachyandesite and dacite magma falling into a relatively restricted compositional range (56-67% SiO2) with high-K calc-alkaline and adakitic trace element (Sr/Y) signatures. Previous K-Ar dating suggested protracted eruptive activity between 5.6 and 1.4 Ma, and a two stage evolution which resulted in the construction of the Paleo- and Neo-Sabalan edifices, respectively. The presence of a topographic moat surrounding Neo-Sabalan and volcanic breccias with locally intense hydrothermal alteration are indicative of intermittent caldera collapse of the central part of Paleo-Sabalan. Volcanic debris-flow and debris-avalanche deposits indicate earlier episodes of volcanic edifice collapse during the Paleo-Sabalan stage. In the Neo-Sabalan stage, three dacitic domes extruded to form the summits of Sabalan (Soltan, Heram, and Kasra). Ignimbrites and minor pumice fall-out deposits are exposed in strongly dissected drainages that in part have breached the caldera depression. Lavas and pyroclastic rocks are varyingly porphyritic with Paleo-Sabalan rocks being trachyandesites carrying abundant phenocrysts (plagioclase + amphibole + pyroxene + biotite). The Neo-Sabalan rocks are slightly more evolved and include dacitic compositions with phenocrysts of plagioclase + amphibole ± alkali-feldspar ± quartz. All Sabalan rock types share a common accessory assemblage (oxides + apatite + zircon). High spatial resolution and sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry yielded two clusters of zircon ages which range from 4.5 to 1.3 Ma and 545 to 149 ka, respectively (all ages are averages of multiple determinations per sample). U-Th zircon geochronology for selected Neo-Sabalan rocks agrees with the U-Pb ages, with the youngest zircon rims dating

  19. Ceramic with zircon coating

    NASA Technical Reports Server (NTRS)

    Wang, Hongyu (Inventor)

    2003-01-01

    An article comprises a silicon-containing substrate and a zircon coating. The article can comprise a silicon carbide/silicon (SiC/Si) substrate, a zircon (ZrSiO.sub.4) intermediate coating and an external environmental/thermal barrier coating.

  20. Compositional and phase relations among rare earth element minerals

    NASA Technical Reports Server (NTRS)

    Burt, D. M.

    1989-01-01

    A review is presented that mainly treats minerals in which the rare-earth elements are essential constituents, e.g., bastnaesite, monazite, xenotime, aeschynite, allanite. The chemical mechanisms and limits of REE substitution in some rock-forming minerals (zircon, apatite, titanite, garnet) are also derived. Vector representation of complex coupled substitutions in selected REE-bearing minerals is examined and some comments on REE-partitioning between minerals as related to acid-based tendencies and mineral stabilities are presented. As the same or analogous coupled substitutions involving the REE occur in a wide variety of mineral structures, they are discussed together.

  1. Isotope U-Pb age on single zircon and REE distribution in rocks and zircon from paleoproterozoic Kandalaksha-Kolvitsa complex Baltic shield

    NASA Astrophysics Data System (ADS)

    Steshenko, Ekaterina; Bayanova, Tamara; Drogobuzhskaya, Svetlana; Lyalina, Ludmila; Serov, Pavel; Chashchin, Viktor; Elizarov, Dmitriy

    2017-04-01

    -05-00305, 16-05-00367, 16-05-00427) and theme of state assignment № 0231-2015-0005. References: 1. Boynton W.V. Cosmochemistry of the rare earth elements: meteorite studies // Ed. Henderson P. Rare earth element geochemistry. Amsterdam: Elsevier. 1984. P. 63-114. 2. Watson E. B., Wark D.A., Thomas J.B. Crystallization thermometers for zircon and rutile // Contrib. Miner. Petrol. 2006. V. 151. P. 413-433. 3. Hoskin P.W.O. and Schaltegger U. The Composition of zirconand igneous and metamorphic petrogenesis // Reviews in mineralogy & geochemistry. 2003. V. 53. P. 27-62.

  2. Characteristics of zircon suitable for REE extraction

    NASA Astrophysics Data System (ADS)

    Watanabe, Y.; Hoshino, M.

    2011-12-01

    Zircons (ZrSiO4) from Naegi and Ohro granitic pegmatites, Japan and from Saigon alkaline basalt, Vietnam, were mineralogically characterized by inductively couples plasma mass spectrometry (ICP-MS), electron-microprobe analysis (EMPA), X-ray powder diffraction, micro-Raman spectroscopy and leaching experiment. The powder XRD and Raman spectra analyses show that the degree of crystallinity decreases from Saigon, to Ohro and Naegi zircons. Quantitative analytical results by the EMPA indicate that the Naegi and Ohro zircon samples contain a large amount of REE2O3, while REE contents in Saigon zircon are below detection limit. The leaching experiments for the present zircons under the condition of a solvent 1M-HCl, at a room temperature to 250 °C and retention time of 30h resulted in about 100 %, 50 % and 1 % recoveries of REE from the Naegi, Ohro and Saigon zircons, respectively. Leaching experiments for the Naegi zircon under the condition of a solvent 1N-HCl, heating temperature of 50 °C, 100 °C, 150 °C and 200 °C, and retention time 30h, showed that a significant amount of REE was leached out at a temperature above 150 °C. However, the leaching experiments of the Naegi and Ohro zircons at room temperature (about 25 °C) show that REE were hard to be leached. These results indicates that both low crystallinity of zircon and higher leaching temperature are requisite for effective leaching of REE from zircon.

  3. Applying the Ce-in-zircon oxygen geobarometer to diverse silicic magmatic systems

    NASA Astrophysics Data System (ADS)

    Claiborne, L. L.; Miller, C. F.

    2012-12-01

    Zircon provides information on age, temperature, and composition of the magma from which it grew. In systems such as Mount St. Helens, where zircon is not coeval with the rest of the crystal cargo, it provides the only accessible record of the extended history of the magmatic system, including cycles of intrusion, crystallization and rejuvenation beneath an active volcano (Claiborne et al., 2010). The rare earth elements, which are present in measureable quantities in zircon, provide information about the composition of the magma from which zircon grew. Unique among the generally trivalent rare earth elements, cerium can exist as either trivalent or tetravalent, depending on the oxidation state of the magma. The tetravalent ion is highly compatible in zircon, in the site that usually hosts tetravalent zirconium, and so the amount of Cerium in zircon relative (relative to what would be expected of trivalent Ce) depends the oxidation state of the magma from which it grew. Trail et al. (2011) proposed a calibration based on experimental data that uses the Ce anomaly in zircon as a direct proxy for magma oxidation (fugacity), describing the relationship between Ce in zircon and magma oxygen fugacity as ln(Ce/Ce*)D = (0.1156±0.0050)xln(fO2)+(13860±708)/T-(6.125±0.484). For systems like Mount St. Helens, where the major minerals record only events in the hundreds to thousands of years leading to eruption, (including the Fe-Ti oxides traditionally relied upon for records of oxidation state of the magmas), this presents a novel approach for understanding more extended histories of oxidation of magmas in the tens and hundreds of thousands of years of magmatism at a volcanic center. This calibration also promises to help us better constrain conditions of crystallization in intrusive portions of volcanic systems, as well as plutonic bodes. We apply this new oxygen geobarometer to natural volcanic and plutonic zircons from a variety of tectonic settings, and compare to

  4. Zircon U-Pb geochronology and geochemistry of granites in the Zhuguangshan complex, South China: Implications for uranium mineralization

    NASA Astrophysics Data System (ADS)

    Zhang, Long; Chen, Zhenyu; Li, Xiaofeng; Li, Shengrong; Santosh, M.; Huang, Guolong

    2018-05-01

    The Zhuguangshan complex, composed of Caledonian, Indosinian, and Yanshanian granites, and Cretaceous mafic dykes, is one of the most important granite-hosted uranium producers in South China. Here we present LA-ICP-MS zircon U-Pb and hornblende 40Ar/39Ar geochronology and whole-rock and biotite geochemistry for the granites in this complex to evaluate the magmatism and its constraints on uranium mineralization. Samples collected from the Fuxi, Youdong, Longhuashan, Chikeng, Qiling, and Sanjiangkou intrusions yield zircon weighted 206Pb/238U ages of 426.7 ± 5.4 Ma, 226.4 ± 3.5 Ma, 225.0 ± 2.7 Ma, 152.2 ± 3.0 Ma, 153.9 ± 2.1 Ma, and 155.2 ± 2.1 Ma, respectively. A new Ar-Ar dating of the hornblende of the diabase from the Changjiang uranium ore field yields a plateau age of 145.1 ± 1.5 Ma. These results coupled with published geochronological data indicate that six major magmatic events occurred in the study area at 420-435 Ma, 225-240 Ma, 150-165 Ma, 140 Ma, 105 Ma, and 90 Ma. Both U-bearing and barren granites occur in this complex, and they display differences in whole-rock and biotite geochemistry. The barren granites show higher Al2O3, CaO, TFMM, Rb, Zr, Ba, SI, Mg#, (La/Yb)N, and Eu/Eu*, but lower SiO2, ALK, Rb, DI, Rb/Sr, and TiO2/MgO than those of the U-bearing granites. Biotites in the U-bearing granites are close to the Fe-rich siderophyllite-annite end member with Fe/(Fe + Mg) ratios higher than 0.66, whereas those in the barren granites are relatively close to the Mg-rich eastonite-phlogopite end member with Fe/(Fe + Mg) ratios <0.66. The U-bearing granites were mainly derived from the partial melting of pelitic sedimentary source, whereas the psammitic source generated the barren granites. In addition, the barren granites show higher TFMM, Ba, and Eu/Eu* but lower SiO2, Rb/Sr and Al2O3/TiO2 ratios with higher zircon saturation temperatures relative to the U-bearing granites. These results indicate that the geochemical compositions of the U

  5. Algal Accessory Pigment Detection Using AVIRIS Image-Derived Spectral Radiance Data

    NASA Technical Reports Server (NTRS)

    Richardson, Laurie L.; Ambrosia, Vincent G.

    1996-01-01

    Visual and derivative analyses of AVIRIS spectral data can be used to detect algal accessory pigments in aquatic communities. This capability extends the use of remote sensing for the study of aquatic ecosystems by allowing detection of taxonomically significant pigment signatures which yield information about the type of algae present. Such information allows remote sensing-based assessment of aquatic ecosystem health, as in the detection of nuisance blooms of cyanobacteria or toxic blooms of dinoflagellates. Remote sensing of aquatic systems has traditionally focused on quantification of chlorophyll a, a photoreactive (and light-harvesting) pigment which is common to all algae as well as cyanobacteria (bluegreen algae). Due to the ubiquitousness of this pigment within algae, chl a is routinely measured to estimate algal biomass both during ground-truthing and using various airborne or satellite based sensors, including AVIRIS. Within the remote sensing and aquatic sciences communities, ongoing research has been performed to detect algal accessory pigments for assessment of algal population composition. This research is based on the fact that many algal accessory pigments are taxonomically significant, and all are spectrally unique. Aquatic scientists have been refining pigment analysis techniques, primarily high performance liquid chromatography, or HPLC, to detect specific pigments as a time-saving alternative to individual algal cell identifications and counts. Remote sensing scientists are investigating the use of pigment signatures to construct pigment libraries analogous to mineral spectral libraries used in geological remote sensing applications. The accessory pigment approach has been used successfully in remote sensing using data from the Thematic Mapper, low-altitude, multiple channel scanners, field spectroradiometers and the AVIRIS hyperspectral scanner. Due to spectral and spatial resolution capabilities, AVIRIS is the sensor of choice for such

  6. Zircon U-Pb ages and Hf isotope data from the Kukuluma Terrain of the Geita Greenstone Belt, Tanzania Craton: Implications for stratigraphy, crustal growth and timing of gold mineralization

    NASA Astrophysics Data System (ADS)

    Kwelwa, S. D.; Sanislav, I. V.; Dirks, P. H. G. M.; Blenkinsop, T.; Kolling, S. L.

    2018-03-01

    The Geita Greenstone Belt is a late Archean greenstone belt located in the Tanzania Craton, trending approximately E-W and can be subdivided into three NW-SE trending terrains: the Kukuluma Terrain to the east, the Central Terrain in the middle and the Nyamullilima Terrain in the west. The Kukuluma Terrain, forms a NW-SE trending zone of complexly deformed sediments, intruded by the Kukuluma Intrusive Complex which, contains an early-syntectonic diorite-monzonite suite and a late-syntectonic granodiorite suite. Three gold deposits (Matandani, Kukuluma and Area 3W) are found along the contact between the Kukuluma Intrusive Complex and the sediments. A crystal tuff layer from the Kukuluma deposits returned an age of 2717 ± 12 Ma which can be used to constrain maximum sedimentation age in the area. Two granodiorite dykes from the same deposit and a small granodiorite intrusion found along a road cut yielded zircon ages of 2667 ± 17 Ma, 2661 ± 16 Ma and 2663 ± 11 Ma respectively. One mineralized granodiorite dyke from the Matandani deposit has an age of 2651 ± 14 Ma which can be used to constrain the maximum age of the gold mineralization in the area. The 2717 Ma crystal tuff has zircon grains with suprachondritic 176Hf/177Hf ratios (0.28108-0.28111 at 2717 Ma) and positive (+1.6 to +2.6) εHf values indicating derivation from juvenile mafic crust. Two of the granodiorite samples have suprachondritic 176Hf/177Hf ratios (avg. 0.28106 and 0.28107 at 2663 and 2651 Ma respectively) and nearly chondritic εHf values (avg. -0.5 and -0.3 respectively). The other two granodiorite samples have chondritic 176Hf/177Hf ratios (avg. 0.28104 and 0.28103 at 2667 and 2661 Ma respectively) and slightly negative εHf values (avg. -1.1 and -1.5 respectively). The new zircon age and isotope data suggest that the igneous activity in the Kukuluma Terrain involves a significant juvenile component and occurred within the 2720 to 2620 Ma period which, is the main period of crustal growth

  7. In-situ measurements of U-series nuclides by electron microprobe on zircons and monazites from Gandak river sediments

    NASA Astrophysics Data System (ADS)

    Bosia, C.; Deloule, E.; France-Lanord, C.; Chabaux, F.

    2015-12-01

    Determination of sediment transfer time during transport in the alluvial plains is a critical issue to correctly understand the relationship between climate, tectonics and Earth surface evolution. The residence time of river sediments may be constrained by analyzing the U series nuclides fractionations (e.g. [1] and [2]), which are created during water rock interactions by the ejection of the daughter nuclides of the grain (α-recoil) and the preferential mobilization of nuclides in decay damaged crystal structure. However, recent studies on sediments from the Gandak river, one of the main Ganga tributary, highlighted the difficulties to obtain reproducible data on bulk sediments, due to the nuggets distribution of U-Th enriched minor minerals in the samples (Bosia et al., unpublished data). We therefore decided to analyze the U and Th isotopic systematic at a grain-scale for Himalayan sediments from the Gandak river. This has been tested by performing in situ depth profiles of 238U-234U-230Th and 232Th on zircons and monazites (50-250 μm) by Secondary Ion Mass Spectrometry (SIMS) at the CRPG, Nancy, France. The first results point the occurrence of 238U-234U-230Th disequilibria in the outermost parts of both monazite and zircon minerals with a return to the equilibrium state in the core of the grains. The relative U and Th enrichment is however slightly different depending on considered minerals, suggesting possible adsorption processes of 230-Th. Coupled to a simple model of U and Th mobility during water-mineral interactions, these data should help to constrain the origin of 238U-234U-230Th disequilibria in these minerals. Moreover, the results of the study should be relevant to discuss the potential of this approach to constrain the residence time of zircons and monazites in the Gandak alluvial plain. [1] Chabaux et al., 2012, C. R. Geoscience, 344 (11-12): 688-703; [2] Granet et al., 2007, Earth and Planet. Sci. Lett., 261 (3-4): 389-406.

  8. Li isotopes in archean zircons

    NASA Astrophysics Data System (ADS)

    Bouvier, A.; Ushikubo, T.; Kita, N.; Cavosie, A. J.; Kozdon, R.; Valley, J. W.

    2009-12-01

    Li is a fluid mobile, moderately incompatible element with a large mass difference between its two stable isotopes. Different processes can fractionate 7Li/6Li (fluid-rock interaction, metamorphic reactions, and Li diffusion), leading to variation by over 50‰ of δ7Li for common crustal material. These large variations make δ7Li a potential tracer of continental weathering and of the fluids affecting magma sources. Here, we report δ7Li and trace elements in Archean igneous zircons from TTG and sanukitoid granitoids from the Superior Province (Canada) in order to characterize Li in Archean zircons from well-described samples. These data are compared to detrital zircons from the Jack Hills (Western Australia) for which parent rock-type is uncertain. This study aims to better understand Li substitution in zircon and to evaluate the utility of δ7Li and [Li] for Archean petrogenesis. Zircons (n=71) were analyzed for δ7Li and trace elements (Li, P, Ca, Ti, V, Fe, Y, REE, U, Th) using an IMS-1280 ion microprobe. Most of the zircons display typical igneous REE patterns and zoning by CL. [Li] averages 13.1 ± 9 for TTG, 25.7 ± 19 for Sanukitoid and 31.0 ± 14 ppm for Jack Hills zircons, which are distinct from mantle-related zircons (<0.1 ppm). Values of δ7Li average 1.0 ± 4.5‰ for TTGs, 6.3 ± 4.4‰ for sanukitoids and -2.6 ± 8.8‰ for Jack Hills samples. Trace elements were analyzed from single spots in order to evaluate coupled substitutions. Atomic ratios (3Li+Y+REE)/P average 2.6, showing that Li and trivalent atoms are not charge-balanced by P, and suggesting that Li does not replace Zr, according to the xenotime substitution. However, (Y+REE)/(Li+P) atomic ratios average 1.0 ± 0.6, supporting the hypothesis that Li is interstitial and partly compensates trivalent cations. Several observations in this study suggest that [Li] is primary in the studied zircons: i) if Li is interstitial, charge-balance and slow diffusion of REE would control Li mobility

  9. 14 CFR 25.1163 - Powerplant accessories.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or sparking... to prevent rotation without interfering with the continued operation of the engine. [Doc. No. 5066... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine...

  10. 14 CFR 25.1163 - Powerplant accessories.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or sparking... to prevent rotation without interfering with the continued operation of the engine. [Doc. No. 5066... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine...

  11. 14 CFR 25.1163 - Powerplant accessories.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or sparking... to prevent rotation without interfering with the continued operation of the engine. [Doc. No. 5066... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine...

  12. 14 CFR 25.1163 - Powerplant accessories.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or sparking... to prevent rotation without interfering with the continued operation of the engine. [Doc. No. 5066... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine...

  13. Petrogenesis of the Bosworgey granitic cusp in the SW England tin province and its implications for ore mineral genesis

    NASA Astrophysics Data System (ADS)

    Ball, T. K.; Basham, I. R.

    1984-01-01

    The Bosworgey granite cusp forms an apical portion of the concealed northern extension of the Tregonning-Godolphin granite ridge. It is characterised by unusually high values of B, P, Mn, Fe, As, Cu, Nb, Ta, Bi, Sn, W, U and S which are present largely as tourmaline, apatite, pyrite, arsenopyrite, chalcopyrite, bismuth, columbite, cassiterite, wolframite and uraninite; and low levels of Zr, Hf, Ti and REE present in zircon, ilmenite and monazite. The granite is classified as Sn and W “specialised” (Tischendorf, 1974) and it belongs to the ilmenite series of Japanese workers. The classification of Chappell and White (1974) (“S” and “I” type granites) is shown to be inapplicable to Cornubian rocks although the Bosworgey samples show characteristics of “S” type granites. The accessory mineral assemblages are typical of high temperature lodes (cassiterite, wolframite, arsenopyrite, chalcopyrite) and the assamblage is concluded to be the cusp analogue of hypothermal lodes produced by extreme differentiation and concentration of volatiles. It is speculated that such granites could provide the parent material for the mesothermal crosscourse mineralisation (pitchblende, bismuth, pyrite, galena, sphalerite).

  14. Petrological and zircon evidence for the Early Cretaceous granulite-facies metamorphism in the Dabie orogen, China

    NASA Astrophysics Data System (ADS)

    Gao, Xiao-Ying; Zhang, Qiang-Qiang; Zheng, Yong-Fei; Chen, Yi-Xiang

    2017-07-01

    An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite-facies reworking of the ultrahigh-pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U-Pb ages are clearly categorized into two groups at 122-127 Ma and 188 ± 2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of garnet + clinopyroxene ± quartz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains only contain a few quartz inclusions and the garnet-clinopyroxene-plagioclase-quartz barometry yields pressures of 4.9 to 12.5 kb. In addition, the clinopyroxene-garnet Fe-Mg exchange thermometry gives temperatures of 738-951 °C. Therefore, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite-facies metamorphic age is in agreement not only with the adjacent diorite at 125 ± 1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite-facies metaigneous rocks in the Dabie orogen. In combination with major-trace elements and zircon Lu-Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab-mantle interface in the continental subduction channel

  15. Hadean Crustal Processes Revealed from Oxygen Isotopes and U-Th-Pb Depth Profiling of Pre-4.0 Ga Detrital Zircons from Western Australia

    NASA Technical Reports Server (NTRS)

    Trail, D.; Mojzsis, S. J.; Harrison, T. M.

    2005-01-01

    Because physical and chemical processes of the past are determined from analysis of a preserved geologic record, little is known about terrestrial crustal processes of the first 500 Ma during the so-called Hadean Eon. What is known from direct measurements has been derived almost exclusively from the study of greater than 4.0 Ga detrital zircons from the Jack Hills, Western Australia. The geochemistry of these zircons has direct application to understanding the origin and evolution of the rocks during the Hadean because: (i) U-Th-Pb age determinations by ion microprobe suggests the presence of crust as early as 4.37 Ga, or shortly after lunar formation; (ii) high-resolution U-Th-Pb zircon depth profiles reported here reveal several episodes of zircon growth in the Hadean previously unrecognized; (iii) core regions of pre-4.0 Ga zircons with igneous compositions are enriched in O-18 and contain metaluminous and peraluminous mineral inclusions, both features indicative of S-type grainitod protoliths. Study of these ancient zircons provides a unique window into the first half billion years that permits assessment of the potential of the Hadean Earth to host an emergent biosphere.

  16. Sulfur in zircons: A new window into melt chemistry

    NASA Astrophysics Data System (ADS)

    Tang, H.; Bell, E. A.; Boehnke, P.; Barboni, M.; Harrison, T. M.

    2017-12-01

    The abundance and isotopic composition of sulfur are important tools for exploring the photochemistry of the atmosphere, the thermal history of mantle and igneous rocks, and ancient metabolic processes on the early Earth. Because the oldest terrestrial samples are zircons, we developed a new in-situ procedure to analyze the sulfur content of zircons using the CAMECA ims 1290 at UCLA. We analyzed zircons from three metaluminous/I-type granites (reduced and oxidized Peninsular range and Elba), which exhibit low sulfur abundance with the average of 0.5ppm, and one peraluminous/S-type zircon (Strathbogie Range), which shows an elevated sulfur level with the average of 1.5ppm. Additionally, we found that sulfur content ranges between 0.4 and 2.3 ppm in young volcanic zircons (St. Lucia). Our analyses of zircons from the Jack Hills, Western Australia, whose ages range between 3.4 and 4.1 Ga, show a variety of sulfur contents. Three out of the ten zircons are consistent with the sulfur contents of S-type zircons; the rest have low sulfur contents, which are similar to those of I-type zircons. The high sulfur content in some of these Jack Hills zircons can be interpreted as indicating their origin in either a S-type granite or a volcanic reservoir. We favor the former interpretation since the Ti-in-zircon temperatures of our Jack Hills zircons is lower than those of volcanic zircons. Future work will be undertaken to develop a systematic understanding of the relationship between melt volatile content, melt chemistry, and zircon sulfur content.

  17. Assessing the role of detrital zircon sorting on provenance interpretations in an ancient fluvial system using paleohydraulics - Permian Cutler Group, Paradox Basin, Utah and Colorado

    NASA Astrophysics Data System (ADS)

    Findlay, C. P., III; Ewing, R. C.; Perez, N. D.

    2017-12-01

    Detrital zircon age signatures used in provenance studies are assumed to be representative of entire catchments from which the sediment was derived, but the extent to which hydraulic sorting can bias provenance interpretations is poorly constrained. Sediment and mineral sorting occurs with changes in hydraulic conditions driven by both allogenic and autogenic processes. Zircon is sorted from less dense minerals due to the difference in density, and any age dependence on zircon size could potentially bias provenance interpretations. In this study, a coupled paleohydraulic and geochemical provenance approach is used to identify changes in paleohydraulic conditions and relate them to spatial variations in provenance signatures from samples collected along an approximately time-correlative source-to-sink pathway in the Permian Cutler Group of the Paradox Basin. Samples proximal to the uplift have a paleoflow direction to the southwest. In the medial basin, paleocurrent direction indicates salt movement caused fluvial pathways divert to the north and northwest on the flanks of anticlines. Channel depth, flow velocity, and discharge calculations were derived from field measurements of grain size and dune and bar cross-stratification indicate that competency of the fluvial system decreased from proximal to the medial basin by up to a factor of 12. Based upon the paleohydraulic calculations, zircon size fractionation would occur along the transect such that the larger zircons are removed from the system prior to reaching the medial basin. Analysis of the size and age distribution of zircons from the proximal and distal fluvial system of the Cutler Group tests if this hydraulic sorting affects the expected Uncompahgre Uplift age distribution.

  18. Zircon U-Pb ages and Hf isotopic compositions indicate multiple sources for Grenvillian detrital zircon deposited in western Laurentia

    NASA Astrophysics Data System (ADS)

    Howard, Amanda L.; Farmer, G. Lang; Amato, Jeffrey M.; Fedo, Christopher M.

    2015-12-01

    Combined U-Pb ages and Hf isotopic data from 1.0 Ga to 1.3 Ga (Grenvillian) detrital zircon in Neoproterozoic and Cambrian siliciclastic sedimentary rocks in southwest North America, and from igneous zircon in potential Mesoproterozoic source rocks, are used to better assess the provenance of detrital zircon potentially transported across Laurentia in major river systems originating in the Grenville orogenic highlands. High-precision hafnium isotopic analyses of individual ∼1.1 Ga detrital zircon from Neoproterozoic siliciclastic sedimentary rocks in Sonora, northern Mexico, reveal that these zircons have low εHf (0) (-22 to -26) and were most likely derived from ∼1.1 Ga granitic rocks embedded in local Mojave Province Paleoproterozoic crust. In contrast, Grenvillian detrital zircons in Cambrian sedimentary rocks in Sonora, the Great Basin, and the Mojave Desert, have generally higher εHf (0) (-15 to -21) as demonstrated both by high precision solution-based, and by lower precision laser ablation, ICPMS data and were likely derived from more distal sources further to the east/southeast in Laurentia. Comparison to new and existing zircon U-Pb geochronology and Hf isotopic data from Grenvillian crystalline rocks from the Appalachian Mountains, central and west Texas, and from Paleoproterozoic terranes throughout southwest North America reveals that zircon in Cambrian sandstones need not entirely represent detritus transported across the continent from Grenville province rocks in the vicinity of the present-day southern Appalachian Mountains. Instead, these zircons could have been derived from more proximal, high εHf (0), ∼1.1 Ga, crystalline rocks such as those exposed today in the Llano Uplift in central Texas and in the Franklin Mountains of west Texas. Regardless of the exact source(s) of the Grenvillian detrital zircon, new and existing whole-rock Nd isotopic data from Neoproterozoic to Cambrian siliciclastic sedimentary rocks in the Mojave Desert

  19. 21 CFR 878.4960 - Operating tables and accessories and operating chairs and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Operating tables and accessories and operating chairs and accessories. 878.4960 Section 878.4960 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Surgical...

  20. 21 CFR 878.4960 - Operating tables and accessories and operating chairs and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Operating tables and accessories and operating chairs and accessories. 878.4960 Section 878.4960 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Surgical...

  1. 21 CFR 878.4960 - Operating tables and accessories and operating chairs and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Operating tables and accessories and operating chairs and accessories. 878.4960 Section 878.4960 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Surgical...

  2. 21 CFR 878.4960 - Operating tables and accessories and operating chairs and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Operating tables and accessories and operating chairs and accessories. 878.4960 Section 878.4960 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Surgical...

  3. 21 CFR 878.4960 - Operating tables and accessories and operating chairs and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Operating tables and accessories and operating chairs and accessories. 878.4960 Section 878.4960 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Surgical...

  4. Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer

    USGS Publications Warehouse

    Reid, M.R.; Vazquez, J.A.; Schmitt, A.K.

    2011-01-01

    Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720??C for zircon rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage in its evolution. There is also no compelling evidence for punctuated heat ?? chemical influxes during the intermediate stages of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir by-or zircon entrainment in-a less evolved melt from the one in which the zircons had previously resided. ?? 2010 Springer-Verlag.

  5. First application of the revised Ti-in-zircon geothermometer to Paleoproterozoic ultrahigh-temperature granulites of Tuguiwula, Inner Mongolia, North China Craton

    NASA Astrophysics Data System (ADS)

    Liu, S. J.; Li, J. H.; Santosh, M.

    2010-02-01

    The revised titanium-in-zircon geothermometer was applied to Paleoproterozoic ultrahigh-temperature (UHT) granulites at Tuguiwula, Inner Mongolia, North China Craton. The Tuguiwula granulites contain diagnostic UHT mineral assemblages such as sapphirine + quartz and high alumina orthopyroxene + sillimanite + quartz, suggesting formation under temperatures of ca. 1,000°C and pressures of up to 10 kbar. Here, we report detailed petrographic studies and ICP-MS data on titanium concentration in zircons associated with the UHT assemblages. The zircons associated with sapphirine-spinel-sillimanite-magnetite assemblages have the highest Ti concentration of up to 57 ppm, yielding a temperature of 941°C, and suggesting that the growth of zircons occurred under ultrahigh-temperature conditions. The maximum temperatures obtained by the revised Ti-in-zircon geothermometer is lower than the equilibrium temperature of sapphirine + quartz, indicating an interval of cooling history of the granulites from UHT condition to ca. 940°C. Many of the zircons have Ti concentrations ranging from 10 to 33 ppm, indicating their growth or recrystallization under lower temperatures of ca. 745-870°C. These zircons are interpreted to have recrystallized during the retrograde stage indicated by microstructures such as cordierite rim or corona between spinel and quartz, and orthopyroxene-cordierite symplectite around garnet. Previous geochronological study on the zircons of the Tuguiwula UHT granulites gave a mean U-Pb SHRIMP age of 1.92 Ga. However, based on the Ti-in-zircon geothermometer results reported in this work, and considering the relatively slow thermal relaxation of these rocks, we infer that the timing of peak UHT metamorphism in the Tuguiwula area could be slightly older than 1.92 Ga.

  6. Etching fission tracks in zircons

    USGS Publications Warehouse

    Naeser, C.W.

    1969-01-01

    A new technique has been developed whereby fission tracks can be etched in zircon with a solution of sodium hydroxide at 220??C. Etching time varied between 15 minutes and 5 hours. Colored zircon required less etching time than the colorless varieties.

  7. 14 CFR 29.1163 - Powerplant accessories.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed in such a way as to prevent contamination of the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or...

  8. 14 CFR 29.1163 - Powerplant accessories.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed in such a way as to prevent contamination of the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or...

  9. 14 CFR 29.1163 - Powerplant accessories.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed in such a way as to prevent contamination of the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or...

  10. 14 CFR 29.1163 - Powerplant accessories.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed in such a way as to prevent contamination of the engine oil system and the accessory system. (b) Electrical equipment subject to arcing or...

  11. At what conditions does zircon grow/dissolve during high-T metamorphism? Relating zircon textures to PT-conditions

    NASA Astrophysics Data System (ADS)

    Kunz, Barbara E.; Regis, Daniele; Manzotti, Paola; Engi, Martin

    2015-04-01

    A key question in ziconology is when and how zircon grows during metamorphism. To shed light on zircon forming processes and the corresponding PT-conditions during high-T metamorphism a case study was undertaken. The Ivrea Zone (N-Italy) exposes a lower continental crustal section in which a continuous metamorphic field gradient from amphibolite to granulite facies is documented. This field gradient is thought to reflect protracted heating during late Paleozoic times, with a probable high-T peak in the Permian. We present first results from a primarily textural study supported by U-Pb ages, Th/U ratios and Ti-in-Zrn thermometry. Four types of zircon were identified based on their overgrowth proportions and the preservation of detrital cores. Zircon grains were thus classified as Type1 - detrital grains with no overgrowth or very narrow rims (300 Ma) and appears to reflect an early dehydration phase. Rim2b has Permian ages (median 275 Ma), is by far the most common overgrowth type, found in a wide PT-range. Its development appears related to biotite breakdown. Rim3 is texturally indicative of magmatic zircon, occurs only in diatexites. Rim4 is the latest overgrowth and is locally found at all metamorphic grades. Textural features suggest late fluid-related recrystallization of existing zircon. At lowest grade (675±35°C, 6±2 kbar) zircons show type1 only, overgrowths are too thin to clearly identify the rim type. Further upgrade (~700°C, 7 kbar) type1 and type2 dominate. Type2 zircons show rim1, rim2a and occasionally rim4. At the Mu-out isograd (750±50°C, 8.2±1.4 kbar) most zircons are of type2, now with rim2b instead of 2a, in addition to rim1 and rim4. Near and in granulite facies (to 800°C, 8±2 kbar) mostly zircon type2 and type4 are present. While rim1 gets more narrow with increasing metamorphic grade, rim2b grows significantly thicker. Occasionally rim2a and rim4 occur. Close to the Bt-out isograd (~860°C, 9.2±1.7 kbar), mostly type3 and type4 are

  12. Petrologic and zircon U-Pb geochronological characteristics of the pelitic granulites from the Badu Complex of the Cathaysia Block, South China

    NASA Astrophysics Data System (ADS)

    Zhao, Lei; Zhou, Xiwen; Zhai, Mingguo; Liu, Bo; Cui, Xiahong

    2018-06-01

    The recognition of the Indosinian Orogeny in the South China block has been controversial and difficult because of strong weathering and thick cover. High temperature (HT) and high pressure (HP) metamorphic rocks related to this orogeny were considered to be absent from this orogenic belt until the recent discovery of eclogite and granulite facies meta-igneous rocks, occurring as lenses within the meta-sedimentary rocks of the Badu Complex. However, metamorphic state of these meta-sedimentary rocks is still not clear. Besides, there have been no geochronological data of HT pelitic granulites previously reported from the Badu Complex. This paper presents petrographic characteristics and zircon geochronological results on the newly discovered kyanite garnet gneiss, pyroxene garnet gneiss and the HT pelitic granulites (sillimanite garnet gneiss). Mineral assemblages are garnet + sillimanite + ternary feldspar + plagioclase + quartz + biotite for the HT pelitic granulite, kyanite + ternary feldspar + garnet + sillimanite + plagioclase + quartz + biotite for the kyanite garnet gneiss, and garnet + biotite + pyroxene + plagioclase + ternary feldspar + quartz for the pyroxene garnet gneiss, respectively. Decompressional coronas around garnet grains can be observed in all these pelitic rocks. Typical granulite facies mineral assemblages and reaction textures suggest that these rocks experienced HP granulite facies metamorphism and overprinted decompression along a clockwise P-T loop. Results from integrated U-Pb dating and REE analysis indicate the growth of metamorphic zircons from depleted heavy REE sources (100-50 chondrite) compared with detrital zircons derived from granitic sources (typically > 1000 chondrite). Metamorphic zircons in HP granulite exhibit no or subdued negative Eu anomalies, which perhaps indicate zircon overgrowth under eclogite facies conditions. The zircon overgrowth ages range from 250 to 235 Ma, suggesting that HP granulite (eclogite) to

  13. Duration of convergence at the Pacific-Gondwana plate margin: insights from accessory phase petrochronology of the Alpine Schist, New Zealand

    NASA Astrophysics Data System (ADS)

    Briggs, S. I.; Cottle, J. M.; Smit, M. A.; Arnush, N. F.

    2016-12-01

    The timing, duration and along-strike synchroneity of metamorphism and anataxis in the Alpine Schist of New Zealand is a matter of considerable debate. Our preliminary data indicate that metamorphism resulting in garnet growth occurred from 97 - 75 Ma, and anatectic melting occurred from 80 - 51 Ma. These events are contemporaneous with rifting of Zealandia from East Gondwana, and Tasman Sea spreading from 83 - 52 Ma. An important implication of these results is that Late Cretaceous convergence along the Zealandia segment of the Pacific-Gondwana plate margin may have persisted much later than previously thought, and that convergence and extension occurred coevally in adjacent areas. This poses the question: for how long did convergence continue along the Pacific-Gondwana plate margin during East Gondwana breakup? To fully decipher the multiple stages of the complex metamorphic history recorded in the Alpine Schist, we combine Lu-Hf garnet geochronology with U-Th/Pb and REE analyses of zircon and monazite. We use the newly developed `single-shot laser ablation split stream' (SS-LASS) analysis method to obtain depth profiles through 5-10 µm metamorphic zircon overgrowths at 100 nm depth resolution to constrain both the timing and petrological context of discrete metamorphic zircon (re-)crystallization events recorded in the Alpine Schist. We also employ high spatial resolution LASS analysis to target rare 5 - 20 µm monazite in thin section to augment garnet and zircon data. Our multi-accessory phase petrochronology approach is capable of resolving discrete short-duration thermal events, strengthening the geological interpretation of `mean' Lu-Hf garnet ages and discerning between an episodic versus a prolonged history of metamorphism. In addition, comparison with geochronology from anatectic pegmatites clarifies the temporal relationship between metamorphism and melting in the Alpine Schist, while providing direct constraints on the timing and duration of

  14. Two mineralization events in the Baiyinnuoer Zn-Pb deposit in Inner Mongolia, China: Evidence from field observations, S-Pb isotopic compositions and U-Pb zircon ages

    NASA Astrophysics Data System (ADS)

    Jiang, Si-Hong; Chen, Chun-Liang; Bagas, Leon; Liu, Yuan; Han, Ning; Kang, Huan; Wang, Ze-Hai

    2017-08-01

    The Xing-Mong Orogenic Belt (XMOB) is located in the eastern part of the Central Asian Orogenic Belt (CAOB) and has experienced multiple tectonic events. The Baiyinnuoer Pb-Zn deposit may be a rare case that documents two periods of mineralization in the tectonically complex XMOB. There are two types of Pb-Zn mineralization in the deposit: (1) skarn-type ore, hosted by the skarn in the contact zone between marble and granodiorite and within the marble and (2) vein-type ore, hosted by crystal tuff and feldspar porphyry. This study revealed that the host rocks, mineral assemblages, mineralization occurrences, S-Pb isotopes, and ages between the two types of ore are notably different. Zircon U-Pb dating indicates that the granodiorite was emplaced in the Early Triassic (244 ± 1 to 242 ± 1 Ma), the crystal tuff was deposited in the Early Cretaceous (140 ± 1 to 136 ± 1 Ma), and the feldspar porphyry was intruded in the Early Cretaceous (138 ± 2 to 136 ± 2 Ma). The first skarn mineralization occurred at ∼240 Ma and the second vein-type Pb-Zn mineralization took place between 136 and 129 Ma. Thus the Triassic orebodies were overprinted by Early Cretaceous mineralization. The sphalerite and galena from the skarn mineralization have higher δ34S values (-4.7 to +0.3‰) than the sphalerite, galena and aresenopyrite from the vein-type mineralization (-7.5 to -4.2‰), indicating different sulfur sources or ore-forming processes for the two types of mineralization. The Pb isotopic compositions of the two types of ore are very similar, suggesting similar lead sources. Geochemistry and Nd-Pb-Hf isotopic systematics of the igneous rocks in the region show that the Triassic granodiorite was generated from hybridization of mafic and felsic magmas due to strong crust-mantle interaction under the collisional setting that resulted following the closure of the Paleo-Asian Ocean and the collision of North China and Siberian cratons at the end of the Permian; while the

  15. Detrital Zircon Geochronology of Cretaceous and Paleogene Strata Across the South-Central Alaskan Convergent Margin

    USGS Publications Warehouse

    Bradley, Dwight; Haeussler, Peter J.; O'Sullivan, Paul; Friedman, Rich; Till, Alison; Bradley, Dan; Trop, Jeff

    2009-01-01

    Ages of detrital zircons are reported from ten samples of Lower Cretaceous to Paleogene metasandstones and sandstones from the Chugach Mountains, Talkeetna Mountains, and western Alaska Range of south-central Alaska. Zircon ages are also reported from three igneous clasts from two conglomerates. The results bear on the regional geology, stratigraphy, tectonics, and mineral resource potential of the southern Alaska convergent margin. Chugach Mountains - The first detrital zircon data are reported here from the two main components of the Chugach accretionary complex - the inboard McHugh Complex and the outboard Valdez Group. Detrital zircons from sandstone and two conglomerate clasts of diorite were dated from the McHugh Complex near Anchorage. This now stands as the youngest known part of the McHugh Complex, with an inferred Turonian (Late Cretaceous) depositional age no older than 91-93 Ma. The zircon population has probability density peaks at 93 and 104 Ma and a smattering of Early Cretaceous and Jurassic grains, with nothing older than 191 Ma. The two diorite clasts yielded Jurassic U-Pb zircon ages of 179 and 181 Ma. Together, these findings suggest a Mesozoic arc as primary zircon source, the closest and most likely candidate being the Wrangellia composite terrane. The detrital zircon sample from the Valdez Group contains zircons as young as 69 and 77 Ma, consistent with the previously assigned Maastrichtian to Campanian (Late Cretaceous) depositional age. The zircon population has peaks at 78, 91, 148, and 163 Ma, minor peaks at 129, 177, 330, and 352 Ma, and no concordant zircons older than Devonian. A granite clast from a Valdez Group conglomerate yielded a Triassic U-Pb zircon age of 221 Ma. Like the McHugh Complex, the Valdez Group appears to have been derived almost entirely from Mesozoic arc sources, but a few Precambrian zircons are also present. Talkeetna Mountains - Detrital zircons ages were obtained from southernmost metasedimentary rocks of the

  16. An evaluation of the zircon method of isotopic dating in the Southern Arabian Craton

    USGS Publications Warehouse

    Cooper, J.A.; Stacey, J.S.; Stoeser, D.G.; Fleck, R.J.

    1979-01-01

    A zircon study has been made on eleven samples of igneous rocks from the Saudi Arabian Craton. Ages of sized and magnetic fractions of zircon concentrates show variable degrees of discordance which seem to result from a very young disturbance that produces linear arrays in the Concordia plot. Model age calculations based on a statistically and geologically reasonable lower intercept produce very consistent internal relationships. The Pan African Orogeny, considered to be responsible for loss of radiogenic argon and strontium from minerals of many rocks, does not appear to have affected the zircon data, even though uplift had exposed the rocks of the Arabian Shield at that time. Tonalite, granodiorite, and crosscutting leucoadamellite bodies in the southern part of the An Nimas Bathylith yield ages in the time range 820-760 Ma. A narrow time range of 660 to 665 million years was indicated for ages of widely separated and compositionally different intrusive bodies all to the east of the An Nimas Bathylith. This work suggests that the younger end of the age spectrum established from regional K-Ar and Rb-Sr measurements may be underestimated, and that magmatic activity could be more episodic than previously assumed.

  17. Mineralogy of parent rock and peaty-podzolic soil of Iremel Ridge, Southern Urals

    NASA Astrophysics Data System (ADS)

    Khalitov, R. M.; Perova, E. N.; Abakumov, E. V.; Suleimanov, R. R.

    2017-08-01

    The mineralogy of soils and parent rocks of the Iremel Ridge has been studied by the methods of micromorphology, laser diffraction, computed X-ray microtomography, and X-ray fluorescence analysis. In hard rock and soil, the major minerals have been identified: quartz, illite, and a chlorite-group mineral (Fe analogue of sudoite), as well as accessory minerals: monazite, xenotime, rutile, zircon, and florencite. It has been found that chlorite, illite, and quartz are present in all horizons of the studied peaty-podzolic soil. Insignificant amounts of mixed-layered mineral and kaolinite could be suggested in the T and EL horizons of peaty-podzolic soil. The mixed-layered mineral is most probably of soil origin, which is related to the transformation of illites inherited from the parent rock under acidic conditions.

  18. Constraints on the timing of Co-Cu ± Au mineralization in the Blackbird district, Idaho, using SHRIMP U-Pb ages of monazite and xenotime plus zircon ages of related Mesoproterozoic orthogneisses and metasedimentary rocks

    USGS Publications Warehouse

    Aleinikoff, John N.; Slack, John F.; Lund, Karen; Evans, Karl V.; Fanning, C. Mark; Mazdab, Frank K.; Wooden, Joseph L.; Pillers, Renee M.

    2012-01-01

    The Blackbird district, east-central Idaho, contains the largest known Co reserves in the United States. The origin of strata-hosted Co-Cu ± Au mineralization at Blackbird has been a matter of controversy for decades. In order to differentiate among possible genetic models for the deposits, including various combinations of volcanic, sedimentary, magmatic, and metamorphic processes, we used U-Pb geochronology of xenotime, monazite, and zircon to establish time constraints for ore formation. New age data reported here were obtained using sensitive high resolution ion microprobe (SHRIMP) microanalysis of (1) detrital zircons from a sample of Mesoproterozoic siliciclastic metasedimentary country rock in the Blackbird district, (2) igneous zircons from Mesoproterozoic intrusions, and (3) xenotime and monazite from the Merle and Sunshine prospects at Blackbird. Detrital zircon from metasandstone of the biotite phyllite-schist unit has ages mostly in the range of 1900 to 1600 Ma, plus a few Neoarchean and Paleoproterozoic grains. Age data for the six youngest grains form a coherent group at 1409 ± 10 Ma, regarded as the maximum age of deposition of metasedimentary country rocks of the central structural domain. Igneous zircons from nine samples of megacrystic granite, granite augen gneiss, and granodiorite augen gneiss that crop out north and east of the Blackbird district yield ages between 1383 ± 4 and 1359 ± 7 Ma. Emplacement of the Big Deer Creek megacrystic granite (1377 ± 4 Ma), structurally juxtaposed with host rocks in the Late Cretaceous ca. 5 km north of Blackbird, may have been involved in initial deposition of rare earth elements (REE) minerals and, possibly, sulfides. In situ SHRIMP ages of xenotime and monazite in Co-rich samples from the Merle and Sunshine prospects, plus backscattered electron imagery and SHRIMP analyses of trace elements, indicate a complex sequence of Mesoproterozoic and Cretaceous events. On the basis of textural relationships

  19. Micrometer-scale U-Pb age domains in eucrite zircons, impact re-setting, and the thermal history of the HED parent body

    NASA Astrophysics Data System (ADS)

    Hopkins, M. D.; Mojzsis, S. J.; Bottke, W. F.; Abramov, O.

    2015-01-01

    Meteoritic zircons are rare, but some are documented to occur in asteroidal meteorites, including those of the howardite-eucrite-diogenite (HED) achondrite clan (Rubin, A. [1997]. Meteorit. Planet. Sci. 32, 231-247). The HEDs are widely considered to originate from the Asteroid 4 Vesta. Vesta and the other large main belt asteroids record an early bombardment history. To explore this record, we describe sub-micrometer distributions of trace elements (U, Th) and 235,238U-207,206Pb ages from four zircons (>7-40 μm ∅) separated from bulk samples of the brecciated eucrite Millbillillie. Ultra-high resolution (∼100 nm) ion microprobe depth profiles reveal different zircon age domains correlative to mineral chemistry and to possible impact scenarios. Our new U-Pb zircon geochronology shows that Vesta's crust solidified within a few million years of Solar System formation (4561 ± 13 Ma), in good agreement with previous work (e.g. Carlson, R.W., Lugmair, G.W. [2000]. Timescales of planetesimal formation and differentiation based on extinct and extant radioisotopes. In: Canup, R., Righter, K. (Eds.), Origin of the Earth and Moon. University of Arizona Press, Tucson, pp. 25-44). Younger zircon age domains (ca. 4530 Ma) also record crustal processes, but these are interpreted to be exogenous because they are well after the effective extinction of 26Al (t1/2 = 0.72 Myr). An origin via impact-resetting was evaluated with a suite of analytical impact models. Output shows that if a single impactor was responsible for the ca. 4530 Ma zircon ages, it had to have been ⩾10 km in diameter and at high enough velocity (>5 km s-1) to account for the thermal field required to re-set U-Pb ages. Such an impact would have penetrated at least 10 km into Vesta's crust. Later events at ca. 4200 Ma are documented in HED apatite 235,238U-207,206Pb ages (Zhou, Q. et al. [2011]. Early basaltic volcanism and Late Heavy Bombardment on Vesta: U-Pb ages of small zircons and phosphates in

  20. Micrometer-scale U–Pb age domains in eucrite zircons, impact re-setting, and the thermal history of the HED parent body

    USGS Publications Warehouse

    Hopkins, M.D.; Mojzsis, S.J.; Bottke, W.F.; Abramov, Oleg

    2015-01-01

    Meteoritic zircons are rare, but some are documented to occur in asteroidal meteorites, including those of the howardite–eucrite–diogenite (HED) achondrite clan (Rubin, A. [1997]. Meteorit. Planet. Sci. 32, 231–247). The HEDs are widely considered to originate from the Asteroid 4 Vesta. Vesta and the other large main belt asteroids record an early bombardment history. To explore this record, we describe sub-micrometer distributions of trace elements (U, Th) and 235,238U–207,206Pb ages from four zircons (>7–40 μm ∅) separated from bulk samples of the brecciated eucrite Millbillillie. Ultra-high resolution (∼100 nm) ion microprobe depth profiles reveal different zircon age domains correlative to mineral chemistry and to possible impact scenarios. Our new U–Pb zircon geochronology shows that Vesta’s crust solidified within a few million years of Solar System formation (4561 ± 13 Ma), in good agreement with previous work (e.g. Carlson, R.W., Lugmair, G.W. [2000]. Timescales of planetesimal formation and differentiation based on extinct and extant radioisotopes. In: Canup, R., Righter, K. (Eds.), Origin of the Earth and Moon. University of Arizona Press, Tucson, pp. 25–44). Younger zircon age domains (ca. 4530 Ma) also record crustal processes, but these are interpreted to be exogenous because they are well after the effective extinction of 26Al (t1/2 = 0.72 Myr). An origin via impact-resetting was evaluated with a suite of analytical impact models. Output shows that if a single impactor was responsible for the ca. 4530 Ma zircon ages, it had to have been ⩾10 km in diameter and at high enough velocity (>5 km s−1) to account for the thermal field required to re-set U–Pb ages. Such an impact would have penetrated at least 10 km into Vesta’s crust. Later events at ca. 4200 Ma are documented in HED apatite 235,238U–207,206Pb ages (Zhou, Q. et al. [2011]. Early basaltic volcanism and Late Heavy Bombardment on Vesta: U–Pb ages of small

  1. Zircon age-temperature-compositional spectra in plutonic rocks

    DOE PAGES

    Samperton, Kyle M.; Bell, Elizabeth A.; Barboni, Mélanie; ...

    2017-08-23

    We present that geochronology can resolve dispersed zircon dates in plutonic rocks when magma cooling time scales exceed the temporal precision of individual U-Pb analyses; such age heterogeneity may indicate protracted crystallization between the temperatures of zircon saturation (T sat) and rock solidification (T solid). Diffusive growth models predict asymmetric distributions of zircon dates and crystallization temperatures in a cooling magma, with volumetrically abundant old, hot crystallization at T sat decreasing continuously to volumetrically minor young, cold crystallization at T solid. We present integrated geochronological and geochemical data from Bergell Intrusion tonalites (Central Alps, Europe) that document zircon compositional changemore » over hundreds of thousands of years at the hand-sample scale, indicating melt compositional evolution during solidification. Ti-in-zircon thermometry, crystallization simulation using MELTS software, and U-Pb dates produce zircon mass-temperature-time distributions that are in excellent agreement with zircon growth models. In conclusion, these findings provide the first quantitative validation of longstanding expectations from zircon saturation theory by direct geochronological investigation, underscoring zircon’s capacity to quantify supersolidus cooling rates in magmas and resolve dynamic differentiation histories in the plutonic rock record.« less

  2. Zircon age-temperature-compositional spectra in plutonic rocks

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Samperton, Kyle M.; Bell, Elizabeth A.; Barboni, Mélanie

    We present that geochronology can resolve dispersed zircon dates in plutonic rocks when magma cooling time scales exceed the temporal precision of individual U-Pb analyses; such age heterogeneity may indicate protracted crystallization between the temperatures of zircon saturation (T sat) and rock solidification (T solid). Diffusive growth models predict asymmetric distributions of zircon dates and crystallization temperatures in a cooling magma, with volumetrically abundant old, hot crystallization at T sat decreasing continuously to volumetrically minor young, cold crystallization at T solid. We present integrated geochronological and geochemical data from Bergell Intrusion tonalites (Central Alps, Europe) that document zircon compositional changemore » over hundreds of thousands of years at the hand-sample scale, indicating melt compositional evolution during solidification. Ti-in-zircon thermometry, crystallization simulation using MELTS software, and U-Pb dates produce zircon mass-temperature-time distributions that are in excellent agreement with zircon growth models. In conclusion, these findings provide the first quantitative validation of longstanding expectations from zircon saturation theory by direct geochronological investigation, underscoring zircon’s capacity to quantify supersolidus cooling rates in magmas and resolve dynamic differentiation histories in the plutonic rock record.« less

  3. Insight into the geology of the East Antarctic hinterland: a study of sediment inclusions from ice cores of the Lake Vostok borehole

    USGS Publications Warehouse

    Leitchenkov, G.L.; Belyatsky, B.V.; Rodionov, N.V.; Sergeev, S.A.

    2007-01-01

    refrozen from the lake water. This ice layer contains random sediment inclusions, eight of which have been studied using state-of the-art analytical techniques. Six inclusions comprise soft aggregates consisting mainly of clay-mica minerals and micron-sized quartz grains while two others are solid clasts of fine-grained cemented rocks. The largest rock clast consists of poorly-rounded quartz and minor amounts of accessory minerals and is classified as quartzose siltstone. More than twenty grains of zircon and monazite have been identified in this siltstone and dated by SIMS SHRIMP-II. Two age clusters have been recognized for these detrital grains, in the ranges 0.8−1.2 Ga and 1.6−1.8 Ga. The compositions of the rock clasts suggest that the bedrock situated to the west of Lake Vostok is sedimentary. The age data on the detrital accessory minerals suggest that the provenance of these sedimentary rocks − the Gamburtsev Mountains and Vostok Subglacial Highlands, is mainly represented by Paleoproterozoic and MesoproterozoicNeoproterozoic crustal provinces

  4. Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska

    USGS Publications Warehouse

    Bacon, Charles R.; Vazquez, Jorge A.; Wooden, Joseph L.

    2012-01-01

    Historically Sactive Redoubt volcano is an Aleutian arc basalt-to-dacite cone constructed upon the Jurassic–Early Tertiary Alaska–Aleutian Range batholith. The batholith intrudes the Peninsular tectonostratigraphic terrane, which is considered to have developed on oceanic basement and to have accreted to North America, possibly in Late Jurassic time. Xenoliths in Redoubt magmas have been thought to be modern cumulate gabbros and fragments of the batholith. However, new sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages for zircon from gabbro xenoliths from a late Pleistocene pyroclastic deposit are dominated by much older, ca. 310 Ma Pennsylvanian and ca. 1865 Ma Paleoproterozoic grains. Zircon age distributions and trace-element concentrations indicate that the ca. 310 Ma zircons date gabbroic intrusive rocks, and the ca. 1865 Ma zircons also are likely from igneous rocks in or beneath Peninsular terrane basement. The trace-element data imply that four of five Cretaceous–Paleocene zircons, and Pennsylvanian low-U, low-Th zircons in one sample, grew from metamorphic or hydrothermal fluids. Textural evidence of xenocrysts and a dominant population of ca. 1865 Ma zircon in juvenile crystal-rich andesite from the same pyroclastic deposit show that this basement has been assimilated by Redoubt magma. Equilibration temperatures and oxygen fugacities indicated by Fe-Ti–oxide minerals in the gabbros and crystal-rich andesite suggest sources near the margins of the Redoubt magmatic system, most likely in the magma accumulation and storage region currently outlined by seismicity and magma petrology at ∼4–10 km below sea level. Additionally, a partially melted gabbro from the 1990 eruption contains zircon with U-Pb ages between ca. 620 Ma and ca. 1705 Ma, as well as one zircon with a U-Th disequilibrium model age of 0 ka. The zircon ages demonstrate that Pennsylvanian, and probably Paleoproterozoic, igneous rocks exist in, or possibly beneath, Peninsular

  5. Equilibrium and Disequilibrium of 230Th-238U in Zircon from the Minoan Eruption, Santorini, Aegean Sea, Greece

    NASA Astrophysics Data System (ADS)

    Schmitt, A. K.; Stockli, D. F.; Song, E. J.; Storm, S.

    2016-12-01

    The Minoan eruption (ca. 1600 BCE; 40-80 km3 dense rock equivalent) occurred after a ca. 18 ka period of dormancy followed by rapid reinvigoration through arrival of new magma from deep reservoirs colliding with evolved magmas in shallow storage. Although zoned phenocrysts indicate brief timescales ranging between years to decades for final pre-eruptive magma recharge and mixing, it remains unclear how magma accumulation vs. crystallization were balanced in the subvolcanic reservoir during the preceding inter-eruptive cycle. To directly probe magma presence over the repose interval prior to the Minoan eruption and further back in time, we reconnoitered the potential of U-Th zircon geochronology to date the crystallization of individual zircon crystals from pumice from the Minoan eruption. Zircon crystals were extracted from composite pumice samples (several kg each) from basal fall out deposits using gravity and magnetic separation. Etching in cold HF removed adherent glass and revealed the shape of crystals, which were pressed into indium metal to expose unpolished rims to the ion beam of a CAMECA IMS 1270 secondary ionization mass spectrometer. Adherent glass was ubiquitous, indicating that crystals were in contact with melt at the time of eruption. Six of 18 crystals were in 230Th/238U secular equilibrium, two crystals yielded ages of ca. 160 ka, and the remaining rims dated between eruption age and ca. 20 ka. Low Th/U of some secular equilibrium zircon suggests recycling of metamorphic basement zircon, which is also indicated by the presence of rutile in heavy mineral separates. U-Th dates also reveal recycling of zircon from Pleistocene intrusions that likely represent left-over magma from antecedent eruption cycles. We tentatively interpret the dominant zircon population with near-eruption to ca. 20 ka ages to indicate continuous melt presence underneath Santorini during the last repose interval. Distinguishing a hiatus in zircon crystallization between 20 ka

  6. The Effect of Element Substitution on Ti-in-Zircon Geothermometry in Volcanic Zircons from Mount Pinatubo, Philippines

    NASA Astrophysics Data System (ADS)

    Lee, S. L.; Hattori, K.

    2017-12-01

    Despite the extensive application of the Ti-in-zircon geothermometer, its accuracy in natural systems remains uncertain. In order to investigate the parameters contributing to Ti in zircon, we examined zircons from dacitic eruption products of Mount Pinatubo, Philippines, from the Pliocene (>2.5-2.7 Ma), 35000BP and 1991AD. All samples are unaltered and quenched from magmas at 790-825°C (Fe-Ti-oxide thermometry). Furthermore, the magma conditions of 1991 samples are well characterized: 780°C (cummingtonite rims on hornblende, Fe-Ti-oxide thermometry), 2 kbar pressure, 5.5-6.5 wt.% H2O and fO2 of NNO+1.6. Calculated zircon saturation temperatures are 760, 744 and 738°C (oldest to youngest). Zircon Ti concentrations are low (2.0-8.8 ppm), show positive covariation with U (35.6-639 ppm), Th (18.7-696 ppm), ∑REE (237-1310 ppm) and Y (247-1770 ppm), and negative covariation with Hf (7610-12000 ppm). The Ti-in-zircon geothermometer by Ferry and Watson (2007) yields mean temperatures of 690, 666 and 663°C (oldest to youngest), using TiO2 activity=0.6, SiO2 activity=1 and -40°C pressure correction. Therefore, temperatures calculated using this method are underestimated by >100°C. We suggest that elements in the Zr site impact the substitution of Ti in the Si site of zircon. Ti shows a positive covariation with Zr/Hf (37.0-57.3, r2=0.551). The ionic radius of Hf4+ is smaller than Zr4+, whereas cations like U4+, Th4+, REE3+ and Y3+ are larger. The departure from the ideal crystal configuration is evaluated using the parameter Zr/(Hf-x), whereby x=U4+, Th4+, ∑REE and Y3+. Ti contents are more strongly correlated with the parameter than Zr/Hf (r2=0.559, 0.565, 0.608, 0.616; respectively). This suggests that large cations replacing Zr strain the lattice, reducing the amount of Ti incorporated into zircon. This further suggests that ZrSiO4 activity is less than 1 in natural rocks, resulting in the systematic underestimation of Ti-in-zircon temperatures.

  7. Record of Fluctuating Magmatic Environments, Melt Fractionation, and Mixing of Crystals: Elemental Compositions of Zircon Zones, Spirit Mountain Batholith, Nevada

    NASA Astrophysics Data System (ADS)

    Miller, C. F.; Claiborne, L. L.; Wooden, J. L.; Mazdab, F. K.; Walker, B. A.

    2006-12-01

    Spirit Mountain batholith is a large, tilted, subvolcanic intrusion in southernmost Nevada (Walker et al., in press; Lowery Claiborne et al., in press). Field relations and elemental chemistry of rocks ranging from felsic cumulates to leucogranites demonstrate both fractionation and frequent recharging. SHRIMP U-Pb analysis of zircon reveals a 2 m.y. history (17.4-15.3 Ma) for the batholith; almost all of the samples record multiple age populations. Elemental concentrations and zoning patterns document the utility of zircon in tracking magmatic environments and crystal transfer processes and provide important insights into the complex and protracted history of the batholith. The data lend strong support to the Watson et al. (2006) Ti-in-zircon thermometer. At reasonable a(TiO2) between 0.5 and 0.9, all calculated T's are consistent with petrological constraints and granite phase equilibria; using a(TiO2) = 0.7, T ranges from 675-900 C. Over this apparent T interval, which reflects a range in Ti from 3.2-34 ppm, concentrations of Hf (6000-18000 ppm), U (20-5000 ppm), and Th (50-13,000 ppm), and REE patterns all vary dramatically and systematically. Hf, U, Th, and Ce/Ce* are negatively correlated with T; LREE/MREE, MREE/HREE, and Eu/Eu* are positively correlated with T. These variations indicate that zircon preferentially incorporated Zr over Hf (hence falling Zr/Hf); U and Th behaved as strongly incompatible elements in the crystallizing assemblage as a whole; compatibility of REE increased with decreasing atomic number (effect of LREE accessories?); Eu+2 was more compatible (feldspars) and Ce+4 less compatible than equivalent +3 REE. All of these trends are consistent with the observed crystallizing assemblage and with general trends in whole rocks. More striking, however, is intrasample and intragrain variability. Although leucogranite samples have a larger proportion of zircon with compositions indicating low T and growth from fractionated melt, all samples have

  8. Geochemical signatures and magmatic stability of terrestrial impact produced zircon

    NASA Astrophysics Data System (ADS)

    Wielicki, Matthew M.; Harrison, T. Mark; Schmitt, Axel K.

    2012-03-01

    Understanding the role of impacts on early Earth has major implications to near surface conditions, but the apparent lack of preserved terrestrial craters > 2 Ga does not allow a direct sampling of such events. Ion microprobe U-Pb ages, REE abundances and Ti-in-zircon thermometry for impact produced zircon are reported here. These results from terrestrial impactites, ranging in age from ~ 35 Ma to ~ 2 Ga, are compared with the detrital Hadean zircon population from Western Australia. Such comparisons may provide the only terrestrial constraints on the role of impacts during the Hadean and early Archean, a time predicted to have a high bolide flux. Ti-in-zircon thermometry indicates an average of 773 °C for impact-produced zircon, ~ 100 °C higher than the average for Hadean zircon crystals. The agreement between whole-rock based zircon saturation temperatures for impactites and Ti-in-zircon thermometry (at aTiO2 = 1) implies that Ti-in-zircon thermometry record actual crystallization temperatures for impact melts. Zircon saturation modeling of Archean crustal rock compositions undergoing thermal excursions associated with the Late Heavy Bombardment predicts equally high zircon crystallization temperatures. The lack of such thermal signatures in the Hadean zircon record implies that impacts were not a dominant mechanism of producing the preserved Hadean detrital zircon record.

  9. What Hf isotopes in zircon tell us about crust-mantle evolution

    NASA Astrophysics Data System (ADS)

    Iizuka, Tsuyoshi; Yamaguchi, Takao; Itano, Keita; Hibiya, Yuki; Suzuki, Kazue

    2017-03-01

    The 176Lu-176Hf radioactive decay system has been widely used to study planetary crust-mantle differentiation. Of considerable utility in this regard is zircon, a resistant mineral that can be precisely dated by the U-Pb chronometer and record its initial Hf isotope composition due to having low Lu/Hf. Here we review zircon U-Pb age and Hf isotopic data mainly obtained over the last two decades and discuss their contributions to our current understanding of crust-mantle evolution, with emphasis on the Lu-Hf isotope composition of the bulk silicate Earth (BSE), early differentiation of the silicate Earth, and the evolution of the continental crust over geologic history. Meteorite zircon encapsulates the most primitive Hf isotope composition of our solar system, which was used to identify chondritic meteorites best representative of the BSE (176Hf/177Hf = 0.282793 ± 0.000011; 176Lu/177Hf = 0.0338 ± 0.0001). Hadean-Eoarchean detrital zircons yield highly unradiogenic Hf isotope compositions relative to the BSE, providing evidence for the development of a geochemically enriched silicate reservoir as early as 4.5 Ga. By combining the Hf and O isotope systematics, we propose that the early enriched silicate reservoir has resided at depth within the Earth rather than near the surface and may represent a fractionated residuum of a magma ocean underlying the proto-crust, like urKREEP beneath the anorthositic crust on the Moon. Detrital zircons from world major rivers potentially provide the most robust Hf isotope record of the preserved granitoid crust on a continental scale, whereas mafic rocks with various emplacement ages offer an opportunity to trace the Hf isotope evolution of juvenile continental crust (from εHf[4.5 Ga] = 0 to εHf[present] = + 13). The river zircon data as compared to the juvenile crust composition highlight that the supercontinent cycle has controlled the evolution of the continental crust by regulating the rates of crustal generation and intra

  10. U-Pb zircon geochronology and Zr-in-rutile thermometry of eclogites from the Dulan area, North Qaidam ultra-high pressure (UHP) terrane, western China

    NASA Astrophysics Data System (ADS)

    Hernández Uribe, D.; Stubbs, K.; Lehman, M. R.; Gilmore, V.; Kylander-Clark, A. R.; Mattinson, C. G.

    2016-12-01

    The Dulan area, in the North Qaidam terrane, exposes UHP eclogites and gneisses that experienced a 20 Myr UHP event at P-T conditions of 30 kbar and 700 °C. Two eclogites were analyzed using Zr-in-rutile thermometry and zircon U-Pb + trace element analysis to constrain the metamorphic evolution of the area. A kyanite-phengite eclogite presents a mineral assemblage of grt + omp + ph + ky + rt + zo + qz. Rutile analyses show a Zr concentration of 173-250 ppm with a mean of 207 ± 19 ppm. The calculated temperatures yielded 685-716 °C with an average of 700 ± 7°C. Zircon U-Pb analyses gave an upper intercept age of 880 ± 89 Ma. These analyses from cathodoluminiscence (CL)-dark core zircons show a negative Eu anomaly and a steep HREE slope suggesting a magmatic origin for the protolith. Analyses from CL-bright rims gave a weighted mean age of 427 ± 2 Ma. These zircons show an eclogite facies trace elements pattern suggesting that the age represent the HP-UHP event. Titanium concentration in zircons gave a weighted mean of 4.41 ± 0.25 ppm. This Ti concentration yielded a calculated temperature of 674 °C A phengite eclogite shows a mineral assemblage of grt + omp + ph + rt + zo + qz. Rutile in matrix analyses show a Zr concentration of 123-161 ppm with a mean of 139 ± 9 ppm. Calculated temperatures for these rutiles ranges from 659-680 °C with a mean temperature of 668 ± 5 °C. U-Pb analyses from CL-dark zircon cores gave a weighted mean age of 844 ± 7 Ma. These zircons show a negative Eu anomaly and a steep HREE slope suggesting a magmatic origin for the protolith. Analyses from CL-grey rims gave a weighted mean age of 433 ± 4 Ma. These zircons show an eclogite facies trace elements pattern, representing the timing of the HP-UHP event. Titanium concentration in zircons gave a weighted mean of 3.13 ± 0.34 ppm. This concentration yielded calculated temperature 647 °C. The obtained ages are in the same range as the ones obtained for the northern and southern

  11. (De)coupled zircon metamictization, radiation damage, and He diffusivity

    NASA Astrophysics Data System (ADS)

    Ault, A. K.; Guenthner, W.; Reiners, P. W.; Moser, A. C.; Miller, G. H.; Refsnider, K. A.

    2017-12-01

    We develop and apply a new protocol for targeting crystals for the zircon (U-Th)/He (He) thermochronometry to maximize effective U (eU) and corresponding closure temperature variability to develop zircon He date-eU correlations observed in some datasets. Our approach exploits visual proxies for radiation damage accumulation (metamictization) during zircon selection. We show that by purposefully targeting a spectrum of zircon textures from pristine to metamict grains, it is possible to generate broad eU variation in suites of zircon from a single sample and zircon He date-eU-metamictization trends that can be exploited to resolve increasingly complex thermal histories. We present plane light photographs, eU concentration, and zircon He results from 59 individual zircons from nine crystalline rock samples. Six of the nine samples come from exposed Proterozoic granitoids on SE Baffin Island, Canada; Boulder Creek, CO; Sandia Mountains, NM; and Mecca Hills, CA. We report data from three Archean Baffin samples to compare with the Proterozoic Baffin sample date-eU-metamictization trend. In each Proterozoic sample, target zircons display a spectrum of metamictization from pristine, transparent crystals to purple-brown, translucent grains. Progressive loss of transparency and increase in discoloration consistently corresponds to an increase in eU in all samples. Individual zircon eU varies from 89-1885 ppm and, within each sample, the total eU spread is 538 ppm to 1374 ppm. For any given eU value, the Archean zircon appear comparatively more metamict than the Proterozoic Baffin grains and samples collectively define a 1681 ppm range in eU, with more restrictive intrasample eU spreads (199-1120 ppm). Proterozoic samples from Baffin, Sandia, and Front Range yield negative zircon He date-eU correlations with intrasample date ranges of 90-783 Ma. Increasing eU and younger dates correspond with increasing metamictization. In contrast, all three Proterozoic Mecca Hills samples

  12. Accessory and rock forming minerals monitoring the evolution of zoned mafic ultramafic complexes in the Central Ural Mountains

    NASA Astrophysics Data System (ADS)

    Krause, J.; Brügmann, G. E.; Pushkarev, E. V.

    2007-04-01

    This study describes major and trace element compositions of accessory and rock forming minerals from three Uralian-Alaskan-type complexes in the Ural Mountains (Kytlym, Svetley Bor, Nizhnii Tagil) for the purpose of constraining the origin, evolution and composition of their parental melts. The mafic-ultramafic complexes in the Urals are aligned along a narrow, 900 km long belt. They consist of a central dunite body grading outward into clinopyroxenite and gabbro lithologies. Several of these dunite bodies have chromitites with platinum group element mineralization. High Fo contents in olivine (Fo 92-93) and high Cr/(Cr + Al) in spinel (0.67-0.84) suggest a MgO-rich (> 15 wt.%) and Al 2O 3-poor ultramafic parental magma. During its early stages the magma crystallized dominantly olivine, spinel and clinopyroxene forming cumulates of dunite, wehrlite and clinopyroxenite. This stage is monitored by a common decrease in the MgO content in olivine (Fo 93-86) and the Cr/(Cr + Al) value of coexisting accessory chromite (0.81-0.70). Subsequently, at subsolidus conditions, the chromite equilibrated with the surrounding silicates producing Fe-rich spinel while Al-rich spinel exsolved chromian picotite and chromian titanomagnetite. This generated the wide compositional ranges typical for spinel from Uralian-Alaskan-type complexes world wide. Laser ablation analyses (LA-ICPMS) reveal that clinopyroxene from dunites and clinopyroxenite from all three complexes have similar REE patterns with an enrichment of LREE (0.5-5.2 prim. mantle) and other highly incompatible elements (U, Th, Ba, Rb) relative to the HREE (0.25-2.0 prim. mantle). This large concentration range implies the extensive crystallization of olivine and clinopyroxene together with spinel from a continuously replenished, tapped and crystallizing magma chamber. Final crystallization of the melt in the pore spaces of the cooling cumulate pile explains the large variation in REE concentrations on the scale of a thin

  13. Role of zircon in tracing crustal growth and recycling

    NASA Astrophysics Data System (ADS)

    Compston, W.; Williams, I. S.; Armstrong, R. A.; Claoue-Long, J. C.; Kinny, P. D.; Foster, J. J.; Kroener, A.; Pidgeon, R. T.; Myers, J. S.

    Single crystal ion probe ages of zircons is discussed, which allow much better time resolution compared to other geochronological methods, although the technique is not without problems. Rocks from two areas that contain composite zircon populations, including true magmatic zircons as well as a variety of xenocrystic types are described. It is often difficult to distinguish these; xenocrystic zircons, for example, cannot always be identified on the basis of morphology alone. Additional evidence is needed before making age interpretations. Evidence is also presented of zircon growth long after the original time of crystallization, in some cases apparently at temperatures less than 300 C. The spectacular discovery of 4.1 to 4.2 Ga detrital zircons in metaquartzites from the Mount Narryer area of Western Australia is described. Similar zircons with ages as old as 4276 Ma have been found in the nearby Jack Hills area. The source areas or parent lithologies of these zircons have not yet been determined, but the author expects that they may be unrecognized or buried antecedents of the K rich Narryer gneisses. U or Th concentrations of zircon cannot be used to discriminate between felsic and mafic source rocks.

  14. Role of zircon in tracing crustal growth and recycling

    NASA Technical Reports Server (NTRS)

    Compston, W.; Williams, I. S.; Armstrong, R. A.; Claoue-Long, J. C.; Kinny, P. D.; Foster, J. J.; Kroener, A.; Pidgeon, R. T.; Myers, J. S.

    1988-01-01

    Single crystal ion probe ages of zircons is discussed, which allow much better time resolution compared to other geochronological methods, although the technique is not without problems. Rocks from two areas that contain composite zircon populations, including true magmatic zircons as well as a variety of xenocrystic types are described. It is often difficult to distinguish these; xenocrystic zircons, for example, cannot always be identified on the basis of morphology alone. Additional evidence is needed before making age interpretations. Evidence is also presented of zircon growth long after the original time of crystallization, in some cases apparently at temperatures less than 300 C. The spectacular discovery of 4.1 to 4.2 Ga detrital zircons in metaquartzites from the Mount Narryer area of Western Australia is described. Similar zircons with ages as old as 4276 Ma have been found in the nearby Jack Hills area. The source areas or parent lithologies of these zircons have not yet been determined, but the author expects that they may be unrecognized or buried antecedents of the K rich Narryer gneisses. U or Th concentrations of zircon cannot be used to discriminate between felsic and mafic source rocks.

  15. Zircon oxygen isotopes reveal Ivrea-Verbano Zone source characteristics of the Sesia Valley Caldera

    NASA Astrophysics Data System (ADS)

    Economos, R. C.; Quick, J. E.; Sinigoi, S.; de Silva, S. L.

    2013-12-01

    The Sesia Valley, in the Italian Alpine foothills, contains >14 km diameter caldera adjacent to and structurally shallower than the famous Ivrea-Verbano Zone deep crustal section. The caldera and its associated eruptive sequence presents opportunity to explore volcanic magmatism in light of exposed and well characterized source candidates, namely lower crustal gabbros and the mid-crustal metasedimentary Kinzigite formation. Original geochemical characteristics of volcanic units have been obscured by the effects of subsequent hydrothermal alteration. The resistance of the mineral zircon to fluid alteration makes it a prime candidate for the preservation and exploration of these geochemical signals, such as O isotopes. Lower crustal gabbros in the Ivrea-Verbano Zone have broadly monotonic whole-rock δ18O values between +8 and +9‰VSMOW (Sinigoi et al., 1994). Kinzigites preserve a much higher and more heterogeneous δ18O values, typically ranging from +10‰ up to +15‰ (Baker, 1990). Zircons from the caldera-forming rhyolitic eruption units and a pre-caldera rhyodacitic unit were analyzed by ion microprobe at UCLA for in-situ oxygen isotope ratios. External reproducibility of within-mount standard R33 grains range from 0.27 to 0.36‰. Rhyolites from the caldera-forming eruption yield a range of δ18O(zircon) values from 6.3‰ to 8.3‰. This range displays rough correlation with CL activity - CL active grains have lower δ18O(zircon) values while CL dark grains have higher δ18O(zircon) values. This variation may correlate with U contents, which are notoriously low in zircons from Ivrea-Verbano Zone gabbros. We argue that the range in O isotope values suggests zircons are a good fit for magmas influenced by gabbro and Kinzigite sources. However, these zircons do not appear to be inherited directly from either the gabbro or Kinzigite sources as their O isotope signatures are typically intermediate between the two. The pre-caldera rhyodacite sample displays a

  16. SHRIMP U-Pb dating, trace elements and the Lu-Hf isotope system of coesite-bearing zircon from amphibolite in the SW Sulu UHP terrane, eastern China

    NASA Astrophysics Data System (ADS)

    Liu, Fulai; Gerdes, Axel; Zeng, Lingsen; Xue, Huaimin

    2008-06-01

    In this study, we link mineral inclusion data, trace element analyses, U-Pb age and Hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi-stage metamorphic evolution of amphibolites from the Sulu ultrahigh-pressure (UHP) terrane, eastern China. Zircon grains separated from amphibolites from the CCSD-MH drill hole (G12) and Niushan outcrop (G13) were subdivided into two main types based on cathodoluminescence (CL) and Laser Raman spectroscopy: big dusty zircons with inherited cores and UHP metamorphic rims and small clear zircons. Weakly zoned, grey-white luminescent inherited cores preserve mineral inclusions of Cpx + Pl + Ap ± Qtz indicative of a mafic igneous protolith. Dark grey luminescent overgrowth rims contain the coesite eclogite-facies mineral inclusion assemblage Coe + Grt + Omp + Phe + Ap, and formed at T = 732-839 °C and P = 3.0-4.0 GPa. In contrast, white luminescent small clear zircons preserve mineral inclusions formed during retrograde HP quartz eclogite to LP amphibolite-facies metamorphism (T = 612-698 °C and P = 0.70-1.05 GPa). Inherited zircons from both samples yield SHRIMP 206Pb/238U ages of 695-520 Ma with an upper intercept age of 800 ± 31 Ma. The UHP rims yield consistent Triassic ages around 236-225 and 239-225 Ma for G12 and G13 with weighted means of 229 ± 3 and 231 ± 3 Ma, respectively. Small clear zircons from both samples give 206Pb/238U ages around 219-210 Ma with a weighted mean of 214 ± 3 Ma, interpreted as the age of retrograde quartz eclogite-facies metamorphism. Matrix amphibole from both samples indicate Ar-Ar ages of 209 ± 0.7 and 207 ± 0.7 Ma, respectively, probably dating late amphibolite-facies retrogression. The data suggest subduction of Neoproterozoic mafic igneous rocks to UHP conditions in Middle Triassic (∼230 Ma) times and subsequent exhumation to an early HP (∼214 Ma) and a late LP stage (∼208 Ma) over a period of ∼16 and 6 Myr, respectively

  17. New zircon (U-Th)/He and U/Pb eruption age for the Rockland tephra, western USA

    USGS Publications Warehouse

    Coble, Matthew A.; Burgess, Seth; Klemetti, Erik W.

    2017-01-01

    Eruption ages of a number of prominent Quaternary volcanic deposits remain inaccurately and/or imprecisely constrained, despite their importance as regional stratigraphic markers in paleo-environment reconstruction and as evidence of climate-altering eruptions. Accurately dating volcanic deposits presents challenging analytical considerations, including poor radiogenic yield, scarcity of datable minerals, and contamination of crystal populations by magma, eruption, and transport processes. One prominent example is the Rockland tephra, which erupted from the Lassen Volcanic Center in the southern Cascade arc. Despite a range in published eruption ages from 0.40 to 0.63 Ma, the Rockland tephra is extensively used as a marker bed across the western United States. To more accurately and precisely constrain the age of the Rockland tephra-producing eruption, we report U/Pb crystallization dates from the outermost ∼2 μm of zircon crystal faces (surfaces) using secondary ion mass spectrometry (SIMS). Our new weighted mean 238U/206Pb age for Rockland tephra zircon surfaces is 0.598 ± 0.013 Ma (2σ) and MSWD = 1.11 (mean square weighted deviation). As an independent test of the accuracy of this age, we obtained new (U-Th)/He dates from individual zircon grains from the Rockland tephra, which yielded a weighted mean age of 0.599 ± 0.012 Ma (2σ, MSWD = 5.13). We also obtained a (U-Th)/He age of 0.628 ± 0.014 Ma (MSWD = 1.19) for the Lava Creek Tuff member B, which was analyzed as a secondary standard to test the accuracy of the (U-Th)/He technique for Quaternary tephras, and to evaluate assumptions made in the model-age calculation. Concordance of new U/Pb and (U-Th)/He zircon ages reinforces the accuracy of our preferred Rockland tephra eruption age, and confirms that zircon surface dates sample zircon growth up to the time of eruption. We demonstrate the broad applicability of coupled U/Pb zircon-surface and single-grain zircon (U-Th)/He geochronology to

  18. New zircon (U-Th)/He and U/Pb eruption age for the Rockland tephra, western USA

    NASA Astrophysics Data System (ADS)

    Coble, Matthew A.; Burgess, Seth D.; Klemetti, Erik W.

    2017-09-01

    Eruption ages of a number of prominent Quaternary volcanic deposits remain inaccurately and/or imprecisely constrained, despite their importance as regional stratigraphic markers in paleo-environment reconstruction and as evidence of climate-altering eruptions. Accurately dating volcanic deposits presents challenging analytical considerations, including poor radiogenic yield, scarcity of datable minerals, and contamination of crystal populations by magma, eruption, and transport processes. One prominent example is the Rockland tephra, which erupted from the Lassen Volcanic Center in the southern Cascade arc. Despite a range in published eruption ages from 0.40 to 0.63 Ma, the Rockland tephra is extensively used as a marker bed across the western United States. To more accurately and precisely constrain the age of the Rockland tephra-producing eruption, we report U/Pb crystallization dates from the outermost ∼2 μm of zircon crystal faces (surfaces) using secondary ion mass spectrometry (SIMS). Our new weighted mean 238U/206Pb age for Rockland tephra zircon surfaces is 0.598 ± 0.013 Ma (2σ) and MSWD = 1.11 (mean square weighted deviation). As an independent test of the accuracy of this age, we obtained new (U-Th)/He dates from individual zircon grains from the Rockland tephra, which yielded a weighted mean age of 0.599 ± 0.012 Ma (2σ, MSWD = 5.13). We also obtained a (U-Th)/He age of 0.628 ± 0.014 Ma (MSWD = 1.19) for the Lava Creek Tuff member B, which was analyzed as a secondary standard to test the accuracy of the (U-Th)/He technique for Quaternary tephras, and to evaluate assumptions made in the model-age calculation. Concordance of new U/Pb and (U-Th)/He zircon ages reinforces the accuracy of our preferred Rockland tephra eruption age, and confirms that zircon surface dates sample zircon growth up to the time of eruption. We demonstrate the broad applicability of coupled U/Pb zircon-surface and single-grain zircon (U-Th)/He geochronology to accurate

  19. Accessory Muscles of the Extremities.

    PubMed

    Vanhoenacker, Filip M; Desimpel, Julie; Mespreuve, Marc; Tagliafico, Alberto

    2018-07-01

    Accessory muscles and variations are not uncommon at the upper and lower extremity. They are often overlooked because they are asymptomatic and present as incidental findings on imaging. However, they may present as a soft tissue swelling, thereby mimicking soft tissue tumors. Other symptoms are attributed to impingement on neurovascular structures and to exercise-related pain. Thorough knowledge of the anatomy, systematic imaging analysis, and the awareness of it are the clues to correct identification. On ultrasound, accessory muscles have a similar echotexture as other muscles, whereas the signal intensity on magnetic resonance imaging (MRI) is similar to muscle. Because of the intrinsic contrast with the adjacent intermuscular fat, accessory muscles are best depicted on MRI without fat suppression. This article provides a short overview of the anatomy of most prevalent accessory muscles of the upper and lower limb and its potential pathogenic nature. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

  20. Geochronology and Geochemistry of Zircons from the IODP Site U1437 in the Rear of the Izu-Bonin Volcanic Arc

    NASA Astrophysics Data System (ADS)

    Andrews, G. D.; Schmitt, A. K.; Busby, C. J.; Brown, S. R.

    2015-12-01

    Zircons recovered from International Ocean Discovery Program Expedition 350 Site U1437 (31°47.390'N, 139°01.580'E) in the Izu-Bonin arc were analyzed by SIMS to constrain their age (U/Pb geochronology) and geochemistry (trace elements, δ18O); LA-ICP-MS ɛHf analyses are pending. Seven intervals were dated successfully: six tuffs and lapilli-tuffs between 680.99 and 1722.46 m below sea floor (mbsf) and a single peperitic rhyolitic intrusion at 1388.86 - 1390.07 mbsf. Thirty-two intervals which underwent mineral separation lacked zircon, or yielded zircon much older than age expectations for U1437. Geochronology results from separated zircons confirm and extend the shipboard age model to 1360.77 mbsf where Late Miocene (Tortonian) submarine volcanic rocks (11.3 ±0.7 Ma; n = 17) were sampled. In-situ measurement of zircons associated with magnetite crystals in the rhyolite intrusion yield an age of 13.6 ±1.7 Ma (n = 9). Zircon U contents are low (typically <300 ppm), with trace element ratios characteristic of oceanic lithosphere and near-mantle δ18O values (4-6 ‰). Individual Miocene zircon crystals are difficult to distinguish by age alone from those in the drilling mud (sepiolite) used during Expedition 350; the sepiolite is quarried by IMV Nevada in the Amargosa Valley. Our analysis of thirty-three zircons from the sepiolite finds that they have a broad and varied age distribution (2 - 2033 Ma) with a prominent peak at 12-14 Ma, bimodal δ18O values (peaks at 5-5.5 and 6.5-7.5 ‰), and dominantly continental trace element signatures. Three zircons from U1437 are tentatively identified as sepiolite-derived, but a single Eocene grain (51.7 ±2.4 Ma) recovered from 1722.46 mbsf has an age unlike those in the sepiolite, and potentially is genuinely xenocrystic. The majority of U1437 zircons thus crystallized from evolved melts lacking continental characteristics, although thermal and compositional conditions conducive for zircon crystallization appear to have

  1. 21 CFR 878.4350 - Cryosurgical unit and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... and accessories. (a) Identification—(1) Cryosurgical unit with a liquid nitrogen cooled cryoprobe and accessories. A cryosurgical unit with a liquid nitrogen cooled cryoprobe and accessories is a device intended...

  2. Zircon/fluid trace element partition coefficients measured by recrystallization of Mud Tank zircon at 1.5 GPa and 800-1000 °C

    NASA Astrophysics Data System (ADS)

    Ayers, John C.; Peters, Timothy J.

    2018-02-01

    Hydrothermal zircon grains have trace element characteristics such as low Th/U, high U, and high rare earth element (REE) concentrations that distinguish them from magmatic, metamorphic, and altered zircon grains, but it is unclear whether these characteristics result from distinctive fluid compositions or zircon/fluid fractionation effects. New experiments aimed at measuring zircon/fluid trace element partition coefficients Dz/f involved recrystallizing natural Mud Tank zircon with low trace element concentrations in the presence of H2O, 1 m NaOH, or 1 m HCl doped with ∼1000 ppm of rare earth elements (REE), Y, U and Th and ∼500 ppm of Li, B, P, Nb, Ba, Hf, and Ta. Experiments were run for 168 h at 1.5 GPa, 800-1000 °C, and fO2 = NNO in a piston cylinder apparatus using the double capsule method. LA-ICP-MS analysis shows that run product zircon crystals have much higher trace element concentrations than in Mud Tank zircon starting material. Dz/f values were estimated from run product zircon analyses and bulk composition using mass balance. Most elements behave incompatibly, with median Dz/f being highest for Hf = 8 and lowest for B = 0.02. Addition of NaOH or HCl had little influence on Dz/f values. Dz/f for LREE are anomalously high, likely due to contamination of run product zircon with quenched solutes enriched in incompatible elements, so DLREE were estimated using lattice strain theory. Brice curves for +3 ions yield zircon/fluid DLu/DLa of ∼800-5000. A Brice curve fit to +4 ions yielded DCe4+ values. Estimated concentrations of Ce3+ and Ce4+ show that the average Ce4+/Ce3+ in zircon of 27 is much higher than in fluid of 0.02. Th and U show little fractionation, with median DTh/DU = 0.7, indicating that the low Th/U in natural hydrothermal zircon is inherited from the fluid. Natural fluid compositions estimated from measured Dz/f and published compositions of hydrothermal zircon grains from aplite and eclogite reflect the mineralogy of the host rock, e

  3. 21 CFR 878.4950 - Manual operating table and accessories and manual operating chair and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Manual operating table and accessories and manual operating chair and accessories. 878.4950 Section 878.4950 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES...

  4. 21 CFR 878.4950 - Manual operating table and accessories and manual operating chair and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Manual operating table and accessories and manual operating chair and accessories. 878.4950 Section 878.4950 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES...

  5. 21 CFR 878.4950 - Manual operating table and accessories and manual operating chair and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Manual operating table and accessories and manual operating chair and accessories. 878.4950 Section 878.4950 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES...

  6. 21 CFR 878.4950 - Manual operating table and accessories and manual operating chair and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Manual operating table and accessories and manual operating chair and accessories. 878.4950 Section 878.4950 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES...

  7. 21 CFR 878.4950 - Manual operating table and accessories and manual operating chair and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Manual operating table and accessories and manual operating chair and accessories. 878.4950 Section 878.4950 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES...

  8. Zircons reveal magma fluxes in the Earth's crust.

    PubMed

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2014-07-24

    Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet.

  9. Fission track dating of kimberlitic zircons

    USGS Publications Warehouse

    Haggerty, S.E.; Raber, E.; Naeser, C.W.

    1983-01-01

    The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ?? 6.5 m.y.), Orapa (87.4 ?? 5.7 and 92.4 ?? 6.1 m.y.), Nzega (51.1 ?? 3.8 m.y.), Koffiefontein (90.0 ?? 8.2 m.y.), and Val do Queve (133.4 ?? 11.5 m.y.). In addition we report the first radiometric ages (707.9 ?? 59.6 and 705.5 ?? 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. ?? 1983.

  10. 14 CFR 25.1163 - Powerplant accessories.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed to prevent contamination of...

  11. Secondary ionization mass spectrometry analysis in petrochronology: Chapter 7

    USGS Publications Warehouse

    Schmitt, Axel K.; Vazquez, Jorge A.

    2017-01-01

    The goal of petrochronology is to extract information about the rates and conditions at which rocks and magmas are transported through the Earth’s crust. Garnering this information from the rock record greatly benefits from integrating textural and compositional data with radiometric dating of accessory minerals. Length scales of crystal growth and diffusive transport in accessory minerals under realistic geologic conditions are typically in the range of 1–10’s of μm, and in some cases even substantially smaller, with zircon having among the lowest diffusion coefficients at a given temperature (e.g., Cherniak and Watson 2003). Intrinsic to the compartmentalization of geochemical and geochronologic information from intra-crystal domains is the requirement to determine accessory mineral compositions using techniques that sample at commensurate spatial scales so as to not convolute the geologic signals that are recorded within crystals, as may be the case with single grain or large grain fragment analysis by isotope dilution thermal ionization mass spectrometry (ID-TIMS; e.g., Schaltegger and Davies 2017, this volume; Schoene and Baxter 2017, this volume). Small crystals can also be difficult to extract by mineral separation techniques traditionally used in geochronology, which also lead to a loss of petrographic context. Secondary Ionization Mass Spectrometry, that is SIMS performed with an ion microprobe, is an analytical technique ideally suited to meet the high spatial resolution analysis requirements that are critical for petrochronology (Table 1).

  12. Testing the reliability of information extracted from ancient zircon

    NASA Astrophysics Data System (ADS)

    Kielman, Ross; Whitehouse, Martin; Nemchin, Alexander

    2015-04-01

    Studies combining zircon U-Pb chronology, trace element distribution as well as O and Hf isotope systematics are a powerful way to gain understanding of the processes shaping Earth's evolution, especially in detrital populations where constraints from the original host are missing. Such studies of the Hadean detrital zircon population abundant in sedimentary rocks in Western Australia have involved analysis of an unusually large number of individual grains, but also highlighted potential problems with the approach, only apparent when multiple analyses are obtained from individual grains. A common feature of the Hadean as well as many early Archaean zircon populations is their apparent inhomogeneity, which reduces confidence in conclusions based on studies combining chemistry and isotopic characteristics of zircon. In order to test the reliability of information extracted from early Earth zircon, we report results from one of the first in-depth multi-method study of zircon from a relatively simple early Archean magmatic rock, used as an analogue to ancient detrital zircon. The approach involves making multiple SIMS analyses in individual grains in order to be comparable to the most advanced studies of detrital zircon populations. The investigated sample is a relatively undeformed, non-migmatitic ca. 3.8 Ga tonalite collected a few kms south of the Isua Greenstone Belt, southwest Greenland. Extracted zircon grains can be combined into three different groups based on the behavior of their U-Pb systems: (i) grains that show internally consistent and concordant ages and define an average age of 3805±15 Ma, taken to be the age of the rock, (ii) grains that are distributed close to the concordia line, but with significant variability between multiple analyses, suggesting an ancient Pb loss and (iii) grains that have multiple analyses distributed along a discordia pointing towards a zero intercept, indicating geologically recent Pb-loss. This overall behavior has

  13. Cross correlation of chemical profiles in minerals: insights into the architecture of magmatic reservoirs

    NASA Astrophysics Data System (ADS)

    Probst, Line; Caricchi, Luca; Gander, Martin; Wallace, Glenn

    2016-04-01

    Analysis of chemical zoning in minerals offers the opportunity to reconstruct the pre-eruptive conditions and the temporal evolution of magmatic reservoirs. The chemical composition of minerals is a function of the thermodynamic conditions of the reservoir from which they grow and therefore minerals record the evolution and variation of residual melt chemistry and intensive parameters within the magmatic system. A quantitative approach is required to determine if similar crystals actually shared a portion of their crystallisation history. These analyses are in many cases extremely time consuming and rather expensive. Therefore, it is not always possible to analyse a statically significant number of crystals, especially within their textural context in thin sections and that is the main reason to build automated methods. We are presenting a numerical cross-correlation method that compares the zonation pattern of minerals to identify if they share the totality or part of their growth history. We modified the method first developed by Wallace and Bergantz (2004) to compare profiles in minerals also from samples collected in different outcrops and that can be used for any dataset (i.e. geochemical proxies in stratigraphic sections). The main purpose of this method is to objectively compare chemical profiles in minerals (collected by electron microprobe, LA-ICP-MS or cathodoluminescence images) and quantify their degree of similarity. For this purpose, we use a well-known mathematical tool: the cross correlation which is a way of quantifying the difference between two given signals at a given position. Once our program was built, we performed tests using a set of synthetic profiles, profiles acquired along different transects of the same mineral and also on different minerals. Finally we applied our program to about 100 zircons from Kilgore Tuff, Heise Volcanic Field (USA) collected at different stratigraphic levels in two different outcrops. The correlation shows that

  14. Hydrogen incorporation and charge balance in natural zircon

    NASA Astrophysics Data System (ADS)

    De Hoog, J. C. M.; Lissenberg, C. J.; Brooker, R. A.; Hinton, R.; Trail, D.; Hellebrand, E.

    2014-09-01

    The water and trace element contents of natural igneous zircons were determined to constrain the mechanism of hydrogen incorporation. The low radiation-damage zircons were derived from Fe-Ti oxide gabbros from the Vema Fracture Zone (11°N, Mid-Atlantic Ridge). They contain up to 1212 ppmw H2O, 1.9 wt.% Y2O3 and 0.6 wt.% P2O5 and are generally strongly zoned. REE + Y are partially charge-balanced by P (Y, REE3+ + P5+ = Zr4+ + Si4+), but a large REE excess is present. On an atomic basis, this excess is closely approximated by the amount of H present in the zircons. We therefore conclude that H is incorporated by a charge-balance mechanism (H+ + REE3+ = Zr4+). This interpretation is consistent with FTIR data of the Vema zircons, which shows a strongly polarised main absorption band at ca. 3100 cm-1, similar to experimentally grown Lu-doped hydrous zircon. The size of this 3100 cm-1 band scales with H and REE contents. Apart from a small overlapping band at 3200 cm-1, no other absorption bands are visible, indicating that a hydrogrossular-type exchange mechanism does not appear to be operating in these zircons. Because of charge-balanced uptake of H, P and REE in zircon, the partitioning of these elements into zircon is dependent on each of their concentrations. For instance, DREEzrc/melt increases with increasing H and P contents of the melt, whereas DHzrc/melt increases with increasing REE content but decreases with increasing P content. In addition, H-P-REE systematics of sector zoning indicate kinetic effects may play an important role. Hence, using H in zircon to determine the water content of melts is problematic, and REE partitioning studies need to take into account P and H2O contents of the melt.

  15. Advantages of conducting in-situ U-Pb age dating of multiple U-bearing minerals from a single complex: Case in point - the Oka Carbonatite Complex

    NASA Astrophysics Data System (ADS)

    Chen, W.; Simonetti, A.

    2012-12-01

    A detailed radiometric investigation is currently underway focusing on U-bearing accessory minerals apatite, perovskite, and niocalite from the Oka Carbonatite Complex (Canada). One of the main objectives is to obtain a comparative chronology of melt crystallization for the complex. Unlike other commonly adopted U-bearing minerals (e.g., zircon, monazite) for in-situ dating investigations, apatite, perovskite, and niocalite contain relatively high contents of common Pb. Hence, careful assessment of the proportion and composition of the common Pb, and usage of appropriate matrix-matched external standards are imperative. The Madagascar apatite was utilized as the external standard for apatite dating, and the Emerald Lake and Durango apatites were adopted as secondary standards; the latter yield ages of 92.6 ±1.8 and 32.2 ±1.1 Ma, respectively, and these are identical to their accepted ages. Pb/U ages for apatite from Oka were obtained for different rock types, including 8 carbonatites, 4 okaites, 3 ijolites and 3 alnoites, and these define a range of ages between ~105 and ~135 Ma; this result suggests a protracted crystallization history. In total, 266 individual analyses define two peaks at ~115 and ~125Ma. For perovskite dating, the Ice River perovskite standard was utilized as the external standard. The perovskites from one okaite sample yield an age of 112.2 ±1.9 Ma, and is much younger than the previously reported U-Pb perovskite age of 131 ±7 Ma. Hence, the combined U-Pb perovskite ages also suggest a rather prolonged time of melt crystallization. Niocalite is a rare, accessory silicate mineral that occurs within the carbonatites at Oka. The international zircon standard BR266 was selected for use as the external standard and rastering was employed to minimize the Pb-U fractionation. Two niocalite samples give young ages at 110.6 ±1.2 and 115.0 ±1.9 Ma, and are identical to their respective apatite ages (given associated uncertainties) from the same

  16. 14 CFR 29.1163 - Powerplant accessories.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Powerplant accessories. (a) Each engine mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed in such a way as to prevent...

  17. 14 CFR 27.1163 - Powerplant accessories.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Powerplant accessories. (a) Each engine-mounted accessory must— (1) Be approved for mounting on the engine involved; (2) Use the provisions on the engine for mounting; and (3) Be sealed in such a way as to prevent...

  18. Estimating the formation age distribution of continental crust by unmixing zircon ages

    NASA Astrophysics Data System (ADS)

    Korenaga, Jun

    2018-01-01

    Continental crust provides first-order control on Earth's surface environment, enabling the presence of stable dry landmasses surrounded by deep oceans. The evolution of continental crust is important for atmospheric evolution, because continental crust is an essential component of deep carbon cycle and is likely to have played a critical role in the oxygenation of the atmosphere. Geochemical information stored in the mineral zircon, known for its resilience to diagenesis and metamorphism, has been central to ongoing debates on the genesis and evolution of continental crust. However, correction for crustal reworking, which is the most critical step when estimating original formation ages, has been incorrectly formulated, undermining the significance of previous estimates. Here I suggest a simple yet promising approach for reworking correction using the global compilation of zircon data. The present-day distribution of crustal formation age estimated by the new "unmixing" method serves as the lower bound to the true crustal growth, and large deviations from growth models based on mantle depletion imply the important role of crustal recycling through the Earth history.

  19. Oxygen isotopic composition and U-Pb discordance in zircon

    USGS Publications Warehouse

    Booth, A.L.; Kolodny, Y.; Chamberlain, C.P.; McWilliams, M.; Schmitt, A.K.; Wooden, J.

    2005-01-01

    We have investigated U-Pb discordance and oxygen isotopic composition of zircon using high-spatial resolution ??18O measurement by ion microprobe. ??18O in both concordant and discordant zircon grains provides an indication of the relationship between fluid interaction and discordance. Our results suggest that three characteristics of zircon are interrelated: (1) U-Pb systematics and concomitant age discordance, (2) ??18O and the water-rock interactions implied therein, and (3) zircon texture, as revealed by cathodoluminescence and BSE imaging. A key observation is that U-Pb-disturbed zircons are often also variably depleted in 18O, but the relationship between discordance and ??18O is not systematic. ??18O values of discordant zircons are generally lighter but irregular in their distribution. Textural differences between zircon grains can be correlated with both U-Pb discordance and ??18O. Discordant grains exhibit either a recrystallized, fractured, or strongly zoned CL texture, and are characteristic of 18O depletion. We interpret this to be a result of metamictization, leading to destruction of the zircon lattice and an increased susceptibility to lead loss. Conversely, grains that are concordant have less-expressed zoning and a smoother CL texture and are enriched in 18O. From this it is apparent that various stages of water-rock interaction, as evidenced by systematic variations in ??18O, leave their imprint on both the texture and U-Pb systematics of zircon. Copyright ?? 2005 Elsevier Ltd.

  20. 21 CFR 884.6120 - Assisted reproduction accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... II (special controls) (design specifications, labeling requirements, and clinical testing). ... Assisted reproduction accessories. (a) Identification. Assisted reproduction accessories are a group of...

  1. 21 CFR 884.6120 - Assisted reproduction accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... II (special controls) (design specifications, labeling requirements, and clinical testing). ... Assisted reproduction accessories. (a) Identification. Assisted reproduction accessories are a group of...

  2. 21 CFR 884.6120 - Assisted reproduction accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... II (special controls) (design specifications, labeling requirements, and clinical testing). ... Assisted reproduction accessories. (a) Identification. Assisted reproduction accessories are a group of...

  3. 21 CFR 872.3980 - Endosseous dental implant accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Endosseous dental implant accessories. 872.3980... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3980 Endosseous dental implant accessories. (a) Identification. Endosseous dental implant accessories are manually powered devices intended...

  4. 21 CFR 872.3980 - Endosseous dental implant accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Endosseous dental implant accessories. 872.3980... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3980 Endosseous dental implant accessories. (a) Identification. Endosseous dental implant accessories are manually powered devices intended...

  5. 21 CFR 872.3980 - Endosseous dental implant accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Endosseous dental implant accessories. 872.3980... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3980 Endosseous dental implant accessories. (a) Identification. Endosseous dental implant accessories are manually powered devices intended...

  6. 21 CFR 872.3980 - Endosseous dental implant accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Endosseous dental implant accessories. 872.3980... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3980 Endosseous dental implant accessories. (a) Identification. Endosseous dental implant accessories are manually powered devices intended...

  7. 21 CFR 872.3980 - Endosseous dental implant accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Endosseous dental implant accessories. 872.3980... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Prosthetic Devices § 872.3980 Endosseous dental implant accessories. (a) Identification. Endosseous dental implant accessories are manually powered devices intended...

  8. Chemical evolution of Himalayan leucogranites based on an O, U-Pb and Hf study of zircon

    NASA Astrophysics Data System (ADS)

    Hopkinson, Thomas N.; Warren, Clare J.; Harris, Nigel B. W.; Hammond, Samantha J.; Parrish, Randall R.

    2015-04-01

    Crustal melting is a characteristic process at convergent plate margins, where crustal rocks are heated and deformed. Miocene leucogranite sheets and plutons are found intruded into the high-grade metasedimentary core (the Greater Himalayan Sequence, GHS) across the Himalayan orogen. Previously-published Himalayan whole-rock data suggest that these leucogranites formed from a purely meta-sedimentary source, isotopically similar to those into which they now intrude. Bulk rock analyses carry inherent uncertainties, however: they may hide contributions from different contributing sources, and post-crystallization processes such as fluid interaction may significantly alter the original chemistry. In contrast, zircon is more able to retain precise information of the contributing sources of the melt from which it crystallises whilst its resistant nature is impervious to post-magmatic processes. This multi-isotope study of Oligocene-Miocene leucogranite zircons from the Bhutan Himalaya, seeks to differentiate between various geochemical processes that contribute to granite formation. Hf and O isotopes are used to detect discrete changes in melt source while U-Pb isotopes provide the timing of zircon crystallisation. Our data show that zircon rims of Himalayan age yield Hf-O signatures that lie within the previously reported whole-rock GHS field, confirming the absence of a discernible mantle contribution to the leucogranite source. Importantly, we document a decrease in the minimum ɛHf values during Himalayan orogenesis through time, correlating to a change in Hf model age from 1.4 Ga to 2.4 Ga. Nd model ages for the older Lesser Himalayan metasediments (LHS) that underthrust the GHS are significantly older than those for the GHS (2.4-2.9 Ga compared with 1.4-2.2 Ga), and as such even minor contributions of LHS material incorporated into a melt would significantly increase the resulting Hf model age. Hence our leucogranite data suggest either a change of source within

  9. Anisotropic mechanical properties of zircon and the effect of radiation damage

    NASA Astrophysics Data System (ADS)

    Beirau, Tobias; Nix, William D.; Bismayer, Ulrich; Boatner, Lynn A.; Isaacson, Scott G.; Ewing, Rodney C.

    2016-10-01

    This study provides new insights into the relationship between radiation-dose-dependent structural damage due to natural U and Th impurities and the anisotropic mechanical properties (Poisson's ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. in Am Mineral 76:1510-1532, 1991) and synthetic samples, covering a dose range of zero up to 6.8 × 1018 α-decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by Özkan (J Appl Phys 47:4772-4779, 1976), revealed a general radiation-induced decrease in stiffness (~54 %) and hardness (~48 %) and an increase in the Poisson's ratio (~54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Ríos et al. in J Phys Condens Matter 12:2401-2412, 2000a; Farnan and Salje in J Appl Phys 89:2084-2090, 2001; Zhang and Salje in J Phys Condens Matter 13:3057-3071, 2001). The excellent agreement, revealed by the different methods, indicates a large influence of structural and even local phenomena on the macroscopic mechanical properties. Therefore, this study indicates the importance of acquiring better knowledge about the mechanical long-term stability of radiation-damaged materials.

  10. Fission track dating of kimberlitic zircons

    NASA Astrophysics Data System (ADS)

    Haggerty, Stephen E.; Raber, Ellen; Naeser, Charles W.

    1983-04-01

    The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ± 6.5 m.y.), Orapa (87.4 ± 5.7 and 92.4 ± 6.1 m.y.), Nzega (51.1 ± 3.8 m.y.), Koffiefontein (90.0 ± 8.2 m.y.), and Val do Queve (133.4 ± 11.5 m.y.). In addition we report the first radiometric ages (707.9 ± 59.6 and 705.5 ± 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption.

  11. Oxygen diffusion in zircon

    NASA Astrophysics Data System (ADS)

    Watson, E. B.; Cherniak, D. J.

    1997-05-01

    Oxygen diffusion in natural, non-metamict zircon was characterized under both dry and water-present conditions at temperatures ranging from 765°C to 1500°C. Dry experiments were performed at atmospheric pressure by encapsulating polished zircon samples with a fine powder of 18O-enriched quartz and annealing the sealed capsules in air. Hydrothermal runs were conducted in cold-seal pressure vessels (7-70 MPa) or a piston cylinder apparatus (400-1000 MPa) on zircon samples encapsulated with both 18O-enriched quartz and 18O water. Diffusive-uptake profiles of 18O were measured in all samples with a particle accelerator, using the 18O(p, α) 15N reaction. For dry experimental conditions at 1100-1500°C, the resulting oxygen diffusivities (24 in all) are well described by: D dry (m 2/s) = 1.33 × 10 -4exp(-53920/T) There is no suggestion of diffusive anisotropy. Under wet conditions at 925°C, oxygen diffusion shows little or no dependence upon P H 2O in the range 7-1000 MPa, and is insensitive to total pressure as well. The results of 27 wet experiments at 767-1160°C and 7-1000 MPa can be described a single Arrhenius relationship: D wet (m 2/s) = 5.5 × 10 -12exp(-25280/T) The insensitivity of oxygen diffusion to P H 2O means that applications to geologic problems can be pursued knowing only whether the system of interest was 'wet' (i.e., P H 2O > 7MPa ) or 'dry'. Under dry conditions (presumably rare in the crust), zircons are extremely retentive of their oxygen isotopic signatures, to the extent that δ 18O would be perturbed at the center of a 200 μm zircon only during an extraordinarily hot and protracted event (e.g., 65 Ma at 900°C). Under wet conditions, δ 18O may or may not be retained in the central regions of individual crystals, cores or overgrowth rims, depending upon the specific thermal history of the system.

  12. Radiation Damage Study in Natural Zircon Using Neutrons Irradiation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lwin, Maung Tin Moe; Amin, Yusoff Mohd.; Kassim, Hasan Abu

    2011-03-30

    Changes of atomic displacements in crystalline structure of natural zircon (ZrSiO{sub 4}) can be studied by using neutron irradiation on the surface of zircon and compared the data from XRD measurements before and after irradiation. The results of neutron irradiation on natural zircon using Pneumatic Transfer System (PTS) at PUSPATI TRIGA Research Reactor in the Malaysian Nuclear Agency are discussed in this work. The reactor produces maximum thermal power output of 1 MWatt and the neutron flux of up to 1x10{sup 13} ncm{sup -2}s{sup -1}. From serial decay processes of uranium and thorium radionuclides in zircon crystalline structure, the emissionmore » of alpha particles can produce damage in terms of atomic displacements in zircon. Hence, zircon has been extensively studied as a possible candidate for immobilization of fission products and actinides.« less

  13. Are there impact-formed zircons in the Hadean record?

    NASA Astrophysics Data System (ADS)

    Wielicki, M. M.; Lu, X.; Bell, E. A.; Schmitt, A. K.; Harrison, T. M.

    2008-12-01

    Detrital Hadean zircons from the Jack Hills, Western Australia, show a remarkable cluster of crystallization temperatures at 680±25°C. This is particularly surprising as a simple model relating rock composition and Zr concentration predicts that a very broad spectrum of crystallization temperatures (ca. 650°C to 1000°C) with a median value of 780°C, would result from impact melting of the Earth's surface. Magmatic fractionation would tend to increase the aforementioned values. Given the predicted high rate of impacts during the Hadean, the absence of such a population in the Jack Hills zircons could signal a profound sampling problem, a hint of a history much different than previously supposed, or our lack of understanding of zircon formation due to impact related processes. We have begun to examine the latter issue by investigating the crystallization temperatures of zircons formed in melt sheets preserved in the geologic record. The Sudbury Igneous Complex, formed at 1850±3 Ma within the second largest impact crater on Earth, includes two igneous units termed the Black and Felsic Norites. Examination of zircons from each by SIMS confirms their crystallization age at 1847.3±2.2 Ma and yields Ti-in-zircon temperatures of 720°C and 750°C, respectively. This is consistent with that predicted from zircon saturation systematics. A statistical test indicates that the combined norite population is distinct from the Hadean temperature distribution. Thus the question arises: where are the Hadean zircons expected to have formed at >780°C via impact processes? Similar analysis is being pursued for zircons from the Vredefort Impact Structure, South Africa, which should provide further information on impact-formed zircon temperature spectra.

  14. 21 CFR 876.5250 - Urine collector and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Urine collector and accessories. 876.5250 Section... (CONTINUED) MEDICAL DEVICES GASTROENTEROLOGY-UROLOGY DEVICES Therapeutic Devices § 876.5250 Urine collector and accessories. (a) Identification. A urine collector and accessories is a device intended to collect...

  15. 21 CFR 876.5250 - Urine collector and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Urine collector and accessories. 876.5250 Section... (CONTINUED) MEDICAL DEVICES GASTROENTEROLOGY-UROLOGY DEVICES Therapeutic Devices § 876.5250 Urine collector and accessories. (a) Identification. A urine collector and accessories is a device intended to collect...

  16. 21 CFR 876.5250 - Urine collector and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Urine collector and accessories. 876.5250 Section... (CONTINUED) MEDICAL DEVICES GASTROENTEROLOGY-UROLOGY DEVICES Therapeutic Devices § 876.5250 Urine collector and accessories. (a) Identification. A urine collector and accessories is a device intended to collect...

  17. 21 CFR 876.5250 - Urine collector and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Urine collector and accessories. 876.5250 Section... (CONTINUED) MEDICAL DEVICES GASTROENTEROLOGY-UROLOGY DEVICES Therapeutic Devices § 876.5250 Urine collector and accessories. (a) Identification. A urine collector and accessories is a device intended to collect...

  18. 21 CFR 876.5250 - Urine collector and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Urine collector and accessories. 876.5250 Section... (CONTINUED) MEDICAL DEVICES GASTROENTEROLOGY-UROLOGY DEVICES Therapeutic Devices § 876.5250 Urine collector and accessories. (a) Identification. A urine collector and accessories is a device intended to collect...

  19. 21 CFR 868.5860 - Pressure tubing and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Pressure tubing and accessories. 868.5860 Section... (CONTINUED) MEDICAL DEVICES ANESTHESIOLOGY DEVICES Therapeutic Devices § 868.5860 Pressure tubing and accessories. (a) Identification. Pressure tubing and accessories are flexible or rigid devices intended to...

  20. Three Accessories for a Rotating Platform.

    ERIC Educational Resources Information Center

    Riley, James A.; Fryer, Oscar G.

    1980-01-01

    Describes three accessories developed to be used in conjunction with the rotating platform or turntable. Three demonstrations using these accessories are included. These demonstrations are: (a) conservation of angular momentum; (b) gravity-defying goblets; and (c) direct measurement of centripetal force. (HM)

  1. Deformation-related microstructures in magmatic zircon and implications for diffusion

    NASA Astrophysics Data System (ADS)

    Reddy, Steven Michael; Timms, Nicholas E.; Hamilton, Patrick Joseph; Smyth, Helen R.

    2009-02-01

    An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common <100> misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of <001>{100} and <100>{010} slip systems. The restriction of deformation microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon grains, indicate that zircon deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain deformation of the cumulate in the late

  2. 14 CFR 25.1192 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Engine accessory section diaphragm. 25.1192....1192 Engine accessory section diaphragm. For reciprocating engines, the engine power section and all portions of the exhaust system must be isolated from the engine accessory compartment by a diaphragm that...

  3. 14 CFR 25.1192 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Engine accessory section diaphragm. 25.1192....1192 Engine accessory section diaphragm. For reciprocating engines, the engine power section and all portions of the exhaust system must be isolated from the engine accessory compartment by a diaphragm that...

  4. 14 CFR 25.1192 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Engine accessory section diaphragm. 25.1192....1192 Engine accessory section diaphragm. For reciprocating engines, the engine power section and all portions of the exhaust system must be isolated from the engine accessory compartment by a diaphragm that...

  5. U-Pb systematics in coexisting zircon, rutile and titanite from granophyres in the Archean Stillwater Complex: metamictization and the fate of radiogenic Pb

    NASA Astrophysics Data System (ADS)

    Friedman, R. M.; Wall, C. J.; Scoates, J. S.; Meurer, W. P.

    2009-12-01

    Self-irradiation of zircon causes structural damage (metamictization) that can result in the loss of radiogenic Pb during interaction with aqueous solutions. To evaluate this behavior in metamict zircon, and in other U-bearing accessory phases like titanite and rutile, we are examining the U-Pb systematics of granophyric rocks from the ca. 2.7 Ga Stillwater layered intrusion, Montana. Four samples were studied in detail, including a pegmatitic ksp-qtz core to a gabbroic pegmatoid in the Lower Banded Series (N1), an alaskite and an amphibole-rich reaction zone between the alaskite and anorthosite (AN1) in the Middle Banded Series, and an amphibole-bearing granophyre from the Upper Banded Series (GN3). Except in the pegmatite, zircon is variably metamict with amorphous zones characterized by distinctive Ca-enrichment. Single zircon grains were analyzed by ID-TIMS following annealing and chemical abrasion, and multi-grain (n=4-5) fractions of titanite and rutile were analyzed by conventional ID-TIMS; the UBC 233-235U-205Pb isotopic tracer is calibrated against mixed U-Pb gravimetric reference solutions made available through the EarthTime initiative. The U-Pb systematics are coherent only for the pegmatite yielding both a Concordia age of 2709.60 ± 0.80 Ma (2σ, including tracer calibration, decay-constant errors not included) for low-U zircon (76-237 ppm) and concordant titanite results with 207Pb/206Pb ages from 2701-2710 Ma. The results for high-U zircon (up to 1438 ppm) for the other three samples are strongly discordant (9-43%, 85-89%, 28-71%, respectively) with a wide range of 207Pb/206Pb ages (2583-2647 Ma, 2210-2357 Ma, 2345-2499 Ma). Given the extreme incompatibility of Pb2+ in zircon and the highly metamict state of zircon in these granophyres, we are investigating the extent to which radiogenic lead is selectively removed during the chemical abrasion and annealing process from step-wise leaching experiments and image analysis (CL, SEM). In contrast

  6. Zircon-Based Ceramics Composite Coating for Environmental Barrier Coating

    NASA Astrophysics Data System (ADS)

    Suzuki, M.; Sodeoka, S.; Inoue, T.

    2008-09-01

    Studies on plasma spraying of zircon (ZrSiO4) have been carried out by the authors as one of the candidates for an environmental barrier coating (EBC) application, and had reported that substrate temperature is one of the most important factors to obtain crack-free and highly adhesive coating. In this study, several amounts of yttria were added to zircon powder, and the effect of the yttria addition on the structure and properties of the coatings were evaluated to improve the stability of the zircon coating structure at elevated temperature. The coatings obtained were composed of yttria-stabilized zirconia (YSZ), glassy silica, whereas the one prepared from monolithic zircon powder was composed of the metastable high temperature tetragonal phase of zirconia and glassy silica. After the heat treatment over 1200 °C, silica and zirconia formed zircon in all coatings. However, coatings with higher amounts of yttria exhibited lower amounts of zircon. This resulted in the less open porosity of the coating at elevated temperature. These yttria-added coatings also showed good adhesion even after the heat treatment, while monolithic zircon coating pealed off.

  7. Correlated microanalysis of zircon: Trace element, δ 18O, and U-Th-Pb isotopic constraints on the igneous origin of complex >3900 Ma detrital grains

    NASA Astrophysics Data System (ADS)

    Cavosie, Aaron J.; Valley, John W.; Wilde, Simon A.; E. I. M. F.

    2006-11-01

    The origins of >3900 Ma detrital zircons from Western Australia are controversial, in part due to their complexity and long geologic histories. Conflicting interpretations for the genesis of these zircons propose magmatic, hydrothermal, or metamorphic origins. To test the hypothesis that these zircons preserve magmatic compositions, trace elements [rare earth elements (REE), Y, P, Th, U] were analyzed by ion microprobe from a suite of >3900 Ma zircons from Jack Hills, Western Australia, and include some of the oldest detrital zircons known (4400-4300 Ma). The same ˜20 μm domains previously characterized for U/Pb age, oxygen isotope composition (δ 18O), and cathodoluminescence (CL) zoning were specifically targeted for analysis. The zircons are classified into two types based on the light-REE (LREE) composition of the domain analyzed. Zircons with Type 1 domains form the largest group (37 of 42), consisting of grains that preserve evolved REE compositions typical of igneous zircon from crustal rocks. Grains with Type 1 domains display a wide range of CL zoning patterns, yield nearly concordant U/Pb ages from 4400 to 3900 Ma, and preserve a narrow range of δ 18O values from 4.7‰ to 7.3‰ that overlap or are slightly elevated relative to mantle oxygen isotope composition. Type 1 domains are interpreted to preserve magmatic compositions. Type 2 domains occur in six zircons that contain spots with enriched light-REE (LREE) compositions, here defined as having chondrite normalized values of La N > 1 and Pr N > 10. A subset of analyses in Type 2 domains appear to result from incorporation of sub-surface mineral inclusions in the analysis volume, as evidenced by positively correlated secondary ion beam intensities for LREE, P, and Y, which are anti-correlated to Si, although not all Type 2 analyses show these features. The LREE enrichment also occurs in areas with discordant U/Pb ages and/or high Th/U ratios, and is apparently associated with past or present

  8. 21 CFR 872.4200 - Dental handpiece and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Dental handpiece and accessories. 872.4200 Section... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4200 Dental handpiece and accessories. (a) Identification. A dental handpiece and accessories is an AC-powered, water-powered, air-powered, or belt-driven...

  9. 21 CFR 872.4200 - Dental handpiece and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Dental handpiece and accessories. 872.4200 Section... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4200 Dental handpiece and accessories. (a) Identification. A dental handpiece and accessories is an AC-powered, water-powered, air-powered, or belt-driven...

  10. 21 CFR 872.4200 - Dental handpiece and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Dental handpiece and accessories. 872.4200 Section... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4200 Dental handpiece and accessories. (a) Identification. A dental handpiece and accessories is an AC-powered, water-powered, air-powered, or belt-driven...

  11. 21 CFR 872.4200 - Dental handpiece and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Dental handpiece and accessories. 872.4200 Section... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4200 Dental handpiece and accessories. (a) Identification. A dental handpiece and accessories is an AC-powered, water-powered, air-powered, or belt-driven...

  12. 21 CFR 872.4200 - Dental handpiece and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Dental handpiece and accessories. 872.4200 Section... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4200 Dental handpiece and accessories. (a) Identification. A dental handpiece and accessories is an AC-powered, water-powered, air-powered, or belt-driven...

  13. 21 CFR 876.5900 - Ostomy pouch and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ostomy pouch and accessories. 876.5900 Section 876...) MEDICAL DEVICES GASTROENTEROLOGY-UROLOGY DEVICES Therapeutic Devices § 876.5900 Ostomy pouch and accessories. (a) Identification. An ostomy pouch and accessories is a device that consists of a bag that is...

  14. Isotopic Composition of Oxygen in Lunar Zircons

    NASA Technical Reports Server (NTRS)

    Nemchin, A. A.; Whitehouse, M. J.; Pidgeon, R. T.; Meyer, C.

    2005-01-01

    The recent discovery of heavy oxygen in zircons from the Jack Hills conglomerates Wilde et al. and Mojzsis et al. was interpreted as an indication of presence of liquid water on the surface of Early Earth. The distribution of ages of Jack Hills zircons and lunar zircons appears to be very similar and therefore analysis of oxygen in the lunar grains may provide a reference frame for further study of the early history of the Earth as well as give additional information regarding processes that operated on the Moon. In the present study we have analysed the oxygen isotopic composition of zircon grains from three lunar samples using the Swedish Museum of Natural History CAMECA 1270 ion microprobe. The samples were selected as likely tests for variations in lunar oxygen isotopic composition. Additional information is included in the original extended abstract.

  15. 21 CFR 872.6250 - Dental chair and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Dental chair and accessories. 872.6250 Section 872...) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6250 Dental chair and accessories. (a) Identification. A dental chair and accessories is a device, usually AC-powered, in which a patient sits. The...

  16. 21 CFR 872.6250 - Dental chair and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Dental chair and accessories. 872.6250 Section 872...) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6250 Dental chair and accessories. (a) Identification. A dental chair and accessories is a device, usually AC-powered, in which a patient sits. The...

  17. 21 CFR 872.6250 - Dental chair and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Dental chair and accessories. 872.6250 Section 872...) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6250 Dental chair and accessories. (a) Identification. A dental chair and accessories is a device, usually AC-powered, in which a patient sits. The...

  18. 21 CFR 872.6250 - Dental chair and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Dental chair and accessories. 872.6250 Section 872...) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6250 Dental chair and accessories. (a) Identification. A dental chair and accessories is a device, usually AC-powered, in which a patient sits. The...

  19. 21 CFR 872.6250 - Dental chair and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Dental chair and accessories. 872.6250 Section 872...) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6250 Dental chair and accessories. (a) Identification. A dental chair and accessories is a device, usually AC-powered, in which a patient sits. The...

  20. Accessories make the outfit: Accessory Chromosomes and other dispensable DNA regions in plant-pathogenic Fungi.

    PubMed

    Bertazzoni, Stefania; Williams, Angela; Jones, Darcy A B; Syme, Robert A; Tan, Kar-Chun; Hane, James Kyawzwar

    2018-04-17

    Fungal pathogen genomes can often be divided into core and accessory regions. Accessory regions may be comprised of either accessory regions (ARs) within core chromosomes (CCs), or wholly-dispensable (accessory) chromosomes (ACs). Fungal ACs and ARs typically accumulate mutations and structural rearrangements more rapidly over time than CCs, and many harbour genes relevant to host-pathogen interactions. These regions are of particular interest in plant pathology and include host-specific virulence factors and secondary metabolite synthesis gene clusters. This review outlines known ACs and ARs in fungal genomes, methods used for their detection, their common properties that differentiate them from the core genome, and what is currently known of their various roles in pathogenicity. Reports on the evolutionary processes generating and shaping AC/AR compartments are discussed, including repeat induced point mutation (RIP) and breakage-fusion-bridge (BFB) cycles. Previously ACs have been studied extensively within key genera including Fusarium, Zymoseptoria and Alternaria, but are growing in their frequency of observation and perceived importance across a wider range of fungal species. Recent advances in sequencing technologies permit affordable genome assembly and re-sequencing of populations that will facilitate further discovery and routine screening of ACs.

  1. 21 CFR 890.5925 - Traction accessory.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Traction accessory. 890.5925 Section 890.5925 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Therapeutic Devices § 890.5925 Traction accessory. (a...

  2. 21 CFR 890.5925 - Traction accessory.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Traction accessory. 890.5925 Section 890.5925 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Therapeutic Devices § 890.5925 Traction accessory. (a...

  3. 21 CFR 890.5925 - Traction accessory.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Traction accessory. 890.5925 Section 890.5925 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Therapeutic Devices § 890.5925 Traction accessory. (a...

  4. 21 CFR 890.5925 - Traction accessory.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Traction accessory. 890.5925 Section 890.5925 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Therapeutic Devices § 890.5925 Traction accessory. (a...

  5. 21 CFR 890.5925 - Traction accessory.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Traction accessory. 890.5925 Section 890.5925 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Therapeutic Devices § 890.5925 Traction accessory. (a...

  6. Irradiation effects in monazite-(Ce) and zircon: Raman and photoluminescence study of Au-irradiated FIB foils

    NASA Astrophysics Data System (ADS)

    Nasdala, Lutz; Akhmadaliev, Shavkat; Artac, Andreas; Chanmuang N., Chutimun; Habler, Gerlinde; Lenz, Christoph

    2018-05-01

    Lamellae of 1.5 µm thickness, prepared from well-crystallised monazite-(Ce) and zircon samples using the focused-ion-beam technique, were subjected to triple irradiation with 1 MeV Au+ ions (15.6% of the respective total fluence), 4 MeV Au2+ ions (21.9%) and 10 MeV Au3+ ions (62.5%). Total irradiation fluences were varied in the range 4.5 × 1012 - 1.2 × 1014 ions/cm2. The highest fluence resulted in amorphisation of both minerals; all other irradiations (i.e. up to 4.5 × 1013 ions/cm2) resulted in moderate to severe damage. Lamellae were subjected to Raman and laser-induced photoluminescence analysis, in order to provide a means of quantifying irradiation effects using these two micro-spectroscopy techniques. Based on extensive Monte Carlo calculations and subsequent defect-density estimates, irradiation-induced spectroscopic changes are compared with those of naturally self-irradiated samples. The finding that ion irradiation of monazite-(Ce) may cause severe damage or even amorphisation, is in apparent contrast to the general observation that naturally self-irradiated monazite-(Ce) does not become metamict (i.e. irradiation-amorphised), in spite of high self-irradiation doses. This is predominantly assigned to the continuous low-temperature damage annealing undergone by this mineral; other possible causes are discussed. According to cautious estimates, monazite-(Ce) samples of Mesoproterozoic to Cretaceous ages have stored only about 1% of the total damage experienced. In contrast, damage in ion-irradiated and naturally self-irradiated zircon is on the same order; reasons for the observed slight differences are discussed. We may assess that in zircon, alpha decays create significantly less than 103 Frenkel-type defect pairs per event, which is much lower than previous estimates. Amorphisation occurs at defect densities of about 0.10 dpa (displacements per lattice atom).

  7. Continental crustal history in SE Asia: Insights from zircon geochronology

    NASA Astrophysics Data System (ADS)

    Sevastjanova, I.; Hall, R.; Gunawan, I.; Ferdian, F.; Decker, J.

    2012-12-01

    It is well known that SE Asia is underlain mostly by continental crust derived from Gondwana. However, there are still many uncertainties about the ages of protoliths, origin, arrival ages and history of different blocks, because much of the basement is unexposed. We have compiled previously published and new zircon U-Pb age and Hf isotope data from SE Asia. Our data set currently contains over 8400 U-Pb ages and over 600 Hf isotope analyses from sedimentary, metamorphic and igneous rocks and work is continuing to increase its size and the area covered. Zircons range in age from 3.4 Ga to near-zero. Archean zircons (>2.5 Ga) are rare in SE Asia and significant Archean populations (particularly zircons >2.8 Ga) are found only in East Java and the Sibumasu block of the Malay Peninsula. The presence of Archean zircons strongly suggests that the East Java and Sibumasu blocks were once situated near present-day Western Australia. Detrital Paleoproterozoic (ca. 1.9-1.8 Ga) zircons are abundant in many parts of SE Asia. In Sundaland (Malay Peninsula, Sumatra, West Java, Borneo) the most likely source for these zircons is the tin belt basement, but a north Australian source is more likely for eastern Indonesian samples. An early Mesoproterozoic (ca. 1.6-1.5 Ga) zircon population, particularly common in eastern Indonesia, is interpreted to be derived from central or northern Australia. Mesoproterozoic zircons, ca. 1.4 Ga, are common only on fragments that are now attached to or were previously part of the north Australian margin, such as the Bird's Head of New Guinea, Timor, Seram, Sulawesi and SW Borneo. Hf isotope characteristics of zircons from Seram are similar to those of zircons from eastern Australia. This supports the suggestion that Seram was part of the Australian margin. Late Meso- and early Neoproterozoic zircons (ca. 1.2-1.1 Ga, 900 Ma, and 600 Ma) are present, but not abundant, in SE Asia. Dominant Phanerozoic populations are Permian-Triassic, Cretaceous, and

  8. 47 CFR 15.27 - Special accessories.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... information required by this section may be included in the manual in that alternative form, provided the user..., shall ensure that these special accessories are provided with the equipment. The instruction manual for... responsibility of the user to use the needed special accessories supplied with the equipment. In cases where the...

  9. Proterozoic events recorded in quartzite cobbles at Jack Hills, Western Australia: New constraints on sedimentation and source of > 4 Ga zircons

    NASA Astrophysics Data System (ADS)

    Grange, Marion L.; Wilde, Simon A.; Nemchin, Alexander A.; Pidgeon, Robert T.

    2010-03-01

    Rare heavy mineral bands within quartzite cobbles were identified in two conglomerate units within the Jack Hills belt, Western Australia. Seven zircon-bearing cobbles were analysed from one location (site 152) and three from another (site 154), both approximately 1 km west of the site where zircons in excess of 4 Ga are abundant (W74 'discovery' site). Individual pebbles from the 152 site reveal three distinctive features, containing either zircons > 3.0 Ga in age, < 1.9 Ga in age or a range of ages from ˜ 1.2 to ˜ 3.6 Ga. Those from site 154 are more uniform, containing only zircons with ages between 3.1 and 3.9 Ga. Only one grain > 4 Ga was discovered from the entire suite of pebbles, in contrast to the well-studied W74 site. A single detrital zircon with an age of 1220 ± 42 Ma from location 152 is the youngest grain so far reported from sedimentary rocks at Jack Hills. It shows magmatic oscillatory zoning and thus implies at least two sedimentary cycles within the Proterozoic; requiring erosion of an igneous precursor, incorporation into a clastic sediment, induration and subsequent erosion and transport to be hosted in the conglomerate. The nearest source for rocks of this age is the Bangemall Supergroup in the Collier Basin, ˜ 100 km northeast in the Capricorn Orogen. This would imply tectonic interleaving of originally more extensive Bangemall rocks, possibly related to activity along the Cargarah Shear Zone that traverses the Jack Hills belt. The lack of > 4.1 Ga zircons in the pebbles is highly significant, suggesting the immediate source of ancient zircons was no longer present at the Earth's surface. This equates with a general lack of ancient crystals noted in rocks that contain Proterozoic zircons from previous studies and implies that such grains diminish in number as earlier sedimentary rocks were successively recycled.

  10. Detrital zircon U-Pb Geochronology of the Boleo Formation of Santa RosalÍa Basin, Baja California Sur, México

    NASA Astrophysics Data System (ADS)

    Henry, M.; Alvarez Ortega, K. G.; Banes, A.; Holm-Denoma, C.; Busby, C.; Niemi, T.

    2017-12-01

    The Santa Rosalía Basin (SRB) is a rift basin related to the opening of the Gulf of California. The Boleo Formation is the oldest and dominant sedimentary fill of the SRB, with a poorly constrained age. We carried out a U-Pb detrital zircon (DZ) study of the Boleo Formation to constrain its maximum depositional age. The Boleo Formation has a basal limestone-gypsum section, overlain by an up to 250 m thick clastic sequence, with coarsening upward cycles of mudstone, sandstone, and conglomerate. Cu-Zn-Co-Mn stratiform ore deposits ("mantos") cap the conglomerate in each cycle, numbered 0, 1, 2, 3 and 4 (from top to bottom of section1). Sandstone samples were collected for U-Pb detrital zircon geochronology from four stratigraphic levels beneath a manto, including one each below mantos 1, 3 and 4, as well as two localities beneath manto 2. Additionally, one sample was collected above the gypsum. The sandstones are lithic feldspathic wackes derived from erosion of andesitic arc volcanic rocks, which generally lack zircon, so large DZ samples were collected. A field Wilfley table was constructed from local materials as a first step to concentrate heavy minerals, from 88 kg/sample to 16 kg/sample. The field-processed samples were further concentrated in the lab using standard zircon separation methods. Yields were excellent, 1,000 zircons per sample. We analyzed 315 zircons per sample by LA-ICPMS, using the Arizona LaserChron Center. DZ ages from the Boleo Formation range dominantly from Late Miocene through Early Cretaceous, with minor Paleozoic and Precambrian ages. However, the maximum depositional age of the formation is constrained by 40 Ar/39 Ar age of 9.42 +/- 0.29 Ma on underlying volcanic rocks2. Only 5 to 22 zircons per sample are less than 10 Ma, and of those, all stratigraphic levels are dominated mostly by 9 Ma zircons, except for the stratigraphically highest sample. Zircons from this form a coherent group of 3 with a TuffZirc age of 6.04 +/- 0.02 (75

  11. Improved zircon iron corals for the 1990s

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Decker, C.

    1992-03-01

    CIBA-GEIGY/Drakenfeld Colors is dedicated to the research and development of consistent and cost-effective ceramic stains for the whitewares industry. After identifying the trends in color for the 1990s. CIBA-GEIGY/Drakenfeld Colors initiated an extensive R D project to improve zircon ion corals for the whitewares industry. These color trends indicated a need for stronger and cleaner zircon iron corals. This paper discusses the chemistry and crystal structure of zircon iron corals. A historical review of Drakenfeld corals will also be presented. The most recent development in Drakenfeld corals will then be compared to other commercially available zircon iron corals. Taking intomore » consideration these comparisons, conclusions will be drawn suggesting the coral of choice for the 1990s.« less

  12. Twinning in Zircon: Not a High-Pressure Phenomenon

    NASA Astrophysics Data System (ADS)

    Jones, G. A.; Moser, D.; Shieh, S. R.; Barker, I.

    2017-12-01

    Microtwins in zircon are commonly found in shocked terrestrial and extraterrestrial samples and are potentially important for shock history and crater reconstruction. Twinning is easily observed with both the optical microscope and variety of electron beam techniques. Twinning as a deformation mechanism is consistent with the high strain rates generated during impact. No constitutive relationships, or even general limits on the physical conditions required for twinning in zircon are known, however. Present speculation on the critical quantity for twin formation, i.e. 10s of GPa of shock pressure (Moser et al. 2011, Timms et al., 2012), has no basis in the underlying mechanisms of twin nucleation, which are related to the motion of dislocations. This erroneous value is due to conflation of twinning sensu stricto with a phase transformation to reidite. Reidite occurs as twin-like lamellae occupying the {112} planes which are thought to be a mirror plane for twinning. We review the crystallographic theory of twinning in zircon. We then evaulate several theories on the nucleation of twins along with their necessary stresses involved. Our aim is to show that shock microtwins in zircon can be a `low pressure' shock phenomenon. This 'low pressure' hypothesis is supported by natural samples. These zircons are from the lower crust nearly 80 km from the centre of the Vredefort impact structure—the most distal zircon shock microstructures yet found in the lithosphere. Twins are present in 10% of the zircon grains greater than 50 µm in diameter. As an extensive, 'low pressure' phenomenon, twins are an easily recognized and potentially widespread record of Earth's impact history.Moser, D.E., Cupelli, C. L., Barker, I., Flowers, R. M., Mowman, J. R., Wooden, J. and Hart, R. (2011) New zircon shock phenomena and their use for dating and […] analysis of the Vredefort dome, Canadian Journal of Earth Sciences 48(2), 117-139.Timms, N.E., Reddy, S. M., Healy, D., Nemchin, A. A

  13. Dating sub-20 micron zircons in granulite-facies mafic dikes from SW Montana: a new approach using automated mineralogy and SIMS U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Ault, A. K.; Mahan, K. H.; Flowers, R. M.; Chamberlain, K.; Appleby, S. K.; Schmitt, A. K.

    2010-12-01

    Geochronological data is fundamental to all tectonic studies, but a major limitation for many lithologies is a paucity of sizeable zircons suitable for conventional U-Pb techniques. In particular, mafic dike swarms provide important time markers for tectonometamorphic activity in Precambrian terranes, but commonly yield little or no zircon or baddeleyite sufficient for TIMS or standard ion-probe analysis of crystal separates. We apply a new approach involving in-situ automated mineralogy and high spatial resolution Secondary Ion Mass Spectrometry (SIMS) geochronology to a mafic dike swarm exposed in the Northern Madison Range of SW Montana. The dikes cross-cut early fabrics but are also variably deformed and metamorphosed to P-T conditions as high as 1.2 GPa and 850 C. The swarm emplacement age is inferred to be ca. 2.1 Ga based on similarities to dated dikes in the adjacent Tobacco Root Mountains. Resolving the timing of dike emplacement and high-grade metamorphism in the study area is important for understanding the extent of post-Archean modification to the northwest margin of the Wyoming craton. Identification and textural characterization of zircons were facilitated by in-situ automated mineralogical analysis, in contrast to a standard elemental X-ray mapping approach. Our technique uses an SEM-based platform coupling calibrated BSE data with X-ray data collected by multiple energy dispersive spectrometers to rapidly identify target accessory phases at high spatial resolution. Whole thin section search maps were generated in ~30 minutes at 4 µm pixel resolution. Our dike thin sections commonly contained >300 zircons in a variety of textural settings, with 80% having a short dimension <10 µm. Zircons were dated in-situ by adjusting the field aperture of the CAMECA ims1270 to preferentially collect secondary ions emitted from within the inner few microns of the ~15 µm diameter analysis pit. This allows us to analyze zircon grains with a minimum dimension as

  14. Future Development of Endoscopic Accessories for Endoscopic Submucosal Dissection

    PubMed Central

    Jang, Jae-Young

    2017-01-01

    Endoscopic submucosal dissection (ESD) has recently been accepted as a standard treatment for patients with early gastric cancer (EGC), without lymph node metastases. Given the rise in the number of ESDs being performed, new endoscopic accessories are being developed and existing accessories modified to facilitate the execution of ESD and reduce complication rates. This paper examines the history underlying the development of these new endoscopic accessories and indicates future directions for the development of these accessories. PMID:28609819

  15. Correlating rates of magmatic arc unroofing and sedimentation using detrital zircon U/Pb and (U-Th)/He thermochronology

    NASA Astrophysics Data System (ADS)

    Fosdick, J. C.

    2017-12-01

    Double and triple dating of minerals using multiple geo-thermochronometers has revolutionized efforts to evaluate complex thermotectonic histories of orogens, isolate unique sedimentary sources, and quantify basin burial reheating. A persisting challenge is to distinguish volcanic sources from rapidly exhumed sources, with the simplistic premise that coincident cooling dates among high- to low-temperature thermochronometers are diagnostic of volcanic sources. Coupled zircon U/Pb and (U-Th)/He geo-thermochronometry from the Miocene Bermejo foreland basin in the southern Central Andes reveals a high temporal resolution of unroofing signatures of the Choiyoi Group, a Permian-Triassic silicic volcanic and plutonic complex, and the Pennsylvanian-Permian Colangüil batholith. Both units are important sediment sources within the High Andes for the Cenozoic east-flowing sediment routing systems. Results show fluvial sourcing of Colangüil detrital zircons with progressively greater partial loss of He (<8% to 12-23% fractional loss from 9.5 Ma to 6 Ma), as indicated by upsection younging of zircon He dates for a given U/Pb age cluster. These findings suggest erosion of increasingly deeper levels of the Colangüil arc during late Miocene development of the High Andes. This progression of higher He loss and thus younger He dates during sedimentation for a given U/Pb age cluster is analogous to the magmatic arc unroofing trend revealed by undissected to dissected arc provenance fields in sandstone petrography. Multi-method thermochronometry of detrital minerals may reveal an added level of information regarding rates of cooling, unroofing, and thermal evolution of magmatic systems as preserved in the detrital record.

  16. New data on carbonatites of the Il'mensky-Vishnevogorsky alkaline complex, the southern Urals, Russia

    NASA Astrophysics Data System (ADS)

    Nedosekova, I. L.

    2007-04-01

    Carbonatites that are hosted in metamorphosed ultramafic massifs in the roof of miaskite intrusions of the Il’mensky-Vishnevogorsky alkaline complex are considered. Carbonatites have been revealed in the Buldym, Khaldikha, Spirikha, and Kagan massifs. The geological setting, structure of carbonatite bodies, distribution of accessory rare-metal mineralization, typomorphism of rock-forming minerals, geochemistry, and Sr and Nd isotopic compositions are discussed. Dolomite-calcite carbonatites hosted in ultramafic rocks contain tetraferriphlogopite, richterite, accessory zircon, apatite, magnetite, ilmenite, pyrrhotite, pyrite, and pyrochlore. According to geothermometric data and the composition of rock-forming minerals, the dolomite-calcite carbonatites were formed under K-feldspar-calcite, albite-calcite, and amphibole-dolomite-calcite facies conditions at 575-300°C. The Buldym pyrochlore deposit is related to carbonatites of these facies. In addition, dolomite carbonatites with accessory Nb and REE mineralization (monazite, aeschynite, allanite, REE-pyrochlore, and columbite) are hosted in ultramafic massifs. The dolomite carbonatites were formed under chlorite-sericite-ankerite facies conditions at 300-200°C. The Spirikha REE deposit is related to dolomite carbonatite and alkaline metasomatic rocks. It has been established that carbonatites hosted in ultramafic rocks are characterized by high Sr, Ba, and LREE contents and variable Nb, Zr, Ti, V, and Th contents similar to the geochemical attributes of calcio-and magnesiocarbonatites. The low initial 87Sr/86Sr = 0.7044-0.7045 and ɛNd ranging from 0.65 to -3.3 testify to their derivation from a deep mantle source of EM1 type.

  17. Creation of a continent recorded in zircon zoning

    USGS Publications Warehouse

    Moser, D.E.; Bowman, J.R.; Wooden, J.; Valley, J.W.; Mazdab, F.; Kita, N.

    2008-01-01

    We have discovered a robust microcrystalline record of the early genesis of North American lithosphere preserved in the U-Pb age and oxygen isotope zoning of zircons from a lower crustal paragneiss in the Neoarchean Superior province. Detrital igneous zircon cores with ??18O values of 5.1???-7.1??? record creation of primitive to increasingly evolved crust from 2.85 ?? 0.02 Ga to 2.67 ?? 0.02 Ga. Sharp chemical unconformity between cores and higher ??18O (8.4???-10.4???) metamorphic overgrowths as old as 2.66 ?? 0.01 Ga dictates a rapid sequence of arc unroofing, burial of detrital zircons in hydrosphere-altered sediment, and transport to lower crust late in upper plate assembly. The period to 2.58 ?? 0.01 Ga included ???80 m.y. of high-temperature (???700-650 ??C), nearly continuous overgrowth events reflecting stages in maturation of the subjacent mantle root. Huronian continental rifting is recorded by the youngest zircon tip growth at 2512 ?? 8 Ma (??? 600 ??C) signaling magma intraplating and the onset of rigid plate behavior. This >150 m.y. microscopic isotope record in single crystals demonstrates the sluggish volume diffusion of U, Pb, and O in zircon throughout protracted regional metamorphism, and the consequent advances now possible in reconstructing planetary dynamics with zircon zoning. ?? 2008 The Geological Society of America.

  18. High-pressure minerals in shocked meteorites

    NASA Astrophysics Data System (ADS)

    Tomioka, Naotaka; Miyahara, Masaaki

    2017-09-01

    Heavily shocked meteorites contain various types of high-pressure polymorphs of major minerals (olivine, pyroxene, feldspar, and quartz) and accessory minerals (chromite and Ca phosphate). These high-pressure minerals are micron to submicron sized and occur within and in the vicinity of shock-induced melt veins and melt pockets in chondrites and lunar, howardite-eucrite-diogenite (HED), and Martian meteorites. Their occurrence suggests two types of formation mechanisms (1) solid-state high-pressure transformation of the host-rock minerals into monomineralic polycrystalline aggregates, and (2) crystallization of chondritic or monomineralic melts under high pressure. Based on experimentally determined phase relations, their formation pressures are limited to the pressure range up to 25 GPa. Textural, crystallographic, and chemical characteristics of high-pressure minerals provide clues about the impact events of meteorite parent bodies, including their size and mutual collision velocities and about the mineralogy of deep planetary interiors. The aim of this article is to review and summarize the findings on natural high-pressure minerals in shocked meteorites that have been reported over the past 50 years.

  19. Geology and timing of mineralization at the Cangshang gold deposit, north-western Jiaodong Peninsula, China

    USGS Publications Warehouse

    Zhang, X.; Cawood, Peter A.; Wilde, S.A.; Liu, R.; Song, H.; Li, W.; Snee, L.W.

    2003-01-01

    The Cangshang gold deposit of the northwestern Jiaodong Peninsula contains reserves of greater than 50 tonnes (t) and is developed by the largest open pit gold mine in China. This deposit is a Jiaojia-style (i.e. disseminated-and-veinlet) deposit. It is controlled by the San-Cang fault zone, which trends ???040?? and dips 40-75??SE at the mine site. The main (no. 1) orebody lies between a hanging wall of Precambrian metamorphic rocks (mainly amphibolite) of the Fenzishan Group and a footwall composed of the Mesozoic Linglong granitoid. The ore zone is mainly composed of pyritized, sericitized and silicified granitoid, which has undergone variable degrees of cataclasis. SHRIMP U-Pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 ?? 17 Ma and underwent metamorphism at 1852 ?? 37 Ma. The footwall granodiorite has been dated at 166 ?? 4 Ma, whereas zircons from the ore zone yield a younger age of 154 ?? 5 Ma. Cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons, therefore, are all interpreted to be representative of magmatic crystallization. Dating of sericite by 40Ar-39Ar has been used to directly determine the timing of formation of the Cangshang deposit, providing the first time absolute age on formation of the Jiaojia-style gold deposits. The well-defined age of 121.3 ?? 0.2 Ma provides the precise timing of gold mineralization at the Cangshang deposit. This age is consistent with those of Linglong-style (vein type) gold mineralization, also from the north-western Jiaodong Peninsula, at between 126 and 120 Ma. Therefore, our work indicates that both styles of gold deposits in the Jiaodong Peninsula were formed during the same mineralization event.

  20. 21 CFR 876.1500 - Endoscope and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... within this generic type of device include cleaning accessories for endoscopes, photographic accessories for endoscopes, nonpowered anoscopes, binolcular attachments for endoscopes, pocket battery boxes... endoscope, smoke removal tube, rechargeable battery box, pocket battery box, bite block for endoscope, and...

  1. 21 CFR 876.1500 - Endoscope and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... within this generic type of device include cleaning accessories for endoscopes, photographic accessories for endoscopes, nonpowered anoscopes, binolcular attachments for endoscopes, pocket battery boxes... endoscope, smoke removal tube, rechargeable battery box, pocket battery box, bite block for endoscope, and...

  2. 21 CFR 876.1500 - Endoscope and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... within this generic type of device include cleaning accessories for endoscopes, photographic accessories for endoscopes, nonpowered anoscopes, binolcular attachments for endoscopes, pocket battery boxes... endoscope, smoke removal tube, rechargeable battery box, pocket battery box, bite block for endoscope, and...

  3. 21 CFR 876.1500 - Endoscope and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... within this generic type of device include cleaning accessories for endoscopes, photographic accessories for endoscopes, nonpowered anoscopes, binolcular attachments for endoscopes, pocket battery boxes... endoscope, smoke removal tube, rechargeable battery box, pocket battery box, bite block for endoscope, and...

  4. 21 CFR 876.1500 - Endoscope and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... within this generic type of device include cleaning accessories for endoscopes, photographic accessories for endoscopes, nonpowered anoscopes, binolcular attachments for endoscopes, pocket battery boxes... endoscope, smoke removal tube, rechargeable battery box, pocket battery box, bite block for endoscope, and...

  5. 21 CFR 872.4920 - Dental electrosurgical unit and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Dental electrosurgical unit and accessories. 872... SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4920 Dental electrosurgical unit and accessories. (a) Identification. A dental electrosurgical unit and accessories is an AC-powered...

  6. 21 CFR 872.4920 - Dental electrosurgical unit and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Dental electrosurgical unit and accessories. 872... SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4920 Dental electrosurgical unit and accessories. (a) Identification. A dental electrosurgical unit and accessories is an AC-powered...

  7. 21 CFR 872.4920 - Dental electrosurgical unit and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Dental electrosurgical unit and accessories. 872... SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4920 Dental electrosurgical unit and accessories. (a) Identification. A dental electrosurgical unit and accessories is an AC-powered...

  8. 21 CFR 872.4920 - Dental electrosurgical unit and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Dental electrosurgical unit and accessories. 872... SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4920 Dental electrosurgical unit and accessories. (a) Identification. A dental electrosurgical unit and accessories is an AC-powered...

  9. 21 CFR 872.4920 - Dental electrosurgical unit and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Dental electrosurgical unit and accessories. 872... SERVICES (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4920 Dental electrosurgical unit and accessories. (a) Identification. A dental electrosurgical unit and accessories is an AC-powered...

  10. The Triassic reworking of the Yunkai massif (South China): EMP monazite and U-Pb zircon geochronologic evidence

    NASA Astrophysics Data System (ADS)

    Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Sano, Yuji; Zhou, Han-Wen; Xiang, Hua; Takahata, Naoto

    2017-01-01

    Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex (amphibolite facies, NE-striking) and the Yunkai Group (greenschist facies, NW-striking) of this massif and adjacent undeformed granites. Some EMP monazite ages are consistent with the NanoSIMS results. Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at 244-236 Ma and 236-233 Ma, respectively. They also yield ages of 233-230 Ma for core domain gneissic granites and 232-229 Ma for undefomed granites. Combining U-Pb zircon ages of the same group, 245 Ma and 230 Ma are suggested to constrain the time of two phases of deformation. Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic (1.0-0.9 Ga) and Early Paleozoic (444-431 Ma). Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited. With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province (E-LIP).

  11. Zircon U-Pb geochronology and Sr-Nd-Pb-Hf isotopic constraints on the timing and origin of Mesozoic granitoids hosting the Mo deposits in northern Xilamulun district, NE China

    NASA Astrophysics Data System (ADS)

    Shu, Qihai; Lai, Yong; Zhou, Yitao; Xu, Jiajia; Wu, Huaying

    2015-12-01

    Located in the east section of the Central Asian orogen in northeastern China, the Xilamulun district comprises several newly discovered molybdenum deposits, primarily of porphyry type and Mesozoic ages. This district is divided by the Xilamulun fault into the southern and the northern parts. In this paper, we present new zircon U-Pb dating, trace elements and Hf isotope, and/or whole rock Sr-Nd-Pb isotopic results for the host granitoids from three Mo deposits (Yangchang, Haisugou and Shabutai) in northern Xilamulun. Our aim is to constrain the age and petrogenesis of these intrusions and their implications for Mo mineralization. Zircon U-Pb LA-ICP-MS dating shows that the monzogranites from the Shabutai and Yangchang deposits formed at 138.4 ± 1.5 and 137.4 ± 2.1 Ma, respectively, which is identical to the molybdenite Re-Os ages and coeval well with the other Mo deposits in this region, thereby indicating an Early Cretaceous magmatism and Mo mineralization event. Zircon Ce/Nd ratios from the mineralized intrusions are significantly higher than the barren granites, implying that the mineralization-related magmas are characterized by higher oxygen fugacity. These mineralized intrusions share similar zircon in-situ Hf and whole rock Sr-Nd isotopic compositions, with slightly negative to positive εHf(t) ranging from - 0.8 to + 10.0, restricted εNd(t) values from - 3.7 to + 1.6 but a little variable (87Sr/86Sr)i ratios between 0.7021 and 0.7074, indicative of formation from primary magmas generated from a dominantly juvenile lower crust source derived from depleted mantle, despite diverse consequent processes (e.g., magma mixing, fractional crystallization and crustal contamination) during their evolution. The Pb isotopes (whole rock) also show a narrow range of initial compositions, with (206Pb/204Pb)i = 18.03-18.88, (207Pb/204Pb)i = 15.48-15.58 and (208Pb/204Pb)i = 37.72-38.28, in agreement with Sr-Nd-Hf isotopes reflecting the dominance of a mantle component

  12. 21 CFR 872.4120 - Bone cutting instrument and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Bone cutting instrument and accessories. 872.4120... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4120 Bone cutting instrument and accessories. (a) Identification. A bone cutting instrument and accessories is a metal device intended for use...

  13. 21 CFR 872.4120 - Bone cutting instrument and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Bone cutting instrument and accessories. 872.4120... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4120 Bone cutting instrument and accessories. (a) Identification. A bone cutting instrument and accessories is a metal device intended for use...

  14. 21 CFR 872.4120 - Bone cutting instrument and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Bone cutting instrument and accessories. 872.4120... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4120 Bone cutting instrument and accessories. (a) Identification. A bone cutting instrument and accessories is a metal device intended for use...

  15. 21 CFR 872.4120 - Bone cutting instrument and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Bone cutting instrument and accessories. 872.4120... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4120 Bone cutting instrument and accessories. (a) Identification. A bone cutting instrument and accessories is a metal device intended for use...

  16. 21 CFR 872.4120 - Bone cutting instrument and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Bone cutting instrument and accessories. 872.4120... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Surgical Devices § 872.4120 Bone cutting instrument and accessories. (a) Identification. A bone cutting instrument and accessories is a metal device intended for use...

  17. 21 CFR 872.6640 - Dental operative unit and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Dental operative unit and accessories. 872.6640... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6640 Dental operative unit and accessories. (a) Identification. A dental operative unit and accessories is an AC-powered device that is...

  18. 21 CFR 872.6640 - Dental operative unit and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Dental operative unit and accessories. 872.6640... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6640 Dental operative unit and accessories. (a) Identification. A dental operative unit and accessories is an AC-powered device that is...

  19. 21 CFR 872.6640 - Dental operative unit and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Dental operative unit and accessories. 872.6640... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6640 Dental operative unit and accessories. (a) Identification. A dental operative unit and accessories is an AC-powered device that is...

  20. 21 CFR 872.6640 - Dental operative unit and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Dental operative unit and accessories. 872.6640... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6640 Dental operative unit and accessories. (a) Identification. A dental operative unit and accessories is an AC-powered device that is...

  1. 21 CFR 872.6640 - Dental operative unit and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Dental operative unit and accessories. 872.6640... (CONTINUED) MEDICAL DEVICES DENTAL DEVICES Miscellaneous Devices § 872.6640 Dental operative unit and accessories. (a) Identification. A dental operative unit and accessories is an AC-powered device that is...

  2. Determination of uranium in zircon

    USGS Publications Warehouse

    Cuttitta, F.; Daniels, G.J.

    1959-01-01

    A routine fluorimetric procedure is described for the determination of trace amounts of uranium in zircon. It employs the direct extraction of uranyl nitrate with ethyl acetate using phosphate as a retainer for zirconium. Submicrogram amounts or uranium are separated in the presence of 100,000 times the amount of zirconium. The modified procedure has been worked out using synthetic mixtures of known composition and zircon. Results of analyses have an accuracy of 97-98% of the contained uranium and a standard deviation of less than 2.5%. ?? 1959.

  3. Applications of biotite inclusion composition to zircon provenance determination

    NASA Astrophysics Data System (ADS)

    Bell, Elizabeth A.; Boehnke, Patrick; Mark Harrison, T.

    2017-09-01

    Detrital zircons are the only confirmed surviving remnants of >4.03 Ga crust while younger detrital zircons provide a parallel record of more recent crustal evolution to that preserved in crystalline rocks. Zircons often preserve inclusions that may provide clues as to the origins of out-of-context grains in the sedimentary record. Previous studies have established that inclusions of biotite in magmatic zircon are compositionally well-matched to biotite in the source rock matrix, although a direct application to ancient detrital zircons has not been made. A number of studies have documented variations in the Fe, Mg, and Al contents of magmatic biotite from different source rocks and tectonic settings, suggesting that biotite inclusions may indeed serve as provenance indicators for detrital zircons. Consistent with earlier studies, we find that the FeO*/MgO ratio of magmatic biotite from continental arcs, collisional, and within-plate settings varies with relative oxidation state as well as whole-rock FeO*/MgO, while its Al2O3/(FeO* + MgO) varies with whole-rock A/CNK (molar Al/(2 ṡ Ca + Na + K)). Biotite from oxidized metaluminous and reduced S-type granitoids can be readily distinguished from each other using FeO*/MgO and Al2O3/(FeO* + MgO), while biotite from reduced I-type and oxidized peraluminous granites may in some cases be more ambiguous. Biotite from peralkaline and reduced A-type granites are also distinguishable from all other categories by Al2O3/(FeO* + MgO) and FeO*/MgO, respectively. Biotite inclusions in Hadean zircons from Jack Hills, Western Australia indicate a mixture of metaluminous and reduced S-type host rocks, while inclusions in 3.6-3.8 Ga detrital zircons from the Nuvvuagittuq Supracrustal Belt indicate more oxidized peraluminous magmas. These results highlight the diversity of felsic materials on the early Earth and suggest that biotite inclusions are applicable to zircon provenance throughout the sedimentary record.

  4. Response of zircon to melting and metamorphism in deep arc crust, Fiordland (New Zealand): implications for zircon inheritance in cordilleran granites

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Shrema; Kemp, A. I. S.; Collins, W. J.

    2018-04-01

    The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths

  5. 21 CFR 878.3925 - Plastic surgery kit and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Plastic surgery kit and accessories. 878.3925... (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Prosthetic Devices § 878.3925 Plastic surgery kit and accessories. (a) Identification. A plastic surgery kit and accessories is a device intended to...

  6. 21 CFR 878.3925 - Plastic surgery kit and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Plastic surgery kit and accessories. 878.3925... (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Prosthetic Devices § 878.3925 Plastic surgery kit and accessories. (a) Identification. A plastic surgery kit and accessories is a device intended to...

  7. 21 CFR 878.3925 - Plastic surgery kit and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Plastic surgery kit and accessories. 878.3925... (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Prosthetic Devices § 878.3925 Plastic surgery kit and accessories. (a) Identification. A plastic surgery kit and accessories is a device intended to...

  8. 21 CFR 878.3925 - Plastic surgery kit and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Plastic surgery kit and accessories. 878.3925... (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Prosthetic Devices § 878.3925 Plastic surgery kit and accessories. (a) Identification. A plastic surgery kit and accessories is a device intended to...

  9. 21 CFR 878.3925 - Plastic surgery kit and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Plastic surgery kit and accessories. 878.3925... (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Prosthetic Devices § 878.3925 Plastic surgery kit and accessories. (a) Identification. A plastic surgery kit and accessories is a device intended to...

  10. Assessment of Alternative [U] and [Th] Zircon Standards for SIMS

    NASA Astrophysics Data System (ADS)

    Monteleone, B. D.; van Soest, M. C.; Hodges, K.; Moore, G. M.; Boyce, J. W.; Hervig, R. L.

    2009-12-01

    The quality of in situ (U-Th)/He zircon dates is dependent upon the accuracy and precision of spatially distributed [U] and [Th] measurements on often complexly zoned zircon crystals. Natural zircon standards for SIMS traditionally have been used to obtain precise U-Pb ages rather than precise U and Th concentration. [U] and [Th] distributions within even the most homogeneous U-Pb age standards are not sufficient to make good microbeam standards (i.e., yield good precision: 2σ < 5%) for (U-Th)/He dates. In the absence of sufficiently homogeneous natural zircon crystals, we evaluate the use of the NIST 610 glass standard and a synthetic polycrystalline solid “zircon synrock” made by powdering and pressing natural zircon crystals at 2 GPa and 1100°C within a 13 mm piston cylinder for 24 hours. SIMS energy spectra and multiple spot analyses help assess the matrix-dependence of secondary ion emission and [U] and [Th] homogeneity of these materials. Although spot analyses on NIST 610 glass yielded spatially consistent ratios of 238U/30Si and 232Th/30Si (2σ = 2%, n = 14), comparison of energy spectra collected on glass and zircon reveal significant differences in U, UO, Th, and ThO ion intensities over the range of initial kinetic energies commonly used for trace element analyses. Computing [U] and [Th] in zircon using NIST glass yields concentrations that vary by more than 10% for [U] and [Th], depending on the initial kinetic energy and ion mass (elemental, oxide, or sum of elemental and oxide) used for the analysis. The observed effect of chemistry on secondary ion energy spectra suggests that NIST glass cannot be used as a standard for trace [U] and [Th] in zircon without a correction factor (presently unknown). Energy spectra of the zircon synrock are similar to those of natural zircon, suggesting matrix compatibility and therefore potential for accurate standardization. Spot analyses on the zircon powder pellets, however, show that adequate homogeneity of [U

  11. [Excision of accessory navicular with reconstruction of posterior tibial tendon insertion on navicular for treatment of flatfoot related with accessory navicular].

    PubMed

    Cao, Honghui; Tang, Kanglai; Deng, Yinshuan; Tan, Xiaokang; Zhou, Binghua; Tao, Xu; Chen, Lei; Chen, Qianbo

    2012-06-01

    To analyze the excision of accessory navicular with reconstruction of posterior tibial tendon insertion on navicular for the treatment of flatfoot related with accessory navicular and to evaluate its effectiveness. Between May 2006 and June 2011, 33 patients (40 feet) with flatfoot related with accessory navicular were treated. There were 14 males (17 feet) and 19 females (23 feet) with an average age of 30.1 years (range, 16-56 years). All patients had bilateral accessory navicular; 26 had unilateral flatfoot and 7 had bilateral flatfeet. The disease duration ranged from 7 months to 9 years (median, 24 months). The American Orthopaedic Foot and Ankle Society (AOFAS) ankle-midfoot score was 47.9 +/- 7.3. The X-ray films showed type II accessory navicular, the arch height loss, and heel valgus in all patients. All of them received excision of accessory navicular and reconstruction of posterior tibial tendon insertion on navicular with anchor. All patients got primary wound healing without any complication. Thirty patients (36 feet) were followed up 6-54 months with an average of 23 months. All patients achieved complete pain relief at 6 months after surgery and had good appearance of the feet. The AOFAS ankle-midfoot score was 90.4 +/- 2.0 at last follow-up, showing significant difference when compared with preoperative score (t=29.73, P=0.00). X-ray films showed that no screw loosening or breakage was observed. There were significant differences in the arch height, calcaneus inclination angle, talocalcaneal angle, and talar-first metatarsal angle between pre-operation and last follow-up (P < 0.01). The excision of accessory navicular with reconstruction of posterior tibial tendon insertion on navicular is a good choice for the treatment of flatfoot related with accessory navicular, with correction of deformity, excellent effectiveness, and less complications.

  12. Zircon solubility and of Zr species in subduction zone fluids

    NASA Astrophysics Data System (ADS)

    Wilke, M.; Schmidt, C.; Rickers, K.; Pascarelli, S.; Manning, C. E.; Stechern, A.

    2009-12-01

    The geochemical signature of igneous rocks at convergent plate margins is thought to result from complex melt formation processes involving aqueous solutions derived from dehydration of the subducted slab. In these processes, the depletion of high-field-strength elements (HFSE) may be controlled by the presence of accessory phases such as zircon and rutile, which can strongly fractionate these elements; however, the stability and solubility of these phases depends strongly on the fluid composition, including concentration and stoichiometry of Na-Al silicate components. Here we present new data on the influence of the fluid composition on zircon solubility as well as data on the Zr complexation in these fluids at P&T. Experiments were conducted using a modified hydrothermal diamond-anvil cell (HDAC). Zr contents at P&T were determined using SR-µXRF spectra. Zr K-edge X-ray Absorption Fine Structure (XAFS) spectra were acquired to investigate the Zr complexation in-situ at P&T. A grain of synthetic crystalline zircon was equilibrated with an aqueous fluid containing Na2Si2O5 or Na2Si2O5 + Al2O3 components. XAFS and SR-µXRF spectra were taken at the dispersive beamline ID24 of the ESRF, Grenoble, France. Some additional SR-µXRF spectra were taken at HASYLAB, Hamburg, beamline L. The observed Zr concentrations in fluids containing 7-33 wt% Na2Si2O5 and variable Al contents were between 75 and 720 ppm at 500 to 750°C and ~300 MPa to ~700 MPa. These values match expected solubilities calculated from linear interpolation of the maximum solubility in pure H2O (from the detection limit) and the solubility in the most alkaline high-silica melts reported by Ellison and Hess (1986, CMP, 94, 343). The high Zr solubility in sodium silicate-bearing solutions signifies that aqueous fluids with alkali silicates offer an efficient mechanism for HFSE transport. This can be explained by complexation of HFSE with Si, Na, and perhaps also Al, via formation of polymerized solutes

  13. 19 CFR 10.537 - Accessories, spare parts, or tools.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... parts, or tools will be taken into account as originating or non-originating materials, as the case may... 19 Customs Duties 1 2010-04-01 2010-04-01 false Accessories, spare parts, or tools. 10.537 Section... Free Trade Agreement Rules of Origin § 10.537 Accessories, spare parts, or tools. Accessories, spare...

  14. URANIUM IN ROCK MINERALS OF THE INTRUSION OF KYZL-OMPUL MOUNTAINS (NORTH KIRGISIA) (in Russian)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Leonova, L.L.; Pogiblova, L.S.

    1961-01-01

    The uranium distribution in rock minerals (syenites, granosyenites, and alaskite granites) of the Kyzyl-Ompul raassif is studied. Alaskite granites are characterized by the granite type of uranium distribution in minerals, about 50 percent of this element being connected with rockforming and about 50 percent with accessory uranium minerals. ln syenites uranium (about 70 percent) is bound to rockforming minerals. The same minerals from syenites and granites strongly differ by their uranium content and are constant in the ranges of each of those rock types. Granosyenites have aa intermediate (between syenites and granites) type of uranium distribution in minerals. (auth)

  15. Accessory Mineral Depth-Profiling Applied to the Corsican Lower Crust: A Continuous Thermal History of Mesozoic Continental Rifting

    NASA Astrophysics Data System (ADS)

    Seymour, N. M.; Stockli, D. F.; Beltrando, M.; Smye, A.

    2015-12-01

    Despite advances in understanding the structural development of hyperextended magma-poor rift margins, the temporal and thermal evolution of lithospheric hyperextension during rifting remains only poorly understood. In contrast to classic pure-shear models, multi-stage rift models that include depth-dependent thinning predict significant lower-crustal reheating during the necking phase due to buoyant rise of the asthenosphere. The Santa Lucia nappe of NE Corsica is an ideal laboratory to test for lower-crustal reheating as it preserves Permian lower crust exhumed from granulitic conditions during Mesozoic Tethyan rifting. This study presents the first use of apatite U-Pb depth-profile thermochronology in conjunction with novel rutile U-Pb and zircon U-Pb thermo- and geochronology to reconstruct a continuous t-T path to constrain the syn-rift thermal evolution of this exposed lower-crustal section. LASS-ICP-MS depth-profile analyses of zircon reveal thin (<10 μm) ~210-180 Ma overgrowths on 300-270 Ma cores in lower-crustal lithologies, indicative of renewed thermal activity during Mesozoic rifting. Cooling due to rapid rift margin exhumation is recorded by the topology of rutile and apatite depth profiles caused by thermally-activated volume diffusion at T >400°C. Lower-crustal rutile reveal a rounded progression from core plateaus at ~170 Ma to 150-145 Ma at the outer 8-10 μm of grains while middle-crustal apatite records 170 Ma cores grading to 140-135 Ma rims. Inverse modeling of rutile profiles suggests the lower crust cooled from 700°C at 200 Ma to 425°C at 140 Ma. Middle-crustal apatite yield a two-stage history, with rapid cooling from 500°C at 200 Ma to 420°C at ~180 Ma followed by slow cooling to 400°C by 160 Ma. Combined with zircon overgrowth ages, these data indicate the Santa Lucia nappe underwent a thermal pulse in the late Triassic-early Jurassic associated with depth-dependent thinning and hyperextension of the Corsican margin.

  16. Zircons as a Probe of Early Luanr History

    NASA Astrophysics Data System (ADS)

    Crow, C. A.; McKeegan, K. D.; Gilmour, J. D.; Crowther, S. A.; Talor, D. J.

    2013-09-01

    Zircons are ideal for investigating the early lunar bombardment because we can measure both U-Pb crystallization ages and fissiongenic Xe degassing ages for the same crystal. We report U-Pb, Pb-Pb and U-Xe ages for three lunar zircons.

  17. 21 CFR 886.1930 - Tonometer and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...) MEDICAL DEVICES OPHTHALMIC DEVICES Diagnostic Devices § 886.1930 Tonometer and accessories. (a) Identification. A tonometer and accessories is a manual device intended to measure intraocular pressure by applying a known force on the globe of the eye and measuring the amount of indentation produced (Schiotz...

  18. 21 CFR 864.3600 - Microscopes and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Microscopes and accessories. 864.3600 Section 864.3600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES HEMATOLOGY AND PATHOLOGY DEVICES Pathology Instrumentation and Accessories § 864.3600...

  19. 21 CFR 864.3600 - Microscopes and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Microscopes and accessories. 864.3600 Section 864.3600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES HEMATOLOGY AND PATHOLOGY DEVICES Pathology Instrumentation and Accessories § 864.3600...

  20. 21 CFR 864.3600 - Microscopes and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Microscopes and accessories. 864.3600 Section 864.3600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES HEMATOLOGY AND PATHOLOGY DEVICES Pathology Instrumentation and Accessories § 864.3600...

  1. 21 CFR 864.3600 - Microscopes and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Microscopes and accessories. 864.3600 Section 864.3600 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES HEMATOLOGY AND PATHOLOGY DEVICES Pathology Instrumentation and Accessories § 864.3600...

  2. Archean Arctic continental crust fingerprints revealing by zircons from Alpha Ridge bottom rocks

    NASA Astrophysics Data System (ADS)

    Sergeev, Sergey; Petrov, Oleg; Morozov, Andrey; Shevchenko, Sergey; Presnyakov, Sergey; Antonov, Anton; Belyatsky, Boris

    2015-04-01

    Whereas thick Cenozoic sedimentary cover overlapping bedrock of the Arctic Ocean, some tectonic windows were sampled by scientific submarine manipulator, as well as by grabbing, dredging and drilling during «Arctic-2012» Russian High-Arctic expedition (21 thousands samples in total, from 400-km profile along Alpha-Mendeleev Ridges). Among others, on the western slope of Alpha Ridge one 10x10 cm fragment without any tracks of glacial transportation of fine-layered migmatitic-gneiss with prominent quartz veinlets was studied. Its mineral (47.5 vol.% plagioclase + 29.6% quartz + 16.6% biotite + 6.1% orthoclase) and chemical composition (SiO2:68.2, Al2O3:14.9, Fe2O3:4.44, TiO2:0.54, MgO:2.03, CaO:3.13, Na2O:3.23, K2O:2.16%) corresponds to trachydacite vulcanite, deformed and metamorphozed under amphibolite facies. Most zircon grains (>80%) from this sample has an concordant U-Pb age 3450 Ma with Th/U 0.8-1.4 and U content of 100-400 ppm, epsilon Hf from -4 up to 0, and ca 20% - ca 3.3 Ga with Th/U 0.7-1.4 and 90-190 ppm U, epsilon Hf -6.5 to -4.5, while only 2% of the grains show Proterozoic age of ca 1.9 Ga (Th/U: 0.02-0.07, U~500 ppm, epsilon Hf about 0). No younger zircons were revealed at all. We suppose that magmatic zircon crystallized as early as 3450 Ma ago during acid volcanism, the second phase zircon crystallization from partial melt (or by volcanics remelting) under amphibolite facies metamorphism was at 3.3 Ga ago with formation of migmatitie gneisses. Last zircon formation from crustal fluids under low-grade metamorphic conditions was 1.9 Ga ago. There are two principal possibilities for the provenance of this metavolcanic rock. The first one - this is ice-rafted debris deposited by melted glacial iceberg. However, presently there are no temporal and compositional analogues of such rocks in basement geology of peri-oceanic regions, including Archean Itsaq Gneiss Complex, Lewisian Complex and Baltic Shield but these regions are far from the places of

  3. Electronic Position Sensor for Power Operated Accessory

    DOEpatents

    Haag, Ronald H.; Chia, Michael I.

    2005-05-31

    An electronic position sensor for use with a power operated vehicle accessory, such as a power liftgate. The position sensor includes an elongated resistive circuit that is mounted such that it is stationary and extends along the path of a track portion of the power operated accessory. The position sensor further includes a contact nub mounted to a link member that moves within the track portion such that the contact nub is slidingly biased against the elongated circuit. As the link member moves under the force of a motor-driven output gear, the contact nub slides along the surface of the resistive circuit, thereby affecting the overall resistance of the circuit. The position sensor uses the overall resistance to provide an electronic position signal to an ECU, wherein the signal is indicative of the absolute position of the power operated accessory. Accordingly, the electronic position sensor is capable of providing an electronic signal that enables the ECU to track the absolute position of the power operated accessory.

  4. Detrital Zircons Split Sibumasu in East Gondwana

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Chung, S. L.

    2017-12-01

    It is widely accepted that Sibumasu developed as a united terrane and originated from NW Australian margin in East Gondwana. Here we report new detrital zircon U-Pb-Hf isotopic data from Sumatra that, in combination with literature data, challenge and refute the above long-held view. In particular, the East and West Sumatra terranes share nearly identical Precambrian to Paleozoic detrital zircon age distributions and Hf isotopes, indicating a common provenance/origin for them. The Sumatra detrital zircons exhibit a prominent population of ca. 1170-1070 Ma, indistinguishable from those of the Lhasa and West Burma terranes, with detritus most probably sourcing from western Australia. By contrast, Sibuma (Sibumasu excluding Sumatra) detrital zircons display a prevailing population of ca. 980-935 Ma, strongly resembling those of the western Qiangtang terrane, with detrital materials most likely derived from Greater India and Himalayas. Such markedly distinct detrital zircon age profiles between Sumatra and Sibuma require disparate sources/origin for them, provoking disintegration of the widely-adopted, but outdated, term Sibumasu and thus inviting a new configuration of East Gondwana in the early Paleozoic, with Sumatra and West Burma lying outboard the Lhasa terrane in the NW Australian margin and Sibuma situated in the northern Greater Indian margin. More future investigations are needed to establish the precise rifting and drifting histories of Sumatra and Sibuma, as two separated terranes, during the breakup of Gondwana.

  5. The 3.5 Ga granulites of the Bug polymetamorphic complex, Ukraine (U-Pb SHRIMP-II zircon data)

    NASA Astrophysics Data System (ADS)

    Lobach-Zhuchenko, Svetlana; Kaulina, Tatiana; Baltybaev, Shauket; Yurchenko, Anastasija; Balagansky, Victor; Skublov, Sergei; Sukach, Vitaliji

    2014-05-01

    The Bug polymetamorphic complex composes the south-west of the Ukrainian Shield. It experienced multistage deformation and metamorphism of 3.6 to 1.95 Ga. The age of protolith of the gneiss enderbite is up to 3.7-3.6 Ga (Claesson et al., 2006: Lobach-Zhuchenko et al., 2010, 2013; Bibikova et al, 2013). The 3.5 old granulitic zircon (sample UR132) was found in a light grey massive medium grained with weak foliation granulite from the Odessa quarry located at the right riverside of the Bug (N 48° 13' 55.2''; E 29° 59' 75''). The rock is mafic in composition (SiO2 = 51.50 wt%, #mg=0.43, (La/Yb)n =7.5), and shows enrichment in Sr (333 ppm), Zr (244 ppm), and Nb (12 ppm) compared to MORB. This contains antiperthitic plagioclase (An30-35), hypersthene (En0.46 Fs0.53 Wo0.01 ), diopside (En0.33 Fs0.20Wo0.47), quartz, ilmenite, magnetite, apatite, and zircon. Three types of zircon are recognized. (1) Large (~300 μm) isometric and oval grains displaying bright colour and sector zoning in CL. Some crystals have fir-tree texture. Isometric shape together with fir-tree zoning is typical for zircons growing under conditions of granulite- facies metamorphism (Hoskin and Schaltegger, 2003). These zircons are low in U and Th, have high Th/U ratios (0.61-1.1), and display decreasing of element contents from the centre to margin (ppm): U - 68 to 44, Th - 58 to 19, total REE - 723 to 406, Y - 1049 to 553, and Li - 1.23 to 0.91 at the constant (Lu/La)n ratios (4200-4600). Zircon's crystallization temperature calculated from the Ti content is 705 °C and is consistent with those calculated on the base of the mineral composition. (2) Small sized (60-100 μm) zircons. Most of these occur within plagioclase and truncate antiperthite lamellae. They show euhedral zoned cores and bright rims in CL. (3) Zircons principally distinguished from those of groups 1 and 2. These are dark in CL, some grains are severely structurally damaged and contain numerous inclusions (Qzt, Pl, Kfsp, rare Opx

  6. 21 CFR 878.1800 - Speculum and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Speculum and accessories. 878.1800 Section 878.1800 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Diagnostic Devices § 878.1800 Speculum and accessories...

  7. 21 CFR 878.1800 - Speculum and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Speculum and accessories. 878.1800 Section 878.1800 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Diagnostic Devices § 878.1800 Speculum and accessories...

  8. 21 CFR 878.1800 - Speculum and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Speculum and accessories. 878.1800 Section 878.1800 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Diagnostic Devices § 878.1800 Speculum and accessories...

  9. 21 CFR 878.1800 - Speculum and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Speculum and accessories. 878.1800 Section 878.1800 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Diagnostic Devices § 878.1800 Speculum and accessories...

  10. 21 CFR 878.1800 - Speculum and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Speculum and accessories. 878.1800 Section 878.1800 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Diagnostic Devices § 878.1800 Speculum and accessories...

  11. Petrogenesis of the Baishan granite stock, Eastern Tianshan, NW China: Geodynamic setting and implications for potential mineralization

    NASA Astrophysics Data System (ADS)

    Cao, MingJian; Qin, KeZhang; Li, GuangMing; Evans, Noreen J.; McInnes, Brent I. A.; Lu, WeiWei; Deng, Gang

    2017-11-01

    Located in a region rich in Cu-Ni and Mo mineralization, the Baishan granitic stock is barren for reasons that remain enigmatic. Whole rock elemental and Sr-Nd isotope analysis, major element analysis of a number of minerals, and zircon trace element, U-Pb and Hf isotope analysis were undertaken in order to reveal the petrogenesis of the granites. All granites show typical I-type characteristics including metaluminous to slightly peraluminous, calc-alkaline signatures with a strong depletion of Nb, Ta, Ti and P, enrichment of light rare earth elements and large ion lithophile elements (e.g., Cs, Rb, Th, U, K). In addition, a strong depletion in Ti and P, highly fractionated light rare earth element patterns and less fractionated heavy rare earth element patterns, and negative correlations between SiO2 and TiO2, Al2O3, MgO, FeOT, P2O5, Zr and Hf suggest significant fractional crystallization of amphibole, apatite, zircon and Ti-bearing minerals. Whole rock Sr-Nd and zircon Hf isotopic compositions show wide variations with (87Sr/86Sr)i values of 0.70358 to 0.70505, εNd (t) of 3.8 to 7.2, and εHf (t) of 2.4 to 12.2 indicating derivation from partial melting of juvenile lower crust with obvious addition of ancient crust. Zircon U-Pb ages indicate a formation age of 292 Ma, significantly older than the ore-forming granite porphyry and slightly older than the regional mafic-ultramafic, A-type and diabase magmatism of Eastern Tianshan. The granite stocks were likely derived during heating of ascending asthenospheric mantle above a mantle plume in the Early Permian. Mineral chemistry, saturation thermometry, mineral species and whole rock Fe2O3/FeO ratios indicate a crystallization temperature of > 980 to 665 °C, pressure of 1.6 kbar and oxygen fugacity of ≤ NNO for the granite stock. Comparing the geochemistry, magma source and crystallization environment for the Early Permian barren granite and Late Triassic ore-related granite porphyry, the low ratios of Sr/Y and

  12. The mineralogical and chronological evidences of subducted continent material in deep mantle: diamond, zircon and rutile separated from the Horoman peridotite of Japan

    NASA Astrophysics Data System (ADS)

    Li, Y.; Yang, J.; Nida, K.; Yamamoto, S.; Lin, Y.; Li, Q.; Tian, M.; Kon, Y.; Komiya, T.; Maruyama, S.

    2017-12-01

    The Horoman peridotite complex is an Alpine-type orogenic lherzolite massif of upper-mantle in the Hidaka metamorphic belt, Hokkaido, Japan. The peridotite complex is composed of dunite, harzburgite, spinel lherzolite and plagioclase lherzolite, exhibits a conspicuous layered structure, which is a product of a Cretaceous to early Paleogene arc-trench system formed by westward subduction of an oceanic plate between the paleo-Eurasian and paleo-North American Plates. Various combinations of diamond, corundum, moissanite, zircon, monazite, rutile, and kyanite have been separated from spinel harzburgite (700 kg) and lherzolite (500 kg), respectively. The carbon isotopes analyses of diamond grains by Nano-SIMS yielded significant light carbon isotopes feature as δ13 CPDB values ranging from -29.2 ‰ to -17.2 ‰, with an average of -22.8±0.32 ‰. Zircon grains occur as sub-angular to round in morphological characteristics, similar to zircons of crustal sedimentary rocks. Many zircons contain small inclusions, comprise of quartz, apatite, rutile and muscovite. The U-Pb age of zircon grains analyzed using LA-ICP-MS and SIMS gave a wide age range, from the Jurassic to Archean (ca 159 - 3131 Ma). In the zircon age histogram, four age groups were identified; the age peaks are 2385 Ma, 1890 Ma, 1618 Ma and 1212 Ma, respectively. On the other hand, U-Pb ages of rutile grains analyzed using SIMS gave a peak of 370 Ma in age histogram. The mineralogical and chronological evidences of numerous crustal minerals in peridotite of Horoman suggest that the ancient continent material was subducted in deep mantle and recycled through the upper mantle by multicycle subduction processes.

  13. Genesis of the Permian Kemozibayi sulfide-bearing mafic-ultramafic intrusion in Altay, NW China: Evidence from zircon geochronology, Hf and O isotopes and mineral chemistry

    NASA Astrophysics Data System (ADS)

    Tang, Dongmei; Qin, Kezhang; Xue, Shengchao; Mao, Yajing; Evans, Noreen J.; Niu, Yanjie; Chen, Junlu

    2017-11-01

    The recently discovered Kemozibayi mafic-ultramafic intrusion and its associated magmatic Cu-Ni sulfide deposits are located at the southern margin of the Chinese Altai Mountain, Central Asian Orogenic Belt in north Xinjiang, NW China. The intrusion is composed of olivine websterite, norite, gabbro and diorite. Disseminated and net-textured Ni-Cu sulfide ores are hosted in the center of the gabbro. In this work, new zircon U-Pb ages, Hf-O isotopic and sulfide S isotopic data, and whole rock and mineral chemical analyses are combined in order to elucidate the characteristics of the mantle source, nature of subduction processes, degree of crustal contamination, geodynamic setting of bimodal magmatism in the region, and the metallogenic potential of economic Cu-Ni sulfide deposit at depth. SIMS zircon U-Pb dating of the gabbro yields Permian ages (278.3 ± 1.9 Ma), coeval with the Kalatongke Cu-Ni deposit and with Cu-Ni deposits in the Eastern Tianshan and Beishan areas. Several lines of evidence (positive εHf(t) from + 7.1 to + 13.3, Al2O3, TiO2 and SiO2 contents in clinopyroxene from olivine websterite, high whole rock TiO2 contents) suggest that the primary magma of the Kemozibayi intrusion was a calc-alkaline basaltic magma derived from depleted mantle, and that the degree of partial melting in the magma source was high. The evolution of the Kemozibayi mafic-ultramafic complex was strongly controlled by fractional crystallization and the crystallization sequence was olivine websterite, norite, and then gabbro. This is evidenced by whole rock Fe2O3 contents that are positively correlated with MgO and negatively correlated with Al2O3, CaO and Na2O, similar LREE enrichment and negative Nb, Ta, Hf anomalies in chondrite and primitive mantle-normalized patterns, and a decrease in total REE and trace elements contents and magnetite content from gabbro through to norite and olivine websterite. Varied and low εHf(t) (+ 7.1 to + 13.3) and high δ18O values (+ 6.4‰ to

  14. Zircon-quartz-calcite segregations in carbonate-alkaline metasomatic rocks of the western Baikal region and their petrogenetic implications

    NASA Astrophysics Data System (ADS)

    Savelyeva, V. B.; Bazarova, E. P.; Sharygin, V. V.; Karmanov, N. S.

    2015-12-01

    Fine-grained segregations up to 5 mm in size composed of graphic intergrowths of zircon, quartz, calcite and containing up to 0.8 wt % SrO have been found in albite-riebeckite and dolomite-biotite metasomatic rocks formed after alaskite granite. They contain magnetite, titanomagnetite (25.4 wt % TiO2), cerite-(Ce,Nd), rutile (up to 1.2 wt % Nb2O5), as well as rare micrograins of monazite-(Ce), bastnaesite-(Ce), and barite (up to 5.7 wt % SrO). The fine-grained structure of mineral aggregates suggests a metacolloidal nature. It is assumed that the zircon-quartz-calcite assemblage was formed due to exchange decomposition reaction between the salt phase of hydrothermal solution with predominant Na2CO3, elevated Zr and, to a lesser extent, Fe, Ti, LREE, Nb contents and dissolved calcium and silica compounds of a Na2SiO3 type.

  15. Silicic melt evolution in the early Izu-Bonin arc recorded in detrital zircons: Zircon U-Pb geochronology and trace element geochemistry for Site U1438, Amami Sankaku Basin

    NASA Astrophysics Data System (ADS)

    Barth, A. P.; Tani, K.; Meffre, S.; Wooden, J. L.; Coble, M. A.

    2016-12-01

    Understanding the petrologic evolution of oceanic arc magmas through time is important because these arcs reveal the processes of formation and the early evolution of juvenile continental crust. The Izu-Bonin (IB) arc system has been targeted because it is one of several western Pacific intraoceanic arcs initiated at 50 Ma and because of its prominent spatial asymmetry, with widespread development of relatively enriched rear arc lavas. We examined Pb/U and trace element compositions in zircons recovered at IODP Site 351-U1438 and compared them to regional and global zircon suites. These new arc zircon data indicate that detrital zircons will yield new insights into the generation of IB silicic melts and form a set of useful geochemical proxies for interpreting ancient arc detrital zircon provenance. Project IBM drilling target IBM1 was explored by Expedition 351 at Site U1438, located in the proximal back-arc of the northern Kyushu-Palau Ridge (KPR) at 27.3°N. A 1.2 km thick section of Paleogene volcaniclastic rocks, increasingly lithified and hydrothermally altered with depth, constitutes a proximal rear arc sedimentary record of IB arc initiation and early arc evolution. The ages and compositions of U1438 zircons are compatible with provenance in one or more edifices of the northern KPR and are incompatible with drilling contamination. Melt zircon saturation temperatures and Ti-in-zircon thermometry suggest a provenance in relatively cool and silicic KPR melts. The abundances of selected trace elements with high native concentrations provide insight into the petrogenesis of U1438 detrital zircon host melts, and may be useful indicators of both short and long-term variations in melt compositions in arc settings. The U1438 zircons are slightly enriched in U and LREE and are depleted in Nb compared to zircons from mid-ocean ridges and the Parece-Vela Basin, as predicted for melts in a primitive oceanic arc setting with magmas derived from a highly depleted mantle

  16. From micron to mountain-scale, using accessory phase petrochronology to quantify the rates of deformation in the Himalaya and beyond

    NASA Astrophysics Data System (ADS)

    Mottram, C. M.

    2016-12-01

    Mountains form where the Earth's plates collide; during this upheaval rocks are deformed by massive forces. The rates and timescales over which these deformational processes occur are determined from tiny accessory minerals that record geological time through radioactive decay. However, there remain major unresolved challenges in using chemical and microstructural markers to link the dates yielded from these accessory phases to specific deformation events and discerning the effects of deformation on the isotopic and elemental tracers in these phases. Here, the chemical signatures and deformation textures from micron-scale accessory phases are used to decode the record of mountain belt-scale deformational processes encrypted in the rocks. The Himalayan orogen is used as an ideal natural laboratory to understand the chemical processes that have modified the Earth's crust during orogenesis. Combined laser ablation split-stream U-Th-Pb and REE analysis of deformed monazite and titanite, along with Electron BackScatter Diffraction (EBSD) imaging and Pressure-Temperature (P-T) phase equilibria modelling are used to: (1) link accessory phase `age' to `metamorphic stage'; (2) to quantify the influence of deformation on monazite (re)crystallisation mechanisms and its subsequent effect on the crystallographic structure, ages and trace-element distribution in individual grains; and (3) understand how deformation is accommodated through different chemical and structural processes that operate at varying scales through time. This study highlights the importance of fully integrating the pressure-temperature-time-deformation history of multiple accessory phases to better interpret the deformational history of the cores of evolving mountain belts.

  17. Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

    NASA Astrophysics Data System (ADS)

    Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

    2004-04-01

    A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that

  18. The earth's oldest known crust - A geochronological and geochemical study of 3900-4200 Ma old detrital zircons from Mt. Narryer and Jack Hills, Western Australia

    NASA Astrophysics Data System (ADS)

    Maas, Roland; Kinny, Peter D.; Williams, Ian S.; Froude, Derek O.; Compston, William

    1992-03-01

    Trace element characteristics were analyzed and inclusions were identified within a suite of pre-3.9 Ga detritral zircons from western Australia representing the earth's oldest-known minerals. A diversity of trace-element compositions was found, particularly in the REE compositions of the old Mt. Narryer zircons, implying a variety of source-rock compositions and hence, the presence of a differentiated crust in the earth 4.15-4.20 Ga ago. Comparisons drawn with data obtained from younger detrital zircons occurring within the same deposits indicate nothing unique about the chemical compositions of the old grains. A number of interelement covariations were observed among the analyzed grains which were independent of age and isotopic characteristics, most notably that occurring between Lu and Hf. A general positive correlation between total LREE and the U + Th contents is also apparent. The findings indicate an origin in felsic igneous rocks, which has implications for early-Archaean crustal evolution.

  19. Controlled Speed Accessory Drive demonstration program

    NASA Technical Reports Server (NTRS)

    Hoehn, F. W.

    1981-01-01

    A Controlled Speed Accessory Drive System was examined in an effort to improve the fuel economy of passenger cars. Concept feasibility and the performance of a typical system during actual road driving conditions were demonstrated. The CSAD system is described as a mechanical device which limits engine accessory speeds, thereby reducing parasitic horsepower losses and improving overall vehicle fuel economy. Fuel consumption data were compiled for fleets of GSA vehicles. Various motor pool locations were selected, each representing different climatic conditions. On the basis of a total accumulated fleet usage of nearly three million miles, an overall fuel economy improvement of 6 percent to 7 percent was demonstrated. Coincident chassis dynamometer tests were accomplished on selected vehicles to establish the effect of different accessory drive systems on exhaust emissions, and to evaluate the magnitude of the mileage benefits which could be derived.

  20. Authentication controversies and impactite petrography of the New Quebec Crater

    NASA Technical Reports Server (NTRS)

    Marvin, Ursula B.; Kring, David A.

    1992-01-01

    The literature reports that led to the current acceptance of New Quebec Crater (Chubb Crater) as an authentic impact crater are reviewed, and it is noted that, for reasons that are not entirely clear, a meteoritic origin for the New Quebec Crater achieved wider acceptance at an earlier data than for the Lake Bosumtwi Crater, for which petrographic and chemical evidence is more abundant and compelling. The petrography of two impact melt samples from the New Quebec Crater was investigated, and new evidence is obtained on the degrees of shock metamorphism affecting the accessory minerals such as apatite, sphene, magnetite, and zircon.

  1. Accessory stimulus modulates executive function during stepping task

    PubMed Central

    Watanabe, Tatsunori; Koyama, Soichiro; Tanabe, Shigeo

    2015-01-01

    When multiple sensory modalities are simultaneously presented, reaction time can be reduced while interference enlarges. The purpose of this research was to examine the effects of task-irrelevant acoustic accessory stimuli simultaneously presented with visual imperative stimuli on executive function during stepping. Executive functions were assessed by analyzing temporal events and errors in the initial weight transfer of the postural responses prior to a step (anticipatory postural adjustment errors). Eleven healthy young adults stepped forward in response to a visual stimulus. We applied a choice reaction time task and the Simon task, which consisted of congruent and incongruent conditions. Accessory stimuli were randomly presented with the visual stimuli. Compared with trials without accessory stimuli, the anticipatory postural adjustment error rates were higher in trials with accessory stimuli in the incongruent condition and the reaction times were shorter in trials with accessory stimuli in all the task conditions. Analyses after division of trials according to whether anticipatory postural adjustment error occurred or not revealed that the reaction times of trials with anticipatory postural adjustment errors were reduced more than those of trials without anticipatory postural adjustment errors in the incongruent condition. These results suggest that accessory stimuli modulate the initial motor programming of stepping by lowering decision threshold and exclusively under spatial incompatibility facilitate automatic response activation. The present findings advance the knowledge of intersensory judgment processes during stepping and may aid in the development of intervention and evaluation tools for individuals at risk of falls. PMID:25925321

  2. The origin of zircon and the significance of U-Pb ages in high-grade metamorphic rocks: a case study from the Variscan orogenic root (Vosges Mountains, NE France)

    NASA Astrophysics Data System (ADS)

    Skrzypek, E.; Štípská, P.; Cocherie, A.

    2012-12-01

    U-Pb zircon dating is combined with petrology, Zr-in-rutile thermometry and mineral equilibria modelling to discuss zircon petrogenesis and the age of metamorphism in three units of the Variscan Vosges Mountains (NE France). The monotonous gneiss unit shows results at 700-500 Ma, but no Variscan ages. The varied gneiss unit preserves ages between 600 and 460 Ma and a Variscan group at 340-335 Ma. Zircon analyses from the felsic granulite unit define a continuous array of ages between 500 and 340 Ma. In varied gneiss samples, zoned garnet includes kyanite and rutile and is surrounded by matrix sillimanite and cordierite. In a pseudosection, it points to peak conditions of ~16 kbar/850 °C followed by isothermal decompression to 8-10 kbar/820-860 °C. In felsic granulite samples, the assemblage K-feldspar-garnet-kyanite-Zr-rich rutile is replaced by sillimanite and Zr-poor rutile. Modelling these assemblages supports minimum conditions of ~13 kbar/925 °C, and a subsequent P-T decrease to 6.5-8.5 kbar/800-820 °C. The internal structure and chemistry of zircons, and modelling of zircon dissolution/growth along the inferred P-T paths are used to discuss the significance of the U-Pb ages. In the monotonous unit, inherited zircon ages of 700-500 Ma point to sedimentation during the Late Cambrian, while medium-grade metamorphism did not allow the formation of Variscan zircon domains. In both the varied gneiss and felsic granulite units, zircons with a blurred oscillatory-zoned pattern could reflect solid-state recrystallization of older grains during HT metamorphism, whereas zircons with a dark cathodoluminescence pattern are thought to derive from crystallization of an anatectic melt during cooling at middle pressure conditions. The present work proposes that U-Pb zircon ages of ca. 340 Ma probably reflect the end of a widespread HT metamorphic event at middle crustal level.

  3. U-Th-Pb zircon ages of some Keweenawan Supergroup rocks from the south shore of Lake Superior

    USGS Publications Warehouse

    Zartman, R.E.; Nicholson, S.W.; Cannon, W.F.; Morey, G.B.

    1997-01-01

    New single-crystal zircon U-Th-Pb ages for plutonic and rhyolitic Keweenawan Supergroup rocks from the south shore of Lake Superior provide geochronological constraints on magmatic evolution associated with the 1.1 Ga Midcontinent rift. Analyses of a granophyric phase of the Mineral Lake intrusion and the Meilen granite, both parts of the Meilen Intrusive Complex, and a laterally extensive rhyolite from the top of the Kallander Creek Volcanics have weighted average 207Pb/206Pb ages of 1102.0 ?? 2.8 Ma (N = 2), 1100.9 ?? 1.4 Ma (N = 5), and 1098.8 ?? 1.9 Ma (N = 4), respectively. Analyses of a pyroclastic rhyolite flow at the top of the Porcupine Volcanics result in variable 207Pb/206Pb ages that range from 1080 to 1137 Ma. This rhyolite exhibits a continuum between morphologically complex and simpler prismatic zircon crystals, the latter yielding concordant analyses having a weighted average 207Pb/206Pb age of 1093.6 ?? 1.8 Ma (N = 2). Four prismatic zircons from an aphyric rhyolite of the Chengwatana Volcanics in the Ashland syncline form a linear array intersecting concordia at 1094.6 ?? 2.1 Ma (MSWD = 1.3). Another presumed Chengwatana rhyolite recovered from drill core intersecting the Hudson-Afton horst in southeast Minnesota yielded only ???20 morphologically indistinguishable zircons. Six analyses give 207Pb/206Pb ages ranging from 1112 to 1136 Ma, including one analysis with a virtually concordant age of 1130 Ma. This age, however, is considerably older than that obtained for the Chengwatana Volcanics in the Ashland syncline or any other precisely dated rock from the Midcontinent rift.

  4. First Archean Zircons Found in Oceanic Crustal Rocks of Mauritius

    NASA Astrophysics Data System (ADS)

    Ashwal, L. D.; Wiedenbeck, M.; Torsvik, T. H.

    2016-12-01

    A fragment of continental crust has been postulated to underlie the young plume-related lavas of the Indian Ocean island of Mauritius, on both the basis of inversion of gravity anomaly data (crustal thickness) and the recovery of Proterozoic zircons (660-1971 Ma) from basaltic beach sands (Torsvik et al., Nature Geosci. 6, 227, 2013). We recovered 13 zircon grains from a trachyte associated with the Older Series basalts (9.0-4.7 Ma) of Mauritius, the second youngest member of a hot-spot track extending from the active plume site of Réunion. Extreme care was taken to avoid contamination during sample processing. Ten of the 13 grains are featureless, with no internal structures, and SIMS analyses (Cameca 1280-HR instrument) yield 49 spots with Miocene U-Pb systematics and a mean age of 5.7 ± 0.2 Ma (1 sd), constraining the magmatic crystallization age of the trachyte. Three grains with partially resorbed magmatic zoning, partial metamictization and mineral inclusions (quartz, K-feldspar, monazite) show uniquely mid- to late-Archean systematics: 20 spot analyses give concordant to near-concordant ages of 3030 ± 5 Ma to 2766 ± 13 Ma. This suggests that during ascent, the trachytic magmas incorporated silicic continental crustal material that preserves a record of several hundred m.y. of Archean evolution. This is consistent with Sr-Nd isotope systematics of the Mauritian trachytes, which can be modelled as having been contaminated with 0.4-3.5% of ancient granitoid crustal components. Our new age results, combined with the Proterozoic ages of zircons recovered from Mauritian beach sands, are best correlated with continental crust of east-central Madagascar, presently 700 km west of Mauritius, where Archean gneisses and Neoproterozoic intrusive rocks are juxtaposed such that a 2000 km2 area could correspond to a fragment of continent presently underlying Mauritius. This, and other continental fragments formed during Gondwana break-up, may be scattered across the

  5. Magmatic oxygen fugacity estimated using zircon-melt partitioning of cerium

    NASA Astrophysics Data System (ADS)

    Smythe, Duane J.; Brenan, James M.

    2016-11-01

    Using a newly-calibrated relation for cerium redox equilibria in silicate melts (Smythe and Brenan, 2015), and an internally-consistent model for zircon-melt partitioning of Ce, we provide a method to estimate the prevailing redox conditions during crystallization of zircon-saturated magmas. With this approach, oxygen fugacities were calculated for samples from the Bishop tuff (USA), Toba tuff (Indonesia) and the Nain plutonic suite (Canada), which typically agree with independent estimates within one log unit or better. With the success of reproducing the fO2 of well-constrained igneous systems, we have applied our Ce-in-zircon oxygen barometer to estimating the redox state of Earth's earliest magmas. Using the composition of the Jack Hills Hadean zircons, combined with estimates of their parental magma composition, we determined the fO2 during zircon crystallization to be between FMQ -1.0 to +2.5 (where FMQ is the fayalite-magnetite-quartz buffer). Of the parental magmas considered, Archean tonalite-trondhjemite-granodiorite (TTG) compositions yield zircon-melt partitioning most similar to well-constrained modern suites (e.g., Sano et al., 2002). Although broadly consistent with previous redox estimates from the Jack Hills zircons, our results provide a more precise determination of fO2, narrowing the range for Hadean parental magmas by more than 8 orders of magnitude. Results suggest that relatively oxidized magmatic source regions, similar in oxidation state to that of 3.5 Ga komatiite suites, existed by ∼4.4 Ga.

  6. 14 CFR 23.1437 - Accessories for multiengine airplanes.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Accessories for multiengine airplanes. 23... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Equipment Miscellaneous Equipment § 23.1437 Accessories for multiengine airplanes. For multiengine airplanes...

  7. 14 CFR 23.1437 - Accessories for multiengine airplanes.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Accessories for multiengine airplanes. 23... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Equipment Miscellaneous Equipment § 23.1437 Accessories for multiengine airplanes. For multiengine airplanes...

  8. 14 CFR 23.1437 - Accessories for multiengine airplanes.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Accessories for multiengine airplanes. 23... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Equipment Miscellaneous Equipment § 23.1437 Accessories for multiengine airplanes. For multiengine airplanes...

  9. Characterization of inclusions in terrestrial impact formed zircon: Constraining the formation conditions of Hadean zircon from Jack Hills, Western Australia

    NASA Astrophysics Data System (ADS)

    Faltys, J. P.; Wielicki, M. M.; Sizemore, T. M.

    2017-12-01

    Due to the discovery and subsequent geochemical analysis of Hadean terrestrial material (e.g. detrital zircon from Jack Hills, Western Australia), a dramatic paradigm shift has occurred in the hypothesized near surface conditions of the first 500 million years of Earth's evolution. From a hellish setting riddled with impactors and not fit for life to a much milder environment that may have been uniquely suitable for the origin of life. Geochemical analyses of these ancient materials have been used to suggest the presence of water at or near the surface as well as the existence of continental crust during the Hadean, both of which have been suggested as necessary for the origin of life. However, the intensity of extraterrestrial bombardment during the Hadean and the effects of such events on the origin of life remains poorly understood. Clearly, as evidenced by Phanerozoic impact events, extraterrestrial impactors have the potential to dramatically effect the environment, particularly the biosphere. Early Earth likely experienced multiple large impact events, as evidenced by the lunar record, however whether those impacts were sufficient to frustrate the origin of life remains an open question. Although multiple lines of evidence, including the inclusion population, suggest the formation of Hadean zircon from Jack Hills as crystallizing in an under-thrust environment from S-type magmas, a recent study has suggested their formation in an impact melt environment analogous to a portion of the Sudbury Igneous Complex at the Sudbury impact structure. To determine between these two formation scenarios we have under-taken an inclusion study of terrestrial impact formed zircon from four of the largest terrestrial impact structures (Sudbury, Canada; Manicouagan, Canada; Vredefort, South Africa; Morokweng, South Africa), to compare to the vast inclusion dataset that exists for Jack Hills zircon. Preliminary data suggests a different inclusion population, from Hadean zircon

  10. Do Jack Hills Detrital Zircons Contain Records of the Early Geodynamo?

    NASA Astrophysics Data System (ADS)

    Weiss, B. P.; Maloof, A. C.; Tailby, N. D.; Ramezani, J.; Fu, R. R.; Glenn, D. R.; Kehayias, P.; Walsworth, R. L.; Hanus, V.; Trail, D.; Watson, E. B.; Harrison, T. M.; Bowring, S. A.; Kirschvink, J. L.; Swanson-Hysell, N.; Coe, R. S.; Einsle, J. F.; Harrison, R. J.

    2015-12-01

    It is unknown when Earth's dynamo magnetic field originated. With crystallization ages ranging from 3.0-4.38 Ga, detrital zircon crystals found in the Jack Hills of Western Australia might preserve a record of the missing first billion years of Earth's magnetic field history. Recently, Tarduno et al. (2015) argued that magnetization in Jack Hills zircons provides evidence for a substantial geomagnetic field dating back to their U/Pb formation ages (3.3 and 4.2 Ga). However, the identification of such ancient field records requires establishing that the zircons have avoided remagnetization since their formation. At a minimum, it should be demonstrated that they have not been remagnetized since being deposited at ~3.0 Ga. To establish the timing and intensity of the metamorphic and alteration events experienced by the zircon, we conducted 12 paleomagnetic field tests in combination with U-Pb geochronology on their host rocks (see Weiss et al. 2015, EPSL). Our data show that the Hadean zircon-bearing rocks and surrounding region have been pervasively remagnetized, with the final major overprinting likely from emplacement of the Warakurna large igneous province at 1.1 Ga (see Figure). Even if some Jack Hills zircons do record a pre-depositional magnetization, they still could have been remagnetized sometime during the 1.4 Gy between their crystallization and their deposition. First, the temperatures capable of remagnetizing magnetite inclusions are well below those that could reset a U-Pb date or result in significant discordance. Therefore, thermal events capable of completely remagnetizing Jack Hills zircons could be undetected by the techniques reported by Tarduno at al. (2015). Second, the zircons' magnetization might be dominated by secondary ferromagnetic inclusions or contamination. To address the latter possibility, we are conducting electron microscopy, x-ray tomography, and magnetic field mapping on the zircons. Our initial quantum diamond magnetometry high

  11. Provenance analysis of heavy minerals in beach sands (Falkland Islands/Islas Malvinas) - A view to mineral deposits and the geodynamics of the South Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Dill, Harald G.; Skoda, Radek

    2017-10-01

    Beach sands are ideal traps to collect heavy minerals (HM) from different geodynamic settings and mineral deposits. The coastal sediments contain a mixture of HM derived from the submarine shelf and from source rocks in the hinterland. This is true in a transgressive periglacial regime, where drowned valleys and estuaries are instrumental in draining HM to the arenaceous beach sediments from more distal basement lithologies. A scenario like this can be found in the Falkland Islands/Islas Malvinas. The site under study is the missing link between South Africa and South America, the splitting-apart of which is mirrored by the HM distribution predominantly concentrated in the backshore and dune belt along the coast. The HM are subdivided into three HM associations reflecting the geodynamic evolution of the South Atlantic Ocean and of some of the prominent mineral deposits on the Gondwana Continent: (1) Gondwana cratons and Proterozoic orogens, with Cr and BIF deposits (rutile, zircon, ilmenite, tourmaline, garnet, Cr spinel), (2) rift-related and break-apart magmatic lithologies with mantle-derived pipe rocks such as kimberlites (zircon, pyroxene, spinel, Mg ilmenite), (3) Cordillera-type lithologies with polymetallic stratabound deposits (tourmaline, amphibole, chlorite, REE phosphates). The variation of the major HM from the stable craton (Kalahari-Kaapvaal Craton) in the East to the mobile fold belt (Andes) in the West follows the order of stability of HM. In addition to these 3 geodynamic HM groups, sporadic occurrences of HM originating from alteration (leucoxene, chlorite s.s.s. (= solid solution series)) are part of armored relics such as "nigrine" which on transport disintegrated and thereby released these HM. The major ultrastable and stable HM zircon, rutile, tourmaline s.s.s., spinel s.s.s., and garnet s.s.s. are displayed in a synoptical x-y plot showing the mantle and crustal trends of fractionation and formation of cumulates by means of particular

  12. Thermometers and thermobarometers in granitic systems

    USGS Publications Warehouse

    Anderson, J.L.; Barth, A.P.; Wooden, J.L.; Mazdab, F.; ,

    2008-01-01

    The ability to determine the thermal and barometric history during crystallization and emplacement of granitic plutons has been enhanced by several new calibrations applicable to granitic mineral assemblages. Other existing calibrations for granitic plutons have continued to be popular and fairly robust. Recent advances include the trace element thermometers Ti-in-quartz, Ti-in-zircon, and Zr-in-sphene (titanite), which need to be further evaluated on the roles of reduced activities due to lack of a saturating phase, the effect of pressure dependence (particularly for the Ti-in-zircon thermometer), and how resistive these thermometers are to subsolidus reequilibration. As zircon and sphene are also hosts to radiogenic isotopes, these minerals potentially also provide new insights into the temperature - time history of magmas. When used in conjunction with pressure-sensitive mineral equilibria in the same rocks, a complete assessment of the P-T-t (pressure-temperature-time) path is possible given that the mineralogy of plutons can reflect crystallization over a range of pressure and temperature during ascent and emplacement and that many intrusions are now seen as forming over several millions of years during the protracted history of batholith construction. Accessory mineral saturation thermometers, such as those for zircon, apatite, and allanite, provide a different and powerful perspective, specifically that of the temperature of the onset of crystallization of these minerals, which can allow an estimate of the range of temperature between the liquidus and solidus of a given pluton. In assessment of the depth of crystallization and emplacement of granitic plutons, the Al-in-hornblende remains popular for metaluminous granites when appropriately corrected for temperature. For peraluminous granites, potential new calibrations exist for the assemblages bearing garnet, biotite, plagioclase, muscovite, and quartz. Other thermometers, based on oxygen abundance, and

  13. Accessory mineral U-Th-Pb ages and 40Ar/39Ar eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California

    USGS Publications Warehouse

    Simon, J.I.; Vazquez, J.A.; Renne, P.R.; Schmitt, A.K.; Bacon, C.R.; Reid, M.R.

    2009-01-01

    We determined Ar/Ar eruption ages of eight extrusions from the Pleistocene Coso volcanic field, a long-lived series of small volume rhyolitic domes in eastern California. Combined with ion-microprobe dating of crystal ages of zircon and allanite from these lavas and from granophyre geothermal well cuttings, we were able to track the range of magma-production rates over the past 650 ka at Coso. In ??? 230 ka rhyolites we find no evidence of protracted magma residence or recycled zircon (or allanite) from Pleistocene predecessors. A significant subset of zircon in the ???85 ka rhyolites yielded ages between ???100 and 200 Ma, requiring that generation of at least some rhyolites involves material from Mesozoic basement. Similar zircon xenocrysts are found in an ???200 ka granophyre. The new age constraints imply that magma evolution at Coso can occur rapidly as demonstrated by significant changes in rhyolite composition over short time intervals (???10's to 100's ka). In conjunction with radioisotopic age constraints from other young silicic volcanic fields, dating of Coso rhyolites highlights the fact that at least some (and often the more voluminous) rhyolites are produced relatively rapidly, but that many small-volume rhyolites likely represent separation from long-lived mushy magma bodies. ?? The Author(s) 2009.

  14. Zircons as a Probe of Early Lunar Impact History

    NASA Astrophysics Data System (ADS)

    Crow, C. A.; McKeegan, K. D.; Gilmour, J. D.; Crowther, S. A.; Taylor, D. J.

    2013-08-01

    Zircons are ideal for investigating the early lunar bombardment because we can measure both U-Pb crystallization ages and fissiongenic Xe degassing ages for the same crystal. We report U-Pb, Pb-Pb and U-Xe ages for two lunar zircons.

  15. 21 CFR 876.5820 - Hemodialysis system and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    .... (1) The extracorporeal blood system and accessories consists of tubing, pumps, pressure monitors, air... conditions and that consists of an extracorporeal blood system, a conventional dialyzer, a dialysate delivery system, and accessories. Blood from a patient flows through the tubing of the extracorporeal blood system...

  16. 21 CFR 876.5820 - Hemodialysis system and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    .... (1) The extracorporeal blood system and accessories consists of tubing, pumps, pressure monitors, air... conditions and that consists of an extracorporeal blood system, a conventional dialyzer, a dialysate delivery system, and accessories. Blood from a patient flows through the tubing of the extracorporeal blood system...

  17. 21 CFR 876.5820 - Hemodialysis system and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    .... (1) The extracorporeal blood system and accessories consists of tubing, pumps, pressure monitors, air... conditions and that consists of an extracorporeal blood system, a conventional dialyzer, a dialysate delivery system, and accessories. Blood from a patient flows through the tubing of the extracorporeal blood system...

  18. 21 CFR 876.5820 - Hemodialysis system and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    .... (1) The extracorporeal blood system and accessories consists of tubing, pumps, pressure monitors, air... conditions and that consists of an extracorporeal blood system, a conventional dialyzer, a dialysate delivery system, and accessories. Blood from a patient flows through the tubing of the extracorporeal blood system...

  19. 14 CFR 23.1437 - Accessories for multiengine airplanes.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Accessories for multiengine airplanes. 23.1437 Section 23.1437 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF..., engine-driven accessories essential to safe operation must be distributed among two or more engines so...

  20. 14 CFR 23.1437 - Accessories for multiengine airplanes.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Accessories for multiengine airplanes. 23.1437 Section 23.1437 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF..., engine-driven accessories essential to safe operation must be distributed among two or more engines so...

  1. Coastal deposits of heavy mineral sands; Global significance and US resources

    USGS Publications Warehouse

    Van Gosen, Bradley S.; Bleiwas, Donald I.; Bedinger, George M.; Ellefsen, Karl J.; Shah, Anjana K.

    2016-01-01

    Ancient and modern coastal deposits of heavy mineral sands (HMS) are the principal source of several heavy industrial minerals, with mining and processing operations on every continent except Antarctica. For example, HMS deposits are the main source of titanium feedstock for the titanium dioxide (TiO2) pigments industry, obtained from the minerals ilmenite (Fe2+TiO3), rutile (TiO2) and leucoxene (an alteration product of ilmenite). HMS deposits are also the principal source of zircon (ZrSiO4), from which zirconium dioxide (ZrO2) is obtained for uses mostly in refractory products. Sometimes monazite [(Ce,La,Nd,Th)PO4] is recovered as a byproduct mineral, sought for its rare earth elements and thorium (Ault and others, 2016; Sengupta and Van Gosen, 2016; Van Gosen and Tulsidas, 2016). 

  2. A left lateral accessory pathway unmasked by rivastigmine.

    PubMed

    Guenancia, Charles; Fichot, Marie; Garnier, Fabien; Montoy, Mathieu; Laurent, Gabriel

    A 75-year-old woman was referred for advice regarding surface electrocardiographic modifications after the initiation of rivastigmine. In our patient, the baseline ECGs appeared perfectly normal. However, the initiation of a cholinesterase inhibitor unmasked a left lateral accessory pathway that had never been diagnosed before. Although cholinesterase inhibitors are known to increase vagal tone, the PR interval was shortened after rivastigmine administration, thus excluding this hypothesis to explain the appearance of the accessory pathway. Therefore, we hypothesized that cholinesterase inhibitors may have increased conduction velocity in the accessory pathway or in the atria. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. Developing Zircon as a Probe of Planetary Impact History

    NASA Astrophysics Data System (ADS)

    Wielicki, Matthew

    2014-12-01

    The identification of Meteor Crater in Arizona as an extraterrestrial impact by Eugene Shoemaker provided the first evidence of this geologic phenomenon and opened the door to a new field of research that has eventually lead to the identification of over ~150 terrestrial impact structures. Subsequently impacts have been evoked in the formation of the moon, delivery of volatiles and bio-precursors to early Earth, creation of habitats for the earliest life and, in more recent times, major mass extinction events. However, understanding the impact flux to the Earth-Moon system has been complicated by the constant weathering and erosion at Earth's surface and the complex nature of impactite samples such that only a hand full of terrestrial craters have been accurately and precisely dated. Currently 40Ar/39Ar step-heating analysis of impactite samples is commonly used to infer impact ages but can be problematic due to the presence of relic clasts, incomplete 40Ar outgassing or excess 40Ar, and recoil and shock effects. The work presented here attempts to develop zircon geochronology to probe planetary impact histories as an alternative to current methods and provides another tool by which to constrain the bolide flux to the Earth-Moon system. Zircon has become the premier geo-chronometer in earth science and geochemical investigation of Hadean zircon from Western Australia has challenged the long-standing, popular conception that the near-surface Hadean Earth was an uninhabitable and hellish world; Zircons may preserve environmental information regarding their formation and thus provide a rare window into conditions on early Earth. Isotopic and petrologic analyses of these ancient grains have been interpreted to suggest that early Earth was more habitable than previously envisioned, with water oceans, continental crust, and possibly even plate tectonics. The Hadean is also suspected to be a time of major planetary bombardment however identifying impact signatures within

  4. 21 CFR 884.5350 - Contraceptive diaphragm and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Contraceptive diaphragm and accessories. 884.5350 Section 884.5350 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... Devices § 884.5350 Contraceptive diaphragm and accessories. (a) Identification. A contraceptive diaphragm...

  5. 21 CFR 884.5350 - Contraceptive diaphragm and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Contraceptive diaphragm and accessories. 884.5350 Section 884.5350 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... Devices § 884.5350 Contraceptive diaphragm and accessories. (a) Identification. A contraceptive diaphragm...

  6. 21 CFR 884.5350 - Contraceptive diaphragm and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Contraceptive diaphragm and accessories. 884.5350 Section 884.5350 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... Devices § 884.5350 Contraceptive diaphragm and accessories. (a) Identification. A contraceptive diaphragm...

  7. 21 CFR 884.5350 - Contraceptive diaphragm and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Contraceptive diaphragm and accessories. 884.5350 Section 884.5350 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... Devices § 884.5350 Contraceptive diaphragm and accessories. (a) Identification. A contraceptive diaphragm...

  8. 21 CFR 884.5350 - Contraceptive diaphragm and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Contraceptive diaphragm and accessories. 884.5350 Section 884.5350 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... Devices § 884.5350 Contraceptive diaphragm and accessories. (a) Identification. A contraceptive diaphragm...

  9. U-Pb isotopic results for single shocked and polycrystalline zircons record 550-65.5-Ma ages for a K-T target site and 2700-1850-Ma ages for the Sudbury impact event

    NASA Technical Reports Server (NTRS)

    Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

    1992-01-01

    The refractory mineral zircon develops distinct morphological features during shock metamorphism and retains these features under conditions that would anneal them in other minerals. In addition, weakly shocked zircon grains give primary ages for the impact site, while highly reconstituted (polycrystalline) single grains give ages that approach the age of the impact event. Data for a series of originally coeval grains will define a mixing line that gives both of these ages providing that no subsequent geological disturbances have overprinted the isotopic systematics. In this study, we have shown that the three zircon grain types described by Bohor, from both K-T distal ejecta (Fireball layer, Raton Basin, Colorado) and the Onaping Formation, represent a progressive increase in impact-related morphological change that coincides with a progressive increase in isotopic resetting in zircons from the ejecta and basement rocks. Unshocked grains are least affected by isotopic resetting while polycrystalline grains are most affected. U-Pb isotopic results for 12 of 14 single zircon grains from the Fireball layer plot on or close to a line recording a primary age of 550 +/- 10 Ma and a secondary age of 65.5 +/- 3 Ma. Data for the least and most shocked grains plot closest to the primary and secondary ages respectively. The two other grains each give ages between 300 and 350 Ma. This implies that the target ejecta was dominated by 550-Ma rocks and that the recrystallization features of the zircon were superimposed during the impact event at 65.5 Ma. A predominant age of 550 Ma for zircons from the Fireball layer provides an excellent opportunity to identify the impact site and to test the hypothesis that multiple impacts occurred at this time. A volcanic origin for the Fireball layer is ruled out by shock-related morphological changes in zircon and the fact that the least shocked grains are old. Basement Levack gneisses north of the Sudbury structure have a primary age of

  10. Petrogenesis of Mesozoic granites in the Xitian, South China: Evidence from whole-rock geochemistry and zircon isotopes

    NASA Astrophysics Data System (ADS)

    Liu, Q.; Sun, J.; He, M.; Hou, Q.; Niu, R.

    2017-12-01

    Mesozoic granitoids are widespread in southeastern China, which accompanied with lots of world-famous polymetallic deposits. The mineralization is believed to be related to the Mesozoic granitic magmatism. However, the petrogenesis of these granites and their relation to the mineralization are still debated. As a typical granitic pluton, Xitian granites from the eastern Hunan Province are formed during this period and associated with tungsten-tin deposit. Whole-rock geochemical, SIMS zircon geochronology and oxygen isotopes, as well as LA-ICPMS zircon Lu-Hf isotopic analyses, were carried out on a suite of rocks from Xitian granitic pluton to constrain their magmatic sources and petrogenesis. Xitian granitic pluton is mainly composed of biotite adamellite, biotite granite, fine-grained granite. SIMS and LA-ICPMS U-Pb dating of zircons indicate that there are two episodes of these rocks, i.e., Late Triassic granites (227-233Ma) and Late Jurassic granites (150-154Ma). The Xitian granites are silica-rich, potassic and weakly peraluminous. Petrographic and geochemical features show that they are highly fractionated I-type granites. The combined elemental and isotopic results indicated that the Late Triassic granite in Xitian area experienced a process of crystal fractionation of crustal-derived magmas coupled with strong assimilation of the surrounding rocks. The occurrence of Jurassic granitoids in Xitian area is attributed to ascending of mantle-derived magmas, which provide heat for partial melting of crustal materials. The Late Jurassic granite may be derived from juvenile crust or partial melting of ancient crustal rocks, whereas high degrees of crystal fractionation further enriched tungsten-tin in the evolved granitic rocks. This work was financially supported by the Research Cooperation between Institute and University of Chinese Academy of Sciences grant (Y552012Y00), Public Welfare Project of the Ministry of land and Resources of China (201211024

  11. Zircon U-Pb ages and Sr-Nd-Hf isotopes of the highly fractionated granite with tetrad REE patterns in the Shamai tungsten deposit in eastern Inner Mongolia, China: Implications for the timing of mineralization and ore genesis

    NASA Astrophysics Data System (ADS)

    Jiang, Si-Hong; Bagas, Leon; Hu, Peng; Han, Ning; Chen, Chun-Liang; Liu, Yuan; Kang, Huan

    2016-09-01

    The Shamai tungsten deposit is located in the eastern part of the Central Asian Orogenic Belt (CAOB). Tungsten mineralization is closely related to the emplacement of fine- to medium-grained biotite monzogranite (G1) and porphyritic biotite monzogranite (G2) in the Shamai Granite. NW-trending joints and faults host orebodies in the Shamai Granite and Devonian hornfels. The mineralization is characterized by a basal veinlet zone progressing upwards to a thick vein zone followed by a mixed zone, a veinlet zone, and a thread vein zone at the top. The ore-related alteration typically consists of muscovite, greisen, and hornfels. In order to constrain the timing of the Shamai mineralization and discuss the ore genesis, muscovite Ar-Ar, molybdenite Re-Os, and zircon U-Pb geochronological, geochemical, and Sr-Nd-Hf isotopic studies were completed on the deposit. The U-Pb zircon dating yielded weighted mean ages of 153 ± 1 Ma for G1 and 146 ± 1 Ma for G2. Muscovite from a wolframite-bearing quartz vein yielded an Ar-Ar plateau age of 140 ± 1 Ma, whereas two molybdenite samples yielded identical Re-Os model ages of 137 ± 2 Ma. These two ages are younger than the two monzogranites, suggesting a prolonged magmatic-hydrothermal interaction during tungsten mineralization. Major and trace element geochemistry shows that both G1 and G2 are characterized by high SiO2 and K2O contents, high A/CNK values (1.08-1.40), a spectacular tetrad effect in their REE distribution patterns, and non-CHARAC (charge-and-radius-controlled) trace element behavior. This suggests that both G1 and G2 are highly differentiated peraluminous rocks with strong hydrothermal interaction. The Nd-Hf isotope data for the Shamai Granite (εNd(t) between - 1.9 and + 7.4, ɛHf(t) from 5.2 to 12.8) are largely compatible with the general scenario for much of the Phanerozoic granite emplaced in the CAOB. It is here suggested that the Shamai Granite originated from partial melting of a juvenile lower crust with

  12. Residence, resorption and recycling of zircons in Devils Kitchen rhyolite, Coso Volcanic Field, California

    USGS Publications Warehouse

    Miller, J.S.; Wooden, J.L.

    2004-01-01

    Zircons from the Devils Kitchen rhyolite in the Pleistocene Coso Volcanic field, California have been analyzed by in situ Pb/U ion microprobe (SHRIMP-RG) and by detailed cathodoluminescence imaging. The zircons yield common-Pb-corrected and disequilibrium-corrected 206Pb/238U ages that predate a previously reported K-Ar sanidine age by up to 200 kyr, and the range of ages exhibited by the zircons is also approximately 200 kyr. Cathodoluminescence imaging indicates that zircons formed in contrasting environments. Most zircons are euhedral, and a majority of the zircons are weakly zoned, but many also have anhedral, embayed cores, with euhedral overgrowths and multiple internal surfaces that are truncated by later crystal zones. Concentrations of U and Th vary by two orders of magnitude within the zircon population, and by 10-20 times between zones within some zircon crystals, indicating that zircons were transferred between contrasting chemical environments. A zircon saturation temperature of ???750??C overlaps within error a previously reported phenocryst equilibration temperature of 740 ?? 25??C. Textures in zircons indicative of repeated dissolution and subsequent regrowth are probably caused by punctuated heating by mafic magma input into rhyolite. The overall span of ages and large variation in U and Th concentrations, combined with calculated zircon saturation temperatures and resorption times, are most compatible with crystallization in magma bodies that were emplaced piecemeal in the crust at Coso over 200 kyr prior to eruption, and that were periodically rejuvenated or melted by subsequent basaltic injections. ?? Oxford University Press 2004; all rights reserved.

  13. 21 CFR 884.4120 - Gynecologic electrocautery and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Gynecologic electrocautery and accessories. 884.4120 Section 884.4120 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... under direct visual observation. This generic type of device may include the following accessories: an...

  14. 14 CFR 23.1192 - Engine accessory compartment diaphragm.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Engine accessory compartment diaphragm. 23... Powerplant Powerplant Fire Protection § 23.1192 Engine accessory compartment diaphragm. For aircooled radial engines, the engine power section and all portions of the exhaust sytem must be isolated from the engine...

  15. 14 CFR 23.1192 - Engine accessory compartment diaphragm.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Engine accessory compartment diaphragm. 23... Powerplant Powerplant Fire Protection § 23.1192 Engine accessory compartment diaphragm. For aircooled radial engines, the engine power section and all portions of the exhaust sytem must be isolated from the engine...

  16. 14 CFR 23.1192 - Engine accessory compartment diaphragm.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Engine accessory compartment diaphragm. 23... Powerplant Powerplant Fire Protection § 23.1192 Engine accessory compartment diaphragm. For aircooled radial engines, the engine power section and all portions of the exhaust sytem must be isolated from the engine...

  17. The 230Th correction is the 1st priority for accurate dates of young zircons: U/Th partitioning experiments and measurements

    NASA Astrophysics Data System (ADS)

    Krawczynski, M.; McLean, N.

    2017-12-01

    One of the most accurate and useful ways of determining the age of rocks that formed more than about 500,000 years ago is uranium-lead (U-Pb) geochronology. Earth scientists use U-Pb geochronology to put together the geologic history of entire regions and of specific events, like the mass extinction of all non-avian dinosaurs about 66 million years ago or the catastrophic eruptions of supervolcanoes like the one currently centered at Yellowstone. The mineral zircon is often utilized because it is abundant, durable, and readily incorporates uranium into its crystal structure. But it excludes thorium, whose isotope 230Th is part of the naturally occurring isotopic decay chain from 238U to 206Pb. Calculating a date from the relative abundances of 206Pb and 238U therefore requires a correction for the missing 230Th. Existing experimental and observational constraints on the way U and Th behave when zircon crystallizes from a melt are not known precisely enough, and thus currently the uncertainty in dates introduced by they `Th correction' is one of the largest sources of systematic error in determining dates. Here we present preliminary results on our study of actinide partitioning between zircon and melt. Experiments have been conducted to grow zircon from melts doped with U and Th that mimic natural magmas at a range of temperatures, and compositions. Synthetic zircons are separated from their coexisting glass and using high precision and high-spatial-resolution techniques, the abundance and distribution of U and Th in each phase is determined. These preliminary experiments are the beginning of a study that will result in precise determination of the zircon/melt uranium and thorium partition coefficients under a wide variety of naturally occurring conditions. This data will be fit to a multidimensional surface using maximum likelihood regression techniques, so that the ratio of partition coefficients can be calculated for any set of known parameters. The results of

  18. 21 CFR 876.4890 - Urological table and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ..., stirrups, and belts used to support a patient in a suitable position for endoscopic procedures of the lower...) Class II (special controls) for the electrically powered urological table and accessories. The device is... § 876.9. (2) Class I for the manually powered table and accessories, and for stirrups for electrically...

  19. Extinct 244Pu in ancient zircons.

    PubMed

    Turner, Grenville; Harrison, T Mark; Holland, Greg; Mojzsis, Stephen J; Gilmour, Jamie

    2004-10-01

    We have found evidence, in the form of fissiogenic xenon isotopes, for in situ decay of 244Pu in individual 4.1- to 4.2-billion-year-old zircons from the Jack Hills region of Western Australia. Because of its short half-life, 82 million years, 244Pu was extinct within 600 million years of Earth's formation. Detrital zircons are the only known relics to have survived from this period, and a study of their Pu geochemistry will allow us to date ancient metamorphic events and determine the terrestrial Pu/U ratio for comparison with the solar ratio.

  20. Raman study of radiation-damaged zircon under hydrostatic compression

    NASA Astrophysics Data System (ADS)

    Nasdala, Lutz; Miletich, Ronald; Ruschel, Katja; Váczi, Tamás

    2008-12-01

    Pressure-induced changes of Raman band parameters of four natural, gem-quality zircon samples with different degrees of self-irradiation damage, and synthetic ZrSiO4 without radiation damage, have been studied under hydrostatic compression in a diamond anvil cell up to ~10 GPa. Radiation-damaged zircon shows similar up-shifts of internal SiO4 stretching modes at elevated pressures as non-damaged ZrSiO4. Only minor changes of band-widths were observed in all cases. This makes it possible to estimate the degree of radiation damage from the width of the ν3(SiO4) band of zircon inclusions in situ, almost independent from potential “fossilized pressures” or compressive strain acting on the inclusions. An application is the non-destructive analysis of gemstones such as corundum or spinel: broadened Raman bands are a reliable indicator of self-irradiation damage in zircon inclusions, whose presence allows one to exclude artificial color enhancement by high-temperature treatment of the specimen.

  1. Hf isotope compositions In detrital zircons as a new tool for provenance studies

    NASA Astrophysics Data System (ADS)

    Jacobsen, Y. J.; Münker, C.; Mezger, K.

    2003-04-01

    Identifying the provenance of continental sediments is a major issue in palaeo-tectonic studies, providing important information for paleogeographic reconstructions. Isotope studies, e.g. those of whole rock Sm-Nd or detrital zircon U-Pb dating, have widely been used for this purpose. Here we assess the potential of combined Lu-Hf data and U-Pb ages determined on the same single detrital zircons as a new tool for provenance studies. Due to the low Lu/Hf ratios in zircons the Hf isotope composition of a zircon changes insignificantly after its crystallization. Thus each particular grain preserves information on the Hf-siotpe composition of its source and the age of this source. Provided that both the U-Pb and Lu-Hf isotope systems have not been disturbed, this information can be used to constrain the sources of each individual zircon. In order to demonstrate the capability of Hf isotope studies on detrital zircons for provenance studies, we obtained combined U-Pb ages and Lu-Hf isotope data for zircons from the Cambrian Junction Formation in New Zealand. The Junction Formation was deposited on the (present) SE margin of Gondwana near the Australian continent and consists of turbidites, siltstones and conglomerates [1]. Typical continent derived Paleozoic sediments in SE Gondwana generally show characteristic age maxima at 500-600 Ma, 1000-1200 Ma (Grenvillian) and additional older peaks (early Proterozoic to Archean) [2]. We focused on two groups of detrital zircons with Grenvillian and Proterozoic to Late Archean ages. The initial ɛHf values for these zircons range from 0.7 to -15.5 for the Grenvillian and from -5.2 to -14.1 for the Proterozoic/Archean zircons. Corresponding two stage Hf model ages range from ca. 1500 to 2500 Ma for the Grenvillian and from ca. 3200 to 3600 Ma for the Proterozoic/Archean zircons. Furthermore it can be shown that the Grenvillian zircons must have been derived from recycled Grenvillian provinces. Comparison of these Hf model ages

  2. U-Pb zircon and 40Ar/39Ar geochronology of sericite from hydrothermal alteration zones: new constraints for the timing of Ediacaran gold mineralization in the Sukhaybarat area, western Afif terrane, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Harbi, Hesham M.; Ali, Kamal A.; McNaughton, Neal J.; Andresen, Arild

    2018-04-01

    The Sukhaybarat East and Red Hill deposits, in the northeastern part of the Arabian Shield, are mesothermal vein-type gold deposits hosted by late Cryogenian-Ediacaran intrusive rocks of the Idah suites (diorite, tonalite, granodiorite) and, at Sukhaybarat East, also by Ediacaran metasedimentary rocks. Gold mineralization comprises quartz-arsenopyrite veins (Sukhaybarat East), quartz-carbonate-pyrite veins (Red Hill), and subordinate gold-base metal sulfide veins. In the Red Hill deposit, alteration is complicated due to multiple overprinting hydrothermal events and is characteristically affected by pervasive, pink quartz-K-feldspar-hematite alteration which is overprinted by potassic alteration characterized by a quartz-biotite-carbonate-muscovite/sericite-rutile-apatite assemblage. This assemblage is associated with molybdenite veins which appear to form late in the paragenetic sequence and may represent either evolution of the ore fluid composition, or a later, unrelated mineralized fluids. Hydrothermal alteration at the Sukhaybarat East deposit is dominated by quartz-carbonate-sericite-arsenopyrite assemblages. Zircon from ore-hosting tonalite at Sukhaybarat East yields a U-Pb age of 629 ± 6 Ma, and biotite from the same rock gives an 40Ar/39Ar age of 622 ± 23 Ma. The 40Ar/39Ar age is within the uncertainty range for the U-Pb age of the host intrusion and is interpreted as a minimally disturbed cooling age for the tonalite. In the Red Hill area, granodiorite was emplaced at 615 ± 5 Ma, whereas muscovite/sericite separated from a mineralized sample of a quartz-carbonate-pyrite vein, that was overprinted by molybdenite-bearing veinlets, yields an 40Ar/39Ar age of 597 ± 8 Ma. We interpreted this age to represent the maximum age of the molybdenite mineralization and the probable minimum age of gold mineralization in the Red Hill deposit.

  3. 14 CFR 125.149 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Engine accessory section diaphragm. 125.149... Requirements § 125.149 Engine accessory section diaphragm. Unless equivalent protection can be shown by other means, a diaphragm that complies with § 125.145 must be provided on air-cooled engines to isolate the...

  4. 14 CFR 125.149 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false Engine accessory section diaphragm. 125.149... Requirements § 125.149 Engine accessory section diaphragm. Unless equivalent protection can be shown by other means, a diaphragm that complies with § 125.145 must be provided on air-cooled engines to isolate the...

  5. 14 CFR 125.149 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false Engine accessory section diaphragm. 125.149... Requirements § 125.149 Engine accessory section diaphragm. Unless equivalent protection can be shown by other means, a diaphragm that complies with § 125.145 must be provided on air-cooled engines to isolate the...

  6. 14 CFR 125.149 - Engine accessory section diaphragm.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false Engine accessory section diaphragm. 125.149... Requirements § 125.149 Engine accessory section diaphragm. Unless equivalent protection can be shown by other means, a diaphragm that complies with § 125.145 must be provided on air-cooled engines to isolate the...

  7. Laser Ablation in situ (U-Th-Sm)/He and U-Pb Double-Dating of Apatite and Zircon: Techniques and Applications

    NASA Astrophysics Data System (ADS)

    McInnes, B.; Danišík, M.; Evans, N.; McDonald, B.; Becker, T.; Vermeesch, P.

    2015-12-01

    We present a new laser-based technique for rapid, quantitative and automated in situ microanalysis of U, Th, Sm, Pb and He for applications in geochronology, thermochronometry and geochemistry (Evans et al., 2015). This novel capability permits a detailed interrogation of the time-temperature history of rocks containing apatite, zircon and other accessory phases by providing both (U-Th-Sm)/He and U-Pb ages (+trace element analysis) on single crystals. In situ laser microanalysis offers several advantages over conventional bulk crystal methods in terms of safety, cost, productivity and spatial resolution. We developed and integrated a suite of analytical instruments including a 193 nm ArF excimer laser system (RESOlution M-50A-LR), a quadrupole ICP-MS (Agilent 7700s), an Alphachron helium mass spectrometry system and swappable flow-through and ultra-high vacuum analytical chambers. The analytical protocols include the following steps: mounting/polishing in PFA Teflon using methods similar to those adopted for fission track etching; laser He extraction and analysis using a 2 s ablation at 5 Hz and 2-3 J/cm2fluence; He pit volume measurement using atomic force microscopy, and U-Th-Sm-Pb (plus optional trace element) analysis using traditional laser ablation methods. The major analytical challenges for apatite include the low U, Th and He contents relative to zircon and the elevated common Pb content. On the other hand, apatite typically has less extreme and less complex zoning of parent isotopes (primarily U and Th). A freeware application has been developed for determining (U-Th-Sm)/He ages from the raw analytical data and Iolite software was used for U-Pb age and trace element determination. In situ double-dating has successfully replicated conventional U-Pb and (U-Th)/He age variations in xenocrystic zircon from the diamondiferous Ellendale lamproite pipe, Western Australia and increased zircon analytical throughput by a factor of 50 over conventional methods

  8. Effect of α-damage on fission-track annealing in zircon

    USGS Publications Warehouse

    Kasuya, Masao; Naeser, Charles W.

    1988-01-01

    The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e., different amounts of ??-damage) has been studied by one-hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon.

  9. Early Paleozoic tectonic reconstruction of Iran: Tales from detrital zircon geochronology

    NASA Astrophysics Data System (ADS)

    Moghadam, Hadi Shafaii; Li, Xian-Hua; Griffin, William L.; Stern, Robert J.; Thomsen, Tonny B.; Meinhold, Guido; Aharipour, Reza; O'Reilly, Suzanne Y.

    2017-01-01

    In this study we use detrital zircons to probe the Early Paleozoic history of NE Iran and evaluate the link between sediment sources and Gondwanan pre-Cadomian, Cadomian and younger events. U-Pb zircon ages and Hf isotopic compositions are reported for detrital zircons from Ordovician and Early Devonian sedimentary rocks from NE Iran. These clastic rocks are dominated by zircons with major age populations at 2.5 Ga, 0.8-0.6 Ga, 0.5 Ga and 0.5-0.4 Ga as well as a minor broad peak at 1.0 Ga. The source of 2.5 Ga detrital zircons is enigmatic; they may have been supplied from the Saharan Metacraton (or West African Craton) to the southwest or Afghanistan-Tarim to the east. The detrital zircons with age populations at 0.8-0.6 Ga probably originated from Cryogenian-Ediacaran juvenile igneous rocks of the Arabian-Nubian Shield; this inference is supported by their juvenile Hf isotopes, although some negative εHf (t) values suggest that other sources (such as the West African Craton) were also involved. The age peak at ca 0.5 Ga correlates with Cadomian magmatism reported from Iranian basement and elsewhere in north Gondwana. The variable εHf (t) values of Cadomian detrital zircons, resembling the εHf (t) values of zircons in magmatic Cadomian rocks from Iran and Taurides (Turkey), suggest an Andean-type margin and the involvement of reworked older crust in the generation of the magmatic rocks. The youngest age population at 0.5-0.4 Ga is interpreted to represent Gondwana rifting and the opening of Paleotethys, which probably started in Late Cambrian-Ordovician time. A combination of U-Pb dating and Hf-isotope data from Iran, Turkey and North Gondwana confirms that Iran and Turkey were parts of Gondwana at least until late Paleozoic time.

  10. Dating High Temperature Mineral Fabrics in Lower Crustal Granulite Facies Rocks

    NASA Astrophysics Data System (ADS)

    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

  11. Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

    NASA Astrophysics Data System (ADS)

    Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia

    2016-04-01

    A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18-24Ab79-82Or0.3-0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

  12. U-Pb zircon geochronologycal investigation on the Morro dos Seis Lagos Carbonatite Complex and associated Nb deposit (Amazonas, Brazil)

    NASA Astrophysics Data System (ADS)

    Rossoni, Marco B.; Bastos Neto, Artur C.; Souza, Valmir S.; Marques, Juliana C.; Dantas, Elton; Botelho, Nilson F.; Giovannini, Arthur L.; Pereira, Vitor P.

    2017-12-01

    We present results of U-Pb dating (by MC-ICP-MS) of zircons from samples that cover all of the known lithotypes in the Seis Lagos Carbonatite Complex and associated lateritic mineralization (the Morro dos Seis Lagos Nb deposit). The host rock (gneiss) yielded an age of 1828 ± 09 Ma interpreted as the crystallization time of this unit. The altered feldspar vein in the same gneiss yielded an age of 1839 ± 29 Ma. Carbonatite samples provided 3 groups of ages. The first group comprises inherited zircons with ages compatible with the gneissic host rock: 1819 ± 10 Ma (superior intercept), 1826 ± 5 Ma (concordant age), and 1812 ± 27 Ma (superior intercept), all from the Orosirian. The second and the third group of ages are from the same carbonatite sample: the superior intercept age of 1525 ± 21 Ma (MSWD = 0.77) and the superior intercept age of 1328 ± 58 Ma (MSWD = 1.4). The mineralogical study indicates that the ∼1.3 Ga zircons have affinity with carbonatite. It is, however, a tendence rather than a well-defined result. The data allow state that the age of 1328 ± 58 Ma represents the maximum age of the carbonatite. Without the same certainty, we consider that the data suggest that this age may be the carbonatite age, whose emplacement would have been related to the evolution of the K'Mudku belt. The best age obtained in laterite samples (a superior intercept age of 1828 ± 12 Ma) is considered the age of the main source for the inherited zircons related to the gneissic host rock.

  13. Can Single Crystal (U-Th)/He Zircon Ages from Nördlinger Ries Suevite be Linked to Impact-Related Shock Effects?

    NASA Astrophysics Data System (ADS)

    van Soest, M. C.; Cooper, F. J.; Wartho, J.; Hodges, K.; Buchner, E.; Schmieder, M.; Koeberl, C.

    2010-12-01

    Dating of impact-related material is difficult especially when pristine impact melt is unavailable. In the absence of such melts, most geochronometers in shocked basement or melt-poor impact rocks yield only partially reset or non-reset ages. In such cases, application of the low closure temperature apatite and zircon (U-Th)/He geochronometers can be successful, since impact-related physical and thermal shock should reset the He systematics in both minerals in most materials affected by the impact. For a proof of concept study on the well-studied Ries impact structure, we (U-Th)/He dated apatites (14.08 ± 0.26 Ma 2σ, n = 5) and zircons (14.26 ± 0.31 Ma 2σ, n = 10) from two Aumühle quarry suevite samples and one Polsingen quarry impact melt rock, which was dated at 14.37 ± 0.30 Ma (2σ) using Ar-Ar stepwise heating of recrystallized K-feldspar melt (Buchner et al., 2010). The (U-Th)/He ages agree well with the 14.37 Ma age, but are slightly younger than the suggested age of 14.59 ± 0.20 Ma (2σ - based on recent, post 1995, Ar-Ar data, Buchner et al., 2010) for the impact structure. However, among the 27 zircons dated, 6 were partially reset (>16Ma), and 11 zircons yielded younger dates (<13.5 Ma).The younger dates are problematic for successful (U-Th)/He dating of impact structures of unknown age, as they would be identified incorrectly as the age of the impact event. The cause for these younger dates may be: a) partial He loss due to a post-impact thermal event, which at Ries is unlikely as there is no geological evidence for such an event; b) compromised He retention due to metamictization by progressive radiation damage; or c) compromised He retention due to impact shock-related effects. The latter two causes can produce similar visual effects on zircon and the He loss mechanism is also similar, i.e. changes in the zircon crystal structure on a micro scale. However, the effects of these processes on zircon have been documented extensively by non

  14. Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust

    NASA Astrophysics Data System (ADS)

    Ushikubo, Takayuki; Kita, Noriko T.; Cavosie, Aaron J.; Wilde, Simon A.; Rudnick, Roberta L.; Valley, John W.

    2008-08-01

    In situ Li analyses of 4348 to 3362 Ma detrital zircons from the Jack Hills, Western Australia by SIMS reveal that the Li abundances (typically 10 to 60 ppm) are commonly over 10,000 times higher than in zircons crystallized from mantle-derived magmas and in mantle-derived zircon megacrysts (typically < 2 ppb). High Li concentrations in zircons (10 to 250 ppm) have also been found in igneous zircons from three continental parent rocks: granites, Li-rich pegmatites, and migmatites in pelitic metasediment. The substitution of trivalent cations (REEs and Y) in zircon correlates with Li + 1 and P + 5 , suggesting that an interstitial site for Li, as well as the xenotime substitution for P, provides charge balance for REEs. Li is thus fixed in the zircon structure by coupled substitutions, and diffusive changes in [Li] composition are rate-limited by slow diffusion of REEs. The Jack Hills zircons also have fractionated lithium isotope ratios ( δ7Li = - 19 to + 13‰) about five times more variable than those recorded in primitive ocean floor basalts (2 to 8‰), but similar to continental crust and its weathering products. Values of δ7Li below - 10‰ are found in zircons that formed as early as 4300 Ma. The high Li compositions indicate that primitive magmas were not the source of Jack Hills zircons and the fractionated values of δ7Li suggest that highly weathered regolith was sampled by these early Archean magmas. These new Li data provide evidence that the parent magmas of ancient zircons from Jack Hills incorporated materials from the surface of the Earth that interacted at low temperature with liquid water. These data support the hypothesis that continental-type crust and oceans existed by 4300 Ma, within 250 million years of the formation of Earth and the low values of δ7Li suggest that weathering was extensive in the early Archean.

  15. 21 CFR 884.2660 - Fetal ultrasonic monitor and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Fetal ultrasonic monitor and accessories. 884.2660... (CONTINUED) MEDICAL DEVICES OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Monitoring Devices § 884.2660 Fetal ultrasonic monitor and accessories. (a) Identification. A fetal ultrasonic...

  16. 21 CFR 884.2660 - Fetal ultrasonic monitor and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Fetal ultrasonic monitor and accessories. 884.2660... (CONTINUED) MEDICAL DEVICES OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Monitoring Devices § 884.2660 Fetal ultrasonic monitor and accessories. (a) Identification. A fetal ultrasonic...

  17. 21 CFR 884.2660 - Fetal ultrasonic monitor and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Fetal ultrasonic monitor and accessories. 884.2660... (CONTINUED) MEDICAL DEVICES OBSTETRICAL AND GYNECOLOGICAL DEVICES Obstetrical and Gynecological Monitoring Devices § 884.2660 Fetal ultrasonic monitor and accessories. (a) Identification. A fetal ultrasonic...

  18. Zircon crytallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

    USGS Publications Warehouse

    Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.

    2007-01-01

    In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Miff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ??? 60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction). ?? 2007 Geological Society of America.

  19. Zircon crystallization and recycling in the magma chamber of the rhyolitic Kos Plateau Tuff (Aegean arc)

    USGS Publications Warehouse

    Bachman, O.; Charlier, B.L.A.; Lowenstern, J. B.

    2007-01-01

    In contrast to most large-volume silicic magmas in continental arcs, which are thought to evolve as open systems with significant assimilation of preexisting crust, the Kos Plateau Tuff magma formed dominantly by crystal fractionation of mafic parents. Deposits from this ~60 km3 pyroclastic eruption (the largest known in the Aegean arc) lack xenocrystic zircons [secondary ion mass spectrometry (SIMS) U-Pb ages on zircon cores never older than 500 ka] and display Sr-Nd whole-rock isotopic ratios within the range of European mantle in an area with exposed Paleozoic and Tertiary continental crust; this evidence implies a nearly closed-system chemical differentiation. Consequently, the age range provided by zircon SIMS U-Th-Pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus. The age distribution from 160 ka (age of eruption by sanidine 40Ar/39Ar dating; Smith et al., 1996) to ca. 500 ka combined with textural characteristics (high crystal content, corrosion of most anhydrous phenocrysts, but stability of hydrous phases) suggest (1) a protracted residence in the crust as a crystal mush and (2) rejuvenation (reduced crystallization and even partial resorption of minerals) prior to eruption probably induced by new influx of heat (and volatiles). This extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned Aegean microplate acts as a refractory container for magmas in the dying Aegean subduction zone (continent-continent subduction).

  20. 21 CFR 874.4680 - Bronchoscope (flexible or rigid) and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... (flexible or rigid) and accessories. (a) Identification. A bronchoscope (flexible or rigid) and accessories... bronchoscope and is intended to examine or treat the larynx and tracheobronchial tree. It is typically used...

  1. Dating high-grade metamorphism: constraints from zircon and garnet REE compositions

    NASA Astrophysics Data System (ADS)

    Whitehouse, M. J.; Platt, J. P.

    2001-12-01

    We present high spatial resolution ion microprobe REE analyses of zircon and garnet from pelitic granulite adjacent to the Ronda peridotite, Betic Cordillera, southern Spain. The zircons exhibit polyphase growth, with thick structureless (in cathodoluminescence) overgrowths over detrital cores. These overgrowths yield a U-Pb age of 21.3 +/- 0.3 Ma [1, unpublished data] which we intepret as dating an episode of zircon growth during the Alpine orogeny. REE analyses of the dated portions of these zircons reveal profound differences between cores and rims. Cores show patterns typical of magmatic zircon (steep upward slopes from La to Lu with marked positive Ce anomaly), while the overgrowths are characterised by flat or even negatively sloping HREE profiles (Gd - Lu). Garnet, which occupies ca. 30 % by volume of the rock, is the most likely phase to host the HREEs in the rock and has been the subject of further ion-microprobe REE, textural and trace element investigations. The garnets are themselves zoned, with dominant central regions that are relatively free of inclusions overgrown by inclusion-rich, more calcic rims. Inclusions of kyanite +rutile in the central regions and sillimanite +ilmenite in the rims suggests that the garnets grew during decompression, and the Ca-enrichment in the rims suggests that their growth coincided with the initiation of partial melting. The presence of rimmed zircons only in the garnet rims and the matrix further suggests that the zircons also grew during this late decompressional history. An REE traverse of the garnet from core to rim reveals marked HREE depletion in the rims relative to the cores which we suggest is consistent with the textural evidence and probably results from early garnet core growth strongly depleting the HREEs available to subsequent growth. This mechanism can also be invoked to explain depletion in the zircon rims and more closely ties their formation to this stage of garnet growth. We therefore interpret the

  2. Recycling of crustal materials through study of ultrahigh-pressure minerals in collisional orogens, ophiolites, and mantle xenoliths: A review

    NASA Astrophysics Data System (ADS)

    Liou, Juhn G.; Tsujimori, Tatsuki; Yang, Jingsui; Zhang, R. Y.; Ernst, W. G.

    2014-12-01

    Newly recognized occurrences of ultrahigh-pressure (UHP) minerals including diamonds in ultrahigh-temperature (UHT) felsic granulites of orogenic belts, in chromitites associated with ophiolitic complexes, and in mantle xenoliths suggest the recycling of crustal materials through deep subduction, mantle upwelling, and return to the Earth's surface. This circulation process is supported by crust-derived mineral inclusions in deep-seated zircons, chromites, and diamonds from collision-type orogens, from eclogitic xenoliths in kimberlites, and from chromitities of several Alpine-Himalayan and Polar Ural ophiolites; some of these minerals contain low-atomic number elements typified by crustal isotopic signatures. Ophiolite-type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone. In addition to ringwoodite and inferred stishovite, a number of nanometric minerals have been identified as inclusions employing state-of-the-art analytical tools. Reconstitution of now-exsolved precursor UHP phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier UHP conditions. For example, Tibetan chromites containing exsolution lamellae of coesite + diopside suggest that the original chromitites formed at P > 9-10 GPa at depths of >250-300 km. The precursor phase most likely had a Ca-ferrite or a Ca-titanite structure; both are polymorphs of chromite and (at 2000 °C) would have formed at minimum pressures of P > 12.5 or 20 GPa respectively. Some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin, including zircon, feldspars, garnet, kyanite, andalusite, quartz, and rutile; the zircons possess much older U-Pb ages than the time of ophiolite formation. These UHP mineral-bearing chromitite hosts evidently had a deep-seated evolution prior to extensional mantle upwelling and partial

  3. Accessory mental foramina and nerves: Application to periodontal, periapical, and implant surgery.

    PubMed

    Iwanaga, Joe; Watanabe, Koichi; Saga, Tsuyoshi; Tabira, Yoko; Kitashima, Sadaharu; Kusukawa, Jingo; Yamaki, Koh-Ichi

    2016-05-01

    Recent studies investigating accessory mental foramina using developments in diagnostic imaging have primarily defined the morphology of the foramina; however, few studies have described the structures passing through them. Additional clinical knowledge of the foramina is therefore required for preoperative diagnosis prior to surgery, including implant, periodontal and periapical surgery. In this study, we investigated the accessory mental foramina and the associated nerves and arteries in donated cadaveric mandibles using anatomical and radiological observation methods. We examined 63 mandibles with overlying soft tissue by cone-beam computed tomography and noted the existence of the accessory mental foramina. Mandibles with accessory mental foramina were subsequently analyzed. Additionally, the neurovascular bundles passing through these foramina were dissected using anatomical methods.The incidence of accessory mental foramina was 14.3%. The larger foramina tended to be located anteriorly or superiorly and proximal to the mental foramen, while the smaller foramina tended to be located posterosuperiorly and distal to the mental foramen. The mental foramen ipsilateral to the accessory mental foramen was smaller than the one contralateral to it. The comparatively distant and large accessory mental foramen included an artery.This study elucidated the relationship between accessory mental foramina and the associated nerves and arteries. We believe that the results will contribute to the clinical dentistry field. © 2015 Wiley Periodicals, Inc.

  4. U-Pb Dating of Unabraded Detrital Zircon Metamorphic Rims in the Nanaimo Basin, British Columbia

    NASA Astrophysics Data System (ADS)

    Boivin, M. P.; Guest, B.; Matthews, W.

    2016-12-01

    Thin metamorphic rims on detrital zircons from the Nanaimo Basin in SW British Columbia offer a unique opportunity to further constrain the source of these zircons, helping to resolve the long standing Baja BC controversy. Here we present an analytical approach for dating thin zircon rims and use it to show that zircons from the Nanaimo Basin are most likely derived from metamorphic rocks in southern California. Conventional in-situ laser ablation sample preparation typically requires mounting and polishing zircon grains to expose their core. However, in order to date these thin metamorphic zircon rims a depth-profiling approach on unabraded grains was employed. Zircon grains from the Upper Cretaceous Geoffrey, Spray, and Gabriola formations of the Nanaimo Group exposed on Denman and Hornby Islands (British Columbia) were sorted into five groups based on morphology. The zircons were then mounted on tape along with several grains of a well-characterised zircon reference material to validate the uncertainty of the method. The zircons were then imaged using a Zygo Zescope optical profilometer in order to correct for grain-to-grain variations in elevation relative to mounting medium and ensure consistent laser focus. Backscatter electron images (BSE) were used to further characterised the grains and optimize the location of laser ablation targets. Zircons were ablated using a Resonetics 193 nm excimer laser and uranium and lead isotopic ratios were measured using an Agilent 7700 quadrupole mass spectrometer. A low frequency laser repetition rate extended the data collection period on relatively thin zircon rims. Our results show that metamorphic zircon growth occurred in two main phases at 100 Ma and 77 Ma suggesting two sources of detrital zircons with differing metamorphic histories were present in the catchment area. The timing of metamorphism of the source area for the Nanaimo basin is inconsistent with derivation from sources in the Rocky Mountains (Lemhi sub

  5. 21 CFR 884.2700 - Intrauterine pressure monitor and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Intrauterine pressure monitor and accessories. 884.2700 Section 884.2700 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... include the following accessories: signal analysis and display equipment, patient and equipment supports...

  6. 21 CFR 884.2640 - Fetal phonocardiographic monitor and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Fetal phonocardiographic monitor and accessories. 884.2640 Section 884.2640 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... includes the following accessories: signal analysis and display equipment, patient and equipment supports...

  7. 21 CFR 884.2640 - Fetal phonocardiographic monitor and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Fetal phonocardiographic monitor and accessories. 884.2640 Section 884.2640 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... includes the following accessories: signal analysis and display equipment, patient and equipment supports...

  8. 21 CFR 884.2700 - Intrauterine pressure monitor and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Intrauterine pressure monitor and accessories. 884.2700 Section 884.2700 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... include the following accessories: signal analysis and display equipment, patient and equipment supports...

  9. 21 CFR 884.2640 - Fetal phonocardiographic monitor and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Fetal phonocardiographic monitor and accessories. 884.2640 Section 884.2640 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... includes the following accessories: signal analysis and display equipment, patient and equipment supports...

  10. 21 CFR 884.2640 - Fetal phonocardiographic monitor and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Fetal phonocardiographic monitor and accessories. 884.2640 Section 884.2640 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... includes the following accessories: signal analysis and display equipment, patient and equipment supports...

  11. 21 CFR 884.2640 - Fetal phonocardiographic monitor and accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Fetal phonocardiographic monitor and accessories. 884.2640 Section 884.2640 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... includes the following accessories: signal analysis and display equipment, patient and equipment supports...

  12. 21 CFR 884.2700 - Intrauterine pressure monitor and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Intrauterine pressure monitor and accessories. 884.2700 Section 884.2700 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN... include the following accessories: signal analysis and display equipment, patient and equipment supports...

  13. Investigating the Early Carbon Cycle Using Carbonaceous Inclusions and Dissolved Carbon in Detrital Zircon

    NASA Astrophysics Data System (ADS)

    Bell, E. A.; Boehnke, P.; Harrison, M.; Mao, W. L.

    2015-12-01

    Because the terrestrial rock record extends only to ~4 Ga and older materials thus far identified are limited to detrital zircons, information about volatile abundances and cycles on early Earth is limited. Carbon, for instance, plays an important role not only in the modern biosphere but also in deep recycling of materials between the crust and mantle. We are investigating the record of carbon abundance and origin in Hadean zircons from Jack Hills (W. Australia) using two main approaches. First, carbon may partition into the zircon structure at trace levels during crystallization from a magma, and better understanding of this partitioning behavior will allow for zircon's use as a monitor of magmatic carbon contents. We have measured carbon abundances in zircon from a variety of igneous rocks (gabbro; I-, A-, and S-type granitoids) via SIMS and found that although abundances are typically low (average raw 12C/30Si ~ 1x10-6), S-type granite zircons can reach a factor of 1000 over this background. Around 10% of Hadean zircons investigated show similar enrichments, consistent with other evidence for the derivation of many Jack Hills zircons from S-type granitoids and with the establishment of modern-level carbon abundances in the crust by ca. 4.2 Ga. Diamond and graphite inclusions reported in the Jack Hills zircons by previous studies proved to be contamination by polishing debris, leaving the true abundance of these materials in the population uncertain. On a second front, we have identified and investigated primary carbonaceous inclusions in these zircons. From a population of over 10,000 Jack Hills zircons, we identified one concordant 4.10±0.01 Ga zircon that contains primary graphite inclusions (so interpreted due to their enclosure in a crack-free zircon host as shown by transmission X-ray microscopy and their crystal habit). Their δ13CPDB of -24±5‰ is consistent with a biogenic origin and, in the absence of a likely inorganic mechanism to produce such a

  14. Complete Spinal Accessory Nerve Palsy From Carrying Climbing Gear.

    PubMed

    Coulter, Jess M; Warme, Winston J

    2015-09-01

    We report an unusual case of spinal accessory nerve palsy sustained while transporting climbing gear. Spinal accessory nerve injury is commonly a result of iatrogenic surgical trauma during lymph node excision. This particular nerve is less frequently injured by blunt trauma. The case reported here results from compression of the spinal accessory nerve for a sustained period-that is, carrying a load over the shoulder using a single nylon rope for 2.5 hours. This highlights the importance of using proper load-carrying equipment to distribute weight over a greater surface area to avoid nerve compression in the posterior triangle of the neck. The signs and symptoms of spinal accessory nerve palsy and its etiology are discussed. This report is particularly relevant to individuals involved in mountaineering and rock climbing but can be extended to anyone carrying a load with a strap over one shoulder and across the body. Copyright © 2015 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.

  15. Provenance studies by fission-track dating of zircon-etching and counting procedures

    USGS Publications Warehouse

    Naeser, N.D.; Zeitler, P.K.; Naeser, C.W.; Cerveny, P.F.

    1987-01-01

    In sedimentary rocks that have not been heated to high enough temperatures to anneal fission tracks in zircon (greater than ≈ 160°C), fission-track ages of individual detrital zircon grains provide valuable information about the source rocks eroded to form the sediments. The success of such studies depends, however, on the degree to which the ages determined from the detrital suite accurately portray the range of grain ages that are present in the suite. This in turn depends to a large extent on using counting and, in particular, etching procedures that permit proper sampling of grains with a wide range of age and uranium concentrations. Results are reported here of an experimental study of a ‘detrital’ zircon suite manufactured from several zircon populations of known age. This study suggests that multiple etches are required when a complete spectrum of ages in a zircon suite is desired.

  16. Provenance studies by fission-track dating of zircon-etching and counting procedures

    USGS Publications Warehouse

    Naeser, Nancy D.; Zeitler, Peter K.; Naeser, Charles W.; Cerveny, Philip F.

    1987-01-01

    In sedimentary rocks that have not been heated to high enough temperatures to anneal fission tracks in zircon (greater than approximately equals 160 degree C), fission-track ages of individual detrital zircon grains provide valuable information about the source rocks eroded to form the sediments. The success of such studies depends, however, on the degree to which the ages determined from the detrital suite accurately portray the range of grain ages that are present in the suite. This in turn depends to a large extent on using counting and, in particular, etching procedures that permit proper sampling of grains with a wide range of age and uranium concentrations. Results are reported here of an experimental study of a 'detrital' zircon suite manufactured from several zircon populations of known age. This study suggests that multiple etches are required when a complete spectrum of ages in a zircon suite is desired.

  17. New insights into Arctic paleogeography and tectonics from U-Pb detrital zircon geochronology

    USGS Publications Warehouse

    Miller, E.L.; Toro, J.; Gehrels, G.; Amato, J.M.; Prokopiev, A.; Tuchkova, M.I.; Akinin, V.V.; Dumitru, T.A.; Moore, Thomas E.; Cecile, M.P.

    2006-01-01

    To test existing models for the formation of the Amerasian Basin, detrital zircon suites from 12 samples of Triassic sandstone from the circum-Arctic region were dated by laser ablation-inductively coupled plasma-mass spectrometry (ICP-MS). The northern Verkhoyansk (NE Russia) has Permo-Carboniferous (265-320 Ma) and Cambro-Silurian (410-505 Ma) zircon populations derived via river systems from the active Baikal Mountain region along the southern Siberian craton. Chukotka, Wrangel Island (Russia), and the Lisburne Hills (western Alaska) also have Permo-Carboniferous (280-330 Ma) and late Precambrian-Silurian (420-580 Ma) zircons in addition to Permo-Triassic (235-265 Ma), Devonian (340-390 Ma), and late Precambrian (1000-1300 Ma) zircons. These ages suggest at least partial derivation from the Taimyr, Siberian Trap, and/ or east Urals regions of Arctic Russia. The northerly derived Ivishak Formation (Sadlerochit Mountains, Alaska) and Pat Bay Formation (Sverdrup Basin, Canada) are dominated by Cambrian-latest Precambrian (500-600 Ma) and 445-490 Ma zircons. Permo-Carboniferous and Permo-Triassic zircons are absent. The Bjorne Formation (Sverdrup Basin), derived from the south, differs from other samples studied with mostly 1130-1240 Ma and older Precambrian zircons in addition to 430-470 Ma zircons. The most popular tectonic model for the origin of the Amerasian Basin involves counterclockwise rotation of the Arctic Alaska-Chukotka microplate away from the Canadian Arctic margin. The detrital zircon data suggest that the Chukotka part of the microplate originated closer to the Taimyr and Verkhoyansk, east of the Polar Urals of Russia, and not from the Canadian Arctic. Copyright 2006 by the American Geophysical Union.

  18. Detrital thermochronology of Rhine, Elbe and Meuse river sediment (Central Europe): implications for provenance, erosion and mineral fertility

    NASA Astrophysics Data System (ADS)

    Glotzbach, C.; Busschers, F. S.; Winsemann, J.

    2018-03-01

    Here we present detrital apatite fission track (AFT), zircon fission track (ZFT) and a few apatite (U-Th)/He (AHe) data of Middle Pleistocene to modern Rhine, Meuse and Elbe river sediments in order to resolve processes that control detrital age distributions (provenance, erosion and mineral fertility). We used a modelling approach to compare observed with theoretically predicted age distributions from an interpolated in situ AFT and ZFT age map. In situ cooling ages do show large differences in the Rhine drainage basin, facilitating the differentiation between different source regions. Inconsistencies between observed and theoretical age distributions of the Meuse and Elbe samples can be explained by mixing and reworking of sediments with different provenances (Meuse Middle Pleistocene terrace sediment) and a yet unexplored source region with old AFT ages (Elbe samples). Overall, the results show that detrital thermochronology is capable of identifying the provenance of Middle Pleistocene to modern sediments. The AFT age distributions of Rhine sediments are dominated ( 70%) by AFT ages representing the Alps. A possible explanation is higher erosion rates in the Alps as compared to areas outside the Alps. A Late Pleistocene sample from the Upper Rhine Graben contains apatite grains from the Molasse and Hegau volcanics, which we explain with a shift of the headwaters of the Rhine to the north as a result of intense Middle Pleistocene Riss glaciation. Contrary to the observed dominance of Alpine-derived AFT ages in Rhine sediments, the relative contribution of zircon ages with sources in the Alps is lower and significantly decreases downstream, suggesting a major source of zircons outside the Alps. This can be explained by increased zircon fertility of sediments derived from the Rhenish massif. Therefore, we conclude that erosion and mineral fertility are the main processes controlling detrital AFT and ZFT age distributions of the sampled river sediment. In case of

  19. 19 CFR 10.2020 - Accessories, spare parts, or tools.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 19 Customs Duties 1 2014-04-01 2014-04-01 false Accessories, spare parts, or tools. 10.2020 Section 10.2020 Customs Duties U.S. CUSTOMS AND BORDER PROTECTION, DEPARTMENT OF HOMELAND SECURITY... Trade Promotion Agreement Rules of Origin § 10.2020 Accessories, spare parts, or tools. (a) General...

  20. 19 CFR 10.600 - Accessories, spare parts, or tools.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...-Central America-United States Free Trade Agreement Rules of Origin § 10.600 Accessories, spare parts, or... 10.600 Customs Duties U.S. CUSTOMS AND BORDER PROTECTION, DEPARTMENT OF HOMELAND SECURITY; DEPARTMENT... of the good's standard accessories, spare parts, or tools will be treated as originating goods if the...

  1. Uniformly mantle-like δ18O in zircons from oceanic plagiogranites and gabbros

    NASA Astrophysics Data System (ADS)

    Grimes, Craig B.; Ushikubo, Takayuki; John, Barbara E.; Valley, John W.

    2011-01-01

    Lower ocean crust is primarily gabbroic, although 1-2% felsic igneous rocks that are referred to collectively as plagiogranites occur locally. Recent experimental evidence suggests that plagiogranite magmas can form by hydrous partial melting of gabbro triggered by seawater-derived fluids, and thus they may indicate early, high-temperature hydrothermal fluid circulation. To explore seawater-rock interaction prior to and during the genesis of plagiogranite and other late-stage magmas, oxygen-isotope ratios preserved in igneous zircon have been measured by ion microprobe. A total of 197 zircons from 43 plagiogranite, evolved gabbro, and hydrothermally altered fault rock samples have been analyzed. Samples originate primarily from drill core acquired during Ocean Drilling Program and Integrated Ocean Drilling Program operations near the Mid-Atlantic and Southwest Indian Ridges. With the exception of rare, distinctively luminescent rims, all zircons from ocean crust record remarkably uniform δ18O with an average value of 5.2 ± 0.5‰ (2SD). The average δ18O(Zrc) would be in magmatic equilibrium with unaltered MORB [δ18O(WR) ~ 5.6-5.7‰], and is consistent with the previously determined value for equilibrium with the mantle. The narrow range of measured δ18O values is predicted for zircon crystallization from variable parent melt compositions and temperatures in a closed system, and provides no indication of any interactions between altered rocks or seawater and the evolved parent melts. If plagiogranite forms by hydrous partial melting, the uniform mantle-like δ18O(Zrc) requires melting and zircon crystallization prior to significant amounts of water-rock interactions that alter the protolith δ18O. Zircons from ocean crust have been proposed as a tectonic analog for >3.9 Ga detrital zircons from the earliest (Hadean) Earth by multiple workers. However, zircons from ocean crust are readily distinguished geochemically from zircons formed in continental crustal

  2. Mineral equilibria and zircon, garnet and titanite U-Pb ages constraining the PTt path of granite-related hydrothermal systems at the Big Bell gold deposit, Western Australia

    NASA Astrophysics Data System (ADS)

    Mueller, Andreas G.; McNaughton, Neal J.

    2018-01-01

    The Big Bell deposit (75 t gold) is located in a narrow spur of the Meekatharra greenstone belt, Yilgarn Craton, Western Australia. Two ore bodies are located in a calcic-potassic contact alteration zone overprinting lineated granodiorite dykes and amphibolite: almandine-cummingtonite-hornblende skarn (1-3 g/t Au, 1700 g/t As, 330 g/t W) and the muscovite-microcline gneiss (3-5 g/t Au, 580 g/t Sb, 620 g/t W) of the Main Lode. Genetic models vary from pre- to post-metamorphic replacement. Hornblende-plagioclase pairs in amphibolite constrain peak metamorphic temperature to 670 ± 50 °C. In contrast, garnet-biotite thermometry provides estimates of 578 ± 50 and 608 ± 50 °C for garnet-cordierite-biotite schist bordering the skarn and enveloping the Main Lode. Garnet-cordierite and garnet-hornblende pairs extend the range of fluid temperature to 540 ± 65 °C, well below peak metamorphic temperature. At 540-600 °C, the alteration assemblage andalusite + sillimanite constrains pressure to 300-400 MPa corresponding to 11-14 km crustal depth. Published U-Pb ages indicate that metamorphism took place in the aureole of the southeast granodiorite-tonalite batholith (2740-2700 Ma), followed by gold mineralization at 2662 ± 5 Ma and by the emplacement of biotite granite and Sn-Ta-Nb granite-pegmatite dykes at 2625-2610 Ma. Amphibolite xenoliths in granite northwest of the deposit record the lowest temperature (628 ± 50 °C), suggesting it lacks a metamorphic aureole. The rare metal dykes are spatially associated with epidote-albite and andradite-diopside skarns (≤1.5 g/t Au), mined where enriched in the weathered zone. We analysed hydrothermal zircon intergrown with andradite. Concordant U-Pb ages of 2612 ± 7 and 2609 ± 10 Ma confirm the presence of a second granite-related system. The zircons display oscillatory zoning and have low Th/U ratios (0.05-0.08). Low-Th titanite from an albite granite dyke has a concordant but reset U-Pb age of 2577 ± 7 Ma.

  3. Precise K-Ar, 40Ar/39Ar, Rb-Sr and U/Pb mineral ages from the 27.5 Ma fish canyon tuff reference standard

    USGS Publications Warehouse

    Lanphere, M.A.; Baadsgaard, H.

    2001-01-01

    The accuracy of ages measured using the 40Ar/39Ar technique is affected by uncertainties in the age of radiation fluence-monitor minerals. At present, there is lack of agreement about the ages of certain minerals used as fluence monitors. The accuracy of the age of a standard may be improved if the age can be measured using different decay schemes. This has been done by measuring ages on minerals from the Oligocene Fish Canyon Tuff (FCT) using the K-Ar, 40Ar/39Ar. Rb-Sr and U/Pb methods. K-Ar and 40Ar/39Ar total fusion ages of sanidine, biotite and hornblende yielded a mean age of 27.57 ?? 0.36 Ma. The weighted mean 40Ar/39Ar plateau age of sanidine and biotite is 27.57 ?? 0.18 Ma. A biotite-feldspar Rb-Sr isochron yielded an age of 27.44 ?? 0.16 Ma. The U-Pb data for zircon are complex because of the presence of Precambrian zircons and inheritance of radiogenic Pb. Zircons with 207Pb/235U < 0.4 yielded a discordia line with a lower concordia intercept of 27.52 ?? 0.09 Ma. Evaluation of the combined data suggests that the best age for FCT is 27.51 Ma. Published by Elsevier Science B.V.

  4. The role of trace element partitioning between garnet, zircon and orthopyroxene on the interpretation of zircon U-Pb ages: an example from high-grade basement in Calabria (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Fornelli, A.; Langone, A.; Micheletti, F.; Pascazio, A.; Piccarreta, G.

    2014-03-01

    The recognition of the coeval growth of zircon, orthopyroxene and garnet domains formed during the same metamorphic cycle has been attempted with detailed microanalyses coupled with textural analyses. A coronitic garnet-bearing granulite from the lower crust of Calabria has been considered. U-Pb zircon data and zircon, garnet and orthopyroxene chemistries, at different textural sites, on a thin section of the considered granulite have been used to test possible equilibrium and better constrain the geological significance of the U-Pb ages related to zircon separates from other rocks of the same structural level. The garnet is very rich in REE and is characterised by a decrease in HREE from core to outer core and an increase in the margin. Zircons show core-overgrowth structures showing different chemistries, likely reflecting episodic metamorphic new growth. Zircon grains in matrix, corona around garnet and within the inner rim of garnet, are decidedly poorer in HREE up to Ho than garnet interior. Orthopyroxene in matrix and corona is homogeneously poor in REE. Thus, the outer core of garnet and the analysed zircon grains grew or equilibrated in a REE depleted system due to the former growth of garnet core. Zircon ages ranging from 357 to 333 Ma have been determined in the matrix, whereas ages 327-320 Ma and around 300 Ma have been determined, respectively, on cores and overgrowths of zircons from matrix, corona and inner rim of garnet. The calculated DREEzrn/grt and DREEopx/grt are largely different from the equilibrium values of literature due to strong depletion up to Ho in zircon and orthopyroxene with respect to garnet. On the other hand, the literature data show large variability. In the case study, (1) the D zrn/grt values define positive and linear trends from Gd to Lu as many examples from literature do and the values from Er to Lu approach the experimental results at about 900 °C in the combination zircon dated from 339 to 305 Ma with garnet outer core

  5. Accessory neuropathy after sternotomy: Clinico-anatomical correlation supporting an inflammatory cause.

    PubMed

    Kassem, Mohammad W; Iwanaga, Joe; Loukas, Marios; Stone, Jonathan J; Smith, Jay; Spinner, Robert J; Tubbs, R Shane

    2018-04-01

    Inflammatory etiologies are becoming increasingly recognized as explanations of some neuropathies, especially those occurring in the perioperative period. Although "brachial neuritis" is known to affect extraplexal nerves, accessory nerve palsy following median sternotomy has been attributed to stretch on the nerve. To better elucidate stretch as a potential cause, a cadaveric study was performed. Two patients who developed accessory nerve palsy following median sternotomy are presented to illustrate features consistent with the diagnosis of a perioperative inflammatory neuropathy. Five adult unembalmed cadavers underwent exposure of the bilateral accessory nerves in the posterior cervical triangle. A median sternotomy was performed and self-retaining retractors positioned. With the head in neutral, left rotation and right rotation, retractors were opened as during surgery while observing and recording any accessory nerve movements. The self-retaining sternal retractors were fully opened to a mean inter-blade distance of 13 cm. Regardless of head position, from the initial retractor click to maximal opening there was no gross movement of the accessory nerve on the left or right sides. Opening self-retaining sternal retractors does not appear to stretch the accessory nerve in the posterior cervical triangle. Based on our clinical experience and cadaveric results, we believe that inflammatory conditions, (i.e., idiopathic brachial plexitis) can involve the accessory nerve, and might be triggered by surgical procedures. Clin. Anat. 31:417-421, 2018. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  6. 21 CFR 884.2660 - Fetal ultrasonic monitor and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Fetal ultrasonic monitor and accessories. 884.2660... Devices § 884.2660 Fetal ultrasonic monitor and accessories. (a) Identification. A fetal ultrasonic monitor is a device designed to transmit and receive ultrasonic energy into and from the pregnant woman...

  7. The effect of α-damage on fission-track annealing in zircon

    USGS Publications Warehouse

    Kasuya, M.; Naeser, C.W.

    1988-01-01

    The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e. different amounts of ??-damage) has been studied by one hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon. ?? 1988.

  8. Diamond and Unusual Minerals Discovered from the Chromitite in Polar Ural: A First Report

    NASA Astrophysics Data System (ADS)

    Yang, J.; Bai, W.; Fang, Q.; Meng, F.; Chen, S.; Zhang, Z.

    2007-12-01

    Ultrahigh pressure (UHP) minerals, such as diamond, coesite, and pseudomorphs of octahedral olivine, and as well as about 80 other mineral species have been recovered from podiform chromitites of the Luobusa ophiolite, southern Tibet, and a new mineral, Luobusaite (Fe0.82Si2), has been approved recently by CNMMN. The UHP minerals from Luobusa are controversial because they have not found in situ and because ophiolites are currently believed to form at shallow levels above oceanic spreading centers. More detailed study and experimental work are needed to understand the origin and significance of these unusual minerals and investigations of other ophiolites are needed to determine if such minerals occur elsewhere. For this purpose, we collected about 1500 kg of chromitite from two orebodies in an ultramafic body in the Polar Urals. Thus far, more than 60 different mineral species have been separated from these ores. The most exciting discovery is the common occurrence of diamond, a typical UHP mineral in the Luobusa chromitites. Diamonds from Ural chromitite are clear, colorless, well-developed crystals with octahedral morphology, generally 0.2-0.3 mm in size. Attached with the diamonds and perhaps also occurring as inclusions within them are many minerals as chromite, MnNiCrFe alloy, native Si and Ta, corundum, zircon, feldspar, garnet, moissanite, confirming their natural origin and suggesting a long residence time in the mantle. Other mineral group include: (1) native elements: Cr, W, Ni, Co, Si, Al and Ta; (2) carbides: SiC and WC; (3) alloys: Cr-Fe, Si-Al-Fe, Ni-Cu, Ag-Au, Ag-Sn, Fe-Si, Fe-P, and Ag-Zn-Sn; (4) oxides: NiCrFe, PbSn, REE, rutile and Si- bearing rutile, ilmenite, corundum, chromite, MgO, and SnO2; (5) silicates: kyanite, pseudomorphs of octahedral olivine, zircon, garnet, feldspar, and quartz,; (6) sulfides of Fe, Ni, Cu, Mo, Pb, Ab, AsFe, FeNi, CuZn, and CoFeNi; and (7) iron groups: native Fe, FeO, and Fe2O3. These minerals are very similar in

  9. Alps to Apennines zircon roller coaster along the Adria microplate margin.

    PubMed

    Jacobs, J; Paoli, G; Rocchi, S; Ksienzyk, A K; Sirevaag, H; Elburg, M A

    2018-02-09

    We have traced the particle path of high-pressure metasedimentary rocks on Elba Island, Northern Apennines, with the help of a U-Pb-Hf detrital zircon study. One quarter of the analysed zircons are surprisingly young, 41-30 Ma, with a main age peak at ca. 32 Ma, indicating an unexpected early Oligocene maximum deposition age. These Oligocene ages with negative εHf indicate a volcanic source region in the central-southern Alps. Though young by geological means, these zircons record an extraordinary geodynamic history. They originated in a volcanic arc, during the convergence/collision of the the Adria microplate with Europe from ca. 65 to 30 Ma. Thereafter, the Oligocene zircons travelled ca. 400 km southward along the Adria margin and the accretionary prism to present-day Tuscany, where they were subducted to depths of at least 40 km. Shortly thereafter, they were brought to the surface again in the wake of hinge roll back of the Apennine subduction zone and the resulting rapid extensional exhumation. Such a zircon roller coaster requires a microplate that has back-to-back subduction zones with opposing polarities on two sides.

  10. Nb sbnd Th sbnd Zr mineralization in microgranite—microsyenite at Jabal Tawlah, Midyan region, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Drysdall, Alan R.; Douch, Colin J.

    A composite sill of mineralized and highly radioactive microgranite—microsyenite caps Jabal Tawlah, a low ridge in the extreme NW of the Arabian Shield. The leucocratic composition, distribution of quartz and low K 2O:Na 2O ratios indicate that deuteric processes, including separation of a silica-rich phase and albitization, played a major role. Mineralization is in the form of a disseminated enrichment in Nb, Ta, Sn, Th, Y, heavy REE and Zr. Four Y- and heavy REE-bearing minerals, gagarinite [NaCaY(F,Cl) 6], fergusonite [(Y,Er,Ce,Fe)(Nb,Ta,Ti)O 4], xenotime and yttrian fluorite, as well as zircon, columbite, thorite, sphalerite, galena, pyrite, ilmenite, hematite, limonite, magnetite, goethite, siderite, possible chrysocolla and an MnO-bearing mineral have been identified. The geochemical signature of the mineralization is similar to that which distinguishes alkali granites from other granitic rocks. Jabal az Zuhd, a major plutonic complex consisting largely of alkali granite, crops out only 5 km NW of Jabal Tawlah. However, there is no other evidence of possible derivation from a parental alkali granite magma. Reserves indicated by outcrop dimensions and three drill-hole intersections are 6.4 million tonnes to an average depth of 65 m below wadi level, grading 0.34% Nb, 0.52% Y, 0.47% Zn and approximately 4% zircon (plus 175 ppm Ta, 380 ppm Sn, 700 ppm Th and heavy REE).

  11. Accessory wandering spleen: Report of a case of laparoscopic approach in an asymptomatic patient

    PubMed Central

    Perin, Alessandro; Cola, Roberto; Favretti, Franco

    2014-01-01

    INTRODUCTION Accessory wandering spleen is a rare but dangerous condition. Abnormalities of the ligamentous apparatus of an accessory spleen may evolve into torsion of its vascular axis, which can lead to a splenic infarct making surgery necessary. Patients are often asymptomatic and the diagnosis can be accidental. An early diagnosis and a correct treatment are fundamental. PRESENTATION OF CASE In this case report a young woman underwent laparoscopic surgery after an incidental finding at a Pelvic Ultrasound of an accessory wandering spleen. DISCUSSION In literature are reported cases of asymptomatic patients with an accessory wandering spleen treated with a conservative approach. However, a torsion or infarct of the accessory wandering spleen leads to emergency surgery. The presence of an independent vascular axis of the accessory spleen reduces the risk of postoperative complications (e.g. thrombocytosis) and the administration of low molecular weight heparin should prevent the risk of portal thrombosis. CONCLUSION We suggest performing surgery with a laparoscopic approach in patients with accessory wandering spleen, though asymptomatic, because of the risk of serious complications in case of accessory spleen torsion. PMID:25460427

  12. Chemical-abrasion SIMS dating of zircon from the Eocene Caetano caldera, Nevada

    NASA Astrophysics Data System (ADS)

    Colgan, J.; Watts, K. E.; John, D. A.; Henry, C. D.; Coble, M. A.; Vazquez, J. A.

    2012-12-01

    The Eocene Caetano caldera in northern Nevada formed during eruption of ~1100 km3 of crystal-rich rhyolite. Miocene extension cut the caldera into a set of fault blocks that expose minor pre-caldera volcanic rocks, two units of intracaldera Caetano Tuff up to 4 km thick, ash-flow tuff feeder dikes and ring-fracture intrusions, caldera collapse breccias, and post-collapse resurgent intrusions. Single-crystal 40Ar/39Ar sanidine dates on all parts of the caldera system overlap, yielding a 34.01 ± 0.05 Ma (n=17, Fish Canyon sanidine = 28.201 Ma) age for the eruption. 40Ar/39Ar dating also documents several preceding episodes of magmatism: 35.69 ± 0.06 Ma (sanidine, n =13) rhyolite dikes in the nearby Cortez gold district, 35.21 ± 0.18 Ma (plagioclase, n=1) andesite lava underlying Caetano Tuff, and a 38.90 ± 0.11 Ma (biotite, n=1), dacite dike in the northeastern caldera wall. Extensive U-Pb SHRIMP dating of zircon from both the Cortez dikes and all phases of the Caetano system suggests continuous magmatism from 40-34 Ma. However, all samples contain at least some—sometimes many—zircons with U-Pb ages younger than the 34.0 Ma argon age. To determine if anomalously young zircon ages are due to Pb-loss, we analyzed representative samples of the upper Caetano Tuff and the Redrock Canyon resurgent pluton with and without chemical abrasion to mitigate Pb-loss. Bulk zircon separates were annealed at 850°C for 48 hours, then chemically abraded with 10:1 HF/HNO3 vapor in a Parr bomb at 225°C for 8 hours, based on protocols outlined by Mattinson (2005). Both treated and untreated zircons from the same sample were mounted in epoxy and polished to their midsections, then imaged on the SEM using BSE and CL. The SHRIMP-RG at Stanford University was used to determine U-Pb ages and trace element concentrations in single spots for ~25 to 30 individual zircons per sample, using a round-robin procedure and two zircon age standards (R33 and 080) to monitor external precision

  13. Late Cretaceous porphyry copper mineralization in Sonora, Mexico: Implications for the evolution of the Southwest North America porphyry copper province

    NASA Astrophysics Data System (ADS)

    Barra, Fernando; Valencia, Victor A.

    2014-10-01

    Two porphyry Cu-Mo prospects in northern Sonora, Mexico (Fortuna del Cobre and Los Humos) located within the southwestern North American porphyry province have been dated in order to constrain the timing of crystallization and mineralization of these ore deposits. In Fortuna del Cobre, the pre-mineralization granodiorite porphyry yielded an U-Pb zircon age of 76.5 ± 2.3 Ma, whereas two samples from the ore-bearing quartz feldespathic porphyry were dated at 74.6 ± 1.3 and 75.0 ± 1.4 Ma. Four molybdenite samples from Los Humos porphyry Cu prospect yielded a weighted average Re-Os age of 73.5 ± 0.2 Ma, whereas two samples from the ore-bearing quartz monzonite porphyry gave U-Pb zircon ages of 74.4 ± 1.1 and 74.5 ± 1.3 Ma, showing a Late Cretaceous age for the emplacement of this ore deposit. The results indicate that Laramide porphyry Cu mineralization of Late Cretaceous age is not restricted to northern Arizona as previously thought and provide evidence for the definition of NS trending metallogenic belts that are parallel to the paleo-trench. Porphyry copper mineralization follows the inland migration trend of the magmatic arc as a result of the Farallon slab flattening during the Laramide orogeny.

  14. Accessory breasts: a historical and current perspective.

    PubMed

    Loukas, Marios; Clarke, Pamela; Tubbs, R Shane

    2007-05-01

    The presence of accessory breast tissue such as extra nipples (polythelia) and extra breast (polymastia) is relatively common, with a high incidence of being misdiagnosed in clinical medicine. Although polythelia is congenital in origin and is identifiable at childhood, polymastia may not be evident until the influence of sex hormones during puberty. In this article, we present a review of the literature concerning the historical background of accessory breasts, their incidence, their misdiagnoses, and their association with other syndromes and diseases. Finally, we present the common treatment options available today for such conditions.

  15. Interlaboratory comparison of mineral constituents in a sample from the Herrin (No. 6) coal bed from Illinois

    USGS Publications Warehouse

    Finkelman, Robert B.; Fiene, F.L.; Miller, R.N.; Simon, F.O.

    1984-01-01

    and possibly coquimbite and jarosite were also identified. Scanning electron microscopy studies indicated ubiquitous pyrite framboids and, less commonly, euhedral crystals, skeletal grains, irregularly shaped particles, and vein fillings. Minor accessory minerals such as rare-earth phosphates and possibly silicates, zircon, barium sulfate, titanium oxide, and sphalerite were also found. The textural evidence indicates that the minerals in the banded material are detrital whereas the minerals occurring as vein and pore fillings are authigenic. Magnetic measurements indicate that coal crushed in a steel pulverizer is contaminated by small quantities of abrasion fragments from the crusher, which seriously affect the measured magnetic properties of the coal.

  16. Accessory proteins of SARS-CoV and other coronaviruses.

    PubMed

    Liu, Ding Xiang; Fung, To Sing; Chong, Kelvin Kian-Long; Shukla, Aditi; Hilgenfeld, Rolf

    2014-09-01

    The huge RNA genome of SARS coronavirus comprises a number of open reading frames that code for a total of eight accessory proteins. Although none of these are essential for virus replication, some appear to have a role in virus pathogenesis. Notably, some SARS-CoV accessory proteins have been shown to modulate the interferon signaling pathways and the production of pro-inflammatory cytokines. The structural information on these proteins is also limited, with only two (p7a and p9b) having their structures determined by X-ray crystallography. This review makes an attempt to summarize the published knowledge on SARS-CoV accessory proteins, with an emphasis on their involvement in virus-host interaction. The accessory proteins of other coronaviruses are also briefly discussed. This paper forms part of a series of invited articles in Antiviral Research on "From SARS to MERS: 10 years of research on highly pathogenic human coronaviruses" (see Introduction by Hilgenfeld and Peiris (2013)). Copyright © 2014 Elsevier B.V. All rights reserved.

  17. The benefits of using bluetooth accessories with hearing aids.

    PubMed

    Smith, Pauline; Davis, Adrian

    2014-10-01

    To investigate the benefits in reported outcomes after providing bluetooth accessories for established hearing aid users. Prospective observational study using validated quantitative outcome measures and detailed patient narrative before and two months after patients were provided with bluetooth accessories. Twelve patients with bilateral NHS hearing aids participated. They had a wide range of ages and hearing loss. After two months, 10 patients reported substantial additional benefit and kept the accessories; two returned them for various reasons. Statistically significant changes were seen in two validated outcome measures: the Glasgow Hearing Aid Benefit Profile and the International Outcome Inventory - Hearing Aids, but not in the Speech, Spatial and Qualities of Hearing Scale. Two notable benefits were reported: some described hearing the emotion and mood in a voice for the first time; others were amazed to report an improved ability to hear film or to hold conversations over the telephone. The provision of bluetooth accessories can give additional reported benefit for some patients - we need better knowledge about who benefits, and whether further support/training to individuals would make a difference.

  18. Refractory Materials of Zirconate. Part 2: Synthesis and some properties of strontium, zirconate, calcium zirconate and barium zirconate

    NASA Technical Reports Server (NTRS)

    Okubo, Tsutomo; Yonemochi, Osamu; Nakamura, Kazuo; Maeda, Minoru

    1988-01-01

    Chemical compounds SrZrO3, CaZrO3, and BaZrO3 were synthesized by solid reaction and arc fusion, and their properties examined. Results were as follows: (1) in the synthesis of CaZrO3 by solid reaction, ZrO2 solid solution with cubic form was produced, which then changed into CaZrO3; (2) the BaZrO3 was a cubic form and did not show any transformation, while SrZrO3 and CaZrO3 with an orthorhombic form transformed to a cubic form at high temperature; and (3) the solubility of BaZrO3 in acid and its vaporization rate at a high temperature were greater than those of zirconates.

  19. U-Pb (zircon) and geochemical constraints on the age, origin, and evolution of Paleozoic arc magmas in the Oyu Tolgoi porphyry Cu-Au district, southern Mongolia

    USGS Publications Warehouse

    Wainwright, A.J.; Tosdal, R.M.; Wooden, J.L.; Mazdab, F.K.; Friedman, R.M.

    2011-01-01

    Uranium-Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu-Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (??Nd(t) range from +3.1 to +7.5 and 206Pb/204Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have <1.5% TiO2) are consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc. The Late Devonian and Carboniferous felsic rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu-Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium-Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu-Au deposits are ~372Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu-Au mineralization are ~366Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu-Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late

  20. Zircon and cassiterite U-Pb ages, petrogeochemistry and metallogenesis of Sn deposits in the Sibao area, northern Guangxi: constraints on the neoproterozoic granitic magmatism and related Sn mineralization in the western Jiangnan Orogen, South China

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Wang, Zongqi; Yan, Zhen; Gong, Jianghua; Ma, Shouxian

    2018-01-01

    A number of Sn deposits associated with Neoproterozoic granites are located in the western Jiangnan Orogen of northern Guangxi. The distribution of Sn mineralization is controlled by faults occurring within and around the Neoproterozoic granites. The hydrothermal alteration and mineralization of these Sn deposits exhibit zoning from the granite to the wall rock. The laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb ages of the cassiterite and zircon from ore-bearing granite in the Menggongshan Sn deposit are 829 ± 19 Ma and 822 ± 4 Ma, respectively, indicating that the Sn mineralization and granites formed in the Neoproterozoic and can considered to be products of coeval magmatic and hydrothermal activities. The ore-bearing granite and Neoproterozoic granites in northern Guangxi are high-K, calc-alkaline, peraluminous, S-type granites that are depleted in Nb, Ti, Sr and Ba and highly enriched in Rb, U and Pb. All the granites show steep fractionated light rare earth element (LREE) and flat heavy rare earth element (HREE) patterns, with strongly negative Eu anomalies. The ɛHf(t) values of the ore-bearing granite vary from - 9.0 to - 1.7, with an average value of - 4.1. Additionally, the ore-bearing granite exhibits low oxygen fugacity values. The magmatic source experienced partial melting during their evolution, and the source was dominated by recycled heterogeneous continental crustal materials. Our evidence confirms that the Neoproterozoic granites in northern Guangxi formed in a collisional tectonic setting. The collision between the Cathaysia and Yangtze blocks or between the Sibao arc (Jiangnan arc) and the Yangtze Block caused asthenospheric upwelling, leading to partial melting and recycling of the crust, forming the peraluminous S-type granites in the Neoproterozoic. The Sn mineralization has a close genetic relationship with the Neoproterozoic granite. The highly differentiated, peraluminous, B-enriched, crustally derived

  1. 26 CFR 48.4061(b)-3 - Rebuilt, reconditioned, or repaired parts or accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ..., reconditioned, or repaired parts or accessories. (a) Rebuilt parts or accessories. Rebuilding of automobile... for the person reassembling the generator, (6) reground or remetalized crankshafts, and (7) engines in... reassembling (with any necessary replacements of worn parts) of automobile parts or accessories, such as fuel...

  2. 26 CFR 48.4061(b)-3 - Rebuilt, reconditioned, or repaired parts or accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ..., reconditioned, or repaired parts or accessories. (a) Rebuilt parts or accessories. Rebuilding of automobile... for the person reassembling the generator, (6) reground or remetalized crankshafts, and (7) engines in... reassembling (with any necessary replacements of worn parts) of automobile parts or accessories, such as fuel...

  3. 26 CFR 48.4061(b)-3 - Rebuilt, reconditioned, or repaired parts or accessories.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ..., reconditioned, or repaired parts or accessories. (a) Rebuilt parts or accessories. Rebuilding of automobile... for the person reassembling the generator, (6) reground or remetalized crankshafts, and (7) engines in... reassembling (with any necessary replacements of worn parts) of automobile parts or accessories, such as fuel...

  4. New Insights on the Recrystallization and New Growth of Extensively Radiation-damaged Zircon

    NASA Astrophysics Data System (ADS)

    Hanchar, J. M.; Schmitz, M. D.; Wirth, R.

    2012-12-01

    Approximately 10 grams of cm-sized nearly metamict zircon crystals from the Saranac Prospect in the Bancroft District of Ontario were combined by breaking into small pieces and then ground under ethanol to a fine powder with an agate mortar and pestle in order to make enough homogeneously mixed material for multiple powder X-Ray and diffraction scans, high-resolution transmission electron microscopy (HR-TEM) measurements, and chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS). While these large zircon crystals ground to a powder have a larger surface area and not in the same physical state (i.e., brown and metamict) as what is typically analyzed in single zircon CA-ID-TIMS U-Pb analysis (clear euhedral grains), the physical and chemical changes that occur during the heat treatment used in CA-TIMS are thought to be similar processes. Aliquots of the ground zircon powder were annealed in situ using a Pt furnace in a powder diffractometer during which time simultaneous powder diffraction patterns were acquired starting at 25°C, at elevated temperature (from 500°C to 1400°C) at selected time intervals, and then again at 25°C. The powder X-ray diffraction results indicate that below ~900°C the recrystallization of the zircon powder commences but is incomplete, even after 36 hours, with diffuse low intensity diffraction peaks. At 1150°C the zircon powder shows significant recrystallization. At 1150°C, the recrystallization is essentially complete in less than one hour. Before heating the zircon powder samples consisted of clear, transparent to brown, translucent, complexly zoned fragments. After heating at 900°C the zircon powder retained a smaller percentage of clear or brown complexly zoned fragments, while the majority of material had transformed to oscillatory or irregularly zoned, dominantly white opaque microcrystalline fragments. The clear fragments were hypothesized to be preexisting original crystalline zircon, the brown

  5. 14 CFR 221.52 - Airport to airport application, accessorial services.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false Airport to airport application, accessorial... Charges § 221.52 Airport to airport application, accessorial services. Tariffs shall specify whether or not the fares therein include services in addition to airport-to-airport transportation. ...

  6. 14 CFR 221.52 - Airport to airport application, accessorial services.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 4 2013-01-01 2013-01-01 false Airport to airport application, accessorial... Charges § 221.52 Airport to airport application, accessorial services. Tariffs shall specify whether or not the fares therein include services in addition to airport-to-airport transportation. ...

  7. 14 CFR 221.52 - Airport to airport application, accessorial services.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 4 2014-01-01 2014-01-01 false Airport to airport application, accessorial... Charges § 221.52 Airport to airport application, accessorial services. Tariffs shall specify whether or not the fares therein include services in addition to airport-to-airport transportation. ...

  8. 14 CFR 221.52 - Airport to airport application, accessorial services.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 4 2012-01-01 2012-01-01 false Airport to airport application, accessorial... Charges § 221.52 Airport to airport application, accessorial services. Tariffs shall specify whether or not the fares therein include services in addition to airport-to-airport transportation. ...

  9. 14 CFR 221.52 - Airport to airport application, accessorial services.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Airport to airport application, accessorial... Charges § 221.52 Airport to airport application, accessorial services. Tariffs shall specify whether or not the fares therein include services in addition to airport-to-airport transportation. ...

  10. Zircon petrochronology reveals the temporal link between porphyry systems and the magmatic evolution of their hidden plutonic roots (the Eocene Coroccohuayco deposit, Peru)

    NASA Astrophysics Data System (ADS)

    Chelle-Michou, Cyril; Chiaradia, Massimo; Ovtcharova, Maria; Ulianov, Alexey; Wotzlaw, Jörn-Frederik

    2014-06-01

    We present zircon geochronologic (LA-ICPMS and ID-TIMS), trace element and Hf isotopic evidence for a complex evolution of the plutonic roots of the Eocene Coroccohuayco porphyry system, southern Peru. LA-ICPMS U-Pb dating has initially been carried out to optimize grain selection for subsequent high-precision ID-TIMS dating and to characterize crustal assimilation (xenocrystic cores). This combined in-situ and whole-grain U-Pb dating of the same grains has been further exploited to derive a robust temporal interpretation of the complex magmatic system associated with the Coroccohuayco porphyry-skarn deposit. Our data reveal that a heterogeneous gabbrodioritic complex was emplaced at ca. 40.4 Ma and was followed by a nearly 5 Ma-long magmatic lull until the emplacement of dacitic porphyry stocks and dykes associated with the mineralizing event at ca. 35.6 Ma. However, at the sample scale, zircons from the porphyries provide insight into a 2 Ma-long lived “hidden” magmatism (probably at 4-9 km paleodepth) prior to porphyry intrusion and mineralization for which no other evidence can be found on the surface today. These dates together with zircon trace element analysis and Hf isotopes argue for the development of a long-lived magmatic system dominated by amphibole fractionation with an increasing amount of crustal assimilation and the development of a large and sustained thermal anomaly. The system was probably rejuvenated at an increasing rate from 37.5 to 35.6 Ma with injection of fresh and oxidized magma from the lower crust, which caused cannibalism and remelting of proto-plutons. The porphyry intrusions at Coroccohuayco were emplaced at the peak thermal conditions of this upper crustal magma chamber, which subsequently cooled and expelled ore fluids. Zircon xenocrysts and Hf isotopes in the porphyritic rocks suggest that this large upper crustal system evolved at stratigraphic levels corresponding to Triassic sediments similar to the Mitu group that may be

  11. Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

    NASA Astrophysics Data System (ADS)

    Kunz, Barbara E.; Regis, Daniele; Engi, Martin

    2018-03-01

    Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U-Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P-T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U-Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

  12. Mantle Recycling of Crustal Materials through Study of Ultrahigh-Pressure Minerals in Collisional Orogens, Ophiolites, and Xenoliths

    NASA Astrophysics Data System (ADS)

    Liou, J. G.; Tsujimori, T.; Yang, J.; Zhang, R. Y.; Ernst, W. G.

    2014-12-01

    Newly recognized ultrahigh-pressure (UHP) mineral occurrences including diamonds in ultrahigh-temperature (UHT) felsic granulites of orogenic belts, in chromitites associated with ophiolitic complexes, and in mafic/ultramafic xenoliths suggest the recycling of crustal materials through profound subduction, mantle upwelling, and return to the Earth's surface. Recycling is supported by unambiguously crust-derived mineral inclusions in deep-seated zircons, chromites, and diamonds from collision-type orogens, from eclogitic xenoliths, and from ultramafic bodies of several Alpine-Himalayan and Polar Ural ophiolites; some such phases contain low-atomic number elements typified by crustal isotopic signatures. Ophiolite-type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone. In addition to ringwoodite and stishovite, a wide variety of nanometric minerals have been identified as inclusions employing state-of-the-art analysis. Reconstitution of now-exsolved precursor UHP phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier UHP conditions. Some podiform chromitites and associated peridotites contain rare minerals of undoubted crustal origin, including Zrn, corundum, Fls, Grt, Ky, Sil, Qtz, and Rtl; the zircons possess much older U-Pb ages than the formation age of the host ophiolites. These UHP mineral-bearing chromitites had a deep-seated evolution prior to extensional mantle upwelling and its partial melting at shallow depths to form the overlying ophiolite complexes. These new findings plus stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere, recycling of biogenic carbon into the lower mantle, and ascent to the Earth's surface through deep mantle ascent.

  13. Trace-element record in zircons during exhumation from UHP conditions, North-East Greenland Caledonides

    USGS Publications Warehouse

    McClelland, W.C.; Gilotti, J.A.; Mazdab, F.K.; Wooden, J.L.

    2009-01-01

    Coesite-bearing zircon formed at ultrahigh-pressure (UHP) conditions share general characteristics of eclogite-facies zircon with trace-element signatures characterized by depleted heavy rare earth elements (HREE), lack of an Eu anomaly, and low Th/ U ratios. Trace-element signatures of zircons from the Caledonian UHP terrane in North-East Greenland were used to examine the possible changes in signature with age during exhumation. Collection and interpretation of age and trace-element analyses of zircon from three samples of quartzofeldspathic gneiss and two leucocratic intrusions were guided by core vs. rim zoning patterns as imaged by cathodoluminesence. Change from igneous to eclogite-facies metamorphic trace-element signature in protolith zircon is characterized by gradual depletion of HREE, whereas newly formed metamorphic rims have flat HREE patterns and REE concentrations that are distinct from the recrystallized inherited cores. The signature associated with eclogite-facies metamorphic zircon is observed in coesite-bearing zircon formed at 358 ?? 4 Ma, metamorphic rims formed at 348 ?? 5 Ma during the initial stages of exhumation, and metamorphic rims formed at 337 ?? 5 Ma. Zircons from a garnet-bearing granite emplaced in the neck of an eclogite boudin and a leucocratic dike that cross-cuts amphibolite-facies structural fabrics have steeply sloping HREE patterns, variably developed negative Eu anomalies, and low Th/U ratios. The granite records initial decompression melting and exhumation at 347 ?? 2 Ma and later zircon rim growth at 329 ?? 5. The leucocratic dike was likely emplaced at amphibolite-facies conditions at 330 ?? 2 Ma, but records additional growth of compositionally similar zircon at 321 ??2 Ma. The difference between the trace-element signature of metamorphic zircon in the gneisses and in part coeval leucocratic intrusions indicates that the zircon signature varies as a function of lithology and context, thus enhancing its ability to aid in

  14. Zircon U-Pb age, Lu-Hf isotope, mineral chemistry and geochemistry of Sundamalai peralkaline pluton from the Salem Block, southern India: Implications for Cryogenian adakite-like magmatism in an aborted-rift

    NASA Astrophysics Data System (ADS)

    Renjith, M. L.; Santosh, M.; Li, Tang; Satyanarayanan, M.; Korakoppa, M. M.; Tsunogae, T.; Subba Rao, D. V.; Kesav Krishna, A.; Nirmal Charan, S.

    2016-01-01

    The Sundamalai peralkaline pluton is one among the Cryogenian alkaline plutons occurring in the Dharmapuri Rift Zone (DRZ) of the Salem Block in the Southern Granulite Terrane (SGT) of India. Here we present zircon U-Pb age and Lu-Hf isotopic composition, mineral chemistry and geochemistry of the pluton to explore the petrogenesis and geodynamic implications. Systematic modal variation of orthoclase, Na-plagioclase, Ca-amphibole (ferro-edenite and hastingsite) and quartz developed quartz-monzonite and granite litho units in the Sundamalai pluton. Thermometry based on amphibole-plagioclase pair suggests that the pluton was emplaced and solidified at around 4.6 kbar pressure with crystallization of the major phases between 748 and 661 °C. Estimated saturation temperature of zircon (712-698 °C) is also well within this range. However, apatite saturation occurred at higher temperatures between 835 and 870 °C, in contrast with monazite saturation (718-613 °C) that continued up to the late stage of crystallization. Estimated oxygen fugacity values (log fO2: -14 to -17) indicate high oxidation state for the magma that stabilized titanite and magnetite. The magmatic zircons from Sundamalai pluton yielded a weighted mean 206Pb/238U age of 832.6 ± 3.2 Ma. Geochemically, the Sundamalai rocks are high-K to shoshonitic, persodic (Na2O/K2O ratio > 1), silica-saturated (SiO2:65-72 wt.%), and peralkaline in composition (aluminum saturation index, ASI < 1; Alkalinity index, AI < 0). The initial magma was mildly metaluminous which evolved to strongly peralkaline as result of fractional crystallization (plagioclase effect) controlled differentiation between quartz-monzonite and granite. Both rock types have high content of Na2O (5.1-6.3 wt.%), Ba (350-2589 ppm) and Sr (264-1036 ppm); low content of Y (8.7-17 ppm) and Yb (0.96-1.69 ppm); elevated ratios of La/Yb (11-46) and Sr/Y (46-69) and are depleted in Ti, with a positive Sr anomaly suggesting an adakite-like composition and

  15. Accessory Devices Frequently Used for Endoscopic Submucosal Dissection

    PubMed Central

    Choi, Hyuk Soon; Chun, Hoon Jai

    2017-01-01

    Endoscopic submucosal dissection (ESD) is increasingly being considered an essential component of treatment for early gastrointestinal cancers and subepithelial tumors. The ESD technique owes its popularity to the development of sophisticated instruments used for ESD. With an increase in the number of ESD procedures performed, there is rapid development in the number and types of endoscopic accessory devices used for such procedures. Despite the large numbers of new devices developed and marketed, the use of ESD instruments and accessory devices is largely determined by individual preferences and experiences. Accessory devices frequently used during ESD are important tools for ESD techniques. Each instrument possesses characteristic advantages and disadvantages associated with its use, and no one instrument is superior in all respects to others. In this article, we review the characteristics of endoscopic electrical knives, cap and hood, and hemostatic devices commonly used in ESD. PMID:28609818

  16. 21 CFR 884.1300 - Uterotubal carbon dioxide insufflator and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Uterotubal carbon dioxide insufflator and... Gynecological Diagnostic Devices § 884.1300 Uterotubal carbon dioxide insufflator and accessories. (a) Identification. A uterotubal carbon dioxide insufflator and accessories is a device used to test the patency...

  17. 21 CFR 884.1300 - Uterotubal carbon dioxide insufflator and accessories.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Uterotubal carbon dioxide insufflator and... Gynecological Diagnostic Devices § 884.1300 Uterotubal carbon dioxide insufflator and accessories. (a) Identification. A uterotubal carbon dioxide insufflator and accessories is a device used to test the patency...

  18. 21 CFR 884.1300 - Uterotubal carbon dioxide insufflator and accessories.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Uterotubal carbon dioxide insufflator and... Gynecological Diagnostic Devices § 884.1300 Uterotubal carbon dioxide insufflator and accessories. (a) Identification. A uterotubal carbon dioxide insufflator and accessories is a device used to test the patency...

  19. 21 CFR 888.5850 - Nonpowered orthopedic traction apparatus and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Nonpowered orthopedic traction apparatus and accessories. 888.5850 Section 888.5850 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... orthopedic traction apparatus and accessories. (a) Identification. A nonpowered orthopedic traction apparatus...

  20. 21 CFR 888.5850 - Nonpowered orthopedic traction apparatus and accessories.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Nonpowered orthopedic traction apparatus and accessories. 888.5850 Section 888.5850 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... orthopedic traction apparatus and accessories. (a) Identification. A nonpowered orthopedic traction apparatus...

  1. Looking through the Zircon Kaleidoscope: Durations, Rates, and Fluxes in Silicic Magmatic System

    NASA Astrophysics Data System (ADS)

    Schaltegger, U.; Wotzlaw, J. F.

    2014-12-01

    The crystallization rate of zircon in a cooling magma depends on the cooling rate through the saturation interval in addition to compositional and kinetic factors. Repeated influx of hot magma over 10-20 ka leads to short-amplitude temperature oscillations, which are recorded by resorption/crystallization cycles of zircon. Plotting the number of dated zircons versus their high-precision U-Pb date results in curves that qualitatively relate to the evolution of magma temperature over time [1], [2]. The trace elemental, O and Hf isotopic composition of zircon gives indications about the degree of magma homogenization and thermal evolution. Zircons from systems with small volumes and magma fluxes record non-systematic chemical and Hf isotopic heterogeneity, suggesting crystallization in non-homogenized ephemeral magma batches. Such systems typically lead to small, mid-upper crustal plutons [3]. Zircons from large-volume crystal-poor rhyolites record initial heterogeneities and rapid amalgamation of smaller magma batches over 10 ka [4], while zircons from monotonous intermediates record magma evolution over several 100 ka with coherent fractionation trends suggesting homogenization and a coherent thermal evolution [2]. In both cases, volumes and flux rates were sufficient to produce large volumes of eruptible magma on very contrasting time scales. Zircon is therefore recording cyclic crystallization-rejuvenation processes during temperature fluctuations in intermediate to upper crustal magma reservoirs but may not relate to the physical pluton emplacement or eruption. We can quantify volumes, rates of magma influx, rates of cooling and crystallization, and the degree of convective homogenization from zircon data, and infer reservoir assembly and eruption trigger mechanisms. These parameters largely control the evolution of long-lived, low-flux silicic magmatic system typical for mid-to-upper crustal plutons, monotonous intermediates are characterized by intermediate

  2. The geologic relationships of industrial mineral deposits and asbestos in the western united states

    USGS Publications Warehouse

    VanGosen, B.S.

    2009-01-01

    In recent years, U.S. regulatory agencies have placed emphasis on identifying and regulating asbestos dust exposures in the mining environment, with a particular focus upon industrial mineral deposits in which asbestos occurs as an accessory mineral. Because asbestos minerals form in specific geologic environments, only certain predictable types of industrial mineral deposits can potentially host asbestos mineralization. By applying a basic knowledge of asbestos geology, the costly and time consuming efforts of asbestos monitoring and analyses can be directed towards those mineral deposit types most likely to contain asbestos mineralogy, while saving efforts on the mineral deposits that are unlikely to contain asbestos. While the vast majority of industrial mineral deposits in the Western United States are asbestos-free, there are several types that can, in some instances, host asbestos mineralization, or be closely associated with it. These industrial mineral deposits include a few types of aggregate, dimension, and decorative stone, and some deposits of chromite-nickel, magnesite, nepheline syenite, olivine, rare earth elements, talc, vermiculite, and wollastonite.

  3. Long-Term (4 mo) Oxygen Isotope Exchange Experiment between Zircon and Hydrothermal Fluid

    NASA Astrophysics Data System (ADS)

    Bindeman, I. N.; Schmitt, A. K.; Lundstrom, C.; Golledge, S.

    2013-12-01

    Knowing oxygen diffusivity in zircon has several critical applications: 1) establishing zircon stability and solubility in hot silica-saturated hydrothermal solutions; 2) deriving metamorphic and magmatic heating timescales from intra-crystal oxygen isotopic gradients; 3) assessing the survivability of oxygen isotopic signatures in Hadean zircons. We report results of a microanalytical investigation of an isotope exchange experiment using a cold-seal pressure apparatus at 850°C and 500 MPa over 4 months duration. Natural zircon, quartz and rutile were sealed with a silica-rich solution doped with 18-O, D, 7-Li and 10-B in a gold capsule. The diffusion length-scales were examined by depth profiling using time-of-flight (TOF) and high-sensitivity dynamic secondary ionization mass spectrometry (SIMS). Starting materials had distinct and homogeneous δ18O: zircon from Mesa Falls tuff of Yellowstone (+3.6‰), rutile from Karelia (-29‰), Bishop Tuff Quartz (+8.4‰), and δ18O doped water (+400‰). Starting material zircon showed invariant 18O/16O during depth profiling. After the 4 month experiment, rutile crystal surfaces displayed etching (100's of nm), while zircon exteriors lacked visible change. Quartz was completely dissolved and reprecipitated in a minor residue. Rutile developed ~2 μm long Fickian diffusion profiles largely consistent with the wet diffusion coefficients for rutile previously reported [1]. Surface U-Pb dating of zircon detected no significant Pb loss from the outermost ~300 nm of the crystal face and returned identical core-face ages. We performed δ18O depth profiling of zircon in two directions. First, forward profiles (crystal rim inwards) by dynamic SIMS (no surface treatment besides Au-coating; Cs+ beam of 20 kV impact energy) showed initially high and decreasing 18O/16O over ~130 nm; TOF-SIMS forward profiles using a 2 kV Cs+ sputter beam and 25 kV Bi3+ primary ions on uncoated zircon surfaces (cleaned for 2 min with HF) yielded

  4. Paleozoic and Paleoproterozoic Zircon in Igneous Xenoliths Assimilated at Redoubt Volcano, Alaska

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.; Vazquez, J. A.; Wooden, J. L.

    2010-12-01

    Historically active Redoubt Volcano is a basalt-to-dacite cone constructed upon the Jurassic-early Tertiary Alaska-Aleutian Range batholith. New SHRIMP-RG U-Pb age and trace-element concentration results for zircons from gabbroic xenoliths and crystal-rich andesitic mush from a late Pleistocene pyroclastic deposit indicate that ~310 Ma and ~1865 Ma igneous rocks underlie Redoubt at depth. Two gabbros have sharply terminated prismatic zircons that yield ages of ~310 Ma. Zircons from a crystal mush sample are overwhelmingly ~1865 Ma and appear rounded due to incomplete dissolution. Binary plots of element concentrations or ratios show clustering of data for ~310-Ma grains and markedly coherent trends for ~1865-Ma grains; e.g., ~310-Ma grains have higher Eu/Eu* than most of the ~1865-Ma grains, the majority of which form a narrow band of decreasing Eu/Eu* with increasing Hf content which suggests that ~1865-Ma zircons come from igneous source rocks. It is very unlikely that detrital zircons from a metasedimentary rock would have this level of homogeneity in age and composition. One gabbro contains abundant ~1865 Ma igneous zircons, ~300-310 Ma fluid-precipitated zircons characterized by very low U and Th concentrations and Th/U ratios, and uncommon ~100 Ma zircons. We propose that (1) ~310 Ma gabbro xenoliths from Redoubt Volcano belong to the same family of plutons dated by Aleinikoff et al. (USGS Circular 1016, 1988) and Gardner et al. (Geology, 1988) located ≥500 km to the northeast in basement rocks of the Wrangellia and Alexander terranes and (2) ~1865 Ma zircons are inherited from igneous rock, potentially from a continental fragment that possibly correlates with the Fort Simpson terrane or Great Bear magmatic zone of the Wopmay Orogen of northwestern Laurentia. Possibly, elements of these Paleoproterozoic terranes intersected the Paleozoic North American continental margin where they may have formed a component of the basement to the Wrangellia

  5. [Fibroadenoma in an accessory breast. A case of polythelia and fibroadenoma in the left breast region and a perivulvar accessory breast].

    PubMed

    Degrell, I

    1979-08-02

    The case of a 32-year-old female patient with multiple malformations (hare-lip, polythelia, fibroadenoma in an accessory mammary gland) and independent of these, another fibroadenoma in the breast is reported. The fibroadenoma developing in the accessory breast around the vulva, diagnosed by means of aspiration biopsy cytology, should be payed special attention. This case also confirms the applicability in preoperative diagnostics of aspiration biopsy cytology, a method which has proved to be effective for years.

  6. Zircon Messengers Reveal the Age and History of Great Basin Crust, Kern Mountains, Nevada

    NASA Astrophysics Data System (ADS)

    Gottlieb, E. S.; Miller, E. L.; Wooden, J. L.

    2011-12-01

    Results of SHRIMP-RG analyses of complexly zoned zircons from muscovite-bearing granitic rocks exposed in the Kerns Mountains of East-Central Nevada constrain the timing, duration, and loci of zircon growth within the interior of the U.S. Cordillera during Late Cretaceous through Eocene time. The Kern Mountains are an exhumed block of greenschist to amphibolite facies metamorphosed miogeoclinal rocks that were pervasively intruded by the Late Cretaceous Tungstonia granite pluton and the Eocene Skinner Canyon and Uvada plutons (Best et al., 1974). Euhedral zircons separated from a coarse-grained (2-3 cm) muscovite-bearing phase of the Tungstonia pluton exhibit complex cathodeluminescence (CL) zonation. Sub-angular to sub-rounded cores with highly variable CL are overgrown by oscillatory-zoned zircon which in turn is rimmed by dark CL zircon (U>5000 ppm). A weighted mean Pb/U age of 70.2±0.9 Ma (n=20, MSWD=2.5) obtained from the oscillatory-zoned zircon coincides with the end of Cretaceous peak metamorphism at shallow crustal levels. Pb/U ages from core zones (n=18) predominantly are 0.9-1.4 Ga (n=11; 7 of which <15% discordant) or 2.4-2.7 Ga (n=5; 1 of which <15% discordant), consistent with ages of detrital zircons within the Late Proterozoic McCoy Creek Group exposed in adjacent ranges. A previously undated muscovite-bearing dike in Skinner Canyon yielded a texturally complex population of subhedral zircon grains. CL imaging of these grains reveals fragmental, ghost-like cores surrounded by irregularly shaped overgrowth zones with diffuse boundaries which are rimmed by oscillatory-zoned zircon. Both oscillatory zoned and gradational rim areas (n=32) yielded Late Cretaceous to Eocene ages. Twelve spots define the age of intrusion at 41.7±0.3 Ma (MSWD=1.8), consistent with the local onset of Eocene magmatism. An older period of zircon growth from ~75-45 Ma, coincident with the proposed duration of the Laramide shallow slab, is defined by zircon with flat to

  7. Alpha-Recoil Damage Annealing Effecfs on Zircon Crystallinity and He Diffusivity: Improving Damage-Diffusivity Models

    NASA Astrophysics Data System (ADS)

    Thurston, O. G.; Guenthner, W.; Garver, J. I.

    2017-12-01

    The effects of radiation damage on He diffusion in zircon has been a major research focus in thermochronology over the past decade. In the zircon-He system, alpha-recoil damage effects He diffusivity in two ways: a decrease in He diffusivity at low radiation damage levels, and an increase in He diffusivity at high radiation damage levels. The radiation damage accumulation process within zircon is well understood; however, the kinetics of annealing of alpha-recoil damage at geologic timescales as they pertain to damage-diffusivity models, and for metamict zircon (i.e. transition from crystalline to amorphous glass via damage accumulation), has not been well constrained. This study aims to develop a more complete model that describes the annealing kinetics for zircon grains with a broad range of pre-annealing, alpha-induced radiation damage. A suite of zircon grains from the Lucerne pluton, ME were chosen for this study due to their simple thermal history (monotonic cooling), notable range of effective uranium (eU, eU = [U] +0.235*[Th]) (15 - 34,239 ppm eU), and large range of radiation damage as measured by Raman shift from crystalline (>1005 cm-1) to metamict (<1000 cm-1). The zircon grains selected represent the full range of eU and radiation damage present in the pluton. The zircon grains were first mapped for overall crystallinity using Raman spectroscopy, then annealed at different time-temperature (t-T) schedules from 1 hr to 24 hrs at temperatures ranging from 700-1100 °C, followed by remapping with Raman spectroscopy to track the total Raman shift for each t-T step. The temperature window selected is at the "roll-over" point established in prior studies (Zhang et al., 2000), at which most laboratory annealing occurs. Our data show that high radiation damage zircon grains show larger Raman shifts than low radiation damage zircon grains when exposed to the same t-T step. The high damage zircon grains typically show a Raman shift of 4 cm-1 toward crystalline

  8. Molybdenite Re-Os, zircon U-Pb dating and Lu-Hf isotopic analysis of the Xiaerchulu Au deposit, Inner Mongolia Province, China

    NASA Astrophysics Data System (ADS)

    Wang, Jia-xin; Nie, Feng-Jun; Zhang, Xue-ni; Jiang, Si-hong

    2016-09-01

    The Xiaerchulu Au deposit, located in the Southern Orogenic Belt (SOB) of Western Inner Mongolia (WIM), is hosted in an Early Permian (271-261 Ma) volcanic-plutonic sequence. Mineralization took place in silicified biotite granites or along the contact zone between the Neoproterozoic Baiyinbaolage Group and the biotite granite. In order to constrain the timing of the Xiaerchulu mineralization and discuss the petrogenesis of the hosting granites, molybdenite Re-Os, and zircon U-Pb and, Lu-Hf, and REE, geochemical, and Sr-Nd isotopic studies were completed in this study. We measured Re-Os isotopes of six molybdenite samples from the main ore body, which yielded a weighted average model age of 261.7 ± 1.5 Ma with a MSWD of 0.55, indicating that the time of mineralization was at ca. 262 Ma. High precision U-Pb dating for the studied granites yields Permian 206Pb/238U ages ranging from 271 to 269 Ma. These age data confirm that both the intrusion and related mineralization were initiated in Early Permian period. These granites are strongly peraluminous with A/CNK = 1.11-1.12, high SiO2-K2O contents, as well as containing biotite and muscovite, indicating a petrogenesis of typical S-type granites, the above consideration is also consistent with the result of discrimination diagrams. The Re contents of molybdenite, εNd(t), and zircon εHf(t), as well as the 176Hf/177Hf values of the granites, fall into the ranges from 1.153 to 2.740 μg/g, - 11.1 to - 9.3, - 8.8 to - 0.9, and 0.282358 to 0.282688, respectively. All of this evidence suggests that the metals were derived from a predominantly crustal source, the granites originated from crust in an extensional setting, and the rejuvenation of the continent may have play an important role during the ore-forming processes of the Early Permian epoch.

  9. Genesis of late Early Cretaceous high-silica rhyolites in eastern Zhejiang Province, southeast China: A crystal mush origin with mantle input

    NASA Astrophysics Data System (ADS)

    Zhang, Ji-Heng; Yang, Jin-Hui; Chen, Jing-Yuan; Wu, Fu-Yuan; Wilde, Simon A.

    2018-01-01

    Voluminous Mesozoic felsic volcanic rocks and granites in southeastern China provide a unique opportunity for studying the role of crustal magmatism in the evolution and modification of the crust in the eastern Cathaysia Block. The high-silica rhyolites of the upper volcanic sequence in eastern Zhejiang Province were investigated, focusing on their genesis and their relationship with contemporaneous granites. Rhyolites in the Tiantai, Yongkang and Liucheng basins were dated as late Early Cretaceous (from 111 Ma to 106 Ma in age). These rocks contain a large proportion of inherited zircons of ca. 130 Ma, corresponding to the age of the lower volcanic sequence in the area. However, the zircons of different ages have similar ranges of oxygen and Hf isotopes, implying similarities in the magmas from which they were generated. The rhyolites of the upper sequence also resemble those of the lower sequence in terms of their geochemistry. It is concluded that the former were derived by reworking of magma mush formed during the earlier magmatic episode via fractionation of feldspars and accessory minerals, e.g., zircon. Fractionation took place within the magma crystal mush by extraction of interstitial melts and accumulation of residual mineral phases, aided by the emplacement of contemporaneous basaltic magmas at the base of the crust. Overall, the geochemical features of the volcanic rocks in southeastern China indicate that episodic magmatism and reworking of crystal mush were essential mechanisms that drove the evolution of the igneous rocks and the hence crustal architecture in this area.

  10. Point defects in crystalline zircon (zirconium silicate), ZrSiO4: electron paramagnetic resonance studies

    NASA Astrophysics Data System (ADS)

    Tennant, W. C.; Claridge, R. F. C.; Walsby, C. J.; Lees, N. S.

    This article outlines the present state of knowledge of paramagnetic defects in crystalline zircon as obtained mainly, but not exclusively, from electron paramagnetic resonance (EPR) studies in crystalline zircon (zirconium silicate, ZrSiO4). The emphasis is on single-crystal studies where, in principle, unambiguous analysis is possible. Firstly, the crystallography of zircon is presented. Secondly, the relationships between available crystal-site symmetries and the symmetries of observed paramagnetic species in zircon, and how these observations lead to unambiguous assignments of point-group symmetries for particular paramagnetic species are detailed. Next, spin-Hamiltonian (SH) analysis is discussed with emphasis on the symmetry relationships that necessarily exist amongst the Laue classes of the crystal sites in zircon, the paramagnetic species occupying those sites and the SH itself. The final sections of the article then survey the results of EPR studies on zircon over the period 1960-2002.

  11. Geochronological study of zircons from continental crust rocks in the Frido Unit (southern Apennines)

    NASA Astrophysics Data System (ADS)

    Laurita, Salvatore; Prosser, Giacomo; Rizzo, Giovanna; Langone, Antonio; Tiepolo, Massimo; Laurita, Alessandro

    2015-01-01

    Zircon crystals have been separated from gneisses and metagranitoids of the Pollino area (southern Apennines) in order to unravel the origin of these crustal slices within the ophiolite-bearing Frido Unit. The morphology of the zircon has been investigated by SEM, and the internal structure was revealed by cathodoluminescence. Data obtained by U/Pb dating have been used to deduce the age and significance of the different crystallization stages of zircon, connected to the evolutionary stages of the continental crust (Late Paleozoic-Early Mesozoic). Zircons in gneisses are characterized by inherited cores of magmatic origin, bordered by metamorphic rims. Inherited zircons generally show Paleoproterozoic to Ordovician ages, indicating the provenance of the sedimentary protolith from different sources. The exclusive presence of Late Neoproterozoic zircon cores in leucocratic gneisses may suggest a different magmatic source possibly connected to Pan-African events. Late Carboniferous-Early Permian ages are found mainly in zircon rims of metamorphic origin. These are similar to the emplacement ages of protolith of the metagranites in the middle crust portion. Late Carboniferous-Early Permian metamorphism and magmatism testify the extensional collapse of the Hercynian belt, recorded in European, particularly, in the Corsica-Sardinia block and in Calabria. Late Permian-Triassic ages have been detected in zircon rims from gneisses and metagranitoids. These younger ages appear related to deformation and emplacement of albite-quartz veins in both lithologies, and are related to an extensional episode predating the Middle Triassic to Middle Jurassic rifting in the Tethyan domain, followed by Middle to Late Jurassic spreading.

  12. Experimental evidence for use of aluminum in zircon as a new tracer to distinguish peraluminous and metaluminous melts

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Trail, D.

    2017-12-01

    Aluminum (Al) is the third most abundant rock-forming element in Earth's crust. It also substitutes into the zircon lattice as trace impurity. For zircons that lack parent rock information, e.g. Hadean zircon (>4.0 Ga), Al in zircon could be a potentially useful tool to investigate the formation and evolution of the parental magma. Aluminum saturation index (ASI; molar ratio of Al2O3/(CaO+Na2O+K2O)) is widely used to distinguish peraluminous rocks (ASI>1) from metaluminous rocks (ASI<1). We grew zircons in piston cylinder from granitic melts, with different ASI values but same temperature, pressure and water content. Synthetic zircons with variable sizes, as large as 20 µm, were observed under SEM and analyzed using LA-ICP-MS. Our analyses reveal that the Al content of zircons that crystalized from a peraluminous melt (ASI=1.25) is, on average, one magnitude higher than crystals from peralkaline melt (ASI=0.5), e.g., 100s of ppm, vs. 10s of ppm. This indicates that aluminum solubility in zircon is related to the ASI value of parental melt. This experimental result agrees with studies of natural zircons, where Al contents of peraluminous zircons ( 10 ppm) are an order of magnitude higher than zircons from metaluminous rocks ( 1.3 ppm) (Trail et al., 2017). We suggest that melts with ASI>1 can result in an elevated alumina activity, which leads to zircons with elevated Al contents. The notably higher Al concentration in experimental zircons (10s to 100s ppm), compared with natural zircons (1 to 10 ppm), could be explained by the much higher crystallization temperature, e.g., >1100°C vs. <900°C. Both field and experimental studies support the notion that a relationship exists between the Al content in zircon and the melt ASI value. This conclusion has several meaningful applications: 1) it may be used to infer source rock characteristics of Hadean zircons, and to shed light on the formation and evolution of the earliest crust; 2) it may provide additional

  13. Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

    NASA Astrophysics Data System (ADS)

    Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

    2016-05-01

    The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion-collision processes in NW China, and hosts Paleozoic Cu-Pb-Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U-Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U-Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9-213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67-1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere. In contrast, the

  14. The distribution and composition of REE-bearing minerals in placers of the Atlantic and Gulf coastal plains, USA

    USGS Publications Warehouse

    Bern, Carleton R.; Shah, Anjana K.; Benzel, William M.; Lowers, Heather A.

    2016-01-01

    Rare earth element (REE) resources are currently of great interest because of their importance as raw materials for high-technology manufacturing. The REE-phosphates monazite (light REE enriched) and xenotime (heavy REE enriched) resist weathering and can accumulate in placer deposits as part of the heavy mineral assemblage. The Atlantic and Gulf coastal plains of the southeastern United States are known to host heavy mineral deposits with economic concentrations of zircon, ilmenite and rutile. This study provides a perspective on the distribution and composition of REE phosphate minerals in the region. The elemental chemistry and mineralogy of sands and associated heavy-mineral assemblages from new and archived sediment samples across the coastal plains are examined, along with phase-specific compositions of monazite, xenotime and zircon. Both monazite and xenotime are present across the coastal plains. The phase-specific compositions allow monazite content to be estimated using La as a geochemical proxy. Similarly, both Y and Yb are geochemical proxies for xenotime, but their additional presence in zircon and monazite require a correction to prevent overestimation of xenotime content. Applying this correction, maps of monazite and xenotime content across the coastal plains were generated using sample coverage from the National Geochemical Database (NGS) and National Uranium Resource Evaluation (NURE). The NGS and NURE approach of sampling stream sediments in small watersheds links samples to nearby lithologies. The results show an approximately 40 km-wide band of primarily Cretaceous, marine sediments bordering the Piedmont province from North Carolina to Alabama in which monazite and xenotime content are relatively high (up to 4.4 wt. % in < 150 μm bulk sediment). Strong correlations between concentrations of the two phases were found, with estimated monazite:xenotime ratios ranging approximately 6:1 to 12:1 depending upon the dataset analyzed. From a resource

  15. Accessory costs of seed production and the evolution of angiosperms.

    PubMed

    Lord, Janice M; Westoby, Mark

    2012-01-01

    Accessory costs of reproduction frequently equal or exceed direct investment in offspring, and can limit the evolution of small offspring sizes. Early angiosperms had minimum seed sizes, an order of magnitude smaller than their contemporaries. It has been proposed that changes to reproductive features at the base of the angiosperm clade reduced accessory costs thus removing the fitness disadvantage of small seeds. We measured accessory costs of reproduction in 25 extant gymnosperms and angiosperms, to test whether angiosperms can produce small seeds more economically than gymnosperms. Total accessory costs scaled isometrically to seed mass for angiosperms but less than isometrically for gymnosperms, so that smaller seeds were proportionally more expensive for gymnosperms to produce. In particular, costs of abortions and packaging structures were significantly higher in gymnosperms. Also, the relationship between seed:ovule ratio and seed size was negative in angiosperms but positive in gymnosperms. We argue that the carpel was a key evolutionary innovation reducing accessory costs in angiosperms by allowing sporophytic control of pre- and postzygotic mate selection and timing of resource allocation. The resulting reduction in costs of aborting unfertilized ovules or genetically inferior embryos would have lowered total reproductive costs enabling early angiosperms to evolve small seed sizes and short generation times. © 2011 The Author(s). Evolution © 2011 The Society for the Study of Evolution.

  16. [Evaluation of iatrogenic accessory nerve injury in forensic medical practice].

    PubMed

    Somogyi, E; Irányi, J

    1996-04-14

    The authors give a survey of the clinical and medical-legal characteristics of the accessory nerve injury. In the past two decades the conception of the successfulness of the surgical treatment of the accessory nerve injury became prevailing. About the medical-legal aspects of the iatrogenic injury of the nerve reported in connection of the reconstructive surgery chiefly also departments of neurosurgery, orthopedics and traumatology. In the case of the authors a 70 year old patient suffered 10 years ago a iatrogenic accessory nerve injury. The mild trapezius palsy recovered spontaneously practically with cosmetic disadvantage. In connection with the development of extreme dorso-lumbal scoliosis associated with torsion the trapezius atrophy worsened. Physical therapy was partly successful. But the patient became unfit for manual work. Their observations sustain the data of authors who established that in the case of accessory nerve injury not only the surgical but also conservative treatment is usually successful. In opposite to certain data of the literature the authors establish that the iatrogenic injuries of the accessory nerve may lead to significant lifelong disability. The diagnosis is not always made in time with consequent delay in repair. This may be regarded as an unfavorable issue during medical-legal discussions. The authors recommend in interest to prevent nerve injury in the posterior triangle of the neck to perform operation in special department.

  17. Origin of northern Gondwana Cambrian sandstone revealed by detrital zircon SHRIMP dating

    USGS Publications Warehouse

    Avigad, D.; Kolodner, K.; McWilliams, M.; Persing, H.; Weissbrod, T.

    2003-01-01

    Voluminous Paleozoic sandstone sequences were deposited in northern Africa and Arabia following an extended Neoproterozoic orogenic cycle that culminated in the assembly of Gondwana. We measured sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of detrital zircons separated from several Cambrian units in the Elat area of southern Israel in order to unravel their provenance. This sandstone forms the base of the widespread siliciclastic section now exposed on the periphery of the Arabian-Nubian shield in northeastern Africa and Arabia. Most of the detrital zircons we analyzed yielded Neoproterozoic concordant ages with a marked concentration at 0.55–0.65 Ga. The most likely provenance of the Neoproterozoic detritus is the Arabian-Nubian shield; 0.55–0.65 Ga was a time of posttectonic igneous activity, rift-related volcanism, and strike-slip faulting there. Of the zircons, 30% yielded pre-Neoproterozoic ages grouped at 0.9–1.1 Ga (Kibaran), 1.65–1.85 Ga, and 2.45–2.7 Ga. The majority of the pre-Neoproterozoic zircons underwent Pb loss, possibly as a consequence of the Pan-African orogeny resetting their provenance. Rocks of the Saharan metacraton and the southern Afif terrane in Saudi Arabia (∼1000 km south of Elat) are plausible sources of these zircons. Kibaran basement rocks are currently exposed more than 3000 km south of Elat (flanking the Mozambique belt), but the shape of the detrital zircons of that age and the presence of feldspar in the host sandstone are not fully consistent with such a long-distance transport. Reworking of Neoproteorozoic glacial detritus may explain the presence of Kibaran detrital zircons in the Cambrian of Elat, but the possibility that the Arabian-Nubian shield contains Kibaran rocks (hitherto not recognized) should also be explored.

  18. Rhabdovirus accessory genes.

    PubMed

    Walker, Peter J; Dietzgen, Ralf G; Joubert, D Albert; Blasdell, Kim R

    2011-12-01

    The Rhabdoviridae is one of the most ecologically diverse families of RNA viruses with members infecting a wide range of organisms including placental mammals, marsupials, birds, reptiles, fish, insects and plants. The availability of complete nucleotide sequences for an increasing number of rhabdoviruses has revealed that their ecological diversity is reflected in the diversity and complexity of their genomes. The five canonical rhabdovirus structural protein genes (N, P, M, G and L) that are shared by all rhabdoviruses are overprinted, overlapped and interspersed with a multitude of novel and diverse accessory genes. Although not essential for replication in cell culture, several of these genes have been shown to have roles associated with pathogenesis and apoptosis in animals, and cell-to-cell movement in plants. Others appear to be secreted or have the characteristics of membrane-anchored glycoproteins or viroporins. However, most encode proteins of unknown function that are unrelated to any other known proteins. Understanding the roles of these accessory genes and the strategies by which rhabdoviruses use them to engage, divert and re-direct cellular processes will not only present opportunities to develop new anti-viral therapies but may also reveal aspects of cellar function that have broader significance in biology, agriculture and medicine. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

  19. A study of processing parameters in thermal-sprayed alumina and zircon mixtures

    NASA Astrophysics Data System (ADS)

    Li, Y.; Khor, K. A.

    2002-06-01

    A method of plasma spraying of alumina and zircon mixtures to form ZrO2-mullite composites has been proposed and developed. The feedstock is prepared by a combination of mechanical alloying, which allows formation of fine-grained, homogeneous solid-solution mixtures, followed by plasma spheroidization that yields rapid solidified microstructures and enhanced compositional homogeneity. The effects of ball-milling duration and milling media were studied. It was found that zirconia is a more efficient milling media and that increasing milling duration enhanced the dissociation of zircon. Flame spray and plasma spray processes were used to spheroidize the spray-dried powders. The temperature of the flame spray was found to be insufficient to melt the powders completely. The processing parameters of the plasma spray played an important role in zircon decomposition and mullite formation. Increasing the arc current or reducing secondary gas pressure caused more zircon to decompose and more mullite to form after heat treatment at 1200 °C for 3 h. Dissociation of zircon and the amount of mullite for med can be enhanced significantly when using the more efficient, computerized plasma-spraying system and increasing the ball-milling duration from 4 to 8 h.

  20. A Further Investigation of the Exceptional Zircon Aggregate in Lunar Thin Section 73235,82

    NASA Technical Reports Server (NTRS)

    Pidgeon, R. T.; Nemchin, a. A.; Meyer, C.

    2005-01-01

    Introduction: Smith et al. described an exceptional zircon assemblage in thin section 82 from lunar breccia 73235 which, in transmitted light, resembles a cluster of pomegranate seeds, situated in a clast dominated by bytownite (Fig.1). They reported that high-contrast back-scattered electron (BSE) images of the zircon assemblage clearly show an overgrowth around most of the crystals. Most significantly these authors reported that the age of the rims of ca 4.18Ga is 120 million years younger than age of the interiors, dated at ca 4.31Ga. Smith et al. concluded that ca 4.31 billion years ago a relatively large (500+micron) zircon crystallized within a clast of Ca rich plagioclase. The zircon was fractured into numerous smaller crystals and was subsequently overgrown by a second generation of zircon at approximately 4.18Ga.

  1. Diagnostic heavy minerals in Plio-Pleistocene sediments of the Yangtze Coast, China with special reference to the Yangtze River connection into the sea

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Wang, Zhanghua; Chen, Zhongyuan; Wei, Zixin; Wei, Taoyuan; Wei, Wei

    2009-12-01

    This present study revealed five heavy mineral zones in the Yangtze coastal borehole sediments. Ilmenite, garnet and zircon suite of Zone I of the Pliocene characterizes the derivation of basaltic bedrock and local andesitic-granitic rocks. Indicative limonite in the Zone I sediments formed as alluvial fan facies shows strong chemical weathering. The assemblage of amphibole, straurolite, kyanite and idocrase of metamorphic derivation, together with a few zircon and tourmaline of andesitic-granitic origin in Zone II, represents the extension of sediment sources to the lower and middle Yangtze basin in Early Pleistocene as the study area subsided. Also, the braided to meandering riverine facies demonstrates a longer distance sediment transport. Few heavy minerals remained in Zone III of Mid-Pleistocene, when mottled thicker stiff mud occurred as the lacustrine facies, suggesting a quasi-coastal floodplain with lower capability of sediment transport. Heavy minerals appeared significant and continuous in Zone IV of Late Pleistocene, when changing to the shallow marine facies, inferring much extended sediment sources to the upper Yangtze. Hypersthene, identified primarily in Zone IV, was closely associated with the Er-Mei Mountain tholeiite basalt of the upper Yangtze. Heavy minerals of Zone V remained almost the same as IV during Holocene, when the modern delta evolved. The heavy minerals suggested the timing of the Yangtze connection to the sea at ca 0.12 Ma BP.

  2. Differing responses of zircon, chevkinite-(Ce), monazite-(Ce) and fergusonite-(Y) to hydrothermal alteration: Evidence from the Keivy alkaline province, Kola Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Macdonald, Ray; Bagiński, Bogusław; Zozulya, Dmitry

    2017-09-01

    A quartzolite from the Rova occurrence, Keivy alkali granite province, Kola Peninsula, Russia, is used to examine the differing responses of certain rare-metal minerals during interaction with hydrothermal fluids. The minerals are two silicates [chevkinite-(Ce) and zircon], a phosphate [monazite-(Ce)] and an oxide [fergusonite-(Y)]. Textural evidence is taken to show that the dominant alteration mechanism was interface-coupled dissolution-reprecipitation. Zircon was the most pervasively altered, possibly by broadening of cleavage planes or fractures; the other minerals were altered mainly on their rims and along cracks. The importance of cracks in promoting fluid access is stressed. The compositional effects of the alteration of each phase are documented. The hydrothermal fluids carried few ligands capable of transporting significant amounts of rare-earth elements (REE), high field strength elements (HFSE) and actinides; alteration is inferred to have been promoted by mildly alkaline, Ca-bearing fluids. Expansion cracks emanating from fergusonite-(Y) are filled with unidentified material containing up to 35 wt% UO2 and 25 wt% REE2O3, indicating late-stage, short-distance mobility of these elements. Electron microprobe chemical dating of monazite yielded an age of 1665 ± 22 Ma, much younger than the formation age of the Keivy province (2.65-2.67 Ga) but comparable to that of the Svecofennian metamorphic event which affected the area (1.9-1.7 Ga) or during fluid-thermal activation of the region during rapakivi granite magmatism (1.66-1.56 Ga). Dates for altered monazite range from 2592 ± 244 Ma to 773 ± 88 Ma and reflect disturbance of the U-Th-Pb system during alteration.

  3. Zircon and baddeleyite from the economic ultramafic-mafic Noril'sk-1 intrusion (Russia): Hf-isotope constraints on source composition

    NASA Astrophysics Data System (ADS)

    Malitch, K. N.; Belousova, E. A.; Badanina, I. Yu.; Griffin, W. L.

    2012-04-01

    The ultramafic-mafic Noril'sk-1 intrusion in the northwestern part of the Siberian Craton (Russia) represents one of three known Noril'sk-type, ore-bearing intrusions, which host one of the world's major economic sulphide platinum-group-element (PGE)-Cu-Ni deposits. Zircon and baddeleyite dated previously both by SHRIMP (i.e. 248.0 ± 3.7 Ma, Campbell et al. 1992) and ID-TIMS (251.1 ± 3.6 Ma, Kamo et al. 1996) have been restricted to one lithology (e.g. leucogabbro) of the Noril'sk-1 intrusion. To better constrain the age of igneous event and sources involved in its generation our multi-technique study utilized ten rock samples characteristic of unmineralized and mineralized lithologies. The rocks investigated comprise (from top to bottom) gabbro-diorite (sample N1-1), leucogabbro (N1-3), olivine-free gabbro (N1-2 and N1-4), olivine-bearing gabbro (N1-5), olivine gabbro (N1-6), plagiowehrlite and plagiodunite (N1-7), taxitic-textured rocks comprising melanotroctolite, olivine gabbro with relics of ultramafic rocks (N1-8, N1-9) and contact fine-grained gabbro (N1-10). Sulphide PGE-Cu-Ni ores occur in ultramafic (N1-7) and taxitic-textured rocks (N1-8 and N1-9), which have thickness of about 17 m, whereas the low-sulphide horizon of about 1 m thick occurs in the upper part of intrusion (N1-3). In situ U-Pb analyses of zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four zircon populations (Malitch et al. 2012). The U-Pb ages of baddeleyite and the defined zircon populations cover a significant time span, from Late Paleozoic to Early Mesozoic (e.g., 290 ± 2.8; 261.3 ± 1.6; 245.7 ± 1.1; 236.5 ± 1.8 and 226.7 ± 0.9 Ma). The established distribution of U-Pb ages implies that crystallization of baddeleyite and zircon corresponds to several stages of protracted evolution of ultramafic-mafic magmas at deep-seated staging chambers and/or probably characterizes interaction of distinct magmas during formation

  4. Simon Effect with and without Awareness of the Accessory Stimulus

    ERIC Educational Resources Information Center

    Treccani, Barbara; Umilta, Carlo; Tagliabue, Mariaelena

    2006-01-01

    The authors investigated whether a Simon effect could be observed in an accessory-stimulus Simon task when participants were unaware of the task-irrelevant accessory cue. In Experiment 1A a central visual target was accompanied by a suprathreshold visual lateral cue. A regular Simon effect (i.e., faster cue-response corresponding reaction times…

  5. Maps showing mineralogical data for nonmagnetic heavy-mineral concentrates in the Talkeetna Quadrangle, Alaska

    USGS Publications Warehouse

    Tripp, R.B.; Karlson, R.C.; Curtin, G.C.

    1978-01-01

    Reconnaissance geochemical and mineralogical sampling was done in the Talkeetna Quadrangle during 1975 and 1976 as part of the Alaska Mineral Resource Assessment Program (AMRAP). These maps show the distribution of gold, scheelite, chalcopyrite, arsenopyrite, galena, fluorite, cinnabar, and malachite in the nonmagnetic fraction of heavy-mineral concentrates. Heavy-mineral concentrate samples were collected at 812 sites from active stream channels. The heavy-mineral concentrates were obtained by panning stream sediment in the field to remove most of the light minerals. The panned samples were then sieved through a 20-mesh (0.8 mm) sieve in the laboratory, and the minus-20-mesh fraction was further separated with bromoform (specific gravity, 2.86) to remove any remaining light-mineral grains. Magnetite and other strongly magnetic heavy minerals were removed from the heavy-mineral fraction by use of a hand magnet. The remaining sample was passed through a Frantz Isodynamic Separator and a nonmagnetic fraction was examined for its mineralogical content with the aid of a binocular microscope and an x-ray diffractometer. The nonmagnetic concentrates primarily contain phyllite fragments, muscovite, sphene, zircon, apatite, tourmaline, rutile, and anatase. Most ore and ore-related minerals also occur in this fraction.

  6. Visual and auditory accessory stimulus offset and the Simon effect.

    PubMed

    Nishimura, Akio; Yokosawa, Kazuhiko

    2010-10-01

    We investigated the effect on the right and left responses of the disappearance of a task-irrelevant stimulus located on the right or left side. Participants pressed a right or left response key on the basis of the color of a centrally located visual target. Visual (Experiment 1) or auditory (Experiment 2) task-irrelevant accessory stimuli appeared or disappeared at locations to the right or left of the central target. In Experiment 1, responses were faster when onset or offset of the visual accessory stimulus was spatially congruent with the response. In Experiment 2, responses were again faster when onset of the auditory accessory stimulus and the response were on the same side. However, responses were slightly slower when offset of the auditory accessory stimulus and the response were on the same side than when they were on opposite sides. These findings indicate that transient change information is crucial for a visual Simon effect, whereas sustained stimulation from an ongoing stimulus also contributes to an auditory Simon effect.

  7. Meteorite zircon constraints on the bulk Lu-Hf isotope composition and early differentiation of the Earth.

    PubMed

    Iizuka, Tsuyoshi; Yamaguchi, Takao; Hibiya, Yuki; Amelin, Yuri

    2015-04-28

    Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. The (176)Lu-(176)Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of silicate differentiation on Earth, but the data interpretation requires accurate estimation of Hf isotope evolution of the bulk Earth. Because both Lu and Hf are refractory lithophile elements, the isotope evolution can be potentially extrapolated from the present-day (176)Hf/(177)Hf and (176)Lu/(177)Hf in undifferentiated chondrite meteorites. However, these ratios in chondrites are highly variable due to the metamorphic redistribution of Lu and Hf, making it difficult to ascertain the correct reference values for the bulk Earth. In addition, it has been proposed that chondrites contain excess (176)Hf due to the accelerated decay of (176)Lu resulting from photoexcitation to a short-lived isomer. If so, the paradigm of a chondritic Earth would be invalid for the Lu-Hf system. Herein we report the first, to our knowledge, high-precision Lu-Hf isotope analysis of meteorite crystalline zircon, a mineral that is resistant to metamorphism and has low Lu/Hf. We use the meteorite zircon data to define the Solar System initial (176)Hf/(177)Hf (0.279781 ± 0.000018) and further to identify pristine chondrites that contain no excess (176)Hf and accurately represent the Lu-Hf system of the bulk Earth ((176)Hf/(177)Hf = 0.282793 ± 0.000011; (176)Lu/(177)Hf = 0.0338 ± 0.0001). Our results provide firm evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir on Earth as far back as 4.5 billion years ago.

  8. Meteorite zircon constraints on the bulk Lu−Hf isotope composition and early differentiation of the Earth

    PubMed Central

    Iizuka, Tsuyoshi; Yamaguchi, Takao; Hibiya, Yuki; Amelin, Yuri

    2015-01-01

    Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. The 176Lu−176Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of silicate differentiation on Earth, but the data interpretation requires accurate estimation of Hf isotope evolution of the bulk Earth. Because both Lu and Hf are refractory lithophile elements, the isotope evolution can be potentially extrapolated from the present-day 176Hf/177Hf and 176Lu/177Hf in undifferentiated chondrite meteorites. However, these ratios in chondrites are highly variable due to the metamorphic redistribution of Lu and Hf, making it difficult to ascertain the correct reference values for the bulk Earth. In addition, it has been proposed that chondrites contain excess 176Hf due to the accelerated decay of 176Lu resulting from photoexcitation to a short-lived isomer. If so, the paradigm of a chondritic Earth would be invalid for the Lu−Hf system. Herein we report the first, to our knowledge, high-precision Lu−Hf isotope analysis of meteorite crystalline zircon, a mineral that is resistant to metamorphism and has low Lu/Hf. We use the meteorite zircon data to define the Solar System initial 176Hf/177Hf (0.279781 ± 0.000018) and further to identify pristine chondrites that contain no excess 176Hf and accurately represent the Lu−Hf system of the bulk Earth (176Hf/177Hf = 0.282793 ± 0.000011; 176Lu/177Hf = 0.0338 ± 0.0001). Our results provide firm evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir on Earth as far back as 4.5 billion years ago. PMID:25870298

  9. Detrital zircon geochronology of quartzose metasedimentary rocks from parautochthonous North America, east-central Alaska

    USGS Publications Warehouse

    Dusel-Bacon, Cynthia; Holm-Denoma, Christopher S.; Jones, James V.; Aleinikoff, John N.; Mortensen, James K.

    2017-01-01

    We report eight new U-Pb detrital zircon ages for quartzose metasedimentary rocks from four lithotectonic units of parautochthonous North America in east-central Alaska: the Healy schist, Keevy Peak Formation, and Sheep Creek Member of the Totatlanika Schist in the northern Alaska Range, and the Butte assemblage in the northwestern Yukon-Tanana Upland. Excepting 1 of 3 samples from the Healy schist, all have dominant detrital zircon populations of 1.9–1.8 Ga and a subordinate population of 2.7–2.6 Ga. Three zircons from Totatlanika Schist yield the youngest age of ca. 780 Ma. The anomalous Healy schist sample has abundant 1.6–0.9 Ga detrital zircon, as well as populations at 2.0–1.8 Ga and 2.7–2.5 Ga that overlap the ages from the rest of our samples; it has a minimum age population of ca. 1007 Ma.Detrital zircon age populations from all but the anomalous sample are statistically similar to those from (1) other peri-Laurentian units in east-central Alaska; (2) the Snowcap assemblage in Yukon, basement of the allochthonous Yukon-Tanana terrane; (3) Neoproterozoic to Ordovician Laurentian passive margin strata in southern British Columbia, Canada; and (4) Proterozoic Laurentian Sequence C strata of northwestern Canada. Recycling of zircon from the Paleoproterozoic Great Bear magmatic zone in the Wopmay orogen and its Archean precursors could explain both the Precambrian zircon populations and arc trace element signatures of our samples. Zircon from the anomalous Healy schist sample resembles that in Nation River Formation and Adams Argillite in eastern Alaska, suggesting recycling of detritus in those units.

  10. Record of Hybridization Preserved in Zircon, Aztec Wash Pluton, NV

    NASA Astrophysics Data System (ADS)

    Bromley, S. A.; Miller, C. F.; Claiborne, L. L.; Wooden, J. L.; Mazdab, F. K.

    2007-12-01

    The mid-Miocene Aztec Wash pluton comprises a smaller granite zone and a larger, highly heterogeneous zone in which evidence for interaction between basaltic and granitic magmas is ubiquitous. Granitic rocks in both zones show textural and compositional evidence for crystal accumulation and melt fractionation. In the heterogeneous zone, basalts have chilled, crenulate margins against granitic rocks, and there is widespread evidence for mechanical contamination of each lithology (coarse resorbed alkali feldspar in fine-grained mafic rock; mafic enclaves in granite). "Grey rocks" of intermediate composition are exposed on dm to 100's of m-scale as enclaves, pods, and initially subhorizontal sheets. They are variable texturally, but most are dominantly fine- grained and equigranular. Textures of grey rocks are consistent with rapid solidification from melt-rich magma, and, in combination with isotopic compositions intermediate between felsic and mafic rocks of the pluton, suggest an origin by near-complete homogenization of a hybrid melt (Bleick et al. 2005; Ericksen 2005). The elemental chemistry of zircon preserves information about the evolving magmatic environment in which it was hosted (Claiborne et al., 2006). Owing to its slow dissolution rate, it has the potential to survive periods of undersaturation with only partial resorption. Thus, it may record drastic shifts in T and melt chemistry that would accompany mafic-felsic hybridization. We are investigating zircon zoning patterns by cathodoluminescence (CL) and elemental compositions by SHRIMP-RG to evaluate the record of processes that they preserve. Temperatures of zircon growth are estimated using Ti-in-zircon thermometry (Watson et al. 2006), assuming a(TiO2) of ca. 0.7 (sphene +/-ilmenite are ubiquitous). Zircons from the granite zone yield estimated T's of 700-860 C, whereas those from grey rocks range from 710- 910 C. While both granite and grey zircon populations show dramatic T variations among and

  11. 21 CFR 878.4400 - Electrosurgical cutting and coagulation device and accessories.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Electrosurgical cutting and coagulation device and....4400 Electrosurgical cutting and coagulation device and accessories. (a) Identification. An electrosurgical cutting and coagulation device and accessories is a device intended to remove tissue and control...

  12. Xenotime-(Y) formation from zircon dissolution-precipitation and HREE fractionation: an example from a metamorphosed phosphatic sandstone, Espinhaço fold belt (Brazil)

    NASA Astrophysics Data System (ADS)

    Franz, Gerhard; Morteani, Giulio; Rhede, Dieter

    2015-10-01

    We present an example where xenotime-(Y) together with metamorphic zircon replaces detrital zircon in a phosphatic sandstone from the Mesoproterozoic Espinhaço fold belt, Brazil, in a dissolution-precipitation reaction: {{zircon}}1 ( {{relict}} ) + {{P-}}{{bearing fluid}} = {{zircon}}2 ( {{metamorphic}} ) + {{xenotime}}. During the Brasiliano orogeny at 634 ± 19 Ma, the rocks experienced amphibolite facies metamorphism at ≥0.6 GPa/ 550 ± 37 °C (Southern Espinhaço) and ≥0.6 GPa/ 570 ± 35 °C (Northern Espinhaço), constrained by Zr-in-rutile and Ti-in-quartz thermometry and the presence of kyanite + muscovite + quartz. Many of the rocks show unusual rare earth element (REE) patterns with a hump at Gd-Tb-Dy and depletion in light REE. Detrital zircons (with relict ages between 1.5 and 3.3 Ga) show varying degrees of replacement as indicated by the presence of xenotime and associated porosity, from almost pristine to complete alteration. Textural evidence indicates local mobility of Zr and REE at the scale of the thin section. Xenotime-(Y) occurs together with other phosphates, mainly augelite, lazulite, and minerals of the svanbergite-crandallite-goyacite-florencite group. Xenotime-(Y) is very heterogeneous and reaches unusually high contents of up to 14 wt% Gd2O3, 13 wt% Dy2O3, and 3 wt% Tb2O3, corresponding to ≤0.36 REE atoms per formula unit due to the exchange Y = REE. The heavy REE patterns of xenotime-(Y) therefore show variable enrichment in individual elements, which explains the characteristic hump at Gd-Tb-Dy in the REE patterns of the whole rock. Although the rocks reached amphibolite facies conditions, textures indicate that formation of xenotime likely occurred during the early stages of diagenesis—metamorphism. Comparison with REE concentrations in xenotime-(Y) from the literature shows that selective REE incorporation into xenotime-(Y) is controlled by interaction with P-bearing hydrous fluids.

  13. MERS-CoV Accessory ORFs Play Key Role for Infection and Pathogenesis

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Menachery, Vineet D.; Mitchell, Hugh D.; Cockrell, Adam S.

    ABSTRACT While dispensable for viral replication, coronavirus (CoV) accessory open reading frame (ORF) proteins often play critical roles during infection and pathogenesis. Utilizing a previously generated mutant, we demonstrate that the absence of all four Middle East respiratory syndrome CoV (MERS-CoV) accessory ORFs (deletion of ORF3, -4a, -4b, and -5 [dORF3-5]) has major implications for viral replication and pathogenesis. Importantly, attenuation of the dORF3-5 mutant is primarily driven by dysregulated host responses, including disrupted cell processes, augmented interferon (IFN) pathway activation, and robust inflammation.In vitroreplication attenuation also extends toin vivomodels, allowing use of dORF3-5 as a live attenuated vaccine platform.more » Finally, examination of ORF5 implicates a partial role in modulation of NF-κB-mediated inflammation. Together, the results demonstrate the importance of MERS-CoV accessory ORFs for pathogenesis and highlight them as potential targets for surveillance and therapeutic treatments moving forward. IMPORTANCEThe initial emergence and periodic outbreaks of MERS-CoV highlight a continuing threat posed by zoonotic pathogens to global public health. In these studies, mutant virus generation demonstrates the necessity of accessory ORFs in regard to MERS-CoV infection and pathogenesis. With this in mind, accessory ORF functions can be targeted for both therapeutic and vaccine treatments in response to MERS-CoV and related group 2C coronaviruses. In addition, disruption of accessory ORFs in parallel may offer a rapid response platform to attenuation of future emergent strains based on both SARS- and MERS-CoV accessory ORF mutants.« less

  14. Tectonic Recycling in the Paleozoic Ouachita Assemblage from U-Pb Detrital Zircon Studies

    NASA Astrophysics Data System (ADS)

    Gleason, J. D.; Gehrels, G. E.; Finney, S. C.

    2001-05-01

    The Paleozoic Ouachita deep-marine clastic sedimentary assemblage records a complex provenance over the course of its 200 m.y. history, with evidence for mixed sources and multiple dispersal paths. Combined neodymium and U-Pb detrital zircon work has established that most of the assemblage in Arkansas and Oklahoma is derived from Laurentian sources, meaning that regardless of the multiple pathways by which sediment was delivered to Ouachita seafloor, the material had its ultimate origin on the North American continent. More detailed work is in progress to elucidate specific dispersal paths, in particular for the middle to late Ordovician when a major change in provenance is recorded, and during the Carboniferous when voluminous turbidites entered the basin. We sampled three formations for U-Pb detrital zircon studies: the lower Middle Ordovician Blakely Sandstone, the Upper Ordovician/Lower Silurian Blaylock Sandstone, and the Pennsylvanian Jackfork Group. Individual zircon ages from these units document a major change in provenance between deposition of the Blakely Sandstone and Blaylock Sandstone, which is also reflected in the neodymium isotopic signature. Both units have a large population of Grenvillian-age zircons (1.0-1.2 Ga), and a less abundant population of 1.3-1.4 Ga zircons likely derived from sources in the mid-continent region. The Blakely Sandstone also contains abundant Archean zircons (2.5-2.7 Ga, likely derived from the Superior Province), and one grain apparently derived from the Penokean orogen (1.9 Ga). Zircon morphology (highly rounded, spherical), combined with the pure quartz sandstone lithology of the Blakely Sandstone, indicates very mature sedimentary sources. We conclude that zircons from this source were recycled ultimately from source terranes in the North American craton. This is reinforced by neodymium isotopes (eNd = -15), paleocurrents (from the north) and olistoliths (1.3 Ga granites), the latter indicating that Blakely turbidites

  15. Ancient xenocrystic zircon in young volcanic rocks of the southern Lesser Antilles island arc

    NASA Astrophysics Data System (ADS)

    Rojas-Agramonte, Yamirka; Williams, Ian S.; Arculus, Richard; Kröner, Alfred; García-Casco, Antonio; Lázaro, Concepción; Buhre, Stephan; Wong, Jean; Geng, Helen; Echeverría, Carlos Morales; Jeffries, Teresa; Xie, Hangqian; Mertz-Kraus, Regina

    2017-10-01

    The Lesser Antilles arc is one of the best global examples in which to examine the effects of the involvement of subducted sediment and crustal assimilation in the generation of arc crust. Most of the zircon recovered in our study of igneous and volcaniclastic rocks from Grenada and Carriacou (part of the Grenadines chain) is younger than 2 Ma. Within some late Paleogene to Neogene ( 34-0.2 Ma) lavas and volcaniclastic sediments however, there are Paleozoic to Paleoarchean ( 250-3469 Ma) xenocrysts, and Late Jurassic to Precambrian zircon ( 158-2667 Ma) are found in beach and river sands. The trace element characteristics of zircon clearly differentiate between different types of magmas generated in the southern Lesser Antilles through time. The zircon population from the younger arc (Miocene, 22-19 Ma, to Present) has minor negative Eu anomalies, well-defined positive Ce anomalies, and a marked enrichment in heavy rare earth elements (HREE), consistent with crystallization from very oxidized magmas in which Eu2 + was in low abundance. In contrast, zircon from the older arc (Eocene to mid-Oligocene, 30-28 Ma) has two different REE patterns: 1) slight enrichment in the light (L)REE, small to absent Ce anomalies, and negative Eu anomalies and 2) enriched High (H)REE, positive Ce anomalies and negative Eu anomalies (a similar pattern is observed in the xenocrystic zircon population). The combination of positive Ce and negative Eu anomalies in the zircon population of the older arc indicates crystallization from magmas that were variably, but considerably less oxidized than those of the younger arc. All the igneous zircon has positive εHf(t), reflecting derivation from a predominantly juvenile mantle source. However, the εHf(t) values vary significantly within samples, reflecting considerable Hf isotopic heterogeneity in the source. The presence of xenocrystic zircon in the southern Lesser Antilles is evidence for the assimilation of intra-arc crustal sediments and

  16. Electrophysiology of Cranial Nerve Testing: Spinal Accessory and Hypoglossal Nerves.

    PubMed

    Stino, Amro M; Smith, Benn E

    2018-01-01

    Multiple techniques have been developed for the electrodiagnostic evaluation of cranial nerves XI and XII. Each of these carries both benefits and limitations, with more techniques and data being available in the literature for spinal accessory than hypoglossal nerve evaluation. Spinal accessory and hypoglossal neuropathy are relatively uncommon cranial mononeuropathies that may be evaluated in the outpatient electrodiagnostic laboratory setting. A review of available literature using PubMed was conducted regarding electrodiagnostic technique in the evaluation of spinal accessory and hypoglossal nerves searching for both routine nerve conduction studies and repetitive nerve conduction studies. The review provided herein provides a resource by which clinical neurophysiologists may develop and implement clinical and research protocols for the evaluation of both of these lower cranial nerves in the outpatient setting.

  17. Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon.

    PubMed

    Bell, Elizabeth A; Boehnke, Patrick; Harrison, T Mark; Mao, Wendy L

    2015-11-24

    Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼ 3.5 billion years (Ga), the chemofossil record arguably to ∼ 3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 ± 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their δ(13)CPDB of -24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼ 300 My earlier than has been previously proposed.

  18. Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon

    PubMed Central

    Bell, Elizabeth A.; Harrison, T. Mark; Mao, Wendy L.

    2015-01-01

    Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼3.5 billion years (Ga), the chemofossil record arguably to ∼3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 ± 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their δ13CPDB of −24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼300 My earlier than has been previously proposed. PMID:26483481

  19. Geology and U-Pb Zircon ages of the Kavacik Leucogranite in the Bornova Flysch Zone (Western Anatolia, Turkey)

    NASA Astrophysics Data System (ADS)

    Güngör, Talip; Hasözbek, Altuǧ; Akal, Cüneyt; Mertz-Kraus, Regina; Peştemalci Üregel, Reyhan

    2016-04-01

    The Bornova Flysch Zone comprises an olistostrome-melange situated NE-SW direction between the Izmir Ankara Suture Zone and the Menderes Massif. The Bornova Flysch Zone is mainly composed of slightly deformed Late Cretaceous to Paleocene sandstone and shale with Mesozoic limestone and oceanic crustal associations. These large-scale blocks in the matrix of the Bornova Flysch Zone are mostly defined as limestone, basalt, serpentinite and radiolarian cherts. In this study, granitic bodies, situated in the Bornova Flysch Zone, named as Kavacik leucogranite is examined for the first time, in terms its geological features and its U-Pb zircon crystallization ages. Kavacik leucogranite displays a typical granitic texture and its composition indicates ranging between granitic to granodioritic in composition with lack of mafic minerals. The geochemical features of the granite indicate the I-type and subalkaline nature of the granitic body. The geochemical signatures of the Kavacik granite points out Volcanic Arc Granitoids as similarly seen in Karaburun granite. U-Pb zircon LA ages were also obtained from the Kavacik granite ranging between 224.5 ± 2.0 Ma and 230.0 ± 2.8 Ma. Early Triassic zircon ages are also previously observed in the Karaburun Peninsula (Karaburun Granite) and the Menderes Massif (Odemis-Kiraz Submassif). The initial geological boundary relation of the Kavacik Leucogranite is not clear in the field and likely displays tectonic boundary features in the matrix of the Bornova Flysch Zone. Overall, the geochemical features of the Kavacik leucogranite and similar leucomagmatic bodies in the Western Anatolia points out the subduction-related tectonic setting is favorable during the Triassic time.

  20. Late magmatic stage of the zoned Caleu pluton (Central Chile): insights from zircon crystallization conditions

    NASA Astrophysics Data System (ADS)

    Molina, P. G.; Parada, M.; Gutierrez, F. J.; Chang-Qiang, M.; Jianwei, L.; Yuanyuan, L.

    2012-12-01

    The Caleu pluton consists of three N-S elongated lithological zones: Gabbro-Diorite Zone (GDZ), Tonalite Zone (TZ) and Granodiorite Zone (GZ); western, middle and eastern portions of the pluton, respectively. The zones are thought to be previously differentiated in a common, isotopically depleted (Sr-Nd), subjacent magma reservoir at a 4 kbar equivalent depth. The emplacement should have occurred at the climax of the Cretaceous rifting. We present preliminary results of U238/Pb206 zircon geochronology; zircon saturation, Tsat(Zrn), and crystallization temperatures (Ti-in-Zrn); as well as relative oxidation states at time of crystallization, based on: (i) the sluggish REE and HFSE subsolidus diffusivities in zircon; (ii) the behavior of Ti4+↔Si4+ and Ce4+↔Zr4+ isovalent replacement, in addition to a constrained TiO2 activity in almost all typical crustal rocks; and (iii) relative oxidation states at time of crystallization, respectively. The latter are obtained by interpolation of the partition coefficients of trivalent (REE) and tetravalent (HFSE) curves in Onuma diagrams for each zircon, and then estimating relative Ce(IV)/Ce(III) ratios. Results obtained from 4 samples (a total of 77 zircon grains) collected from the three mentioned lithological zones indicate U/Pb ages of approximately 99.5 ±1.5 Ma, 96.8 ±0.6 Ma, and 94.4 +2.2 -0.8 Ma; and Ti-in Zrn ranges of ca. 720-870°C, ca. 680-820°C and ca. 750-840°C, for the GDZ, TZ and GZ samples, respectively. On the other hand Tsat(Zrn) of ca. 750-780°C in the TZ, and ca. 830-890°C in the GZ, were obtained. As expected saturation temperatures are similar or higher than Ti-in-Zrn obtained in zircon grains of TZ and GZ, respectively. Cathodoluminiscence images in zircon suggest a magmatic origin, due to absence of complex zoning patterns and fairly well conserved morphologies. Exceptionally the GDZ sample zircons show evidence of inheritance, indicating a xenocrystic and/or antecrystic origin. A relative Ce