Genesis of Diamond-bearing and Diamond-free Podiform Chromitites in the Luobusa Ophiolite, Tibet

NASA Astrophysics Data System (ADS)

Yang, J.; Xiong, F.; Xu, X.; Robinson, P. T.; Dilek, Y.; Griffin, W. L.

2014-12-01

Micro-diamonds, moissanite and many highly reduced minerals, such as native Fe, Cr, Ni, Si, Al, and metallic alloys, have been reported previously from podiform chromitites and peridotites of the Luobusa ophiolite in the eastern segment of the Yarlung-Zangbo suture of southern Tibet.. Similar mineral associations have now been confirmed in mantle peridotites or chromitites of 11 other ophiolites in 5 orogenic belts, in Tibet, Myanmar, North China and the Polar Urals. However, detailed studies of the Luobusa ophiolite show that not all chromitites contain these UHP and highly reduced minerals. Diamond-bearing chromitites are chiefly massive bodies composed of over 95 modal% magnesiochromite with Cr#s [100Cr/(Cr+Al)] of 77-83 and Mg#s [100Mg/(Mg+Fe)] of 71-82. Most of these bodies have sharp contacts with the host harzburgites and are only rarely enclosed in dunite envelopes. Many magnesiochromite grains in the massive chromitites contain inclusions of forsterite and pyroxene. Forsterite inclusions have Fo numbers of 97-99 and NiO contents of 1.11-1.29 wt%. Mg#s of clinopyroxene inclusions are 96-98 and those of orthopyroxene are 96-97. X-ray studies show that the olivine inclusions have very small unit cells and short cation-oxygen bond distances, suggesting crystallization at high pressure. In contrast, diamond-free chromitites typically occur as layers within thick dunite sequences or as irregular patches surrounded by dunite envelopes. They consist of variable proportions of magnesiochromite (Cr# = 76-78; Mg# = 58-61) and olivine, and have banded, nodular and disseminated textures. The dunite envelopes consist chiefly of granular olivine with a few relatively large, amoeboidal grains of magnesiochromite, and typically grade into the host peridotites with increasing pyroxene. Unlike those in the massive ores, magnesiochromite grains in nodular and disseminated chromitites lack pyroxene inclusions, and their olivine inclusions have relatively low Fo (94-96) and Ni

Re-Os isotopic systematics in chromitites from the Stillwater Complex, Montana, USA

NASA Astrophysics Data System (ADS)

Marcantonio, Franco; Zindler, Alan; Reisberg, Laurie; Mathez, E. A.

1993-08-01

New Re-Os isotopic data on chromitites of the Stillwater Complex demonstrate isotopic equilibrium between cumulate chromite and whole rock. Initial osmium isotopic ratios for the chromitites, chosen for their freshness, are consistent with derivation from a mantle-derived magma that suffered little or no interaction with the continental crust prior to crystallization. Molybdenite, separated from a sample of the G-chromitite, yields a Re-Os age of 2740 Ma, indistinguishable from the age of the intrusion. The presence of molybdenite documents rhenium, and probably osmium, mobilization by hydrothermal fluids that permeated the intrusion shortly after crystallization. Initial osmium isotopic variability observed in chromitites and other rocks from the Stillwater Complex could result from interaction with these fluids. In this context, there is no compelling reason to call on assimilation of crust by mantle-derived magma to explain the osmium or neodymium isotopic variability. Although osmium isotopic systematics have been affected by hydrothermal processes, Re-Os results demonstrate that more than 95 percent of the osmium, and by inference other PGEs in the Stillwater Complex, derive from the mantle.

Compositional variations and tectonic settings of podiform chromitites and associated ultramafic rocks of the Neoproterozoic ophiolite at Wadi Al Hwanet, northwestern Saudi Arabia

NASA Astrophysics Data System (ADS)

Ahmed, Ahmed Hassan; Harbi, Hesham M.; Habtoor, Abdelmonem M.

2012-08-01

Wadi Al Hwanet area in NW of Saudi Arabia is part of the Jebel Ess ophiolite constituting the northeastern part of the ˜700 Ma Yanbu-Sol Hamed-Onib-Allaqi-Heiani suture of the northern Arabian-Nubian Shield. The mantle section of Wadi Al Hwanet ophiolite consists mainly of voluminous harzburgites overlain by thick, massive transition-zone dunites, and small-scale chromitite pods. The harzburgites and massive dunites are exceptionally fresh; primary magmatic textures and silicate minerals are still preserved. Two modes of podiform chromitites exist; small lensoidal pods (group I), and relatively large dike-like pods (group II). Geochemically, the former chromitite type contains chromian spinels with high Cr# (0.79-0.81) and displays a PGE-poor character, with steep negatively-sloped PGE distribution patterns, whereas the latter chromitite type contains chromian spinels with relatively lower Cr# (0.61-0.71) and is PGE-rich (up to 1000 ppb), with positively-sloped PGE distribution patterns. The group II chromitites have much higher sulfide content than the group I suite. Parental melt compositions, in equilibrium with podiform chromitites, vary in Al2O3, FeO*/MgO and TiO2 contents from group I to group II chromitites, although both of them are in the range of the boninitic melts. The differences in the chromitites chemistry are most probably due to variable degrees of partial melting of the involved melts. Two stages of a magmatic activity were inferred for the chromitites genesis. The group I chromitites, of high Cr# of chromian spinels and PGE-poor negatively-sloped patterns, were precipitated in the first stage from a boninitic melt produced by a high degree of partial melting at a supra-subduction zone setting. The second chromitite-forming stage involves a relatively low degree of partial melting under high activities of sulfur and oxygen to produce the group II chromitites with enrichment in sulfides and PGE contents, possibly in a supra-subduction zone setting

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

Petrology and geochemistry of the high-Cr podiform chromitites of the Köycegiz ophiolite, southwest Turkey: implications for the multi-stage evolution of the oceanic upper mantle

NASA Astrophysics Data System (ADS)

Xiong, Fahui; Yang, Jingsui; Dilek, Yildirim; Wang, ChunLian; Hao, Xiaolin; Xu, Xiangzhen; Lian, Dongyang

2018-03-01

Ophiolites exposed across the western Tauride belt in Turkey represent tectonically emplaced fragments of oceanic lithosphere obducted onto the continental margin following the closure of the Neotethys Ocean during the Late Cretaceous. The ultramafic massif of Köycegiz, which is located in the ophiolitic belt of southwestern Turkey, is a major source of metallurgical chromitite ore. The massif comprises a base of tectonized harzburgite with minor dunite overlain by a magmatic sequence of wehrlite, pyroxenite, troctolite and gabbro. Only sparse refractory chromitites occur within the harzburgites; in contrast, the upper and middle sections of the peridotite sequence contain abundant metallurgical chromitites. The peridotites record abundant evidence of mantle metasomatism on various scales, as the Fo values of olivine in harzburgite are 90.1-95.4, whereas those in dunite are 90.1-91.8. The compositions of the melts passing through the peridotites changed gradually from arc tholeiite to boninite due to melt-rock reactions, thus producing more Cr-rich chromitites in the upper part of the body. Most of the chromitites have high Cr numbers (77-78), although systematic changes in the compositions of the olivine and chromian spinel occur from the harzburgites to the dunite envelopes to the chromitites, reflecting melt-rock reactions. The calculated ΔlogfO2 (FMQ) values range from - 2.77 to + 1.03 in the chromitites, - 2.73 to -0.01 in the harzburgites, and - 1.65 to + 0.45 in the dunites. All of the available evidence suggests that the Köycegiz ophiolite formed in a supra-subduction zone (SSZ) mantle wedge. These models indicate that the harzburgites represent the products of first-stage melting and low degrees of melt-rock interaction that occurred in a mid-ocean ridge (MOR) environment. In contrast, the chromitites and dunites represent the products of second-stage melting and related refertilization, which occurred in an SSZ environment.

Parkerite and bismutohauchecornite in chromitites of the Urals: Example of the Uralian Emerald Mines

NASA Astrophysics Data System (ADS)

Koroteev, V. A.; Popov, M. P.; Erokhin, Yu. V.; Khiller, V. V.

2017-04-01

An unusual ore mineralization represented by parkerite, millerite, bismutohauchecornite, bismuthinite, and nickeline was registered in altered chromitite from the Mariinsk emerald-beryllium deposit. Such mineralization is typical of Cu-Ni sulfide ores and hydrothermal veins from the five-element formation. This mineral assemblage was not registered in ophiolitic ultrabasic rocks and related chromitites. The find of bismutohauchecornite is the first in the Urals; the find of parkerite is the third.

Compositional and isotopic heterogeneities in the Neo-Tethyan upper mantle recorded by coexisting Al-rich and Cr-rich chromitites in the Purang peridotite massif, SW Tibet (China)

NASA Astrophysics Data System (ADS)

Xiong, Fahui; Yang, Jingsui; Xu, Xiangzhen; Kapsiotis, Argyrios; Hao, Xiaolin; Liu, Zhao

2018-06-01

The Purang harzburgite massif in SW Tibet (China) hosts abundant chrome ore deposits. Ores consist of 20 to >95% modal chromian spinel (Cr-spinel) with mylonitic fabric in imbricate shaped pods. The composition of Cr-spinel in these ores ranges from Al-rich [Cr#Sp or Cr/(Cr + Al) × 100 = 47.60-57.56] to Cr-rich (Cr#Sp: 62.55-79.57). Bulk platinum-group element (PGE) contents of chromitites are also highly variable ranging from 17.5 ppb to ∼2.5 ppm. Both metallurgical and refractory chromitites show a general enrichment in the IPGE (Os, Ir and Ru) with respect to the PPGE (Rh, Pt and Pd), resulting mostly in right-sloping primitive mantle (PM)-normalized PGE profiles. The platinum-group mineral (PGM) assemblages of both chromitite types are dominated by heterogeneously distributed, euhedral Os-bearing laurite inclusions in Cr-spinel. The Purang chromitites have quite inhomogeneous 187Os/188Os ratios (0.12289-0.13194) that are within the range of those reported for mantle-hosted chromitites from other peridotite massifs. Geochemical calculations demonstrate that the parental melts of high-Cr chromitites were boninitic, whereas those of high-Al chromitites had an arc-type tholeiitic affinity. Chromite crystallization was most likely stimulated by changes in magma compositions due to melt-peridotite interaction, leading to the establishment of a heterogeneous physicochemical environment during the early crystallization of the PGM. The highly variable PGE contents, inhomogeneous Os-isotopic compositions and varying Cr#Sp ratios of these chromitites imply a polygenetic origin for them from spatially distinct melt inputs. The generally low γOs values (<1) of chromitites indicate that their parental melts originated within different sections of a heterogeneously depleted mantle source region. These melts were most likely produced in the mantle wedge above a downgoing lithospheric slab.

Palladium, platinum, rhodium, ruthenium, and iridium in chromitites from the Massif du Sud and Tiebaghi massif, New Caledonia.

USGS Publications Warehouse

Page, N.J.; Cassard, D.; Haffty, J.

1982-01-01

The massive and disseminated podiform chromitites from 43 mines and other occurrences in the area contain up to (in ppb) Pd 9, Pt 45, Rh 31, Ir 410 and Ru 1300. The possble origins of the chromitites are discussed. -K.A.R.

Seasonal Scale Convective-Stratiform Pricipitation Variabilities at Tropics

NASA Astrophysics Data System (ADS)

S, Sreekanth T.

begin{center} Large Seasonal Scale Convective-Stratiform Pricipitation Variabilities at Tropics Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) and V Sasi Kumar (2) *Centre for Earth Science Studies, Akkulam, Thiruvananthapuram (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) 32. NCC Nagar Peroorkada, Thiruvananthapuram ABSTRACT This study investigates the variabilities of convective and stratiform rainfall from 2011 to 2013 at a tropical coastal station in three seasons viz Pre-Monsoon (March-May), Monsoon (June-September) and Post-Monsoon (October-December). Understanding the climatological variability of these two dominant forms of precipitation and their implications in the total rainfall were the main objectives of this investigation. Variabilities in the frequency & duration of events, rain rate & total number of rain drops distribution in different events and the accumulated amount of rain water were analysed. Based on the ground & radar observations from optical & impact disdrometers, Micro Rain Radar and Atmospheric Electric Field Mill, precipitation events were classified into convective and stratiform in three seasons. Classification was done by the method followed by Testud et al (2001) and as an additional information electrical behaviour of clouds from Atmospheric Electric Field Mill is also used. Events which could not be included in both types were termed as 'mixed precipitation' and were included separately. Diurnal variability of the total rainfall in each seasons were also examined. For both convective and stratiform rainfall there exist distinct day-night differences. During nocturnal hours convective rain draged more attention. In all seasons almost 70% of rain duration and 60% of rain events of convective origin were confined to nocturnal hours. But stratiform rain was not affected by diurnal variations greatly because night time occurrences of stratiform duration and events were less than 50%. Also in Monsoon above 35% of

USMC UGS technology advancements

NASA Astrophysics Data System (ADS)

Hartup, David C.; Barr, Michael E.; Hirz, Philip M.; Kipp, Jason; Fishburn, Thomas A.; Waller, Ezra S.; Marks, Brian A.

2008-04-01

Technology advancements for the USMC UGS system are described. Integration of the ARL Blue Radio/CSR into the System Controller and Radio Repeater permit the TRSS system to operate seamlessly within the Family of UGS concept. In addition to the Blue Radio/CSR, the TRSS system provides VHF and SATCOM radio links. The TRSS system is compatible with a wide range of imagers, including those with both analog and digital interfaces. The TRSS System Controller permits simultaneous monitoring of 2 camera inputs. To complement enhanced compatibility and improved processing, the mechanical housing of the TRSS System Controller has been updated. The SDR-II, a system monitoring device, also incorporates four Blue Radio/CSRs along with other communication capabilities, making it an ideal choice for a monitoring station within the Family of UGS. Field testing of L-3 Nova's UGS system at YPG has shown flawless performance, capturing all 126 targets.

Stratiform chromite deposit model

USGS Publications Warehouse

Schulte, Ruth F.; Taylor, Ryan D.; Piatak, Nadine M.; Seal, Robert R.

2010-01-01

Stratiform chromite deposits are of great economic importance, yet their origin and evolution remain highly debated. Layered igneous intrusions such as the Bushveld, Great Dyke, Kemi, and Stillwater Complexes, provide opportunities for studying magmatic differentiation processes and assimilation within the crust, as well as related ore-deposit formation. Chromite-rich seams within layered intrusions host the majority of the world's chromium reserves and may contain significant platinum-group-element (PGE) mineralization. This model of stratiform chromite deposits is part of an effort by the U.S. Geological Survey's Mineral Resources Program to update existing models and develop new descriptive mineral deposit models to supplement previously published models for use in mineral-resource and mineral-environmental assessments. The model focuses on features that may be common to all stratiform chromite deposits as a way to gain insight into the processes that gave rise to their emplacement and to the significant economic resources contained in them.

Tracing ancient events in the lithospheric mantle: A case study from ophiolitic chromitites of SW Turkey

NASA Astrophysics Data System (ADS)

Akbulut, Mehmet; González-Jiménez, José María; Griffin, William L.; Belousova, Elena; O'Reilly, Suzanne Y.; McGowan, Nicole; Pearson, Norman J.

2016-04-01

New major-, minor- and trace-element data on high-Cr chromites from several ophiolitic podiform chromitites from Lycian and Antalya peridotites in southwestern Turkey reveal a polygenetic origin from a range of arc-type melts within forearc and back-arc settings. These forearc and the back-arc related high-Cr chromitites are interpreted to reflect the tectonic juxtaposition of different lithospheric mantle segments during the obduction. The diversity of the γOs(t=0) values (-8.28 to +13.92) in the Antalya and Lycian chromitite PGMs and their good correlations with the sub- to supra-chondritic 187Os/188Os ratios (0.1175-0.1459) suggests a heterogeneous mantle source that incorporated up to 40% recycled crust, probably due to subduction processes of the orogenic events. The few model ages calculated define two significant peaks in TRD model ages at 1.5 and 0.25 Ga, suggesting that the chromitites are younger than 0.25 Ga and include relics of an at least Mesoproterozoic or older (>1.0 Ga) mantle protolith. Eight of the nine zircon grains separated from the chromitites, are interpreted as detrital and/or resorbed xenocrystic relics, whilst a significantly less reworked/resorbed one is considered to be of metasomatic origin. In-situ U-Pb dating of the xenocrystic zircon grains yielded a spread of ages within ca 0.6-2.1 Ga, suggesting recycling of crustal rocks younger than 0.6 Ga (Late Neoproterozoic). The notable coincidence between the lower age limit of the older zircons (ca 1.6 Ga) and the oldest Os model age peak (ca 1.5 Ga) from the PGM may suggest a Mesoproterozoic rifting stage. These findings imply a Paleoproterozoic sub-continental lithospheric mantle (SCLM) protolith for the SW Anatolian mantle which was later converted into an oceanic lithospheric mantle domain possibly following a rifting and continental break-up initiated during Mesoproterozoic (ca 1.5-1.0 Ga). The single metasomatic zircon of ca 0.09 Ga age coinciding with the initiation of the

High- and low-Cr chromitite and dunite in a Tibetan ophiolite: evolution from mature subduction system to incipient forearc in the Neo-Tethyan Ocean

NASA Astrophysics Data System (ADS)

Xiong, Qing; Henry, Hadrien; Griffin, William L.; Zheng, Jian-Ping; Satsukawa, Takako; Pearson, Norman J.; O'Reilly, Suzanne Y.

2017-06-01

The microstructures, major- and trace-element compositions of minerals and electron backscattered diffraction (EBSD) maps of high- and low-Cr# [spinel Cr# = Cr3+/(Cr3+ + Al3+)] chromitites and dunites from the Zedang ophiolite in the Yarlung Zangbo Suture (South Tibet) have been used to reveal their genesis and the related geodynamic processes in the Neo-Tethyan Ocean. The high-Cr# (0.77-0.80) chromitites (with or without diopside exsolution) have chromite compositions consistent with initial crystallization by interaction between boninitic magmas, harzburgite and reaction-produced magmas in a shallow, mature mantle wedge. Some high-Cr# chromitites show crystal-plastic deformation and grain growth on previous chromite relics that have exsolved needles of diopside. These features are similar to those of the Luobusa high-Cr# chromitites, possibly recycled from the deep upper mantle in a mature subduction system. In contrast, mineralogical, chemical and EBSD features of the Zedang low-Cr# (0.49-0.67) chromitites and dunites and the silicate inclusions in chromite indicate that they formed by rapid interaction between forearc basaltic magmas (MORB-like but with rare subduction input) and the Zedang harzburgites in a dynamically extended, incipient forearc lithosphere. The evidence implies that the high-Cr# chromitites were produced or emplaced in an earlier mature arc (possibly Jurassic), while the low-Cr# associations formed in an incipient forearc during the initiation of a new episode of Neo-Tethyan subduction at 130-120 Ma. This two-episode subduction model can provide a new explanation for the coexistence of high- and low-Cr# chromitites in the same volume of ophiolitic mantle.

Diamond and moissanite in ophiolitic mantle rocks and podiform chromitites: A deep carbon source?

NASA Astrophysics Data System (ADS)

Yang, J.; Xu, X.; Wiedenbeck, M.; Trumbull, R. B.; Robinson, P. T.

2010-12-01

Diamonds are known from a variety of occurreces, mainly from mantle-derived kimberlites, meteorite impact craters, and continental deep subduction and collision zones. Recently, an unusual mineral group was discovered in the Luobusa ophiolitic chromitites from the Yarlung Zangbu suture, Tibet, which probably originated from a depth of over 300 km in the mantle. Minerals of deep origin include coesite apparently pseudomorphing stishovite, and diamond as individual grains or inclusions in OsIr alloy. To determine if such UHP and unusual minerals occur elsewhere, we collected about 1.5 t 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. These minerals are very similar in composition and structure to those reported from the Luobusa chromitites. So far diamond and/or moissanite have been discovered from many different ophiolitic ultramafic rocks, including in-situ grains in polished chromitite fragments. These discoveries demonstrate that the Luobusa ophiolite is not a unique diamond-bearing massif. Secondary ion mass spectrometric (SIMS) analysis shows that the ophiolite-hosted diamond has a distinctive 13C-depleted isotopic composition (δ13C from -18 to -28‰, n=70), compatible to the ophiolite-hosted moissanite (δ13C from -18 to -35‰, n=36), both are much lighter than the main carbon reservoir in the upper mantle (δ13C near -5‰). The compiled data from moissanite from kimberlites and other mantle settings share the characteristic of strongly 13C-depleted isotopic composition. This suggests that diamond and moissanite originates from a separate carbon reservoir in the mantle or that its formation involved strong isotopic fractionation. Subduction of biogenic carbonaceous material could potentially satisfy both the unusual isotopic and

Distribution and PGE mineralization in the formation of chromitite in ophiolite complexes (Ospina-Kitoi Kharanur and ultrabasic massifs of Eastern Sayan, Sousern Siberia)

NASA Astrophysics Data System (ADS)

Kiseleva, Olga; Zhmodik, Sergei

2015-04-01

New study of PGE in restitic ultrabasic (Kharanur and Ospin-Kitoi) massifs from North and South branches (Dobretsov et al., 1985) of the ophiolite complexes in south-eastern part of the Eastern Sayan show their presence in chromitites of both branches belonging to the different geodynamic settings. Modern concepts model includes several mechanisms of podiform chromitite origin reflected in the chemistry of Cr-spinels (Arai, Yurimoto, 1994; Ballhaus, 1998; Uysal et al., 2009 et al.): 1) partial melting of upper mantle rocks, 2) mixing of primitive melts with melts enriched in SiO2, 3) melt-rock interaction. We estimated the types of interaction of mafic melts with mantle peridotites, with the formation of chromite bodies. For ore chrome spinelides from northern branch (Al2O3) melt = 8 - 14 wt%, (TiO2) melt = 0 - 0,4 wt%, (Fe/Mg) melt = 0,5 - 2,4; Southern branch (Al2O3) melt = 10 - 13 wt%, (TiO2) melt = 0,1 wt%, (Fe/Mg) melt = 0,3 - 1 (Kiseleva, 2014). There are two types of PGE distribution Os-Ir-Ru (I) and Pt-Pd (II). Type I chromitites (mid-Al#Cr-spinels) revealed only Os-Ir-Ru distributions; type II (low-Al#Cr spinelides) show both Os-Ir-Ru and (Pt-Pd) distributions (Kiseleva et al., 2012, 2014). PGE distribution in ultramafic peridotites and chromitites reflects PGE fractionation during partial melting (Barnes et al., 1985; Rehkämper et al., 1997). Processes bringing to extreme fractionation of PGE, may be associated with fluid-saturated supra subduction environment where melting degree near 20% and above is sufficient for the release of PGE from the mantle source (Dick, Bullen, 1984; Naldrett, 2010). Enrichment in PPGE together with a high content of IPGE in same chromite bodies is attributed to the second step of melting, and formation of S-enriched and saturated in PGE melts (Hamlyn, Keays, 1986; Prichard et al., 1996). For type I chromitites platinum group minerals (PGM) are presented by Os-Ir-Ru system. In type II chromitites PGM are represented by Os

Mineralogy, composition and PGM of chromitites from Pefki, Pindos ophiolite complex (NW Greece): evidence for progressively elevated fAs conditions in the upper mantle sequence

NASA Astrophysics Data System (ADS)

Kapsiotis, Argirios; Grammatikopoulos, Tassos A.; Tsikouras, Basilios; Hatzipanagiotou, Konstantin; Zaccarini, Federica; Garuti, Giorgio

2011-01-01

The Pindos ophiolite complex, located in the northwestern part of continental Greece, hosts various chromite deposits of both metallurgical (high-Cr) and refractory (high-Al) type. The Pefki chromitites are banded and sub-concordant to the surrounding serpentinized dunites. The Cr# [Cr/(Cr + Al)] of magnesiochromite varies between 0.75 and 0.79. The total PGE grade ranges from 105.9 up to 300.0 ppb. IPGE are higher than PPGE, typical of mantle hosted ophiolitic chromitites. The PGM assemblage in chromitites comprises anduoite, ruarsite, laurite, irarsite, sperrylite, hollingworthite, Os-Ru-Ir alloys including osmium and rutheniridosmine, Ru-bearing oxides, braggite, paolovite, platarsite, cooperite, vysotskite, and palladodymite. Iridarsenite and omeiite were also observed as exsolutions in other PGM. Rare electrum and native Ag are recovered in concentrates. This PGM assemblage is of great petrogenetic importance because it is significantly different from that commonly observed in podiform mantle-hosted and banded crustal-hosted ophiolitic chromitites. PGE chalcogenides of As and S are primary, and possibly crystallized directly from a progressively enriched in As boninitic melt before or during magnesiochromite precipitation. The presence of Ru-bearing oxides implies simultaneous desulfurization and dearsenication processes. Chemically zoned laurite and composite paolovite-electrum intergrowths are indicative of the relatively high mobility of certain PGE at low temperatures under locally oxidizing conditions. The PGM assemblage and chemistry, in conjunction with geological and petrologic data of the studied chromitites, indicate that it is characteristic of chromitites found within or close to the petrologic Moho. Furthermore, the strikingly different PGM assemblages between the high-Cr chromitites within the Pindos massif is suggestive of non-homogeneous group of ores.

Micro-Physical characterisation of Convective & Stratiform Rainfall at Tropics

NASA Astrophysics Data System (ADS)

Sreekanth, T. S.

Large Micro-Physical characterisation of Convective & Stratiform Rainfall at Tropics begin{center} begin{center} Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) , and V Sasi Kumar (2) *Centre for Earth Science Studies, Akkulam, Thiruvananthapuram (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) 32. NCC Nagar, Peroorkada, Thiruvananthapuram ABSTRACT Micro-physical parameters of rainfall such as rain drop size & fall speed distribution, mass weighted mean diameter, Total no. of rain drops, Normalisation parameters for rain intensity, maximum & minimum drop diameter from different rain intensity ranges, from both stratiform and convective rain events were analysed. Convective -Stratiform classification was done by the method followed by Testud et al (2001) and as an additional information electrical behaviour of clouds from Atmospheric Electric Field Mill was also used. Events which cannot be included in both types are termed as 'mixed precipitation' and identified separately. For the three years 2011, 2012 & 2013, rain events from both convective & stratiform origin are identified from three seasons viz Pre-Monsoon (March-May), Monsoon (June-September) and Post-Monsoon (October-December). Micro-physical characterisation was done for each rain events and analysed. Ground based and radar observations were made and classification of stratiform and convective rainfall was done by the method followed by Testud et al (2001). Radar bright band and non bright band analysis was done for confimation of stratifom and convective rain respectievely. Atmospheric electric field data from electric field mill is also used for confirmation of convection during convective events. Statistical analyses revealed that the standard deviation of rain drop size in higher rain rates are higher than in lower rain rates. Normalised drop size distribution is ploted for selected events from both forms. Inter relations between various precipitation parameters were analysed in three

Stratiform and Convective Rain Discrimination from Microwave Radiometer Observations

NASA Technical Reports Server (NTRS)

Prabhakara, C.; Cadeddu, M.; Short, D. A.; Weinman, J. A.; Schols, J. L.; Haferman, J.

1997-01-01

A criterion based on the SSM/I observations is developed to discriminate rain into convective and stratiform types. This criterion depends on the microwave polarization properties of the flat melting snow particles that fall slowly in the stratiform clouds. Utilizing this criterion and some spatial and temporal characteristics of hydrometeors in TOGA-COARE area revealed by ship borne radars, we have developed an algorithm to retrieve convective and stratiform rain rate from SSM/I data.

Origin and age of zircon-bearing chromitite layers from the Finero phlogopite peridotite (Ivrea-Verbano Zone, Western Alps) and geodynamic consequences

NASA Astrophysics Data System (ADS)

Zanetti, Alberto; Giovanardi, Tommaso; Langone, Antonio; Tiepolo, Massimo; Wu, Fu-Yuan; Dallai, Luigi; Mazzucchelli, Maurizio

2016-10-01

An investigation has been performed on three chromitite layers segregated in dunite bodies of the Phlogopite Peridotite mantle unit in the Finero complex (FPP, Ivrea-Verbano Zone, Southern Alps) aimed at providing new constraints to their origin and evolution. Field relationships, the sub-chondritic Hf isotopic composition of the zircons (εHf(188) as low as - 5.4), the heavy O isotopic composition of zircons and pyroxenes (δ18O up to 6.9‰), the strict similarity of the trace element composition between the clinopyroxenes and amphiboles from the chromitites and those from the phlogopite harzburgites and pyroxenites forming the typical FPP association, as well as the REE composition of zircons, which approaches equilibrium with the associate clinopyroxene, suggest that the studied chromitites were segregated from melts, highly contaminated from continental crust, during the pervasive cycle of metasomatism recorded by the FPP. An LA-ICP-HRMS survey of chromitite zircon grains has provided Early Jurassic U-Pb ages mostly between 199 ± 3 Ma and 178 ± 2 Ma, with a pronounced peak at 187 Ma. Relevant exceptions are inherited domains of two grains giving Triassic ages of 242 ± 7 Ma and 229 ± 7 Ma, and a third homogeneous zircon giving 208 ± 3 Ma. Our geochronological data and those reported in the literature show that the FPP chromitites have zircon populations with different internal CL textures, but the same sub-chondritic Hf isotopic composition, which define an overall U-Pb age span from 290 Ma to 180. The segregation of the chromitite layers and the main pervasive metasomatism likely occurred in the Early Permian (in a post-collisional, transtensional setting) or before (possibly, in a subduction-related setting). The rejuvenation of the zircon ages was accompanied by a progressive disappearance of the internal zoning, interpreted as the result of a prolonged residence at mantle depths with progressive re-equilibration of the U-Pb system due to thermal

Orthopyroxene oikocrysts in the MG1 chromitite layer of the Bushveld Complex: implications for cumulate formation and recrystallisation

NASA Astrophysics Data System (ADS)

Kaufmann, Felix E. D.; Vukmanovic, Zoja; Holness, Marian B.; Hecht, Lutz

2018-02-01

Two typical mineral textures of the MG 1 chromitite of the Bushveld Complex, South Africa, were observed; one characterised by abundant orthopyroxene oikocrysts, and the other by coarse-grained granular chromitite with only minor amounts of interstitial material. Oikocrysts form elongate clusters of several crystals aligned parallel to the layering, and typically have subhedral, almost chromite-free, core zones containing remnants of olivine. The core zones are surrounded by poikilitic aureoles overgrowing euhedral to subhedral chromite chadacrysts. Chromite grains show no preferred crystal orientation, whereas orthopyroxene grains forming clusters commonly share the same crystallographic orientation. Oikocryst core zones have lower Mg# and higher concentrations of incompatible trace elements compared to their poikilitic aureoles. Core zones are relatively enriched in REE compared to a postulated parental magma (B1) and did not crystallise in equilibrium with the surrounding minerals, whereas the composition of the poikilitic orthopyroxene is consistent with growth from the B1 magma. These observations cannot be explained by the classic cumulus and post-cumulus models of oikocryst formation. Instead, we suggest that the oikocryst core zones in the MG1 chromitite layer formed by peritectic replacement of olivine primocrysts by reaction with an upwards-percolating melt enriched in incompatible trace elements. Poikilitic overgrowth on oikocryst core zones occurred in equilibrium with a basaltic melt of B1 composition near the magma-crystal mush interface. Finally, adcumulus crystallisation followed by grain growth resulted in the surrounding granular chromitite.

Recent Trends of Summer Convective and Stratiform Precipitation in Mid-Eastern China

PubMed Central

Fu, Yunfei; Chen, Fengjiao; Liu, Guosheng; Yang, Yuanjian; Yuan, Renmin; Li, Rui; Liu, Qi; Wang, Yu; Zhong, Lei; Sun, Liang

2016-01-01

Many studies have reported on the trends of precipitation in Mid-Eastern China (EC). However, the trends of convective and stratiform precipitation are still unknown. Here, we examine the trends of summer convective and stratiform precipitation in EC from 2002 to 2012 on the basis of the TRMM observations. Results revealed that the rain frequency (RF) for both convective and stratiform precipitation increased in majority regions of Southern EC (SEC), but decreased in Northwest part of Northern EC (NEC). The decreasing rate of RF for stratiform precipitation in NEC is twice as much as that for convective precipitation, while the increase of convective precipitation in SEC is more evident than stratiform precipitation. The rain rate (RR) exhibited a decreasing trend in most portions of EC for both convective and stratiform precipitation. In SEC, neither PW nor WVT has good ability in explaining the precipitation variability. However, in NEC, PW is closely correlated to convective RF and WVT is more closely related to stratiform RF. PMID:27604846

PALLADIUM, PLATINUM, RHODIUM, RUTHENIUM AND IRIDIUM IN PERIDOTITES AND CHROMITITES FROM OPHIOLITE COMPLEXES IN NEWFOUNDLAND.

USGS Publications Warehouse

Page, Norman J; Talkington, Raymond W.

1984-01-01

Samples of spinel lherzolite, harzburgite, dunite, and chromitite from the Bay of Islands, Lewis Hills, Table Mountain, Advocate, North Arm Mountain, White Hills Periodite Point Rousse, Great Bend and Betts Cove ophiolite complexes in Newfoundland were analyzed for the platinum-group elements (PGE) Pd, Pt, Rh, Ru and Ir. The ranges of concentration (in ppb) observed for all rocks are: less than 0. 5 to 77 (Pd), less than 1 to 120 (Pt), less than 0. 5 to 20 (Rh), less than 100 to 250 (Ru) and less than 20 to 83 (Ir). Chondrite-normalized PGE ratios suggest differences between rock types and between complexes. Samples of chromitite and dunite show relative enrichment in Ru and Ir and relative depletion in Pt and Pd.

46 CFR 54.15-13 - Rupture disks (modifies UG-127).

Code of Federal Regulations, 2011 CFR

2011-10-01

...: (1) Comply with the general provisions of § 54.15-5 except as noted otherwise in this section; (2... 46 Shipping 2 2011-10-01 2011-10-01 false Rupture disks (modifies UG-127). 54.15-13 Section 54.15... VESSELS Pressure-Relief Devices § 54.15-13 Rupture disks (modifies UG-127). (a) Paragraph UG-127 of...

46 CFR 54.15-13 - Rupture disks (modifies UG-127).

Code of Federal Regulations, 2010 CFR

2010-10-01

...: (1) Comply with the general provisions of § 54.15-5 except as noted otherwise in this section; (2... 46 Shipping 2 2010-10-01 2010-10-01 false Rupture disks (modifies UG-127). 54.15-13 Section 54.15... VESSELS Pressure-Relief Devices § 54.15-13 Rupture disks (modifies UG-127). (a) Paragraph UG-127 of...

46 CFR 54.15-13 - Rupture disks (modifies UG-127).

Code of Federal Regulations, 2013 CFR

2013-10-01

...: (1) Comply with the general provisions of § 54.15-5 except as noted otherwise in this section; (2... 46 Shipping 2 2013-10-01 2013-10-01 false Rupture disks (modifies UG-127). 54.15-13 Section 54.15... VESSELS Pressure-Relief Devices § 54.15-13 Rupture disks (modifies UG-127). (a) Paragraph UG-127 of...

46 CFR 54.15-13 - Rupture disks (modifies UG-127).

Code of Federal Regulations, 2014 CFR

2014-10-01

...: (1) Comply with the general provisions of § 54.15-5 except as noted otherwise in this section; (2... 46 Shipping 2 2014-10-01 2014-10-01 false Rupture disks (modifies UG-127). 54.15-13 Section 54.15... VESSELS Pressure-Relief Devices § 54.15-13 Rupture disks (modifies UG-127). (a) Paragraph UG-127 of...

46 CFR 54.15-13 - Rupture disks (modifies UG-127).

Code of Federal Regulations, 2012 CFR

2012-10-01

...: (1) Comply with the general provisions of § 54.15-5 except as noted otherwise in this section; (2... 46 Shipping 2 2012-10-01 2012-10-01 false Rupture disks (modifies UG-127). 54.15-13 Section 54.15... VESSELS Pressure-Relief Devices § 54.15-13 Rupture disks (modifies UG-127). (a) Paragraph UG-127 of...

46 CFR 54.01-30 - Loadings (modifies UG-22).

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 2 2013-10-01 2013-10-01 false Loadings (modifies UG-22). 54.01-30 Section 54.01-30 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-30 Loadings (modifies UG-22). (a) The loadings for pressure vessels shall be as required by UG-22 of section VIII of the...

46 CFR 54.01-30 - Loadings (modifies UG-22).

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 2 2012-10-01 2012-10-01 false Loadings (modifies UG-22). 54.01-30 Section 54.01-30 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-30 Loadings (modifies UG-22). (a) The loadings for pressure vessels shall be as required by UG-22 of section VIII of the...

46 CFR 54.01-30 - Loadings (modifies UG-22).

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 2 2010-10-01 2010-10-01 false Loadings (modifies UG-22). 54.01-30 Section 54.01-30 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-30 Loadings (modifies UG-22). (a) The loadings for pressure vessels shall be as required by UG-22 of section VIII of the...

46 CFR 54.01-30 - Loadings (modifies UG-22).

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 2 2014-10-01 2014-10-01 false Loadings (modifies UG-22). 54.01-30 Section 54.01-30 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-30 Loadings (modifies UG-22). (a) The loadings for pressure vessels shall be as required by UG-22 of section VIII of the...

46 CFR 54.01-30 - Loadings (modifies UG-22).

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 2 2011-10-01 2011-10-01 false Loadings (modifies UG-22). 54.01-30 Section 54.01-30 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-30 Loadings (modifies UG-22). (a) The loadings for pressure vessels shall be as required by UG-22 of section VIII of the...

Stratiform and Convective Precipitation Properties of Tropical Cyclones in the Northwest Pacific

NASA Astrophysics Data System (ADS)

Yang, Zhaohong; Yuan, Tie; Jiang, Haiyan; Zhang, Lei; Zhang, Chen

2018-04-01

The properties of stratiform and the convective precipitation of tropical cyclones (TCs) over the northwest Pacific are examined using the Tropical Rainfall Measuring Mission data for 1998-2013. TCs are classified into inner core (IC), inner rainband (IB), and outer rainband (OB) regions, and the results show that TCs are dominated by stratiform precipitation, which accounts for more than 78% of the total raining area. The highest fraction of the stratiform raining area exists in the IB region and increases as the TC intensity increases (from 80% to 93%). Strong convective signatures generally occur in the IC region, less often in the IB region, and least often in the OB region. Stratiform precipitation in the IC region generally has comparable or even stronger ice scattering signatures and higher 20 dBZ radar echo heights than the convective precipitation in the IB and OB regions. Weak convection decreases significantly as the TC intensity increases, which leads to increased convective intensity. Stratiform (convective) precipitation accounts for 61% (39%) of the total TC volumetric rain and 25% (75%) of the total TC lightning flash, respectively. Moreover, stratiform precipitation's contribution to the total TC volumetric rain and lightning flash increases as the TC intensity increases, which indicates that stronger TCs are favorable for maintaining more stratiform precipitation. The stratiform and convective precipitation properties in different TC regions and intensities cooperatively change with the enhanced ascending branch in the IC region and the radial outflow at the upper levels of the secondary circulation.

Drop Size Distribution - Based Separation of Stratiform and Convective Rain

NASA Technical Reports Server (NTRS)

Thurai, Merhala; Gatlin, Patrick; Williams, Christopher

2014-01-01

For applications in hydrology and meteorology, it is often desirable to separate regions of stratiform and convective rain from meteorological radar observations, both from ground-based polarimetric radars and from space-based dual frequency radars. In a previous study by Bringi et al. (2009), dual frequency profiler and dual polarization radar (C-POL) observations in Darwin, Australia, had shown that stratiform and convective rain could be separated in the log10(Nw) versus Do domain, where Do is the mean volume diameter and Nw is the scaling parameter which is proportional to the ratio of water content to the mass weighted mean diameter. Note, Nw and Do are two of the main drop size distribution (DSD) parameters. In a later study, Thurai et al (2010) confirmed that both the dual-frequency profiler based stratiform-convective rain separation and the C-POL radar based separation were consistent with each other. In this paper, we test this separation method using DSD measurements from a ground based 2D video disdrometer (2DVD), along with simultaneous observations from a collocated, vertically-pointing, X-band profiling radar (XPR). The measurements were made in Huntsville, Alabama. One-minute DSDs from 2DVD are used as input to an appropriate gamma fitting procedure to determine Nw and Do. The fitted parameters - after averaging over 3-minutes - are plotted against each other and compared with a predefined separation line. An index is used to determine how far the points lie from the separation line (as described in Thurai et al. 2010). Negative index values indicate stratiform rain and positive index indicate convective rain, and, moreover, points which lie somewhat close to the separation line are considered 'mixed' or 'transition' type precipitation. The XPR observations are used to evaluate/test the 2DVD data-based classification. A 'bright-band' detection algorithm was used to classify each vertical reflectivity profile as either stratiform or convective

Relating Convective and Stratiform Rain to Latent Heating

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Lang, Stephen; Zeng, Xiping; Shige, Shoichi; Takayabu, Yukari

2010-01-01

The relationship among surface rainfall, its intensity, and its associated stratiform amount is established by examining observed precipitation data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). The results show that for moderate-high stratiform fractions, rain probabilities are strongly skewed toward light rain intensities. For convective-type rain, the peak probability of occurrence shifts to higher intensities but is still significantly skewed toward weaker rain rates. The main differences between the distributions for oceanic and continental rain are for heavily convective rain. The peak occurrence, as well as the tail of the distribution containing the extreme events, is shifted to higher intensities for continental rain. For rainy areas sampled at 0.58 horizontal resolution, the occurrence of conditional rain rates over 100 mm/day is significantly higher over land. Distributions of rain intensity versus stratiform fraction for simulated precipitation data obtained from cloud-resolving model (CRM) simulations are quite similar to those from the satellite, providing a basis for mapping simulated cloud quantities to the satellite observations. An improved convective-stratiform heating (CSH) algorithm is developed based on two sources of information: gridded rainfall quantities (i.e., the conditional intensity and the stratiform fraction) observed from the TRMM PR and synthetic cloud process data (i.e., latent heating, eddy heat flux convergence, and radiative heating/cooling) obtained from CRM simulations of convective cloud systems. The new CSH algorithm-derived heating has a noticeably different heating structure over both ocean and land regions compared to the previous CSH algorithm. Major differences between the new and old algorithms include a significant increase in the amount of low- and midlevel heating, a downward emphasis in the level of maximum cloud heating by about 1 km, and a larger variance between land and ocean in

Impacts of Microphysical Scheme on Convective and Stratiform Characteristics in Two High Precipitation Squall Line Events

NASA Technical Reports Server (NTRS)

Wu, Di; Dong, Xiquan; Xi, Baike; Feng, Zhe; Kennedy, Aaron; Mullendore, Gretchen; Gilmore, Matthew; Tao, Wei-Kuo

2013-01-01

This study investigates the impact of snow, graupel, and hail processes on simulated squall lines over the Southern Great Plains in the United States. The Weather Research and Forecasting (WRF) model is used to simulate two squall line events in Oklahoma during May 2007, and the simulations are validated against radar and surface observations. Several microphysics schemes are tested in this study, including the WRF 5-Class Microphysics (WSM5), WRF 6-Class Microphysics (WSM6), Goddard Cumulus Ensemble (GCE) Three Ice (3-ice) with graupel, Goddard Two Ice (2-ice), and Goddard 3-ice hail schemes. Simulated surface precipitation is sensitive to the microphysics scheme when the graupel or hail categories are included. All of the 3-ice schemes overestimate the total precipitation with WSM6 having the largest bias. The 2-ice schemes, without a graupel/hail category, produce less total precipitation than the 3-ice schemes. By applying a radar-based convective/stratiform partitioning algorithm, we find that including graupel/hail processes increases the convective areal coverage, precipitation intensity, updraft, and downdraft intensities, and reduces the stratiform areal coverage and precipitation intensity. For vertical structures, simulations have higher reflectivity values distributed aloft than the observed values in both the convective and stratiform regions. Three-ice schemes produce more high reflectivity values in convective regions, while 2-ice schemes produce more high reflectivity values in stratiform regions. In addition, this study has demonstrated that the radar-based convective/stratiform partitioning algorithm can reasonably identify WRF-simulated precipitation, wind, and microphysical fields in both convective and stratiform regions.

Observations of Stratiform Lightning Flashes and Their Microphysical and Kinematic Environments

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Williams, Earle

2016-01-01

During the Midlatitude Continental Convective Clouds Experiment (MC3E), combined observations of clouds and precipitation were made from airborne and ground-based in situ and remote sensing platforms. These observations were coordinated for multiple mesoscale convective systems (MCSs) that passed over the MC3E domain in northern Oklahoma. Notably, during a storm on 20 May 2011 in situ and remote sensing airborne observations were made near the times and locations of stratiform positive cloud-to-ground (+CG) lightning flashes. These +CGs resulted from extremely large stratiform lightning flashes that were hundreds of km in length and lasted several seconds. This dataset provides an unprecedented look at kinematic and microphysical environments in the vicinity of large, powerful, and long-lived stratiform lightning flashes. We will use this dataset to understand the influence of low liquid water contents (LWCs) in the electrical charging of MCS stratiform regions.

Observations of Stratiform Lightning Flashes and Their Microphysical and Kinematic Environments

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Williams, Earle

2017-01-01

During the Midlatitude Continental Convective Clouds Experiment (MC3E), combined observations of clouds and precipitation were made from airborne and ground-based in situ and remote sensing platforms. These observations were coordinated for multiple mesoscale convective systems (MCSs) that passed over the MC3E domain in northern Oklahoma. Notably, during a storm on 20 May 2011 in situ and remote sensing airborne observations were made near the times and locations of stratiform positive cloud-to-ground (+CG) lightning flashes. These +CGs resulted from extremely large stratiform lightning flashes that were hundreds of km in length and lasted several seconds. This dataset provides an unprecedented look at kinematic and microphysical environments in the vicinity of large, powerful, and long-lived stratiform lightning flashes. We will use this dataset to understand the influence of low liquid water contents (LWCs) in the electrical charging of MCS stratiform regions.

Paragenesis of multiple platinum-group mineral populations in Shetland ophiolite chromitite: 3D X-ray tomography and in situ Os isotopes

NASA Astrophysics Data System (ADS)

Prichard, H. M.; Barnes, Stephen J.; Dale, C. W.; Godel, B.; Fisher, P. C.; Nowell, G. M.

2017-11-01

Chromitite from the Harold's Grave locality in the mantle section of the Shetland ophiolite complex is extremely enriched in Ru, Os and Ir, at μg/g concentrations. High-resolution X-ray computed tomography on micro-cores from these chromitites was used to determine the location, size, distribution and morphology of the platinum-group minerals (PGM). There are five generations of PGM in these chromitites. Small (average 5 μm in equivalent sphere diameter, ESD) euhedral laurites, often with Os-Ir alloys, are totally enclosed in the chromite and are likely to have formed first by direct crystallisation from the magma as the chromite crystallised. Also within the chromitite there are clusters of larger (50 μm ESD) aligned elongate crystals of Pt-, Rh-, Ir-, Os- and Ru-bearing PGM that have different orientations in different chromite crystals. These may have formed either by exsolution, or by preferential nucleation of PGMs in boundary layers around particular growing chromite grains. Thirdly there is a generation of large (100 μm ESD) composite Os-Ir-Ru-rich PGM that are all interstitial to the chromite grains and sometimes form in clusters. It is proposed that Os, Ir and Ru in this generation were concentrated in base metal sulfide droplets that were then re-dissolved into a later sulfide-undersaturated magma, leaving PGM interstitial to the chromite grains. Fourthly there is a group of almost spherical large (80 μm ESD) laurites, hosting minor Os-Ir-Ru-rich PGM that form on the edge or enclosed in chromite grains occurring in a sheet crosscutting a chromitite layer. These may be hosted in an annealed late syn- or post magmatic fracture. Finally a few of the PGM have been deformed in localised shear zones through the chromitites. The vast majority of the PGM - including small PGM enclosed within chromite, larger interstitial PGM and elongate aligned PGM - have Os isotope compositions that give Re-depletion model ages approximately equal to the age of the

Drop Axis Ratio Distributions in Stratiform and Convective Rain

NASA Technical Reports Server (NTRS)

Thurai, M.; Bringi, V. N.; Petersen, W. A.; Schultz, C.

2010-01-01

A fully calibrated low profile 2D video disdrometer (2DVD) has been recording many different rainfall events in Northern Alabama (USA) since June 2007. An earlier publication reported drop shapes and axis ratio distributions determined for some of the events. For one of the cases examined, a noticeable shift in the 3.5 - 3.75 mm drop axis ratio distribution was noted. In this paper, we extend the earlier work by separating the 2DVD measurements into stratiform and convective rain. The separation is made possible by using the minute-by-minute drop size distribution (DSD) measured by the 2DVD. The 1-minute DSDs are fitted to a gamma distribution, and using a simple indexing technique which involves two of the fitted parameters, periods of convective and stratiform rain are separated for a given event. The output of the DSD indexing technique is qualitatively confirmed by comparing with simultaneous time series observations from a co-located UHF profiler which continuously records height profiles of reflectivity, Doppler mean and spectral width, all of which enable the identification of bright-band periods and, furthermore, periods of moderate and deep convection. Excellent consistency is found between the output of the DSD-based separation method and the profiler observations. Next, we utilize the output of DSD index-based separation method to flag the periods of severe convection for a given event. Drop axis ratios during the flagged periods are derived and compared with those during stratiform rain periods. Five cases have been considered. Axis ratio distributions do not show appreciable differences between stratiform and convective periods for four of the cases. The fifth case (the same case as reported earlier) shows a shift in the 3.5 - 3.75 mm drop axis ratios during a prolonged period of convection. The contoured shapes for these drops determined from the 2DVD camera data indicate the possibility of non-axisymmetric oscillations, compared with the contoured

The electrification of stratiform anvils

NASA Astrophysics Data System (ADS)

Boccippio, Dennis J.

1997-10-01

Stratiform precipitation regions accompany convective activity on many spatial scales. The electrification of these regions is anomalous in a number of ways. Surface and above-cloud fields are often 'inverted' from normal thunderstorm conditions. Unusually large, bright, horizontal 'spider' lightning and high current and charge transfer positive cloud-to-ground (CC) lightning dominates in these regions. Mesospheric 'red sprite' emissions have to date been observed exclusively over stratiform cloud shields. We postulate that a dominant 'inverted dipole' charge structure may account for this anomalous electrification. This is based upon laboratory observations of charge separation which show that in low liquid water content (LWC) environments, or dry but ice- supersaturated environments, precipitation ice tends to charge positively (instead of negatively) upon collision with smaller crystals. Under typical stratiform cloud conditions, liquid water should be depleted and this charging regime favored. An inverted dipole would be the natural consequence of large-scale charge separation (net flux divergence of charged ice), given typical hydrometeor profiles. The inverted dipole hypothesis is tested using radar and electrical observations of four weakly organized, late- stage systems in Orlando, Albuquerque and the Western Pacific. Time-evolving, area-average vertical velocity profiles are inferred from single Doppler radar data. These profiles provide the forcing for a 1-D steady state micro-physical retrieval, which yields vertical hydrometeor profiles and ice/water saturation conditions. The retrieved microphysical parameters are then combined with laboratory charge transfer measurements to infer the instantaneous charging behavior of the systems. Despite limitations in the analysis technique, the retrievals yield useful results. Total charge transfer drops only modestly as the storm enters the late (stratiform) stage, suggesting a continued active generator is

46 CFR 54.05-1 - Scope (replaces UG-84).

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 2 2014-10-01 2014-10-01 false Scope (replaces UG-84). 54.05-1 Section 54.05-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Toughness Tests § 54.05-1 Scope (replaces UG-84). The toughness tests of materials used in pressure vessels shall be as required by this subpart in lieu of...

46 CFR 54.05-1 - Scope (replaces UG-84).

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 2 2012-10-01 2012-10-01 false Scope (replaces UG-84). 54.05-1 Section 54.05-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Toughness Tests § 54.05-1 Scope (replaces UG-84). The toughness tests of materials used in pressure vessels shall be as required by this subpart in lieu of...

46 CFR 54.05-1 - Scope (replaces UG-84).

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 2 2010-10-01 2010-10-01 false Scope (replaces UG-84). 54.05-1 Section 54.05-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Toughness Tests § 54.05-1 Scope (replaces UG-84). The toughness tests of materials used in pressure vessels shall be as required by this subpart in lieu of...

46 CFR 54.05-1 - Scope (replaces UG-84).

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 2 2011-10-01 2011-10-01 false Scope (replaces UG-84). 54.05-1 Section 54.05-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Toughness Tests § 54.05-1 Scope (replaces UG-84). The toughness tests of materials used in pressure vessels shall be as required by this subpart in lieu of...

46 CFR 54.05-1 - Scope (replaces UG-84).

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 2 2013-10-01 2013-10-01 false Scope (replaces UG-84). 54.05-1 Section 54.05-1 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Toughness Tests § 54.05-1 Scope (replaces UG-84). The toughness tests of materials used in pressure vessels shall be as required by this subpart in lieu of...

Dynamics of the Stratiform Sector of a Tropical Cyclone Rainband

NASA Astrophysics Data System (ADS)

Didlake, A. C.; Houze, R.

2013-12-01

Airborne Doppler radar collected observations of the stationary rainband complex of Hurricane Rita (2005) in exceptional detail. Dynamics of the stationary rainband complex play a large role in the evolution of the tropical cyclone's internal structure. The stratiform sector of the stationary rainband complex occurs on the downwind end of the complex. This stratiform rainband is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells. Upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow. Below the cloud layer, descending radial inflow was driven by horizontal buoyancy gradients, and thus horizontal vorticity generation, introduced by regions of sublimational and melting cooling. The organization of this transport initially is robust but fades downwind as the convection dissipates. This descending inflow advected higher angular momentum inward, which resulted in the development of a midlevel tangential jet and broadening of the tangential wind field. This circulation may have also contributed to ventilation of the eyewall as inflow of low-entropy air continued past the rainband in both the boundary layer and midlevels. Given the expanse of the stratiform rainband region, its thermodynamic and kinematic impacts likely help to modify the structure and intensity of the overall storm.

Modeling of Convective-Stratiform Precipitation Processes: Sensitivity to Partitioning Methods

NASA Technical Reports Server (NTRS)

Lang, S. E.; Tao, W.-K.; Simpson, J.; Ferrier, B.; Starr, David OC. (Technical Monitor)

2001-01-01

Six different convective-stratiform separation techniques, including a new technique that utilizes the ratio of vertical and terminal velocities, are compared and evaluated using two-dimensional numerical simulations of a tropical [Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE)] and midlatitude continental [Preliminary Regional Experiment for STORM-Central (PRESTORM)] squall line. Comparisons are made in terms of rainfall, cloud coverage, mass fluxes, apparent heating and moistening, mean hydrometeor profiles, CFADs (Contoured Frequency with Altitude Diagrams), microphysics, and latent heating retrieval. Overall, it was found that the different separation techniques produced results that qualitatively agreed. However, the quantitative differences were significant. Observational comparisons were unable to conclusively evaluate the performance of the techniques. Latent heating retrieval was shown to be sensitive to the use of separation technique mainly due to the stratiform region for methods that found very little stratiform rain.

The ESA Planetary Science Archive User Group (PSA-UG)

NASA Astrophysics Data System (ADS)

Rossi, A. P.; Cecconi, B.; Fraenz, M.; Hagermann, A.; Heather, D.; Rosenblatt, P.; Svedhem, H.; Widemann, T.

2014-04-01

ESA has established a Planetary Science Archive User Group (PSA-UG), with the task of offering independent advice to ESA's Planetary Science Archive (e.g. Heather et al., 2013). The PSA-UG is an official and independent body that continuously evaluates services and tools provided by the PSA to the community of planetary data scientific users. The group has been tasked with the following top level objectives: a) Advise ESA on future development of the PSA. b) Act as a focus for the interests of the scientific community. c) Act as an advocate for the PSA. d) Monitor the PSA activities. Based on this, the PSA-UG will report through the official ESA channels. Disciplines and subjects represented by PSA-UG members include: Remote Sensing of both Atmosphere and Solid Surfaces, Magnetospheres, Plasmas, Radio Science and Auxilliary data. The composition of the group covers ESA missions populating the PSA both now and in the near future. The first members of the PSA-UG were selected in 2013 and will serve for 3 years, until 2016. The PSA-UG will address the community through workshops, conferences and the internet. Written recommendations will be made to the PSA coordinator, and an annual report on PSA and the PSA-UG activities will be sent to the Solar System Exploration Working Group (SSEWG). Any member of the community and planetary data user can get in touch with individual members of the PSA-UG or with the group as a whole via the contacts provided on the official PSA-UG web-page: http://archives.esac.esa.int/psa/psa-ug The PSA is accessible via: http://archives.esac.esa.int/psa

46 CFR 54.10-15 - Pneumatic test (modifies UG-100).

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 2 2013-10-01 2013-10-01 false Pneumatic test (modifies UG-100). 54.10-15 Section 54.10-15 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-15 Pneumatic test (modifies UG-100). (a) Pneumatic testing of welded pressure vessels shall be...

46 CFR 54.10-15 - Pneumatic test (modifies UG-100).

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 2 2012-10-01 2012-10-01 false Pneumatic test (modifies UG-100). 54.10-15 Section 54.10-15 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-15 Pneumatic test (modifies UG-100). (a) Pneumatic testing of welded pressure vessels shall be...

46 CFR 54.10-15 - Pneumatic test (modifies UG-100).

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 2 2014-10-01 2014-10-01 false Pneumatic test (modifies UG-100). 54.10-15 Section 54.10-15 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-15 Pneumatic test (modifies UG-100). (a) Pneumatic testing of welded pressure vessels shall be...

The ESA Planetary Science Archive User Group (PSA-UG)

NASA Astrophysics Data System (ADS)

Pio Rossi, Angelo; Cecconi, Baptiste; Fraenz, Markus; Hagermann, Axel; Heather, David; Rosenblatt, Pascal; Svedhem, Hakan; Widemann, Thomas

2014-05-01

ESA has established a Planetary Science Archive User Group (PSA-UG), with the task of offering independent advice to ESA's Planetary Science Archive (e.g. Heather et al., 2013). The PSA-UG is an official and independent body that continuously evaluates services and tools provided by the PSA to the community of planetary data scientific users. The group has been tasked with the following top level objectives: a) Advise ESA on future development of the PSA. b) Act as a focus for the interests of the scientific community. c) Act as an advocate for the PSA. d) Monitor the PSA activities. Based on this, the PSA-UG will report through the official ESA channels. Disciplines and subjects represented by PSA-UG members include: Remote Sensing of both Atmosphere and Solid Surfaces, Magnetospheres, Plasmas, Radio Science and Auxilliary data. The composition of the group covers ESA missions populating the PSA both now and in the near future. The first members of the PSA-UG were selected in 2013 and will serve for 3 years, until 2016. The PSA-UG will address the community through workshops, conferences and the internet. Written recommendations will be made to the PSA coordinator, and an annual report on PSA and the PSA-UG activities will be sent to the Solar System Exploration Working Group (SSEWG). Any member of the community and planetary data user can get in touch with individual members of the PSA-UG or with the group as a whole via the contacts provided on the official PSA-UG web-page: http://archives.esac.esa.int/psa/psa-ug. The PSA is accessible via: http://archives.esac.esa.int/psa References: Heather, D., Barthelemy, M., Manaud, N., Martinez, S., Szumlas, M., Vazquez, J. L., Osuna, P. and the PSA Development Team (2013) ESA's Planetary Science Archive: Status, Activities and Plans. EuroPlanet Sci. Congr. #EPSC2013-626

46 CFR 54.01-25 - Miscellaneous pressure components (modifies UG-11).

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 2 2014-10-01 2014-10-01 false Miscellaneous pressure components (modifies UG-11). 54.01-25 Section 54.01-25 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-25 Miscellaneous pressure components (modifies UG-11). (a) Pressure components for pressure...

46 CFR 54.01-25 - Miscellaneous pressure components (modifies UG-11).

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 2 2011-10-01 2011-10-01 false Miscellaneous pressure components (modifies UG-11). 54.01-25 Section 54.01-25 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-25 Miscellaneous pressure components (modifies UG-11). (a) Pressure components for pressure...

46 CFR 54.01-25 - Miscellaneous pressure components (modifies UG-11).

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 2 2013-10-01 2013-10-01 false Miscellaneous pressure components (modifies UG-11). 54.01-25 Section 54.01-25 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-25 Miscellaneous pressure components (modifies UG-11). (a) Pressure components for pressure...

46 CFR 54.01-25 - Miscellaneous pressure components (modifies UG-11).

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 2 2010-10-01 2010-10-01 false Miscellaneous pressure components (modifies UG-11). 54.01-25 Section 54.01-25 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-25 Miscellaneous pressure components (modifies UG-11). (a) Pressure components for pressure...

46 CFR 54.01-25 - Miscellaneous pressure components (modifies UG-11).

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 2 2012-10-01 2012-10-01 false Miscellaneous pressure components (modifies UG-11). 54.01-25 Section 54.01-25 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS General Requirements § 54.01-25 Miscellaneous pressure components (modifies UG-11). (a) Pressure components for pressure...

Analysis of 35 GHz Cloud Radar polarimetric variables to identify stratiform and convective precipitation.

NASA Astrophysics Data System (ADS)

Fontaine, Emmanuel; Illingworth, Anthony, J.; Stein, Thorwald

2017-04-01

This study is performed using vertical profiles of radar measurements at 35GHz, for the period going from 29th of February to 1rst October 2016, at the Chilbolton observatory in United Kingdom. During this period, more than 40 days with precipitation events are investigated. The investigation uses the synergy of radar reflectivity factors, vertical velocity, Doppler spectrum width, and linear depolarization ratio (LDR) to differentiate between stratiform and convective rain events. The depth of the layer with Doppler spectrum width values greater than 0.5 m s-1 is shown to be a suitable proxy to distinguish between convective and stratiform events. Using LDR to detect the radar bright band, bright band characteristics such as depth of the layer and maximum LDR are shown to vary with the amount of turbulence aloft. Profiles of radar measurements are also compared to rain gauge measurements to study the contribution of convective and stratiform rainfall to total rain duration and amount. To conclude, this study points out differences between convective and stratiform rains and quantifies their contributions over a precipitation event, highlighting that convective and stratiform rainfall should be considered as a continuum rather than a dichotomy.

A TRMM-Calibrated Infrared Technique for Convective and Stratiform Rainfall: Analysis and Validation

NASA Technical Reports Server (NTRS)

Negri, Andrew; Starr, David OC. (Technical Monitor)

2001-01-01

A satellite infrared technique with passive microwave calibration has been developed for estimating convective and stratiform rainfall. The Convective-Stratiform Technique, calibrated by coincident, physically retrieved rain rates from the TRMM Microwave Imager (TMI), has been applied to 30 min interval GOES infrared data and aggregated over seasonal and yearly periods over northern South America. The diurnal cycle of rainfall, as well as the division between convective and stratiform rainfall is presented. For the period Jan-April 1999, analysis revealed significant effects of local circulations (river breeze, land/sea breeze, mountain/valley) on both the total rainfall and it's diurnal cycle. Results compared well (a one-hour lag) with the diurnal cycle derived from TOGA radar-estimated rainfall in Rondonia. The satellite estimates revealed that the convective rain constituted 24% of the rain area while accounting for 67% of the rain volume. Estimates of the diurnal cycle (both total rainfall and convective/stratiform) for an area encompassing the Amazon Basin (3 x 10(exp 6) sq km) were in phase with those from the TRMM Precipitation Radar, despite the latter's limited sampling. Results will be presented comparing the yearly (2000) diurnal cycle for large regions (including the Amazon Basin), and an intercomparison of January-March estimates for three years, (1999-2001). We hope to demonstrate the utility of using the TRMM PR observations as verification for infrared estimates of the diurnal cycle, and as verification of the apportionment of rainfall into convective and stratiform components.

A TRMM-Calibrated Infrared Technique for Convective and Stratiform Rainfall: Analysis and Validation

NASA Technical Reports Server (NTRS)

Negri, Andrew; Starr, David OC. (Technical Monitor)

2001-01-01

A satellite infrared technique with passive microwave calibration has been developed for estimating convective and stratiform. rainfall. The Convective-Stratiform Technique, calibrated by coincident, physically retrieved rain rates from the TRMM Microwave Imager (TMI), has been applied to 30 min interval GOES infrared data and aggregated over seasonal and yearly periods over northern South America. The diurnal cycle of rainfall, as well as the division between convective and stratiform rainfall is presented. For the period Jan-April 1999, analysis revealed significant effects of local circulations (river breeze, land/sea breeze, mountain/valley) on both the total rainfall and it's diurnal cycle. Results compared well (a one-hour lag) with the diurnal cycle derived from TOGA radar-estimated rainfall in Rondonia. The satellite estimates revealed that the convective rain constituted 24% of the rain area while accounting for 67% of the rain volume. Estimates of the diurnal cycle (both total rainfall and convective/stratiform) for an area encompassing the Amazon Basin (3 x 10(exp 6) square km) were in phase with those from the TRMM Precipitation Radar, despite the latter's limited sampling. Results will be presented comparing the yearly (2000) diurnal cycle for large regions (including the Amazon Basin), and an intercomparison of January-March estimates for three years, 1999-2001. We hope to demonstrate the utility of using the TRMM PR observations as verification for infrared estimates of the diurnal cycle, and as verification of the apportionment of rainfall into convective and stratiform components.

Chemical composition and osmium-isotope systematics of primary and secondary PGM assemblages from high-Mg chromitite of the Nurali lherzolite massif, the South Urals, Russia

NASA Astrophysics Data System (ADS)

Malitch, K. N.; Anikina, E. V.; Badanina, I. Yu.; Belousova, E. A.; Pushkarev, E. V.; Khiller, V. V.

2016-01-01

The isotopic and geochemical characteristics of PGE mineralization in high-Mg chromitite from the banded dunite-wehrlite-clinopyroxenite complex of the Nurali lherzolite massif, the South Urals, Russia is characterized for the first time. Electron microprobe analysis and LA MC-ICP-MS mass spectrometry are used for studying Cr-spinel and platinum-group minerals (PGM). Two processes synchronously develop in high-Mg chromitite subject to metamorphism: (1) the replacement of Mg-Al-rich Cr-spinel, orthopyroxene, and diopside by chromite, Cr-amphibole, chlorite, and garnet; (2) the formation of a secondary mineral assemblage consisting of finely dispersed ruthenium or Ru-hexaferrum aggregate and silicate-oxide or silicate matter on the location of primary Ru-Os-sulfides of the laurite-erlichmanite solid solution series. Similar variations of Os-isotopic composition in both primary and secondary PGM assemblages are evidence for the high stability of the Os isotope system in PGM and for the possibility of using model 187Os/188Os ages in geodynamic reconstructions.

46 CFR 54.10-5 - Maximum allowable working pressure (reproduces UG-98).

Code of Federal Regulations, 2013 CFR

2013-10-01

... 46 Shipping 2 2013-10-01 2013-10-01 false Maximum allowable working pressure (reproduces UG-98). 54.10-5 Section 54.10-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-5 Maximum allowable working pressure (reproduces UG-98). (a) The maximum allowable...

46 CFR 54.10-5 - Maximum allowable working pressure (reproduces UG-98).

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 2 2011-10-01 2011-10-01 false Maximum allowable working pressure (reproduces UG-98). 54.10-5 Section 54.10-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-5 Maximum allowable working pressure (reproduces UG-98). (a) The maximum allowable...

46 CFR 54.10-5 - Maximum allowable working pressure (reproduces UG-98).

Code of Federal Regulations, 2014 CFR

2014-10-01

... 46 Shipping 2 2014-10-01 2014-10-01 false Maximum allowable working pressure (reproduces UG-98). 54.10-5 Section 54.10-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-5 Maximum allowable working pressure (reproduces UG-98). (a) The maximum allowable...

46 CFR 54.10-5 - Maximum allowable working pressure (reproduces UG-98).

Code of Federal Regulations, 2012 CFR

2012-10-01

... 46 Shipping 2 2012-10-01 2012-10-01 false Maximum allowable working pressure (reproduces UG-98). 54.10-5 Section 54.10-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Inspection, Reports, and Stamping § 54.10-5 Maximum allowable working pressure (reproduces UG-98). (a) The maximum allowable...

Palladium, platinum, rhodium, iridium and ruthenium in chromite- rich rocks from the Samail ophiolite, Oman.

USGS Publications Warehouse

Page, N.J.; Pallister, J.S.; Brown, M.A.; Smewing, J.D.; Haffty, J.

1982-01-01

30 samples of chromitite and chromite-rich rocks from two stratigraphic sections, 250 km apart, through the basal ultramafic member of the Samail ophiolite were spectrographically analysed for platinum-group elements (PGE) and for Co, Cu, Ni and V. These data are reported as are Cr/(Cr + Al), Mg/(Mg + Fe) and wt.% TiO2 for most samples. The chromitite occurs as pods or lenses in rocks of mantle origin or as discontinuous layers at the base of the overlying cumulus sequence. PGE abundances in both sections are similar, with average contents in chromite-rich rocks: Pd 8 ppb, Pt 14 ppb, Rh 6 ppb, Ir 48 ppb and Ru 135 ppb. The PGE data, combined with major-element and petrographic data on the chromitite, suggest: 1) relatively larger Ir and Ru contents and highest total PGE in the middle part of each section; 2) PGE concentrations and ratios do not correlate with coexisting silicate and chromite abundances or chromite compositions; 3) Pd/PGE, on average, increases upward in each section; 4) Samail PGE concentrations, particularly Rh, Pt and Pd, are lower than the average values for chromite-rich rocks in stratiform intrusions. 2) suggests that PGEs occur in discrete alloy or sulphide phases rather than in the major oxides or silicates, and 4) suggests that chromite-rich rocks from the oceanic upper mantle are depleted in PGE with respect to chondrites. L.C.C.

Recent Improvements in Estimating Convective and Stratiform Rainfall in Amazonia

NASA Technical Reports Server (NTRS)

Negri, Andrew J.

1999-01-01

In this paper we present results from the application of a satellite infrared (IR) technique for estimating rainfall over northern South America. Our main objectives are to examine the diurnal variability of rainfall and to investigate the relative contributions from the convective and stratiform components. We apply the technique of Anagnostou et al (1999). In simple functional form, the estimated rain area A(sub rain) may be expressed as: A(sub rain) = f(A(sub mode),T(sub mode)), where T(sub mode) is the mode temperature of a cloud defined by 253 K, and A(sub mode) is the area encompassed by T(sub mode). The technique was trained by a regression between coincident microwave estimates from the Goddard Profiling (GPROF) algorithm (Kummerow et al, 1996) applied to SSM/I data and GOES IR (11 microns) observations. The apportionment of the rainfall into convective and stratiform components is based on the microwave technique described by Anagnostou and Kummerow (1997). The convective area from this technique was regressed against an IR structure parameter (the Convective Index) defined by Anagnostou et al (1999). Finally, rainrates are assigned to the Am.de proportional to (253-temperature), with different rates for the convective and stratiform

Convective and stratiform components of a Winter Monsoon Cloud Cluster determined from geosynchronous infrared satellite data

NASA Technical Reports Server (NTRS)

Goldenberg, Stanley B.; Houze, Robert A., Jr.; Churchill, Dean D.

1990-01-01

The horizontal precipitation structure of cloud clusters observed over the South China Sea during the Winter Monsoon Experiment (WMONEX) is analyzed using a convective-stratiform technique (CST) developed by Adler and Negri (1988). The technique was modified by altering the method for identifying convective cells in the satellite data, accounting for the extremely cold cloud tops characteristic of the WMONEX region, and modifying the threshold infrared temperature for the boundary of the stratiform rain area. The precipitation analysis was extended to the entire history of the cloud cluster by applying the modified CST to IR imagery from geosynchronous-satellite observations. The ship and aircraft data from the later period of the cluster's lifetime make it possible to check the locations of convective and stratiform precipitation identified by the CST using in situ observations. The extended CST is considered to be effective for determining the climatology of the convective-stratiform structure of tropical cloud clusters.

High-resolution streaming video integrated with UGS systems

NASA Astrophysics Data System (ADS)

Rohrer, Matthew

2010-04-01

Imagery has proven to be a valuable complement to Unattended Ground Sensor (UGS) systems. It provides ultimate verification of the nature of detected targets. However, due to the power, bandwidth, and technological limitations inherent to UGS, sacrifices have been made to the imagery portion of such systems. The result is that these systems produce lower resolution images in small quantities. Currently, a high resolution, wireless imaging system is being developed to bring megapixel, streaming video to remote locations to operate in concert with UGS. This paper will provide an overview of how using Wifi radios, new image based Digital Signal Processors (DSP) running advanced target detection algorithms, and high resolution cameras gives the user an opportunity to take high-powered video imagers to areas where power conservation is a necessity.

Evaluating stratiform cloud base charge remotely

NASA Astrophysics Data System (ADS)

Harrison, R. Giles; Nicoll, Keri A.; Aplin, Karen L.

2017-06-01

Stratiform clouds acquire charge at their upper and lower horizontal boundaries due to vertical current flow in the global electric circuit. Cloud charge is expected to influence microphysical processes, but understanding is restricted by the infrequent in situ measurements available. For stratiform cloud bases below 1 km in altitude, the cloud base charge modifies the surface electric field beneath, allowing a new method of remote determination. Combining continuous cloud height data during 2015-2016 from a laser ceilometer with electric field mill data, cloud base charge is derived using a horizontal charged disk model. The median daily cloud base charge density found was -0.86 nC m-2 from 43 days' data. This is consistent with a uniformly charged region 40 m thick at the cloud base, now confirming that negative cloud base charge is a common feature of terrestrial layer clouds. This technique can also be applied to planetary atmospheres and volcanic plumes.