Search results for "rock"

Optical diagnostic of temperature in rocket engines by coherent Raman techniques

2004

Abstract This article reviews the study of Raman line shapes of molecular species involved in reactive media, such flames or engines, at high temperature and high pressure. This study is of interest from a fundamental as well as from a practical point of view with regards to the CARS temperature diagnostic of GH2–LOX combustion systems. We will particularly draw attention to recent investigations by means of Stimulated Raman Spectroscopy (SRS) in H2–H2O mixtures at temperature up to 1800 K. Whereas H2–X systems usually exhibit large inhomogeneous effects, due to the speed dependence of the collisional parameters, the absence of such apparent inhomogeneous signatures in the H2–H2O system all…

Rock ja papparock

2009

Structural relations and PbPb zircon ages for the Makuti gneisses: evidence for a crustal-scale Pan-African shear zone in the Zambezi Belt, northwes…

1999

Abstract The Makuti Group of northwest Zimbabwe is composed of mafic and intermediate biotite-rich gneisses interlayered with quartzofeldspathic gneisses of granitic composition, and minor sedimentary units. The gneisses have experienced a multi-staged metamorphic history, including an early high temperature-high pressure event and subsequent reworking at upper- to mid-amphibolite-facies conditions. They are positioned along the strongly deformed, southern margin of the east-west trending Zambezi Belt, and have been correlated with supracrustal gneiss units along the northern margin of the Zimbabwe Craton. The Makuti Group is characterised by an intensely developed gneissic layering and com…

The ESR age of Portlandia arctica shells from glacial deposits of Central Latviaan answer to a controversy on the age and genesis of their enclosing …

1998

Abstract The occurrence of Portlandia arctica shells in glacigenic sediments of Central Latvia had created a controversy in many publications about (1) their age ranging from the Holsteinian to the Late Weichselian and (2) the genesis of their enclosing sediments: glacial, glaciomarine or marine. Our reinvestigation of the main object of controversy, the Licupe site, leads to a conclusion that the sedimentary package of diamictons, clays and sands containing Portlandia arctica shells and marine microfossils is a large glacial raft that had been transported and deposited by the Riga lobe during the Weichselian. The electron spin resonance (ESR) ages on five sets of Portlandia arctica shells …

Further evidence for an early Carboniferous (∼340 Ma) age of high-grade metamorphism in the Saxonian granulite complex

1998

U–Pb and Pb–Pb zircon ages for metamorphic zircons from granulites in the Saxonian granulite complex are reported, using the SHRIMP ion microprobe, conventional multigrain and single-gain techniques and the evaporation method. This is complemented by a Pb–Pb evaporation age for a post-granulite granite emplaced into the schist mantle around the granulites during uplift of the complex. We also demonstrate that zircon ages are not reset during high-grade metamorphism, as commonly argued, but have a very high closure temperature and usually preserve the isotopic composition reflecting the time of their formation. Multifaceted zircons from four granulite samples that probably grew close to the …

The high-grade Tseel Terrane in SW Mongolia: An Early Paleozoic arc system or a Precambrian sliver?

2012

Abstract The high-grade metamorphic Tseel Terrane in southwestern Mongolia is dominated by a strongly deformed sequence of migmatitic gneisses which has previously been interpreted as an early Precambrian continental sliver. However, the protolith age and timing of high-grade metamorphism remain poorly constrained. To resolve this problem, high-grade gneisses selected from the western Tseel Terrane were dated in the present study. Zircons with oscillatory zoning from three paragneisses predominantly yielded early Paleozoic ages between 450 and 550 Ma, with prominent peaks at 471 and 506 Ma. U–Pb dating of zircons from a granitic gneiss revealed that the protolith was emplaced at 420 Ma. Zir…

Zircon Ages from the Baydrag Block and the Bayankhongor Ophiolite Zone: Time Constraints on Late Neoproterozoic to Cambrian Subduction‐ and Accretion…

2009

Central Mongolia represents a heterogeneous crustal domain of the Central Asian Orogenic Belt and is composed of contrasting lithotectonic units with distinct preorogenic histories. We report single-zircon evaporation and SHRIMP ages for high-grade rocks of the Neoarchean-Paleoproterozoic Baydrag block and for metaigneous rocks of the junction between the late Neoproterozoic Bayankhongor ophiolite zone (BOZ) and the Baydrag block. Zircon ages for metamorphic rocks of the Baydrag block indicate a major tectonothermal event between 1840 and 1826 Ma, coeval with the emplacement of granitic rocks at middle-crustal level dated at 1839 Ma. A granite-gneiss yielded a much younger crystallization a…

EARLY NEOPROTEROZOIC CRUST FORMATON IN THE DZABKHAN MICROCONTINENT, CENTRAL ASIAN OROGENIC BELT

2017

The Dzabkhan microcontinent was defined by [Mossakovsky et al., 1994] as a cratonic terrane with an early Precambrian basement that combines highgrade metamorphic complexes of the Songino, Dzabkhan, Otgon, Baidarik, Ider and Jargalant Blocks. However, early Precambrian ages have so far only been recognized in the Baidarik and Ider blocks [Kozakov et al., 2007, 2011; Kroner et al., 2015].

An approximation to the study of black pigments in Cova Remigia (Castell on, Spain). Technical and cultural assessments of the use of carbon-based bl…

2014

International audience; Spanish Levantine Rock Art is a unique pictorial expression within the prehistoric European context. Located in shelters in the inland regions of the Iberian Mediterranean basin, this art form, which must be necessarily studied in the frame of the process of neolithization of this territory, still lacks direct dating, and therefore its authorship is still open to debate. In this paper we present the first characterization of black pigments used in the Cova Remigia shelters in the Valltorta-Gassulla area (Castell on, Spain) by means of EDXRF spectrometry combined with SEM-EDS and Raman spectroscopy. Our aim is both to identify the raw material used for the preparation…

Controllable Solid Propellant Rocket Motor Stability: Deep and Rapid Variable Thrust Operations

2008

When flow and combustion processes couple with the acoustic modes of the combustion chamber, the solid rocket motors experience unsteady gas motion and associated thrust oscillation and motor vibration. The operations of the variable nozzle introduce relevant dynamic changes in the chamber flow and combustion. This article proposes a non-linear approach for the analysis of the effects of severe nozzle manoeuvres on the controllable solid rocket motor stability and provides the evidence that the acoustic wave amplitude evolution is influenced by the nozzle manoeuvre severity, shape and direction. The additional complexity in the problem of the combustion stability analysis introduced by the …