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  • ASTROPHYSICS  (2)
  • Sr mineral dating  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Rb–Sr and K–Ar mineral data of the KTB and the surrounding area and their bearing on the tectonothermal evolution of the metamorphic basement rocks (1997)
    Springer
    Geologische Rundschau 86 (1997), S. S251 
    Details
    ISSN: 0016-7835
    Keywords: Key words Bohemian Massif ; KTB ; K ; Ar and Rb ; Sr mineral dating ; Middle to post-Variscan tectonothermal evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  K–Ar and Rb–Sr age determinations on muscovites and biotites and K–Ar age determinations on amphiboles are presented for leucocratic gneisses, amphibolites and (meta-)igneous rocks from the Zone of Erbendorf Vohenstrauss (ZEV) and the KTB boreholes located in the northeastern ZEV and leucocratic gneisses from the Erbendorf Greenschist zone (EGZ). The investigations were carried out to contribute to the knowledge of the tectonothermal evolution of the area and to the response of the isotope systems to retrograde processes including recent elevated in- situ temperatures in the boreholes. A memory of an early Ordovician igneous event is given by Rb–Sr ages of 480±5–475±5 Ma obtained on very coarse-grained relic igneous muscovites of metapegmatites from the ZEV. This memory is missing in micas from peg matoids of the drill site. Coarse-grained muscovites of gneisses from ZEV and EGZ surface outcrops and of gneisses and pegmatoids from the boreholes yielded maximum K–Ar ages of 377±3–371±3 Ma related to the end of the Devonian regional metamorphism in both units. Consistent K–Ar and Rb–Sr apparent ages of some muscovites from surface outcrops point to a fast cooling of the metamorphic rocks due to rapid tectonic uplift. The lack of a depth-related gradient in model ages of coarse-grained KTB muscovites is explained by post-Variscan stacking processes. For minerals from intermediate to greater depths of the KTB, a strong age dependence on grain size and disturbances of the isotope systems due to various late- to post-Variscan retrograde processes can be demonstrated. A strong decrease in K–Ar model ages with increasing depth as obtained for biotites from the deepest section of the HB borehole probably indicates time-integrated response of the isotope system to elevated in situ temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00014658
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    Paper (German National Licenses)
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  • 2
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    The evolution of red clump stars - Theoretical sequences (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Two grids of horizontal-branch evolutionary sequences are presented which extend the grid of Sweigart and Gross (1976) to higher masses and higher metallicities. These two grids were constructed specifically for the study of red clump stars observed in intermediate-age star clusters in the Magellanic Clouds and in the Galaxy. An additional evolutionary track, with a thick hydrogen-burning shell which simulates the effect of a modest amount of mixing from the helium core into the shell at the time of the helium-core flash, is also presented. It is found that a small amount of mixing does not alter in a significant way the standard course of horizontal-branch evolution.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 63; 917-945
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Intermediate-age core helium burning stars and the distance to the Magellanic Clouds (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The luminosities of the core helium burning stars in six Magellanic Cloud intermediate-age star clusters, whose ages have recently been determined from photometry reaching below the main-sequence turnoff, are compared with the predictions of a new grid of theoretical models. It is found that for the so-called 'short' distance moduli consistent results can be achieved with moderate amounts of mass loss from the main sequence to the core helium burning stage for the older clusters, and with rather more substantial mass loss for the younger objects. For the 'long' moduli, however, the results of the comparison give inconsistent results in that the required masses for the clump stars generally exceed the corresponding turnoff masses, in some cases by several tenths of a solar mass. The results support the adoption of smaller distances to these galaxies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 313; 192-199
    Format: text
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    NASA TECHNICAL REPORTS
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