Sökning: "U-PB"

Visar resultat 1 - 5 av 41 avhandlingar innehållade ordet U-PB.

1. 1. The evolution of lunar breccias : U-Pb geochronology of Ca-phosphates and zircon using Secondary Ion Mass Spectrometry

   Författare :Fiona Karen Thiessen; Martin Whitehouse; Alexander Nemchin; Victoria Pease; Barbara Cohen; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; Moon; impact breccias; Apollo missions; impact event; Late Heavy Bombardment; zircon; Ca-phosphates; U-Pb; SIMS; geochronology; Geology; geologi;

   Sammanfattning : Planetary bodies in our Solar System, including the Moon, were exposed to an intense asteroid bombardment between ~4.5-3.8 Ga, shaping their surfaces and leaving visible “footprints” in the form of large impact basins. The end of this period (~4. LÄS MER

3. 2. The tectonic evolution of the western part of the Svecofennian orogen, central Sweden : Insight from U/Pb and 40Ar/39Ar geochronology at Forsmark

   Författare :Tobias Hermansson; Berggrundsgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; physical geography; Geology; Svecofennian orogen; Tectonic models; Tectonic cycles; Uplift; Cooling; Ductile deformation; Geochronology; U Pb; 40Ar 39Ar; Geologi; fysisk geografi; Petrology; mineralogy; geochemistry; Petrologi; mineralogi; geokemi;

   Sammanfattning : The Forsmark area, in the western part of the Svecofennian orogen, central Sweden, is situated between two major Palaeoproterozoic tectonic domains that show contrasting histories with respect to timing of igneous activity, ductile deformation and metamorphism. At Forsmark, WNW to NW trending, ductile deformation belts anastomose around tectonic lenses with an inferred lower degree of ductile strain. LÄS MER

4. 3. Geography and geometry of pre-Caledonian western Baltica: U-Pb geochronology and Palaeomagnetism

   Författare :Emma Rehnström; Berggrundsgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Physical geography; geomorphology; pedology; cartography; climatology; Fysisk geografi; geomorfologi; marklära; kartografi; klimatologi; Fennoscandia; correlations; Baltica; Early Palaeozoikum; palaeogeography; orthogneisses; nappes; palaeomagnetism; U-Pb geochronology; Caledonian orogen; Scandinavia;

   Sammanfattning : In an attempt to reconstruct the pre-Caledonian cratonic margin of Fennoscandia, U-Pb geochronological and geochemical investigations have been performed on allochthonous orthogneisses in the northern Swedish Caledonides. The crystalline basement of the nappes have also been examined to further constrain the continuation of various chronologically defined orogenic belts. LÄS MER

5. 4. Geochronology of impact structures - constraining syn- and post-impact processes using the 40Ar/39Ar and U-Pb techniques

   Författare :Maria Herrmann; Berggrundsgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Impact structure; Dating impact events; 40Ar 39Ar dating; U-Pb dating; Siljan impact structure; Mien impact structure; Hummeln impact structure; Puchezh-Katunki impact structure;

   Sammanfattning : The discovery, at the beginning of the 20th century, that elements can transform into other elements, due to the spontaneous decay of an instable to a stable atomic nuclei, gave rise to a powerful source for age information in many fields of earth science. For impact structures, it is crucial to establish well-defined and precise ages in order to understand how impact events affect the Earth’s geo and biosphere and also with regard to possible future events that can have devastating effects on our civilization. LÄS MER

7. 5. New Zircon geochronological and Nd isotopic evidence for Neoproterozoic crust reworking events in the Abas terrane, Yemen

   Författare :Fitsum Girum Yeshanew; Victoria Pease; Martin Whitehouse; Hugh Rollinson; Kjell Billström; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Precambrian; Arabian Shield; magmatism; U-Pb; zircon; post-collisional magmatism; Nd isotopes; Geology; geologi;

   Sammanfattning : The Arabian-Nubian Shield is an excellent natural laboratory to study crust formation processes during the Neoproterozoic. It is one of the largest juvenile tracts of continental crust formed during this time. It diachronously evolved between the breakup of Rodinia (c.780 Ma) and amalgamation of Gondwana (c. LÄS MER