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Geochronology of Archean LCT Pegmatites

  • Thomas DittrichEmail author
  • Thomas Seifert
  • Bernhard Schulz
  • Steffen Hagemann
  • Axel Gerdes
  • Jörg Pfänder
Chapter
Part of the SpringerBriefs in World Mineral Deposits book series (BRIEFSWMD)

Abstract

The knowledge of the age of an LCT pegmatite mineralisation is one of the key exploration criteria as most of the major LCT pegmatite systems (e.g., Tanco, Greenbushes, Bikita, Wodgina) were formed in relative narrow time intervals within the earth history. In addition, the temporal and spatial relation-ships of the pegmatites to potential source granites, their crystallisation history and geotectonic settings are still under debate. For the evaluation of the petrogenesis and emplacement history we compared Meso- and Neo-Archean LCT pegmatites of the Zimbabwe (Bikita), Pilbara (Wodgina) and Yilgarn Cratons (Londonderry, Mount Deans, Cattlin Creek). Lepidolite and white mica and lepidolite are an abundant constituent of the investigated LCT pegmatites and potentially accessible for 40Ar/39Ar dating. The U–Pb dating of Ta–Nb–Sn oxides and cassiterite LA-ICPMS turned out to be suitable for the Neo-Archean pegmatites due to the widespread occurrence of these minerals as accessories in almost all samples. Furthermore, they are formed at a virtually constant level during pegmatite crystallisation from main crystallisation to late state hydrothermal overprint. The 40Ar/39Ar ages cover a large spectrum from Neoarchean (~2630 Ma) to Paleoproterozoic (~2316 Ma), and are verified by U/Pb tantalite/ columbite ages (~2870 to 2615 Ma, LA-ICP-MS) and by Th-U-Pb electron microprobe monazite ages (~2700 Ma; ~2500 Ma). Micas from the Yilgarn Craton yield Neoarchean cooling ages indicating an immediate cooling after crystallisation. In contrast, micas from the Zimbabwe (~2625 Ma) and Pilbara Craton (~2870 Ma) exhibit Paleoproterozoic cooling ages that significantly postdate initial crystallisation. This is in good agreement with petrographic data that suggests a post pegmatite hydrothermal overprint. Overall, our new age data are in good agreement with a previously postulated global major LCT pegmatite events between 2850 to 2800 Ma and 2650 to 2600 Ma. During this event specific geodynamic conditions (i.e. a super-continent assembly) and associated anormal high heat flow from the mantle enabled the global formation of large volumes of LCT pegmatites.

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Copyright information

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Thomas Dittrich
    • 1
    Email author
  • Thomas Seifert
    • 1
  • Bernhard Schulz
    • 1
  • Steffen Hagemann
    • 2
  • Axel Gerdes
    • 3
  • Jörg Pfänder
    • 4
  1. 1.Division of Economic Geology and Petrology, Institute of MineralogyTU Bergakademie FreibergFreibergGermany
  2. 2.School of Earth and Environment, Centre for Exploration TargetingThe University of Western AustraliaCrawleyAustralia
  3. 3.Department of GeosciencesGoethe University FrankfurtFrankfurt am MainGermany
  4. 4.Ar-Ar-Lab/Division of Tectonophysics, Institute for GeologyTU Bergakademie FreibergFreibergGermany

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