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Granite genesis related to geodynamics from Hf–Y in zircon

By
Jean-Pierre Pupin
Jean-Pierre Pupin
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Published:
January 01, 2000

Zircon is a very interesting accessory mineral, a kind of ‘crustal diamond’, easily recycled and recording through large morphological variability the main rock-forming events. Since 1985, a systematic study of chemical variability of zircon in magmatic rocks has led to the definition of three main generations in zircon populations: inherited phase 1, magmatic phase 2 and late magmatic phase 3. Hafnium and yttrium appear to be the most useful for source characterisation, especially if using phase 2 data. As a consequence, a new diagram of HfO2 versus Y2O3 is proposed, divided into domains la to 6b to describe the distribution of the genetic groups and the specific domains for anorogenic and orogenic rocks. Zircon in anorogenic granitoids: tholeiitic plagiogranites (high Y, low Hf), hypersolvus (medium to low Y, low Hf) and subsolvus (medium to high Y and Hf) alkaline granites/rhyolites, has separate mean distributions. Genetic relations existing between rocks with obvious textural differences (granites, microgranites, rhyolites) are also recognised. Zircon in orogenic granitoids is Y-poor and shows a very limited distribution, but the minimal average values in magmatic zircon vary from 11000 wt ppm HfO2 in the calc-alkaline suite, to 12 000 ppm in the peraluminous porphyritic granites and to 13 500 ppm in entirely crustal anatectic granites and migmatites. Mixing-mingling processes are proposed to explain the intermediate characteristics of zircons and rocks in the peraluminous porphyritic and K-subalkaline granites. This is consistent with the time emplacement and space distribution of these two orogenic members, but leads to a new proposal of emplacement of some alkaline subsolvus magmas during orogenic cycles.

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GSA Special Papers

The Fourth Hutton Symposium on the Origin of Granites and Related Rocks

Bernard Barbarin
Bernard Barbarin
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William Edryd Stephens
William Edryd Stephens
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Bernard Bonin
Bernard Bonin
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Jean-Luc Bouchez
Jean-Luc Bouchez
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David Barrie Clarke
David Barrie Clarke
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Michel Cuney
Michel Cuney
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Hervé Martin
Hervé Martin
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Geological Society of America
Volume
350
ISBN print:
9780813723501
Publication date:
January 01, 2000

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