Zircon U-Pb age and Hf isotopic constraints on the Late Paleozoic magmatism and crustal evolution in the Caucasus
Abstract
We present the first combined analysis of zircon U-Pb and Hf isotopes of intrusive bodies in the Georgian Caucasus that indicates a significant period of magmatism in the Carboniferous. Magmatic zircons of 14 intrusive rocks from the Georgian Caucasus show similar 206Pb/238U ages clustering between 309 and 331 Ma and ɛHf(T) values ranging from -0.1 to - 11.9, suggesting that the Carboniferous magmatism has a complex contribution from a dominant crustal component and subordinate mantle input. Inherited zircons from the granitoids have ages mostly from ca. 500 to 700 Ma and ɛHf(T) values from +9.5 to -18.2, implying igneous activities of heterogeneous isotopic compositions. We furthermore identify a Triassic gabbro (221±2 Ma) and a Cretaceous rhyolite (86±1 Ma) that have ɛHf(T) values from +6.4 to -1.2 and +11.0 to +6.8, respectively, indicating inputs of the juvenile mantle during these two periods of magmatism. The overall zircon U-Pb and Hf isotopic data suggest four major episodes of magmatism, which may be correlated to the tectonic evolution scenarios by Stampfli and Borel (2002) and Zakariadze et al. (2007). Before the continental collision of the Arabian plate with Eurasia: (1) The first (ca. 700-500 Ma), inferred from detrital zircon data, is attributed to the Cadomian orogeny that occurred along the Gondwanan margin. Our data may be comparable to the detrital zircon results from Central Germany reported by Gerdes and Zeh (2006) that yield U-Pb ages from 501 to 722 Ma and ɛHf(T) values from +10.8 to -15.9. (2) The second and principal (ca. 320±10 Ma) was part of the widespread Variscan magmatism resulting from the collision between the peri-Gondwanan terranes and Laurasia. (3) The third (~220 Ma) with zircon ɛHf(T) values showing an input of a juvenile mantle source related to the Paleo-Tethyan subduction. (4) The fourth (~86 Ma) marked with a strong mantle input may be generated by subduction of the Neo-Tethyan oceanic slab under Eurasia.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T51C1545C
- Keywords:
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- 1040 GEOCHEMISTRY / Radiogenic isotope geochemistry;
- 1115 GEOCHRONOLOGY / Radioisotope geochronology;
- 8104 TECTONOPHYSICS / Continental margins: convergent